The Generation IV and Nuclear Hydrogen Initiative Programs
As of mid-2007, there were 439 operating nuclear power plants totaling 371.7 GWe of capacity in 31 countries and generating nearly 16 percent of the world’s electricity. In addition there are five units in long-term shutdown with a total capacity 2.8 GWe. Thirty reactor units with a total capacity 23.4 GWe are under construction in 12 countries. Nuclear power had improved its performance and achieved an excellent operating record by the end of the twentieth century. In the United States, where no new plants have been ordered since the 1970s, improved operation and power upgrades to 104 nuclear power plants have enabled nuclear energy to maintain a 20 percent share of electricity generation since 1985.
Concerns over energy resource availability, climate change, air quality, and energy security suggest an important role for nuclear power in the future energy supply. Current nuclear power plants (Generation II models in the United States or the more recent Generation III models deployed internationally) supply reliable and economic baseload electricity in many markets. With a total of over 12,000 reactor-years of worldwide experience, the performance of these reactors today is far more satisfactory than it was two decades ago. Also, the NP 2010 program, as noted in Chapter 2, is assisting with the licensing and deployment of some new reactors with improved features (Generation III+) that are ready for the market. However, longer term advances in nuclear energy system design could broaden the desirability and future uses of nuclear energy. The U.S. Department of Energy (DOE) has engaged other governments, the international and domestic industry, and the research community in a wide-ranging effort to develop advanced next-generation nuclear energy systems (Generation IV). The goals are to widen the applications and enhance the economics, safety, and physical protection of the reactors, to improve the management of fuel cycle waste, and to advance proliferation resistance in the coming decades—that is, 2020 and beyond.
OVERALL PROGRAM DESCRIPTION
Six nuclear reactor technology concepts were identified in the DOE-initiated international Generation IV Technology Roadmap (DOE, 2002). Each of these six technologies, as well as several areas of crosscutting research, is now being pursued by a consortium of countries as part of the Generation IV International Forum (GIF), with varying levels of effort being expended by the various members of GIF based on the technology that is of interest to them and its status and potential to meet national goals. Three of the concepts are thermal neutron spectrum systems—very-high-temperature reactors (VHTRs), molten salt reactors (MSRs), and super-critical-water-cooled reactors (SCWRs)—with coolants and temperatures that enable hydrogen or electricity production with high efficiency. The remaining three concepts are fast neutron spectrum systems—gas-cooled fast reactors (GFRs), lead-cooled fast reactors (LFRs), and sodium-cooled fast reactors (SFRs)—that will enable better fuel use and more effective management of actinides by recycling most components in the discharged fuel. DOE has selected the VHTR as the highest priority concept but has given some support for the other concepts (except for the MSR, where DOE has only funded an effort to monitor international activities and university-based programs). The priority ranking of the other concepts has varied over the years, with the SFR recently taking second place. Crosscutting fuel cycle research has been performed under the Advanced Fuel Cycle Initiative (AFCI), which is a national program but could become an international one under the recent Global Nuclear Energy Partnership (GNEP), started in 2006 (see Chapter 4).
There are three major strategic goals on the Generation IV Technology Roadmap:
Electricity generation at competitive cost in large and small reactors,
Use of process heat to produce alternative energy products (e.g., hydrogen), and
Used-fuel recycle and actinide burning to reduce waste and enable the sustainable use of fuel resources.
Other Generation IV goals include enhancing reliability and safety and increasing proliferation resistance and physical security.
Focus Areas of the Generation IV Program
From 2002 to 2005, since the publication of the Generation IV Technology Roadmap (DOE, 2002), the Generation IV program was reviewed by the DOE Nuclear Energy Research Advisory Committee (NERAC) on an ongoing basis. In those years, the primary goal of the program was the use of high-temperature (850°C to 1000°C) process heat and innovative approaches to yield energy products, such as hydrogen, that might benefit the transportation and chemical industries. To that end, DOE published an Expression of Interest (DOE, 2004) in the development of industrial and international partnerships for the Next-Generation Nuclear Plant (NGNP), with the VHTR reactor concept as its key focus. This initiative resulted in reviews of the VHTR concept by the Independent Technology Review Group (ITRG, 2004) as well as by NERAC.1 These reviews recommended a faster schedule for the NGNP but a technologically less aggressive approach for the VHTR concept—for example, lower gas outlet temperature, more traditional materials, and proven UO2 particle fuel. These recommendations have largely been adopted as the NGNP program reaches performance-phase R&D. The DOE VHTR effort was reinforced by the passage of the Energy Policy Act of 2005 (EPAct05),2 which authorized $1.25 billion in funding for the NGNP and identified the VHTR as its lead concept. Since FY 2003, over 90 percent of the line item program funds for the Generation IV systems were used for NGNP (see Table 1-1).
In that same time period (2002 to 2005), the secondary goals of the Generation IV program were to examine innovative reactor concepts for managing spent fuel inventories to minimize waste products as well as improve the power conversion efficiency and minimize the cost of advanced reactor systems. These goals were implemented by much smaller efforts in the other four reactor nuclear energy systems. Each reactor concept research program was focused on its main viability issues:
SCWR: advanced materials, chemistry, and heat transfer (T > 500°C),
GFR: alternative fuel types and innovative safety concepts,
LFR: lead corrosion and materials studies, modular reactor design, and
SFR: development of actinide transmutation fuels, and reduction of capital costs through improved design features and power conversion technologies.
At the end of 2005, DOE shifted the fundamental emphasis of the overall AFCI and the Generation IV program, making spent fuel management using a closed fuel cycle the main goal of the NE program by introducing GNEP in early 2006 as part of the budget request for FY 2007. This new priority had a number of effects on the projected funding for the other programs starting in FY 2007:
Reduced funding for the NP 2010 and NGNP programs;
Phasing out of the SCWR, GFR, and LFR R&D programs;
Refocusing the SFR effort on near-term demonstration (Chang et al., 2006; DOE, 2006).
With these changes, NGNP’s VHTR remains the only major reactor concept that is not integrated into the GNEP program. In the sections that follow, the NGNP concept is reviewed first, and the current status of its program plan and its R&D results are assessed. Subsequently, the Nuclear Hydrogen Initiative (NHI) is addressed. Finally, the progress made on the other Generation IV reactor concepts and their current status are examined. The SFR concept, as applied to near-term demonstration, is discussed in greater detail in Chapter 4 because responsibility for its development has been shifted to the GNEP program.
Reactor Development Evaluation Criteria from the Generation IV Roadmap
During the development of the Generation IV Technology Roadmap (DOE, 2002), three different R&D phases were defined, going from conceptual design to commercialization:
Viability assessment phase R&D. Viability phase R&D examines the feasibility of key technologies. Its objective is to prove out, on a laboratory scale, the basic concepts, technologies, and processes under relevant conditions and to identify and resolve all potential technical show-stoppers.
Performance assessment phase R&D. Performance phase R&D undertakes the development of performance data and optimization of the system on an engineering scale. The objective is to verify and optimize engineering-scale processes, phenomena, and materials capabilities under prototypical conditions.
Demonstration phase R&D. Demonstration phase activities undertake the licensing, construction, and operation of a prototype or demonstration system in partnership with industry or, perhaps, other countries. The detailed design and licensing of the system are performed during this phase. Its objective is to create a new product that is then selected by industry for wide-scale commercial deployment.
Each of these three R&D phases involves increasingly expensive efforts and facilities. For this reason, the Generation IV Technology Roadmap identified nine criteria that a technology would be required to meet before it would be allowed to advance to the next R&D phase. These nine criteria, listed in Table 3-1, set expectations for nuclear energy R&D that had national and international agreement. Each of the six reactor concepts identified on the roadmap had several viability topics that needed resolution through viability R&D before the concept could transition to the performance assessment phase. When these criteria were finalized (mid-2002), it was assumed that there would be a viability downselect in 2007 to choose among the six technologies.
Because these Generation IV R&D end points establish reasonable criteria for evaluating nuclear technologies, the committee has used them as a basis for evaluating the technology readiness of the NGNP. Further, the committee finds these R&D end points useful as criteria to evaluate the major GNEP technologies (UREX+ and pyro-reprocessing, transmutation fuel fabrication, and the SFR).
NEXT-GENERATION NUCLEAR PLANT
The NGNP program represents DOE’s focused effort under the Generation IV program on the VHTR. NGNP is envisioned to be a commercial-scale modular gas-cooled thermal reactor with a power output of ~600 megawatts of thermal energy (MWth). The NGNP will use high-temperature helium coolant with an exit temperature of ~850°C to 950°C to produce electricity and/or hydrogen. (While conceptual design studies totaling $2.9 million were performed in FY 2005 and FY 2006 on a liquid-salt-cooled variant operating at higher power with the same high-temperature fuel design, that design is no longer being considered for the NGNP. However, concept evaluation of salt-cooled reactors continues at universities.) The NGNP will be designed to meet as many as possible of the Generation IV objectives of high reliability, enhanced safety, proliferation resistance, sustainability (low waste generation), and improved economics compared to existing commercial nuclear power plants.
There are two basic candidates for the reactor core: one based on pebble fuel and the other based on prismatic/block fuel. The fundamental element of both fuel types is tristructural isotropic (TRISO)-coated particles that have high fuel integrity characteristics even at high fuel burn-up and excellent fission product retention under steady state and postulated adverse transient and accident conditions. The program benefits from significant past experience with helium cooled reactors in the United States and Germany, but it couples the reactor to a gas-turbine power cycle instead of a steam turbine cycle for power conversion. The program also benefits from the experience in operating small (10- to 30-MWth) test reactors in China and Japan and the design studies for a 400-MWth power plant that is planned to enter construction in 2008 in South Africa. The Generation IV Technology Roadmap identified six R&D areas for the VHTR, which was assumed to have a coolant outlet temperature above 1000°C (DOE, 2002, p. 81):
TABLE 3-1 End Points for Viability Phase and Performance Phase R&D, as Defined in the Generation IV Technology Roadmap
Viability Phase End Points
Performance Phase End Points
1. Preconceptual design of the entire system, with nominal interface requirements between subsystems, and established pathways for disposal of all waste streams
1. Conceptual design of the entire system, sufficient for procurement specifications for construction of a demonstration plant and with validated acceptability of disposal of all waste streams
2. Basic fuel cycle and energy conversion (if applicable) process flowsheets established through testing at appropriate scale
2. Processes validated at scale sufficient for demonstration plant
3. Cost analysis based on preconceptual design
3. Detailed cost evaluation for the system
4. Simplified probabilistic risk assessment for the system
4. Probabilistic risk assessment for the system
5. Definition of analytical tools
5. Validation of analytical tools
6. Preconceptual design and analysis of safety features
6. Demonstration of safety features through testing, analysis, or relevant experience
7. Simplified preliminary environmental impact statement for the system
7. Environmental impact statement for the system
8. Preliminary safeguards and physical protection strategy
8. Safeguards and physical protection strategy for system, including cost estimate for extrinsic features
9. Consultation(s) with regulatory agency on safety approach and framework issues
9. Preapplication meeting(s) with regulatory agency
SOURCE: DOE, 2002, p. 80.
High-temperature helium turbine,
Reactor/hydrogen production process coupling approach,
Identification of targeted operating temperature,
Fuel coating material and design concept,
Adequacy of fuel performance potential, and
Reactor structural material selection.
Subsequently, the desirable maximum temperature of the coolant was reduced to 900°C, with a longer-term target of 950°C, which reduced the challenge to materials and fuel integrity in the construction of NGNP.
The NGNP program is authorized under EPAct05 at total funding of $1.25 billion for Phase I, which extends to 2011. During this phase, fundamental R&D would be carried out for the associated technologies and components. This includes the reactor and its fuel, the energy conversion system, materials, and hydrogen generation technologies. In addition, certain fundamental decisions are to be made, including selection of the mission of the NGNP (efficient electricity production, process heat, hydrogen generation, or a combination of these) and the specific hydrogen generation technology. EPAct05 also discusses Phase II, which extends from 2012 to 2021 and wherein a detailed design should be competitively developed, a license should be obtained from the U.S. Nuclear Regulatory Commission (USNRC), and the plant should be constructed and commissioned.
According to EPAct05, the program will be based on the R&D activities of the Generation IV program, the Idaho National Laboratory (INL) will be the lead national laboratory, and the NGNP demonstration will be sited at INL. INL is charged to organize a consortium of industrial partners to cost-share the project. The NGNP project is to maximize technical exchange and transfer from other relevant sources, including other industries and international Generation IV partners.
The overall program has been estimated to cost approximately $2.3 billion, which means that significant cost share (roughly 50 percent) will be needed from collaborative private sector partners, in the form of actual funding or work in kind and transfer of already developed intellectual property.
INL has formed program plans for the basic NGNP program, and a complementary private sector initiative has been started to form a public/private partnership for bringing end users, industrial suppliers, technology developers, and national laboratories together with DOE for the development and demonstration of NGNP on a commercial scale. Potential end users might include the petroleum industry, industrial gas producers, the transportation industry, the coal industry and their associates who are interested in gasification and liquefaction applications, and traditional electric power companies.
The potential end users represent the broad range of applications for high-temperature process heat; some of them will also need economic bulk hydrogen in the future. This partnership is being formed to show Congress that there is genuine interest in this technology for the intended purposes and to attract the needed cost-share funding to accomplish the goals of the program without asking for more public sector funding, which might be difficult to obtain. This approach is consistent with the R&D model recommended by Electric Power Research Institute (EPRI) and INL, which proposed substantial industry contributions for nearer-term R&D, with the government maintaining primary but not sole responsibility for funding longer-term R&D (Modeen, 2006).
This NGNP public/private partnership initiative has formulated a four-phase program that starts with a currently contracted 1-year NGNP preconceptual engineering effort, scheduled for completion in August 2007, and ends in FY 2017 with full commissioning and start-up of a plant at the INL site. This is a more aggressive schedule than that of EPAct05, which called for 2020. The earlier target date was motivated by congressional supporters, INL management, and the engaged industrial participants as a way to drive the technology to commercialization during a period of strong interest in a nuclear energy renaissance and growing industrial demand for the capabilities of the NGNP.
A Brief History of High-Temperature Reactor Development
The United Kingdom embraced high-temperature reactor (HTR) technology in the early 1950s with the start of a large fleet of graphite-moderated, metal fueled, and CO2-cooled MAGNOX reactors for electricity generation and weapons plutonium production. In total, 28 reactors of this type were built, with outputs ranging from 50 to 490 MWe and a total capacity of 4,200 MWe. In 2006, eight of these MAGNOX reactors remained operational, but all will be shut down by 2011. The 20-MWth helium-cooled Dragon reactor, a cooperative project of the Organisation for Economic Cooperation and Development (OECD) and Euratom, demonstrated the use of thorium/uranium fuel starting in 1964, with operations continuing to 1975. Also in 1964, while the MAGNOX build program was in full swing, the U.K. government decided to start the next phase of CO2-cooled reactor development with advanced gas-cooled reactors (AGRs). Eventually, 14 AGRs would be built, with outputs ranging from 550 to 625 MWe and a total capacity of 8,600 MWe. These reactors had coolant, at 4 MPa, traveling downward in the core and exiting at 645°C, coupled to a steam cycle power conversion system, through a steam generator. The steam, at 17 MPa, entered the turbines at 540°C, which provided over 40 percent thermal conversion efficiency.
The performance of the AGR reactors was poor in the early days because of materials problems and lack of standardization of the design. The principal technical issues
from the U.K. gas reactor experience are related to graphite corrosion and aging under radiation, as well as carbon deposition on the fuel rods. Graphite corrosion can occur for thermal and radiolytic reasons. With experience, a coolant composition was found to inhibit those tendencies with the right levels of CO, CH4 and H2O (Hall and Chaffey, 1982). The CO inhibits corrosion due to radiolysis of CO2, and CH4 inhibits corrosion as it forms a deposit on graphite pores. The oxidation of structural steel materials in the presence of CO2 was also a source of some problems. Subsequently, the United Kingdom turned to light water reactors (LWRs), importing the technology from the United States but building only one large plant, Sizewell B.
France also experimented with CO2-cooled, graphite-moderated reactors. The initial reactors suffered from unsatisfactory fuel performance and graphite corrosion problems. France turned to LWRs based on the U.S. experience in 1974.
The United States and Germany each explored HTR technology about the same time with two small developmental graphite-moderated, helium-cooled reactors, Peach Bottom 1 (operated from 1967 to 1974) and AVR (operated from 1966 to 1988), respectively. These small reactors demonstrated the prismatic and pebble bed fuel/moderator arrangements and technologies and encouraged their promoters to proceed to the commercial demonstration stage. The United States commissioned the Fort St. Vrain reactor in 1979 and Germany commissioned a thorium high-temperature reactor in 1985, both with outputs in the 300-MWe range. With a coolant maximum temperature of 700°C, all these plants operated using indirect steam Rankine cycles to generate electricity. The Fort St. Vrain plant was beset by technical problems. These problems were mainly in the auxiliary systems, such as the cooling and oil systems. However, there was also a significant problem with flow-induced vibration of the reflector and fuel graphite blocks. This was partially corrected by pinning the blocks together, but the overall coolant flow rate still had to be limited, which prevented the reactor from operating at full power. Technical issues also arose in the German program due to the approach of inserting control rods into the pebbles of the core, introducing the problem of broken pebbles in the fuel handling and storage systems. Furthermore, the German HTR program was caught up in the political aftermath of the Chernobyl (water-cooled but graphite-moderated) reactor accident. Both the Fort St. Vrain reactor in the United States and the HTR reactors in Germany were permanently shut down in 1989, ending the early era of gas reactor demonstration in those two countries.
Subsequent to the shutdown of these commercial demonstration reactors, system design and evaluation studies continued and focused on modular, passively safe concepts, including the German MODUL and the U.S. modular high-temperature gas reactor designs. These design studies shifted from an indirect Rankine steam cycle for power conversion to a direct recuperative Brayton cycle, taking advantage of the improved gas-turbine technology to increase thermal efficiency and improve economics. These changes resulted in designs that had plant capacities of about 300 MWe or less, which is a significant challenge economically compared to large LWRs for electricity generation. On the other hand, the small thermal power enables the reactor to transfer decay heat to the surrounding environment without requiring emergency coolant or reaching intolerable temperatures.
HTR development has undergone a resurgence outside the United States over the past decade. Key national programs are being conducted in China, Japan, and South Africa.
In China, the Institute of Nuclear Energy Technology (INET), operated by Tsinghua University, has taken the lead for development of HTR technology. It spearheaded the design and construction of a small HTR-10 test reactor. Construction of the HTR-10 started in 1995, and it achieved criticality in 2000. It is a 10-MWth pebble bed reactor that utilizes UO2 pebble fuel and a steam generator for heat rejection. Numerous tests have been completed confirming the inherent safety features of the design, including reactor shutdown due to fuel heating when power increases following the withdrawal of control rods. The intention is to couple this test reactor directly to a gas turbine, thereby also demonstrating the Brayton cycle.
A commercial project (HTR-PM) has already been established as a collaborative effort between INET, China Nuclear Engineering and Construction Company, and the China Huaneng Group, a large Chinese electric utility company. The plant design was initially sized at 450 MWth with a 750°C coolant outlet temperature and a helical steam generator providing steam to a Rankine cycle. Recently, the thermal output has been reduced to 250 MWth to facilitate early deployment. Construction was planned to start about 2008 and criticality to be achieved around 2013, but delays have been experienced that could push the project back by several years.
Under the direction and sponsorship of the Japan Atomic Energy Agency, an industry collaborative program on HTRs has been in place for nearly two decades. The centerpiece of this program is the high-temperature test reactor (HTTR), which is a 30-MWth reactor using prismatic fuel/moderator arrangement and a coolant outlet temperature of up to 850°C, although 950°C was reached for short operating periods. Construction on the HTTR started in 1991, and criticality was achieved in 2000. The purpose of the project is to establish an HTR technology basis, to develop process heat application technology, and to provide a heat source for a hydrogen production plant based on the thermochemical sulfur-iodine water splitting process. Although no commer-
cial demonstration project has been defined, a conceptual design for a commercial cogeneration plant, called the GTH-TR300C, has been developed.
Pebble Bed Modular Reactor Pty. Ltd. is developing the pebble bed modular reactor (PBMR) design as a national strategic project in South Africa. The design of the demonstration power plant is for a 400-MWth reactor connected to a direct cycle helium turbine, with pebble fuel/moderator and a coolant outlet temperature of 900°C. The project has been defined, all major components ordered and construction will start in 2009 with initial criticality planned for 2013. The plant will be built at ESKOM’s Koeberg site, where two large LWRs already exist. As part of this overall project, extensive testing facilities are planned and several are already being commissioned. A pilot fuel plant has been designed and should start construction in 2008. Advanced fuel will be manufactured in a full-size production line facility (already constructed) starting in late 2007 for irradiation testing in Russia beginning in early 2008.
With successful demonstration of the technology, it is planned that 24-30 PBMRs will be added to the ESKOM grid starting in about 2015 to distribute power along the coast of South Africa and at certain remote inland sites (Rosenberg, 2007; Bloomberg, 2007). A letter of intent has already been issued by ESKOM for these units. In addition, process heat plant development is ongoing to evaluate the best applications for this HTR technology and to assess the economic competitiveness against the competing fuel, natural gas. Finally, preapplication review for design certification of the basic technology has already started in the United States, and the USNRC activity is timed to be consistent with the development of information, including the licensing documentation, on the South African Demonstration Power Plant.
Benefits of High-Temperature Reactor Deployment
Economic benefits of early commercialization of HTRs and VHTRs based on NGNP technology could be realized in four market segments where HTRs could make products at a lower cost than competing technologies: base-load electricity, combined heat and power, high-temperature process heat, and hydrogen. A long-term goal for the NGNP is to support the production of hydrogen as an energy carrier in a hydrogen economy. However, in each of those four market segments listed above, there are specific applications where HTRs will have near-term advantages. By directing NGNP and NHI R&D toward these specific applications, stronger near-term industry interest and investment is more likely, which in turn will support continued R&D investments for subsequent expansion of HTR technology into additional market segments and, in the longer term, support the transition to a hydrogen economy.
Environmental benefits of HTRs arise from their efficiency at producing carbon-free electricity, carbon-free hydrogen, and/or carbon-free process heat. A 1,000-MW combined cycle natural gas plant produces about 3 million tonnes of CO2 per year. In the United States, natural gas power plants emit a billion tonnes of CO2 per year. Replacing combined cycle gas turbine capacity with gas turbine HTRs could significantly reduce carbon emissions. Also, a commercial-scale 3 million cubic meters per day (100 million standard cubic feet) steam methane reforming (SMR) plant producing pipeline hydrogen produces at least 1 million tonnes of CO2 per year. SMR capacity in the United States was 56.4 million cubic meters per day in 2004, producing 18 million tonnes of CO2 per year. Hydrogen demand has been growing at 5 percent per year since 2000. HTR technology could significantly reduce carbon emissions in the hydrogen production industry.
Economic and security benefits follow from reducing dependence of the United States on fuel imports. While a small portion (15 percent) of the U.S. needs for natural gas is currently imported, there is a growing demand but limited supply of it from our major supplier, Canada. Thus liquefied natural gas, probably from the Middle East or Russia, will be increasingly important to meet U.S. needs. (Western Europe depends heavily on supplies from Russia and North Africa even today.) Natural gas is used for electricity production, home heating, and as a feedstock for chemicals and plastics. It is the main source of energy for the U.S. production of process heat and hydrogen for use in the preparation of liquid transport fuels from crude oil. In the future, even larger quantities of natural gas may be required to produce liquid fuels from unconventional sources that are abundant in North America, including tar sands, shale oils, coal, and biomass. Liquid fuels can be expected to continue to play a large role in the transportation sector, supplemented in the longer term by hydrogen fuel cells or chargeable batteries for ground transportation. HTRs may play a role in displacing natural gas consumption in all of these market segments.
For base-load electricity generation, HTRs may initially be competitive with mature LWR technology in niche market segments where HTR’s technical characteristics provide specific advantages. For small grids, as exist in developing countries, modular HTRs have a direct advantage due to their smaller unit power outputs and slower transients compared to market ready, large-capacity LWRs. Also, in regions where water is scarce, as in the U.S. Southwest, HTRs that use direct Brayton cycle power conversion hold an advantage over LWRs because they can operate with greater efficiency while rejecting to the surroundings reduced quantities of waste heat at higher temperatures. This enables economical dry cooling
for inland locations. By breaking the linkage between cooling water availability and electricity production, HTRs can remove a significant constraint on reactor siting.
If a portion of the heat supplied to the gas entering the turbines in gas-fired plants is derived from HTRs, it will reduce the natural gas consumed, which would reduce carbon emissions associated with gas plants. At high natural gas prices (about $8 per million Btu [MMBtu]), the nuclear heat addition is also more economical (Joeng and Kazimi, 2005).
Combined Heat and Power
Currently, combined heat and power applications are fueled dominantly by natural gas. In many cases combined heat and power facilities run steadily because they are coupled to facilities that create a steady demand for heat. In these situations where combined heat and power systems run with high availability, HTRs with direct Brayton power cycles and bottoming steam production can directly displace the carbon-emitting natural gas usage. Current large-scale applications for low- and intermediate-temperature steam include enhanced oil recovery, oil production from tar sands, and process heat for large petrochemical facilities.
High-Temperature Process Heat
Natural gas is also used to supply high-temperature process heat. HTRs can also provide high-temperature process heat between 600°C and 950°C and can directly displace natural gas in these applications, as discussed earlier.
Hydrogen is being used to upgrade heavier crude oils. Also, as more biomass (e.g., corn) is grown to produce biofuels, more ammonia-based fertilizer will be required, increasing the demand for hydrogen. Natural gas is currently the dominant feedstock for production of hydrogen through steam methane reforming (SMR). Unfortunately, each kilogram of hydrogen produced through SMR releases over 9 kg of CO2. EPRI studies (EPRI, 2003) have shown that nuclear heat could be an economic application that partly displaces high-priced natural gas in steam reforming. The use of hydrogen is extensive in the petrochemical industry, including large-scale usage in the production of transportation fuels and fertilizers, and it would increase further if lower cost sources became available. Currently, all major refineries in Texas and Louisiana are connected by a hydrogen pipeline that runs within 100 m of Entergy’s Waterford nuclear power plant. Thus a nuclear plant can be said to have coexisted in close proximity to hydrogen equipment for a long time, obviating the need to widely separate a nuclear plant and a hydrogen plant. In the future, hydrogen may be used directly as a fuel for ground transport. Options for displacing the production of hydrogen from natural gas with nuclear hydrogen include distributed low-temperature electrolysis with off-peak base-load nuclear electricity and centralized hydrogen production using high-temperature electrolysis or thermochemical water-splitting cycles (Yildiz et al., 2005; NRC/NAE, 2004). Currently, NHI supports R&D for all three of these technologies.
LWR-based electrolysis can be applied for hydrogen production with an energy efficiency of about 26-30 percent, while sulfur-iodine (S-I) high-temperature steam electrolysis has the potential to reach an energy efficiency of 45-50 percent. The use of HTR for hydrogen production is motivated by its enabling thermochemical schemes that are possible only at high temperatures. However, the improvement in efficiency to about 60-80 percent will increase the chances that HTR-produced hydrogen could be more economic than hydrogen produced by LWR-based water electrolysis. Second, while the reactor side costs of an MHR are likely to be higher than those of an LWR, owing to the lower energy density, its associated gas turbine power cycle cost is likely to be lower than the cost of the steam power cycle. Third, the financial terms of a large pressurized water reactor plant may be more demanding than those of the smaller capacity, modular HTR unit. Finally, the HTR technology has far more potential for improvement than the more mature LWR technology (for example, moving to liquid salt cooling could increase the power density and significantly reduce capital costs).
HTR/NGNP Technology Challenges and Development Needs
Because several gas-cooled reactors have already been built and operated, significant insight into the reliable operation of such reactors has been gathered. In addition, better economy and process heat applications call for operating the NGNP and future HTRs at even higher temperatures than those attained in past reactors, which implies a need for R&D on materials and other technology needs. Such needs were reviewed by the Independent Technology Review Group (ITRG, 2004) and by NERAC.3 These reviews involved discussions with members of the industrial team building a demonstration plant in South Africa that had assessed the need for technology development. Six areas were identified as needing the most R&D.
Materials Development and Improvements
The unique material challenges for the VHTR are based on the need for adequate strength and dimensional stability at high temperatures and for the transport of corrosion products from metals and graphite in the presence of a potentially impure helium coolant. Although a number of materials and alloys for high-temperature applications are in use in the
petrochemical, metals processing, and aerospace industries, a very limited number of these materials have been tested or qualified for use in nuclear-reactor-related systems. Some primary system components of the VHTR will require use of materials at temperatures above 800°C; at present, there are no such ASME-code-qualified materials. Significant R&D is needed in a number of areas:
Understanding of the high-temperature- and irradiation-induced dimensional and material property changes of nuclear graphite and carbon fiber/carbon matrix composites.
Development of a basis for professional codes and standards for very high-temperature design methodology.
Improved understanding of environmental effects on metallic alloys and thermal aging of the alloys, as well as better models for studying them and mitigating them.
Understanding of thermal radiation and emissivity of large pressure vessels and core barrel surfaces in order to optimize passive core cooling.
Fuels Development and Requirements
The basic fuel element in a gas-cooled reactor is the TRISO particle, consisting initially of a UO2 fuel kernel covered in layers of porous graphite, dense pyrolytic graphite, silicon carbide, and pyrolytic graphite. A number of challenges must be overcome before these fuel forms can be optimized for higher temperature and higher dose operation and before sufficiently high reliability and acceptably low fuel failures can be assured. These challenges include anisotropic shrinkage and swelling of the pyrolytic carbon; adequate mechanical stability at high gas pressure due to fission gas or carbon dioxide; kernel migration due to temperature gradients in the fuel particle; palladium attack on the silicon carbide layer; and selective diffusion and transport of certain fission products, such as silver, through the silicon carbide. Some key research activities for mitigating the current limitations of TRISO particles include using a smaller fuel kernel, using alternative fuel kernels such as UCO, or replacing the silicon carbide with an alternative such as zirconium carbide. Additionally, optimizing the microstructure as a function of the processing conditions under which the particles are produced may improve performance.
Primary to Secondary Heat Transfer
The extraction of process heat from the NGNP requires an intermediate heat transport loop. The two key technology decisions needed are the design of the intermediate heat exchanger (IHX) and the form and composition of the heat transport fluid. The high temperatures and potential induced stresses in the IHX (e.g., as a result of loss of electrical load or shutdown of the process heat plant) place extreme demands on the design. Normal heat exchanger design approaches using conventional materials will most likely not be adequate. The heat transport fluid should (1) be chemically compatible with the surrounding structural materials, (2) have superior fluid-mechanical and heat-transfer properties for an economical design of the process heat exchangers and the heat transport loop, and (3) have acceptable safety characteristics under normal and off-normal conditions. The fluid could be a high-pressure inert gas such as helium or a high-temperature molten salt. A molten salt, if it is properly compatible with the heat exchanger and piping materials, can minimize the temperature drop in the intermediate heat-transport loop and the required pumping power, thereby minimizing the cost of the delivered process heat.
An immediate problem with using molten salts is their corrosive nature at the high temperatures of use. In terms of corrosion mechanisms in materials, the molten fluoride salt environment is quite different from other high-temperature environments. The normally accepted paradigm of developing a protective oxide layer to provide corrosion resistance does not fully apply to this environment, owing to thermodynamically driven dissolution effects. Although the heat transfer characteristics of molten salt are superior to those of inert gas, optimizing heat exchanger design at high temperature and high stresses (due to the pressure differential) is an important area of research.
The potential need to couple two diverse processes (electric power generation and hydrogen production) complicates the mission of the NGNP. Differing dynamic responses of the reactor to the hydrogen production plant or an electricity-generating plant must be carefully assessed for NGNP’s single mission project. Design and analytical studies are needed to investigate possible configurations and control schemes. The results of these studies will provide insights into the reactor design conditions, including provision of direct versus indirect process heat cycles and relying on steam power cycles instead of helium gas turbines at the outset.
Safety and Licensing
There needs to be a discussion with the USNRC on the key aspects of safety and licensing that should be addressed if the NGNP is deployed in the 2017 to 2021 time frame. It is known that USNRC staff has already begun to develop a technology-neutral licensing framework that the NGNP project can use as initial guidance (SECY-05-0130). However, this staff document has not yet been adopted by the USNRC but is still being reviewed by the staff and the Advisory Committee on Reactor Safeguards. EPAct05 requires that DOE and USNRC develop a joint approach to licensing NGNP by August 2008. This activity is currently under way with inputs from the Phase 1 NGNP program. The DOE-USNRC discussions related to NGNP licensing are focused on defining the approach that will be used. It is possible the technol-
ogy-neutral approach will be used, but it is not clear if that approach would be ready in time for the engineering phase of the NGNP. In addition, the PBMR is currently in pre-application review for design certification by the USNRC. The issues being addressed are generic to HTR licensing, and this effort will provide a tangible forum in which to make progress on a licensing strategy for NGNP.
Fuel Cycle and Waste Technology
The disposition of spent fuel from the proposed NGNP reactor has not yet been addressed. HTR fuel is inherently stable in storage because it remains at low temperatures and because of the graphite matrix’s good thermal conductivity and low density of decay heat. However, the fuel volume is relatively large due to the low thermal power density and the fuel being imbedded in the graphite moderator. It has been suggested that the fuel might be consolidated by removing the matrix graphite, leaving only the coated particles, which in pebble bed reactors, reduces volume by more than an order of magnitude. A similar but smaller volume reduction (because of the higher packing density of the fuel particles) is possible with prismatic fuel. After volume reduction, the principal fission barrier is still retained by the TRISO coatings around the fuel kernels. However, the engineering-scale recovery of actinides from TRISO particles in an economic way has never been demonstrated, so that it is uncertain whether the HTR reactor can support a closed fuel cycle.
The treatment of the NGNP as a DOE reactor will allow interim storage of its fuels at DOE sites. However, should this reactor be a demonstration plant for a whole fleet of future reactors, then a broader program to address the disposition of the fuel from a whole fleet of HTRs is needed. In particular, if a closed-fuel cycle is desired for waste management or enhancing the fuel resources in the future, it is important to consider the processing that would be required to achieve a closed cycle for this fuel. This will be a significant challenge since, as already noted, the TRISO coatings that are key to fission product retention could also seriously complicate the reprocessing technologies.
Is the Program Purpose Clear?
The purpose of the NGNP program is to develop a commercial-scale VHTR that can satisfy the Generation IV VHTR goals, which include the generation of electricity and/or hydrogen, but within somewhat less ambitious parameters—for example, lower-temperature helium coolant outlet. This nuclear system, if successful, would provide a method for producing the bulk hydrogen necessary to move the country away from a carbon-based energy economy and could thereby help provide long-term energy security for the United States.
While nuclear hydrogen will have to be competitive with other methods for hydrogen production, the wide oscillations in the price of natural gas, the main source of hydrogen today, and the possibility of taxing carbon fuels in the future open the way for nuclear energy to provide hydrogen and/or heat needed in a wide sector of the chemical processing business. To the extent the HTR is also applied for electricity alone, this would enlarge the technology base and improve the economics of other HTR energy products, such as process heat and hydrogen.
As articulated in EPAct05, the NGNP program did not explicitly address the broader use of high-temperature process heat, but the complementary public/private partnership initiative clearly hopes to extend the HTR to industrial process heat applications that now primarily use expensive natural gas. The generation of bulk hydrogen for a hydrogen economy is an ambitious endeavor that is likely to be decades away because of the requirement to develop a hydrogen infrastructure, as well as the need to overcome many obstacles posed by a fuel-cell-based transportation industry. However, nearer-term applications could use process heat to displace natural gas, including the combined production of electricity and process steam, the direct application of high-temperature process heat in technologies such as steam-methane reforming, and the generation of hydrogen for existing markets. (Existing hydrogen markets include refineries and ammonia plants, which together use about 7 percent of the natural gas consumed in the United States.)
Does the Program Address a Specific and Existing Problem?
The program is designed to develop an advanced new reactor that can provide process heat and/or electricity. The cogeneration function appears to be a complication since electricity might be generated more economically by advanced LWRs. However, no other nuclear technology can generate the high temperatures needed for the broad range of process heat applications discussed. It has been recommended by NERAC that this dual mission be reconsidered and not be accepted without further analysis. It was felt that the dual mission would drive the design, increase the cost of the program, and extend the schedule. It is important to maintain flexibility in the sizing of the NGNP reactor to facilitate obtaining the needed international collaboration or co-funding by end users. Furthermore, while a dual-purpose mission would not be necessary for future commercial plants, it could serve as an engineering-scale heat exchanger for the NGNP plant to demonstrate the viability of coupling of a nuclear plant with a hydrogen production plant.
Is the Program Design Free of Major Flaws That Would Limit Its Effectiveness or Efficiency?
There is not a single articulated program schedule that is coordinated with all the required elements to successfully
commission the NGNP. The current disconnect between the base NGNP program plan and the complementary public/private partnership initiative must be resolved so that all parties are working to achieve a consistent set of milestones. These elements include the reactor design; the heat transport system design, including the IHX; the fuel design and supply; and the hydrogen generation process design. There currently exist both a schedule gap and a funding gap that prevent the hydrogen process plant design and the NGNP reactor design from being available by the time of plant operation (at the end of FY 2017).
Little planning has been done on how the fuel for the NGNP would be supplied. There is a particle fuel R&D program that is focusing on UCO fuel; however, it will take up to two decades to complete the development and testing of this new fuel form before it can be loaded into the NGNP. Further, the source of the fuel for the NGNP has largely been ignored. There is very limited capacity available today for TRISO-coated particle fuel—it exists in Japan, China, and South Africa, but only for UO2 kernels. There is no industrial UCO fuel fabrication capacity, nor has the manufacturing process been proven.
The reactor design is probably the least problematic aspect, although it must soon be decided whether to base it on pebble or prismatic (sometimes called “block”) fuel. The technology area with the most uncertainty and risk is the heat transport system. The intermediate heat exchanger (IHX) is a very demanding component and is critical for most process heat applications, including the generation of hydrogen. University- and industry-based R&D is ongoing for both metallic and ceramic designs, but it is not clear that an acceptable solution will be obtained consistent with the NGNP program schedule given current funding levels.
Are Key Decision Points and Alternative Courses of Action Identified?
The decision points and technical alternatives are well known. The key technical alternatives are the fuel type, the heat transport working fluid and the IHX, and the hydrogen generation process. It is important to evaluate the status of the technology using the Generation IV evaluation criteria given in Table 3-1 to ensure that the demonstration phase begins at the appropriate time.
Another significant decision point is the nuclear licensing approach. The alternatives are the old 10 CFR Part 50 multistep process, the new 10 CFR Part 52 one-step process, or the yet-to-be-developed 10 CFR Part 53 technology-neutral process. To meet the apparently preferred date of FY 2017 for plant operations will require that some of these decisions be made quickly, so that the detailed design, component and system testing, and licensing can be initiated to support this schedule. The approach to licensing the NGNP is critical and should be decided on early.
Is the Program Effectively Targeted So That Resources Will Address the Program’s Purpose Directly?
The budget for NGNP currently requested by DOE is not adequate to meet the preferred schedule: To remedy this state of affairs, a significant ramp-up of roughly $100 million per year would be required within 1 or 2 years. The budget for FY 2008 should be at least $60 million if the program is to be launched on a trajectory that will meet the 2017 operations date. DOE’s notional budget projection for the next 6 years is only about 20 percent of what is required to meet the stated schedule. The budgets for NHI are also probably not adequate if this preferred schedule is to be maintained. Finally, it is imperative that private sector funding be brought into the program to supplement the required research, development, and demonstration. The technology partners must be selected and end users must be convinced to join the public/private partnership at significant levels.
Does the Program Have a Limited Number of Long-Term Performance Measures That Focus on Outcomes and Meaningfully Reflect the Purpose of the Program?
Program milestones have been established, although there is no consistent set of milestones that is used by all the relevant stakeholders. The Generation IV program has developed evaluation methods and measures for assessing nuclear system design options. However, no specific performance metrics that clearly define the real commercial targets—for example, the cost of energy on a MWth or a MWe basis or the cost per kilogram of hydrogen generated—have been established for NGNP. On the other hand, once process heat end users are engaged, it should be possible to develop specific performance metrics for each fundamental application—for example, the cost of petroleum generated from coal.
Has the Program Demonstrated Adequate Progress in Achieving Its Long-Term Performance Goals?
Since the long-term performance goals are not fully established—for example, the final temperature design for the VHTR is not defined—it is not possible to judge the NGNP’s program on this criterion yet. The actual NGNP program remains in an early formative stage. This criterion should be held in abeyance until more progress is made on the program.
NUCLEAR HYDROGEN INITIATIVE
Nuclear Hydrogen Production
NHI is the DOE’s research program for technologies to produce hydrogen and oxygen from water feedstock using nuclear energy. The program includes a small effort supporting advanced low-temperature electrolysis, but the primary
focus of the R&D is three methods that use high-temperature process heat to achieve higher efficiency: thermochemical cycles, hybrid thermochemical cycles, and high-temperature electrolysis. Because the high-temperature methods could realize 60-80 percent greater efficiency than conventional electrolysis, the NHI program is tightly connected to the NGNP program to develop a reactor capable of providing high-temperature process heat. The mission of the NHI program is to operate a nuclear hydrogen plant to produce hydrogen at a price that is cost competitive with other transportation fuels by 2019. NHI activities are coordinated with the larger DOE hydrogen program led by the Office of Energy Efficiency and Renewable Energy, as well as with the NGNP project.
Most of the hydrogen production in the United States today uses steam reforming of natural gas as the source of both the hydrogen (about 10 million tons per year) and the heat needed to enable the chemical processes in steam reforming to take place. With the uncertain availability of low-cost natural gas in the future, it is prudent to look for alternative ways to produce the hydrogen needed for current and future applications. About 50 percent of current hydrogen production in the United States is used to make ammonia, which is mostly used for manufacturing fertilizers. Almost 40 percent of it is used at oil refineries for lightening and sweetening the heavy oils to produce liquid fuel products for vehicles and aircraft. The lightening process used in refineries will grow as production continues to shift toward heavier conventional oils in the United States and in Central and South America. Additionally, even heavier oils are being produced in greater quantities from tar sands in Canada, and new production of shale oils in the United States is anticipated. Given the size of the unconventional oil resources in North America (about 10,000 exajoules, as compared to 2,500 exajoules of conventional oil reserves in the Middle East), it is plausible that these resources may become a major source of U.S. liquid fuels. In fact, Canada already produces over 1 million barrels a day from tar sands, getting the needed heat and hydrogen from natural gas. The environmental burden of extracting and processing of such unconventional fuels is generally very heavy. If the heat and hydrogen needed to lighten and sweeten the heavy oils could be produced from water using nuclear or renewable energy sources, the importation of liquefied natural gas from sources outside North America and the emisson of carbon to the atmosphere could both be reduced.
Applications for hydrogen can be classified into near, intermediate, and long-term markets. The near-term markets involve existing industrial applications for hydrogen: oil refining, ammonia production for fertilizer, methanol production, and tar sands processing. Mid-term markets involve the expanding production of liquid fuels from unconventional resources, including coal, oil shale, and biomass. Some of these mid-term markets have become economic given the higher price of oil and gas in the last 2 years in comparison to the prices before 2004. For example, liquefied coal is used in South Africa to satisfy nearly half of the petroleum fuel demand. Long-term markets involve the direct use of hydrogen as an energy carrier for ground transportation and energy storage. The growth of these markets will be driven by the evolution of the technology and by economics. To support NHI planning, these markets should be studied with the aid of a systems analysis model. Given the escalating prices of gasoline and the mounting desire to reduce carbon emissions, the need for these products is likely to grow substantially, within years rather than decades.
Hydrogen Production Technology Options and R&D Status
Current R&D on high-temperature steam electrolysis focuses on solid oxide electrolysis cells, a process that was recently demonstrated on the laboratory scale at Idaho National Laboratory (INL). The electrolyzer cell energy efficiency of the process was close to 90 percent at a temperature of 850°C; this is higher than the conventional alkaline electrolyzer cell efficiency of 80 percent. A high-temperature cogeneration reactor—for example, the NGNP reactor—could provide both the process heat and the electricity needed for this higher-efficiency production of hydrogen.
The production of hydrogen from water via nuclear energy is also possible by means of high-temperature chemical reactions using heat alone (the so-called thermochemical water-splitting approach). Current NHI R&D focuses on two options, both of which rely on the thermal decomposition of sulfuric acid into oxygen and SO2 at 800°C to 1000°C as the fundamental reaction, and two different approaches—S-I and hybrid processes—to use the SO2 to produce hydrogen, oxygen, and recycled sulfuric acid.
The key elements of the S-I process have been tested separately at the laboratory scale and shown to work in the United States and Japan. In Japan, the synthesized process was demonstrated at low pressure on a small scale (30 L/hr) in December 2004. A similar demonstration (100 L/hr) was accomplished 20 years earlier by the Westinghouse Electric Company using the hybrid sulfur (HyS) process. In the United States, the construction of the S-I Integrated Laboratory Scale Experiment will be completed in FY 2007 in collaboration with the French CEA and will provide the first pilot-scale integrated demonstration at prototypical pressure and process conditions using electrical heating. In addition, small-scale university-based research in the United States is working on alternative thermochemical cycles that do not use sulfuric acid, along with research in catalysts and membranes to improve process efficiency. An integrated laboratory-scale experiment using modern electrolyzer technology is still needed for the HyS process and should be included in the NHI program.
The current NHI schedule calls for construction of an engineering-scale process demonstration (several tens of megawatts) in 2015, to be coupled to the NGNP reactor. The Japanese are also moving ahead with a project producing
30 m3/hr, or 1,000 times bigger than the country’s current laboratory-scale facility. The project will be coupled to Japan’s 30-MW high-temperature nuclear reactor, which started up in 2000.
The NHI program is focused on hydrogen production by nuclear heat or electricity. However, other aspects of the hydrogen technology are being developed by DOE offices other than NE. The research includes technology for the storage, transport, and regeneration of hydrogen, as well as infrastructure and standards for safe use by the public. The NE effort is being coordinated with the efforts of other DOE offices. However, because the use of hydrogen in the near term is likely to be in large chemical plants, much of the practice today for handling hydrogen at large plants can be applied to nuclear hydrogen as well. The only new element might be the potential for generating tritium in some reactors, which then could be of concern if there is a way for it to leak into the hydrogen side of the complex. However, such a possibility appears to be minimal when the reactor coolant is a nonhydrogenous material. In the longer term, when hydrogen might become useful as a distributed energy carrier, new technologies for storage and distribution will be needed.
Nuclear Hydrogen Initiative Evaluation
Is the Program Purpose Clear?
The purpose of the NHI program is to develop technologies that produce hydrogen using nuclear energy. The most efficient methods for producing hydrogen involve the direct use of high-temperature process heat, possibly coupled with some electricity input. The NHI program is closely linked to the NGNP program, which will develop a reactor capable of providing high-temperature process heat. The principal technology issues for the NHI program involve (1) identifying materials and associated fabrication methods for heat exchangers, cell stacks, and other equipment that must operate at high temperatures with very corrosive candidate process fluids such as sulfuric acid and (2) selecting, optimizing, and demonstrating integrated processes capable of producing hydrogen at the laboratory, pilot plant, and, finally, engineering demonstration scales.
Does the Program Address a Specific and Existing Problem?
The successful development of economically efficient methods to generate hydrogen using nuclear energy would address a number of important problems. In the near term, hydrogen produced in this way could replace the large quantities of hydrogen currently produced using natural gas, reducing carbon emissions and reducing the quantities of liquefied natural gas that the United States would need to import. In the longer term, this hydrogen could be used more broadly in other petrochemical applications, including the production of liquid fuels from unconventional sources such as tar sands, shale oils, coal, and biomass, and could be used directly as an energy carrier for transportation vehicles equipped with fuel cells.
Is the Program Design Free of Major Flaws That Would Limit Its Effectiveness or Efficiency?
The program is currently exploring several technology options for hydrogen production using laboratory-scale experiments. For thermochemical processes, integrated laboratory-scale experiments are scheduled to start in 2007, while for high-temperature electrolysis, cell and stack experiments are now under way, and module experiments will start in 2008. This laboratory-scale R&D is intended to inform decisions in 2011 on technologies and materials for two pilot-scale integrated experiments. One or more of these pilot-scale technologies would be selected in 2015 for demonstration at the engineering scale using heat delivered by the NGNP reactor. The current portfolio of research in the program is appropriate for the current phase of the project, and the program is free of major flaws. The committee has concerns, however, that the resources being devoted to the program are insufficient to meet the proposed schedule, and that the schedule is not fully integrated with the NGNP program schedule.
Are Key Decision Points and Alternative Courses of Action Identified?
Two key decision points have been defined by the program, the first in 2011 to select two system designs for pilot-scale experiments and the second to select one or two designs for engineering-scale demonstration in 2015. At each decision point the design options that prove unsuccessful are discarded.
Is the Program Effectively Targeted So That Resources Will Address the Program’s Purpose Directly?
Much of the current NHI R&D is university based, which is appropriate for many aspects of the current laboratory-scale R&D. However, as integrated experiments are started, an increasing fraction of the program support will need to be directed to the national laboratories and industrial participants in the program. More attention to industrial-scale implications of the technology is needed, starting with studying the implications of operating conditions for cost, reliability, and safety.
Does the Program Have a Limited Number of Long-Term Performance Measures That Focus on Outcomes and Meaningfully Reflect the Purpose of the Program?
The NHI program is evaluated using the Generation IV program performance measures. For the NHI program, the
economics and the safety and reliability criteria are the most important. However, specific metrics for evaluating performance have not been established. The committee recommends that the NHI program select specific economic metrics that can be linked to the cost of hydrogen produced by competing technologies, such as natural gas steam reforming. It is reasonable that until materials and fabrication methods have been identified for all of the major system components, a great deal of uncertainty will surround these evaluations. The design information will become available once decisions have been made before entering the pilot-scale demonstration phase in 2011. These decisions should be based on the potential to meet specific economic criteria.
Has the Program Demonstrated Adequate Progress in Achieving Its Long-Term Performance Goals?
The program is making adequate progress, but some acceleration is required to meet the milestones proposed for the NGNP project.
OTHER GENERATION IV REACTOR NUCLEAR ENERGY SYSTEMS
Other Generation IV System Program Descriptions
Six reactor concepts were recommended in the Generation IV Roadmap as having the most promise for meeting the Generation IV goals. Five concepts were selected for further development by DOE. The remaining concept, the MSR, has not been included in the scope of effort supported in the United States, but the United States monitors international progress on this concept. Of the concepts included in the plans of DOE, two are thermal neutron spectrum systems and three are fast neutron spectrum systems. The total amount of annual R&D funding in the United States for the alternative concepts (excluding NGNP) has been about $3 million per year. Therefore, even with the efforts abroad to address these concepts outside the United States, this level of funding allows only basic concept definition and limits focused research to areas of greatest uncertainty. For each technology a brief discussion of the concepts, the scope of R&D effort selected for the DOE effort, and the time line identified for progress is provided as follows.
Thermal Spectrum Reactors
VHTR. As noted above, this concept has been selected as the most promising concept for nuclear energy to produce process heat and hydrogen. Known as NGNP, DOE efforts (discussed above) for this concept have focused on the adoption of a demonstration plant/prototype. DOE has funded conceptual design efforts for a liquid-salt-cooled VHTR that would allow large power-up rates compared to gas-cooled reactors of the same size with the same fuel, offering the potential for improved economics.
SCWR. Like the VHTR, the supercritical-water-cooled reactor concept is a thermal-spectrum reactor that also holds the potential for improved technology. This reactor concept offers significant advances in economics through plant simplification and increased thermal efficiency, with reactor outlet temperatures of 500°C, well above the 300°C of today’s reactors. DOE, through GIF partnerships, has positioned itself to leave the leadership of this reactor concept to its international partners Canada and Japan. The GIF has identified the critical R&D issues that were examined from 2002 to 2005:
Corrosion of structural materials and cladding,
Water chemistry and heat transfer related to the materials issues, and
Demonstration for a base SCWR design of adequate safety and stability during operation and under off-normal conditions.
Fast Spectrum Reactors: the GFR, LFR, and SFR Concepts
Fast spectrum reactors can operate as either burners or breeders of fissile materials. As breeders they can multiply nuclear fuel resources by between 10- and 100-fold, depending on the particular design. As burners of fissile material they have the advantage of burning the minor actinides (neptunium and transplutonium) more efficiently than thermal-spectrum reactors. When operating with a fissile breeding ratio of unity, they are called self-sustaining reactors, although the fuel they breed can be used by thermal as well as fast reactors. The use of thorium in thermal reactors, which results in reduced production of the actinides that affect repository capacity and in improved fuel use, has also been studied as a route to self-sustaining reactors. Widespread deployment of self-sustaining reactors based on some combination of these technologies would extend the fuel resources for nuclear fission for hundreds of years should that be needed. One of the chief issues in the development of a self-sustaining reactor for use in the United States is economic competitiveness, given the requirements for high reliability and safety.
Since the completion of the Generation IV Technology Roadmap, three self-sustaining fast-spectrum reactors concepts—the GFR, LFR, and SFR—have been the subject of R&D efforts. All three systems were to be brought to a state where the best system could be chosen based on economics, safety, reliability, sustainability, proliferation resistance, and physical protection.
Because the SFR was already at a fairly advanced state of basic design, GIF organized a modest effort between 2002 and 2005 in which the Japanese and the French led the development of advanced SFR fuels for actinide transmutation
and more economically competitive designs. In contrast, the much less developed LFR effort focused on corrosion issues and advanced modular designs. The GFR has received the most attention over the last few years in France, where fuels, safety systems, and power conversion were the focus of efforts.
DOE worked with its GIF partners to maintain modest R&D programs for all three fast reactor concepts from 2002 to 2005. Originally the performance downselection for these concepts was planned for the same time frame as NGNP—2011. The R&D goal for the fast reactors (GFR, LFR, and SFR) has been to obtain enough reliable information on materials issues and fuel behavior in the event of an accident, while developing an economically competitive design. For all three reactor concepts, these R&D issues must be sufficiently understood by 2010 to allow a decision to be made about the best concept for further development and demonstration between 2011 and 2021.
Crosscutting R&D can benefit more than one reactor concept. Important fundamental information is needed in the following crosscutting areas:
Data to validate the models for the effects of irradiation on materials characteristics since the expected service time for nuclear power plants has effectively become at least 60 years and could soon be as much as 80 years.
Data on the behavior of UO2 and nonfertile (neutronically inert) actinide-bearing fuels operating at high temperatures for long times. For example, ceria, magnesia, and zirconia could be used in the Generation IV reactors to host the actinide fuel.
Information on advanced energy conversion systems, including equipment that interfaces between the coolant and the turbine working fluids in advanced cycles, such as the supercritical CO2 power cycle.
Information on the application of technology-neutral approaches to reactor licensing and advances in the regulatory system to include performance-based criteria for monitoring.
Current Status and Priorities for the Alternative Concepts
As previously noted, a downselect implicitly took place at DOE in late 2005 and early 2006, given the redirection at DOE toward support of GNEP. The DOE R&D focus has recently been shifted to elevate the priority for development and demonstration of the SFR as an advanced burner reactor (ABR) (Chang et al., 2006). Under the new DOE priorities for near-term deployment of a closed fuel cycle, the SCWR design work and any associated R&D are being closed out in the United States and only the international efforts will continue. The remaining work on the GFR and LFR concepts is gradually being moved to international support within GIF.
Evaluation of Other Generation IV Nuclear Energy System Programs
In effect, the United States selected two Generation IV nuclear energy systems in 2006: the VHTR for NGNP and the SFR for GNEP. Furthermore, the priorities of the two main strategic goals of the Generation IV program have been re-ordered, owing to the emergence of GNEP:
First priority. Used-fuel recycle and actinide burning to minimize waste products.
Second priority. Process heat to produce alternative energy products (e.g., hydrogen).
The committee observes that the Generation IV concept evaluation criteria (see Table 3-1) for reactor development adopted by the Generation IV Technology Roadmap were not applied in this selection. The R&D priorities and concept evaluation have been shifting, with minimal discussion of priorities and alternative courses of action. The Generation IV program formerly had well-defined goals and measures against which to gauge its decisions on the development of reactor technology options for sustainable nuclear energy, among them competitive cost, minimal waste streams, and innovative energy products. Since the arrival of GNEP, the new Generation IV program priorities are not well articulated for the portfolio of concepts, and the development of technology elements that are common to different Generation IV reactor designs are no longer well coordinated.
The committee observes that there is one focus on process heat and hydrogen production and another on reducing the high-level waste burden, but there has been no evaluation of the possibility of developing crosscutting technology in support of the VHTR or the SFR in a way that can take advantage of past related work and expand the base technology. For example, there are technology elements that may be common to both missions, such as supercritical fluid power conversion, high-temperature materials development, and innovative technologies for process heat. In fact, NGNP and GNEP appear to be competing for the chance to be demonstrated and commercialized, with both vying for the same limited DOE budget and not taking advantage of synergisms.
There are established program goals for the NGNP, but it is not clear under the new DOE program plans if the old performance measures for Generation IV will be applied to NGNP. Similarly, it is clear that no performance evaluations were carried out prior to the inclusion of a large demonstration plant for the SFR (i.e., the ABR) or for the large fuel separation facility. The SFR program structure seems vague at this time, appearing to involve selected studies of technology issues that are principally beneficial for commercialization rather than being explicitly linked to the long-term technology needs of nuclear energy.
The use of the Generation IV program metrics to compare the high-temperature reactors and fast-reactor systems
for dual missions—a process heat mission and a fuel cycle flexibility mission—appears to be absent from the current program. For example, there is little attention to how either the VHTR or the SFR technology will compete with existing LWRs in the electricity market.
The program resources are barely adequate for basic studies related to NGNP and the VHTR design (NGNP construction will begin only after an industry alliance matches DOE funds). Thus the program funding level for these programs is inadequate for developing the SFR, investigating the other Generation IV reactor concepts, and developing crosscutting nuclear energy technologies. Currently there is little in the way of synergies that can come from R&D developments across reactor concepts.
FINDINGS AND RECOMMENDATIONS
Next-Generation Nuclear Plant
Finding 3-1. The NGNP program has well-established goals, decision points, and technical alternatives. The key technical alternatives are the fuel type, the heat transport working fluid and the IHX, and the hydrogen generation process. A key decision point is the nuclear licensing approach for NGNP. To keep to the apparently preferred schedule, which has a FY 2017 plant operations date, some of the technical decisions must be made quickly, so that detailed design, component and system testing, and licensing can be initiated. However, it is unlikely that operation can be achieved by 2017 due to significant funding gaps that developed in FY 2006 and FY 2007. These gaps affected the scope and schedule for the planned testing of fuel and structural materials as well as the heat transport equipment.
Finding 3-2. Little planning has been done on how the fuel for the NGNP would be supplied. There is a particle fuel R&D program, but it will take up to two decades to complete the development and testing of this new fuel.
Finding 3-3. The main risk associated with NGNP is that the total funding under the current business plan calls for the private sector to match the government (DOE) funding. So far, however, not a single program has been articulated that coordinates all the elements required to successfully commission the NGNP. The current disconnect between the base NGNP program plan and the complementary public/private partnership initiative must be resolved.
With regard to the NGNP program, the committee recommends the following:
Recommendation 3-1. A schedule that coordinates the required elements for public-private partnership, design evolution, defined regulatory approach, and R&D results should be articulated to enhance the potential for program success.
Recommendation 3-2. DOE should decide whether to pursue a different demonstration plant (perhaps a smaller one with less total energy output or a plant with fewer hydrogen production options or a more basic technology approach for the VHTR) with a smaller contribution from industry.
Recommendation 3-3. In assessing NGNP conceptual designs, NE should favor design approaches that can achieve a variety of objectives at an acceptable technical risk—for example, hydrogen production, other high-temperature process heat products, enabling deep-burn actinide management, and improving economics.
Recommendation 3-4. NE should size the NGNP reactor system to facilitate technology demonstration for future commercial units, including safety. Consistent with resources available, NE should adopt an appropriate power level to demonstrate components and functionality of practical significance to commercial size.
Recommendation 3-5. Because of the very high temperatures and severe material performance requirements for thermochemical water splitting, NE should maintain the flexibility to first operate the NGNP using high-temperature steam electrolysis.
Recommendation 3-6. DOE should focus on the following NGNP technologies that require significant development and ensure that sufficient funds are available to advance these technologies whether or not industry matching funds are available:
Advanced materials for in-reactor operation at temperatures above 900°C.
Fuel particles that can withstand high burn-up and adverse transients.
The heat transport system for process heat applications, specifically to improve its efficiency and reliability.
Waste management technologies related to commercial deployment.
Recommendation 3-7. To ensure good performance of NGNP-based hydrogen production, NE should put more emphasis on the following:
Conceptual integrated process development and optimizing plan flow sheets, before moving to engineering designs.
Selecting the interface between the reactor and the hydrogen plant.
Developing system performance tools to address unsteady conditions, such as plant start-up, plant trip, and maintenance needs.
Assessment of total system economics.
Nuclear Hydrogen Initiative
The NHI program is aimed at developing new technologies to produce hydrogen and oxygen with high efficiency using nuclear energy. The focus of the program is the use of high-temperature process heat as the main energy input for the production of hydrogen, which promises significantly higher efficiency and lower cost than conventional low-temperature electrolysis. These processes involve challenging high-temperature materials problems, which are being addressed with laboratory-scale research at this time for three primary hydrogen production methods. Major technology downselections to allow testing at the pilot and engineering demonstration scales are scheduled for 2011 and 2015, respectively.
NHI is well formulated to identify and develop workable technologies, but the schedules and budgets need to be adjusted to assure appropriate coupling to the larger NGNP program.
With regard to the NHI program, the committee recommends the following:
Recommendation 3-8. DOE should expand NHI program interactions with industrial and international research organizations experienced in chemical processes and operating temperatures similar to those in thermochemical water splitting. NE should also broaden the hydrogen production system performance metrics beyond economics—for example, it could use the Generation IV performance metrics of economics, safety, and sustainability.
Other Generation IV Nuclear Energy System Programs
Finding 3-4. The second major concept for development in the Generation IV program, the SFR program, seems vague at this time and appears to involve selected studies of technology issues that are principally beneficial for commercialization rather than being explicitly linked to long-term nuclear energy technology needs.
Finding 3-5. The committee is concerned that the Generation IV concept evaluation criteria for reactor development adopted by the Generation IV Technology Roadmap were not applied in the selection of the VHTR and SFR. The Generation IV R&D priorities have been shifting, with minimum discussion of criteria and alternatives.
Finding 3-6. The program resources are barely adequate for basic studies related to NGNP and the VHTR design and entirely inadequate for exploring the SFR at a research level (unless the new GNEP program also includes basic research components), for investigating other reactor concepts, and for developing crosscutting reactor technology systems.
Finding 3-7. The use of the Generation IV program metrics to compare the high-temperature reactors and fast-reactor systems for dual missions—a process heat mission and a fuel cycle flexibility mission—appears to be absent from the current program.
With regard to the other Generation IV nuclear energy system programs, the committee recommends the following:
Recommendation 3-9. Within the Generation IV program, NE should modestly and reasonably support long-term base technology options other than the VHTR and the SFR, particularly for actinide management, using thermal and fast reactors and appropriate fuels.
Recommendation 3-10. Though NE currently focuses on the VHTR for process heat and the SFR for advanced fuel cycles, it should assess the cost-benefit of a single reactor system design to meet both needs.
Recommendation 3-11. Funding for NGNP and NHI should be increased if the schedule is to be accelerated to attract more industrial support.
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