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).


Program Description

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.

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