Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration (2009)

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3 Plutonium-238 Supply This chapter addresses NASA’s plutonium-238 (238Pu) production capability. Such a move would require a major needs and how they can be satisfied. investment in Russian production facilities—an investment that Russia seems unlikely to make unless the United States pays for it. Foreign or Domestic 238Pu? Restarting production of 238Pu in Russia would take ­longer When U.S. nuclear weapons production facilities were than restarting domestic production because of the long time shut down in 1988 and subsequently decommissioned, the it would take to negotiate an agreement with Russia and to United States lost the ability to produce 238Pu (except for complete the National Environmental Policy Act (NEPA, very small amounts for research). The substantial cost of 1970) process, which would apply to Russian production of maintaining those facilities could not be justified solely on 238Pu if it were funded by the U.S. government. Based on the basis of producing 238Pu, especially given the large 238Pu prior experience, it would probably take 2 or 3 years just to stockpile that existed at the time. That stockpile was suffi- negotiate and finalize an agreement with Russia before work cient to support radioisotope power system (RPS) missions could begin. In addition, 238Pu obtained from Russia can be through the 1990s and into the early 2000s. To supplement used only for civil applications and cannot be used to satisfy the Department of Energy’s (DOE’s) dwindling stockpile of U.S. national security applications, should they arise. Russia 238Pu, the DOE executed an agreement with Russia in 1992 has agreed to sell 238Pu to the United States with the limitation to purchase 238Pu from Russia. The DOE has taken delivery that it be used only for peaceful space missions, and that same of 20 kg to date. There are three more orders to be delivered, stipulation would presumably apply to future purchases. totaling less than 20 kg. A similar situation would likely exist if the United States To the best of the committee’s knowledge, 238Pu is no attempted to obtain 238Pu from a nation other than Russia: a longer being produced in Russia (or anywhere else), and large capital investment would be needed to construct new there is not a substantial amount of 238Pu left in Russia (or facilities and/or refurbish existing facilities; the work would anywhere else) available to meet NASA’s needs, beyond need to comply with NEPA if it were funded by the United that which Russia has already agreed to sell to the United States; and the long time necessary to negotiate an agree- States. Purchasing 238Pu was intended as a stopgap measure ment, obtain funding, and start work would create a substan- until U.S. production was reestablished, and continued tial shortfall in 238Pu available for NASA missions. procurement from Russia cannot serve as a long-term solu- tion to U.S. needs unless Russia itself reestablishes a 238Pu FINDING. Foreign Sources of 238Pu. No significant amounts of 238Pu are available in Russia or elsewhere in the world, except for the remaining 238Pu that Russia has already Because of radioactive decay, 238Pu cannot be stored indefinitely. How- agreed to sell to the United States. Procuring 238Pu from ever, with a half-life of 88 years, 238Pu decays rather slowly. After a storage period of 20 years, 85 percent of the original amount will still remain. R ­ ussia or other foreign nations is not a viable option. The Department of Energy did not provide an exact estimate of how much 238Pu it expects to have on hand after the deliveries of Russian 238Pu are complete. Based on available information, the committee estimates that there How Much Do We Need? will be a total of approximately 30 kg of 238Pu available for NASA, including On April 29, 2008, the NASA administrator sent a letter the 238Pu that has already been used to fuel the RPS for the Mars Science Laboratory, whose launch date has been postponed from 2009 to 2011. to the secretary of energy with an estimate of NASA’s future 14 

PLUTONIUM-238 SUPPLY 15 TABLE 3.1  NASA’s Demand for 238Pu, 2009-2028 (as of April 2008) 238Pu (kg) Mission Launch Date Watts Type of Radioisotope Power System 3.5 Mars Science Laboratory 2009a 100 MMRTG 1.8 Discovery 12/Scout 2014 250 ASRG 24.6 Outer Planets Flagship 1 2017 600-850 MMRTG 3.5 Discovery 14 2020 500 ASRG 5.3 New Frontiers 4 2021 800 ASRG 14 Pressurized Rover 1 2022 2000 High-performance SRGb 14 ATHLETE Rover 2024 2000 High-performance SRG 1.8-5.3 New Frontiers 5 2026 250-800 ASRG 3.5 Discovery 16 2026 500 ASRG 14 Pressurized Rover 2 2026 2000 High-performance SRG 5.3-6.2 Outer Planets Flagship 2 2027 700-850 ASRG 14 Pressurized Rover 3 2028 2000 High-performance SRG 105-110 Total demand for 238Pu, 2009-2028 (kg) 5.3-5.5 Annual demand (20-year average in kg/year) NOTE: ASRG, Advanced Stirling Radioisotope Generator; ATHLETE, All-Terrain Hex-Legged Extra-Terrestrial Explorer; MMRTG, Multi-Mission Radio- isotope Thermoelectric Generator; SRG, Stirling radioisotope generator. aThe launch date for the Mars Science Laboratory mission is currently 2011. bA high-performance SRG is a yet-to-be-developed concept that would use ASRG technology to meet the high power requirements of the lunar rovers. SOURCE: Letter from the NASA administrator Michael D. Griffin to secretary of energy Samuel D. Bodman, April 29, 2008 (reprinted in Appendix C). demand for 238Pu. The committee has chosen to use this for 12 missions during the 20-year period from 2009 to 2028. letter as a conservative reference point for determining the These missions have electrical power requirements ranging future need for RPSs (see Table 3.1). However, the findings from 100 to 2,000 watts (see Table 3.1). and recommendations in the report are not contingent upon The amount of 238Pu required to meet the needs of these any particular set of mission needs or launch dates. Rather, 12 missions will depend upon the type of RPS used to they are based on a conservative estimate of future needs. convert the thermal energy of the 238Pu fuel to electrical The estimate of future needs is also consistent with historic energy. The Mars Science Laboratory is equipped with precedent. For example, the mission set described in the a Multi-Mission Radioisotope Thermoelectric Generator administrator’s letter is consistent with the mission set in the (MMRTG), and the MMRTG is also currently baselined current Agency Mission Planning Model, although the latter for use on the Outer Planets Flagship (OPF) 1 mission. As includes three additional RPS-powered missions: two Inter- Chapter 4 describes in more detail, this is the only type of national Lunar Network missions (that could be launched RPS that is currently available, and it has a low energy- in 2013 and 2016) and a Mars Lander mission (that could conversion efficiency (of just 6.3 percent). The Advanced be launched in 2016). These additional missions are not Stirling Radioisotope ­Generator’s (ASRG’s) energy conver- included in Table 3.1, but the total amount of 238Pu required sion efficiency is predicted to be 28 to 30 percent, and an to fuel these additional missions is estimated to be 3.6 kg ASRG will produce more electricity than an MMRTG even or less. As noted below, even if the 238Pu required by these though it will be powered by just two general purpose heat missions is not considered, the DOE should take immediate source (GPHS) modules instead of the eight modules used action to reestablish domestic production of 238Pu. Including by an MMRTG. the International Lunar Network and Mars Lander missions The ASRG or some other type of Stirling radioisotope in the demand estimate would only increase the projected generator is baselined for all other missions listed in the 238Pu shortfall. administrator’s letter. All 12 missions will require a total The administrator’s letter requests that the DOE maintain of 105 to 110 kg of 238Pu, which is equivalent to an average the capability to provide NASA with fueled RPS assemblies production rate of 5.3 to 5.5 kg per year for 20 years. Letter from the NASA administrator Michael D. Griffin to secretary of energy Samuel D. Bodman, April 29, 2008 (reprinted in Appendix C). Dur- As described in Chapter 4, the International Lunar Network missions, ing the late 1980s and early 1990s, NASA periodically sent similar letters to if they take place, would likely be powered by a third type of RPS: a yet- DOE to update DOE regarding NASA’s requirements for 238Pu. to-be-defined “Small RPS.” 

16 RADIOISOTOPE POWER SYSTEMS PLUTONIUM-238 Production Process as a process improvement, would increase the yield, perhaps as high as 5.8 kg/year. A yield of 3 to 4 kg/year would allow Production of 238Pu is a complex process. At the top level, ATR to produce 238Pu while still supporting the Office of this process involves the following steps: Naval Reactors as well as other users, such as the National Scientific User Facility. 1. Processing of materials prior to irradiation. Like the ATR, HFIR also has multiple positions where a. Purify neptunium-237 (237Np). targets can be irradiated. The DOE’s Office of Science is b. Fabricate 237Np targets. HFIR’s primary user. Assuming that HFIR will continue to support its primary mission of neutron science, HFIR 2. Irradiation of targets in a nuclear reactor to transform 237Np into 238Pu. can create, at most, about 2 kg/year of 238Pu using standard target designs and reactor operating conditions. However, this would reduce the amount of support that it can provide 3. Processing of materials after irradiation. to secondary activities, such as production of medical and a. Extract, separate, and purify 238Pu and the remain- industrial isotopes. ing 237Np from the irradiated targets. Some test positions tend to produce unacceptably high b. Recycle the extracted 237Np so that it can be used concentrations of an unwanted Pu isotope (236Pu) in irradi- to make more targets. ated targets. Unlike 238Pu, the natural decay of 236Pu pro- c. Process the 238Pu so that it can be used to fabricate duces significant gamma radiation, which makes handling RPS fuel pellets, which are then assembled into and processing of irradiated targets much more difficult and GPHS modules. hazardous. Because 236Pu has a half-life of just 2.9 years, if irradiated targets are determined to have too much 236Pu, they The capabilities of existing facilities and the expertise of are stored until the 236Pu decays sufficiently so that radiation existing staff at the DOE’s Idaho National Laboratory (INL) levels are within acceptable limits. and Oak Ridge National Laboratory (ORNL) make them the Ultimately, the total amount of 238Pu that the United States best places to carry out the above steps. In particular, there can easily produce is limited by the availability of 237Np. are just two operational reactors in the United States that can Trace amounts of 237Np occur naturally in uranium ores, enable the production of large amounts of 238Pu (on the order but as a practical matter, 237Np used for 238Pu production of kilograms per year) in a timely fashion: the Advanced Test must be artificially produced. 237Np is not currently being Reactor (ATR) at INL and the High Flux Isotope Reactor produced in the United States, and it would not be easy to (HFIR) at ORNL. restart production. (The existing stockpile was created as The ATR and HFIR reactors are light-water fission reactors a byproduct of Cold War production of nuclear weapons that use enriched uranium as fuel. Both have numerous cylin- material.) However, the United States has enough 237Np in drical voids at various locations in and around the reactor core storage at INL to produce 5 kg of 238Pu per year for more where targets can be inserted and irradiated. The rate at which 237Np is transformed into 238Pu will vary greatly according to than 50 years. the location of the 237Np targets in the reactor. There are nine primary test positions (flux traps) in the Programmatic Options for Domestic Production ATR. Six of these are dedicated full-time to the DOE’s There are four primary options for initiating domestic Office of Naval Reactors. This office is responsible for production of 238Pu in a timely fashion. All of these options developing reactors to power submarines and aircraft carriers (1) rely exclusively on existing reactors (ATR and/or HFIR) for the U.S. Navy. Naval Reactors is the primary customer to irradiate 237Np targets, (2) would require new or refur- for the ATR and the primary source of funds used to sustain bished processing facilities to fabricate 237Np targets and the ATR. extract 238Pu from the irradiated targets, and (3) would ship There are also many other usable positions in the ATR extracted 238Pu to Los Alamos National Laboratory for where 237Np targets could be irradiated, although the outer encapsulation in fuel pellets. positions have neutron and gamma fields that are an order of magnitude lower than the positions nearest the center of the core. If 237Np targets are placed in all of the core posi- tions except for the six flux traps that are dedicated to Naval Reactors, ATR is thought capable of creating up to 4.6 kg of 238Pu per year using proven, cylindrical 237Np targets and The 238Pu encapsulation facilities at Los Alamos National Laboratory are standard reactor operating conditions. Advanced targets with currently operational and have been used to prepare fuel for past missions a more complex geometry, which could be introduced later as well as the Mars Science Laboratory. All four programmatic options for domestic production of 238Pu assume that 238Pu encapsulation facilities will Flux traps are areas with high levels of thermal neutron radiation, which remain at Los Alamos National Laboratory because it would not be cost- is ideal for converting 237Np to 238Pu with minimal impurities. effective to relocate them to another location such as INL. 

PLUTONIUM-238 SUPPLY 17 Option 1. Use HFIR alone to irradiate 237Np targets, parison to the negative consequences of continued inaction with processing of targets primarily at ORNL. to implement either option. The major cost of implementing either Option 3 or 4 The HFIR, as currently configured, could yield 1 to 2 kg would be for capital improvements at the site where most of 238Pu per year and still accommodate current, high-priority of the processing operations would take place. For both customers for that facility. If the HFIR were wholly dedicated approaches, previous, preliminary estimates by the DOE to support 238Pu production—and if it were configured with indicate that capital costs at the primary laboratory would a new beryllium reflector—the DOE estimates that it could be about $150 million over 5 to 7 years. The cost of capital yield at least 3 kg of 238Pu per year. However, like the ATR, improvements at the supporting center was estimated to be the HFIR is a unique facility, and it is not realistic to expect approximately $10 million to $12 million. The DOE will that the DOE would displace all current users of that facility undoubtedly update these estimates as part of its site selec- in order to dedicate the HFIR wholly to 238Pu production. tion process. A reliable estimate of the incremental cost of producing each new kilogram of 238Pu, after capital improve- Option 2. Use ATR alone to irradiate 237Np targets, with ments are completed, is not available. processing of targets primarily at INL. Option 4 would allow fabrication of 237Np targets to start earlier than with Option 3. Thus, Option 4 would allow test- It may be technically possible to get 5 kg/year from just ing of targets in the ATR and HFIR reactors to start sooner the ATR, but only at the cost of displacing virtually all other than with Option 3. This testing is necessary to validate users except for the Office of Naval Reactors, and at the cost predictions regarding the yield of 238Pu and the presence of of production flexibility when the ATR is out of service for undesirable isotopes in targets irradiated at various locations routine or corrective maintenance. in the reactors. From 1998 to 2000, the DOE prepared a broad Envi- Option 3. Use ATR and HFIR to irradiate 237Np targets, ronmental Impact Statement (EIS) concerning its nuclear with processing of targets primarily at INL. facilities that included reestablishing 238Pu production in the United States. This EIS, entitled Final Programmatic Envi- If both the ATR and HFIR reactors are used to support 238Pu ronmental Impact Statement for Accomplishing Expanded production, a yield of 5 kg/year could be achieved Civilian Nuclear Energy Research and Development and without displacing the primary customers of either facility, Isotope Production Missions in the United States, Including and 238Pu production would continue even when one of the the Role of the Fast Flux Test Facility, is commonly referred reactors is shut down for routine or corrective maintenance. to as the Nuclear Infrastructure Programmatic Environ- Under this option, 237Np targets would be fabricated at INL. mental Impact Statement (NI PEIS) (DOE, 2000). This EIS Irradiation of 237Np targets would occur at both INL and established the need to produce 5 kg/year of 238Pu to meet ORNL. Plutonium-238 recovery and purification would national needs for RPSs. A record of decision was issued that occur at INL. approved the NI PEIS (Federal Register, 2001). To date, no Administration has requested and Congress has not provided Option 4. Use ATR and HFIR to irradiate 237Np targets, funds necessary to implement the work described in the NI with processing of targets primarily at ORNL. PEIS. The DOE could implement Option 3 or Option 4 using (1) a modification of an existing EIS for INL and (2) a sepa- This option is the same as Option 3, except that the rate existing EIS for ORNL (without modification). processing of targets before and after irradiation would be In addition to the four options described earlier, other, conducted primarily at ORNL. With this option, INL would less practical options also exist. For example, building a new continue to store the existing stockpile of 237Np, shipping it reactor similar to HFIR or ATR would enable production rates to ORNL as needed for fabrication of 237Np targets. substantially higher than 5 kg/year. This could completely eliminate 238Pu availability as a constraint on NASA missions If and when the DOE is funded to reestablish 238Pu and RPS designs. However, this approach would probably production, the DOE’s first task will be to decide which of cost on the order of a billion dollars—much more than the the above options to use. The committee believes that both cost of using existing reactors. In addition, it would probably Options 3 and 4 are viable approaches for initiating domestic take 10 to 15 years to complete the necessary reviews and production of 238Pu, and the differences between these two construct a new reactor—too long to satisfy NASA’s future options, in terms of cost, schedule, and so on, pale in com- needs without a long hiatus in RPS-powered missions. Most of the neutrons produced in fission reactors appear as high-energy (“fast”) neutrons. The beryllium reflector increases the rate at which fast Options 3 and 4 would both require existing facilities to be upgraded. neutrons slow down, thereby increasing the level of low-energy (“thermal”) Option 3 would also require some new construction at INL before 237Np neutron radiation in the reactor. targets could be fabricated. 

18 RADIOISOTOPE POWER SYSTEMS Another approach would be to build multiple, large The committee believes that it is reasonable to establish TRIGA (Training, Research, Isotopes, General Atomics) 5 kg/year as the goal for domestic production of 238Pu for reactors, but the effectiveness of this approach has not been several reasons: demonstrated. In any case, this option would take much longer than any option that uses the existing HFIR and ATR • The NI PEIS established that a production rate of reactors, and it may not be possible to generate neutron 5 kg/year would meet national needs for 238Pu. flux levels in a TRIGA reactor high enough for useful 238Pu • NASA’s need for domestic production of 238Pu through production rates. 2028 is on the order of 5 kg/year. It is also possible to produce 238Pu using a commercial • It would be difficult to produce 238Pu at a rate substan- light-water reactor (CLWR) operated by an electric utility. tially higher than 5 kg/year using existing reactors (i.e., Such a reactor could yield 5 kg of 238Pu/year while still pro- the ATR and HFIR) because of technical factors and ducing electricity. However, aluminum-clad 237Np targets, because these reactors meet currently subscribed and which have been used in the past and could be used with ATR funded needs by other users. and HFIR, would not be suitable for the high operating tem- peratures of a CLWR. Thus, this option would require devel- Even so, over the longer term, the national need for 238Pu opment of new 237Np targets with Zircaloy or stainless steel could exceed 5 kg/year, and long-term efforts to enhance cladding (DOE, 2000). It would take years to develop, test, 238Pu production capabilities should consider the need for and validate the performance of new target designs in specific higher production rates, perhaps in concert with an assess- locations in a particular commercial reactor. The Record of ment of long-term national needs and capabilities for the Decision for the NI PEIS notes that CLWR options for pro- production of key radionuclides. ducing 238Pu “were not selected because of uncertainties in the target design, development and fabrication. The design FINDING. Domestic Production of 238Pu. There are two and fabrication technology of neptunium-237 targets for viable approaches for reestablishing production of 238Pu, irradiation in ATR and HFIR is much more mature” (DOE, both of which would use facilities at Idaho National Labora- 2001, p. 7887). Given that nothing has been done to address tory and Oak Ridge National Laboratory. These are the best these uncertainties since the Record of Decision was issued options, in terms of cost, schedule, and risk, for producing in 2001, CLWRs are not a viable option for addressing the 238Pu in time to minimize the disruption in NASA’s space need to reestablish 238Pu production as soon as possible. science and exploration missions powered by RPSs. If funding becomes available, the DOE could issue a university solicitation to consider innovative concepts for FINDING. Alternate Fuels and Innovative Concepts. 238Pu production. This research would be directed at pos- Relying on fuels other than 238Pu and/or innovative con- sible improvements over the long term, but it would not cepts for producing 238Pu as the baseline for reestablishing mitigate the need to provide an assured supply of 238Pu in domestic production of 238Pu would increase technical risk the near term. and substantially delay the production schedule. Neverthe- In summary, there are many different options that, in prin- less, research into innovative concepts for producing 238Pu, ciple, could be used to restart domestic production of 238Pu. such as the use of a commercial light-water reactor, may be Given enough time and money, many approaches could a worthwhile investment in the long-term future of RPSs. likely be made to work. But given NASA’s ongoing need for RPSs; given the technical, cost, and schedule uncertainties Immediate Action Is Required associated with other approaches; and given the schedule and budgetary constraints that exist, the only timely and The DOE’s inability to produce 238Pu and its limited practical approaches for restarting domestic production of ability to sustain its 238Pu stockpile using foreign sources is 238Pu involve the use of the DOE’s ATR and HFIR reactors. inconsistent with NASA’s current plans and future ambitions. These are also the lowest-risk approaches because they rely Because of the short supply of 238Pu, NASA has baselined on proven processes and technologies to a much larger extent future space missions with an RPS that has yet to be flight than any other option. qualified. In addition, NASA has been making mission- ­imiting decisions based on the short supply of 238Pu. NASA l has been eliminating RPSs as an option for some missions TRIGA [Training, Research, Isotopes, General Atomics] reactors, a class and delaying other missions that require RPSs until more 238Pu becomes available. For example, the New Frontiers 3 of small nuclear reactors designed and manufactured by General Atomics, are pool-type reactors that can be installed without a containment build- Announcement of Opportunity is not open to RPS-powered ing, and they are designed for use by scientific institutions and universities missions (NASA, 2009). This will likely eliminate from for undergraduate and graduate education, private commercial research, consideration some of the missions described in the report non­destructive testing, and isotope production. General Atomics has built Opening New Frontiers in Space: Choices for the Next TRIGA reactors in a variety of configurations and capabilities, with steady state power levels ranging from 20 kilowatts to 16 megawatts (GA, 2009). New Frontiers Announcement of Opportunity (NRC, 2008) 

PLUTONIUM-238 SUPPLY 19 TABLE 3.2  Best-Case Estimate of 238Pu Shortfall through 2028: 238Pu Demand Versus Supply Subsequent to Launch of Outer Planets Flagship 1 Mission 238Pu (kg) Discovery 14 3.5 New Frontiers 4 5.3 Pressurized Rover 1 14.0 ATHLETE Rover 14.0 New Frontiers 5 1.8-5.3 Discovery 16 3.5 Pressurized Rover 2 14.0 Outer Planets Flagship 2 5.3-6.2 Pressurized Rover 3 14.0 75.4-79.8 Total 238Pu demand subsequent to OPF 1 −13.0 Remaining inventory of 238Pu after OPF 1 (with ASRGs) 62.4-66.8 Best-case estimate of 238Pu production needed −58.0 Total 238Pu production if work starts in FY 2010 4.4-8.8 Best-case estimate of 238Pu shortfall NOTE: ATHLETE, All-Terrain Hex-Legged Extra-Terrestrial Explorer; FY, fiscal year; OPF, Outer Planets Flagship. because solar power is not feasible for some of the missions baselined, even if the DOE starts work immediately to restore described in that report. its 238Pu production capability, there will be a substantial The report The Sun to the Earth—and Beyond: A Decadal shortfall in meeting NASA’s needs for 238Pu through 2028. Research Strategy in Solar and Space Physics (NRC, 2003) While it remains to be seen whether ASRGs can and describes the solar probe mission as the highest priority in the will be flight qualified in time for OPF 1, if ASRGs can be large mission category, with implementation recommended used, NASA estimates that there will be 13 kg of 238Pu left as soon as possible. The Solar Probe mission, now scheduled from the available stockpile (including future deliveries of for launch in 2015, has been rescoped to eliminate the need ­ ussian 238Pu) to power missions after OPF 1. Those mis- R for an RPS. The rescoped mission will spend more time near sions (through 2028) and their demand for 238Pu are listed in the Sun, but the closest point of approach will be 8.5 solar Table 3.2. They will require a total of 75.4 to 79.8 kg of 238Pu. radii from the surface of the Sun instead of 3 (JHU, 2008). Thus, the required production from now through FY 2028 is Similar considerations affect other missions. The mission at least 62.4 to 66.8 kg. planning teams for OPF 1 have been directed to minimize Assuming that the DOE begins work in FY 2010 to power and consider the use of ASRGs. The use of a mixed establish the capability to produce 5 kg of 238Pu per year, it package of RPSs has also been considered. For example, will be able to produce 1 kg of 238Pu in 2016, 2 kg in 2017, MMRTGs could be used to provide a basic level of power, and 5 kg in 2018 and in each year thereafter. This amounts and ASRGs could be used for additional power for full mis- to a total production of 58 kg through the end of FY 2028. sion capability. For the OPF 1 mission, concurrent science The net result is a shortfall of 4.4 to 8.8 kg. Thus, even in operations will have to be limited unless there are at least 4 or a “best-case” scenario that minimizes 238Pu demands and 5 MMRTGs (or the equivalent number of ASRGs). maximizes 238Pu supply—which is to say, even if it is opti- The decadal survey for solar and space physics identi- mistically assumed that (1) NASA’s future RPS mission set is fies the interstellar probe as another high-priority mission, limited to those missions listed in the NASA administrator’s although it has been deferred until necessary propulsion letter of April 2008,10 (2) the 238Pu required by each mis- capabilities are available (NRC, 2003; 2004). Given the sion is the smallest amount listed in that letter (for missions demise of Project Prometheus (NASA’s space nuclear ­reactor with a demand for 238Pu that is listed as a range of values), power and propulsion program), the interstellar probe is not (3) ASRGs are flight qualified in time to use them instead of possible without RPSs (which are far less expensive than MMRTGs on OPF 1, and (4) funds for 238Pu production are space nuclear reactors). included in the DOE’s budget for FY 2010—it would not be The DOE’s budget does not currently include funds to possible for the DOE to meet NASA’s total demand for 238Pu. reestablish production of 238Pu. Yet, even if funding does Immediate action is required to minimize the mismatch become available in fiscal year (FY) 2010, full-scale pro- between NASA needs and the DOE capabilities and to avoid duction of 238Pu (5 kg/year) is unlikely to be possible until 2018, and that will be too late to meet all of NASA’s needs. 10Letter from the NASA administrator Michael D. Griffin to secretary of In fact, if the OPF 1 mission uses MMRTGs, as is currently energy Samuel D. Bodman, April 29, 2008 (reprinted in Appendix C). 

20 RADIOISOTOPE POWER SYSTEMS a potential hiatus in U.S. capability to launch RPS-powered 238Pu—and uncertainty about the future supply of 238Pu—is spacecraft. Continued inaction will force NASA to make now a major constraint on planning the future of the U.S. additional, difficult decisions to reduce the science return of space program. In recent years, each time a proposal has been some missions and to postpone or eliminate other missions made to restore production of 238Pu, action has been deferred. until a source of 238Pu is available. However, the day of reckoning has arrived, and continued It has long been recognized that the United States would delays in taking action to reestablish domestic production need to restart domestic production of 238Pu in order to of 238Pu will exacerbate the effect of current shortfalls, as continue producing RPSs. The problem is that the United detailed in Figure 3.1. States has delayed taking action to the point where the situ- The top part of Figure 3.1 shows three options for future ation has become critical, and the dwindling inventory of 238Pu supply: (1) funding for 238Pu production is included in 100 Pu supply with FY 2010 funding Kilograms of Pu-238 80 Pu supply with FY 2012 funding 60 Pu supply with no new Pu production 40 20 Pu Supply 0 2008 2010 2012 2014 2016 2018 2020 2022 2024 2026 2028 120 100 Kilograms of Pu-238 ATHLETE Pressurized 80 Pu demand if OPF 1 uses MMRTGs Rover 1 Rover OPF 2 Discovery Pressurized 60 Pu demand if OPF 1 uses ASRGs New Frontiers 16 Rover 3 Discovery 14 Pressurized Rover 2 40 Pu Demand OPF 1 New Frontiers 5 Discovery 20 12 MSL 0 2008 2010 2012 2014 2016 2018 2020 2022 2024 2026 2028 40 30 20 Kilograms of Pu-238 10 Pu Balance Best Case 0 -10 -20 The Problem -30 Status Quo -40 2008 2010 2012 2014 2016 2018 2020 2022 2024 2026 2028 Calendar Year Pu balance if OPF 1 uses ASRGs, with FY 2010 funding for Pu production Pu balance if OPF 1 uses ASRGs, with FY 2012 funding for Pu production Pu balance if OPF 1 uses MMRTGs, with FY 2012 funding for Pu production Pu balance if OPF 1 uses MMRTGs, with no new Pu production FIGURE 3.1  Potential 238Pu supply, demand, and net balance, 2008 through 2028. 

PLUTONIUM-238 SUPPLY 21 the DOE’s FY 2010 budget (red line [square data points]), New Frontiers 4, and the first pressurized lunar rover) to pro- (2) funding for 238Pu production is included in the DOE’s ceed on schedule. However, a delay of one year could force a FY 2012 budget (orange line [triangular data points]), or delay in the New Frontiers 4 schedule, and delay of two years (3) no 238Pu production (black line [circular data points]). or more could force a delay in the schedule of Discovery 14, The middle part of Figure 3.1 shows two options for future the first lunar rover, and subsequent missions. 238Pu demand: (1) OPF 1 uses MMRTGs (green line [square data points]) or (2) OPF 1 uses ASRGs (blue line [triangular FINDING. Current Impact. NASA has already been data points]). This plot assumes that 238Pu must be available m ­ aking mission-limiting decisions based on the short ­supply 1or 2 years before a mission launch date. It also assumes that of 238Pu. missions are launched in accordance with the administrator’s letter. Of course, mission launch dates are always subject to FINDING. Urgency. Even if the Department of Energy change. For example, the best estimate for the OPF 1 launch budget for fiscal year 2010 includes funds for reestablish- date is now 2020, not 2017 as indicated in the administrator’s ing 238Pu production, some of NASA’s future demand for letter. Although changes such as this will change the shape of 238Pu will not be met. Continued delays will increase the the middle portion of the demand and balance curves, they shortfall. do not change the end result, which is that NASA is facing a shortfall in 238Pu that will be difficult to overcome. HIGH-PRIORITY RECOMMENDATION. Plutonium- The bottom part of Figure 3.1 shows the future 238Pu bal- 238 Production. The fiscal year 2010 federal budget should ance for several combinations of 238Pu supply and demand. fund the Department of Energy (DOE) to reestablish produc- The blue lines [triangular data points] depict combinations tion of 238Pu. where OPF 1 uses ASRGs. The green lines [square data points] depict combinations where OPF 1 uses MMRTGs. • As soon as possible, the DOE and the Office of Man- Every possible combination of 238Pu supply and demand, agement and Budget should request—and Congress including those not shown in the figure, results in a future should provide—adequate funds to produce 5 kg of shortfall of 238Pu. 238Pu per year. A continuation of the status quo (no production of 238Pu • NASA should issue annual letters to the DOE defining and OPF 1 uses MMRTGs) results in the largest shortfall, the future demand for 238Pu. with all available 238Pu consumed by 2019. The best-case s ­ cenario has the smallest shortfall. However, it seems unlikely RPS MISSION LAUNCH RATE that all of the assumptions that are built into the best-case scenario will come to pass. MMRTGs are still baselined for Late in the study process—after the committee had com- OPF 1, there remains no clear path to fight qualification of pleted all scheduled meetings—a new issue was raised about ASRGs, and FY 2010 funding for 238Pu production remains the DOE’s ability to support the high launch rate for future more of a hope than an expectation. Thus, the actual shortfall RPS missions that NASA currently anticipates. is likely to fall somewhere between the best-case curve and The United States has launched a total of 26 RPS mis- the status-quo curve, and it could easily be 20 kg or more sions since 1961, but only 4 have been launched since instead of the 4 to 9 kg calculated in Table 3.2. 1977 ­(Galileo, Ulysses, Cassini, and Pluto/New Horizons). Continued inaction is also a problem because of schedule The NASA administrator’s letter of April 2008 anticipates requirements. Space science and exploration missions and 12 RPS missions in the next 20 years, with 9 of those mis- spacecraft design vary according to the type of power sys- sions launched during the 9-year period ending in 2028.11 tems available for use. Mission planners require assurance, Current DOE facilities used for fueling, processing, testing, early in the planning process, that the 238Pu required by a and shipping RPS units—as well as the DOE workforce prospective mission will be there when it is needed. All avail- needed to conduct radiological contingency planning—can able 238Pu will be essentially consumed by the Mars Science accommodate the relatively low RPS launch rate of recent Laboratory, Discovery 12, and OPF 1 missions (assuming decades, but some improvements may be needed to accom- MMRTGs are used for OPF 1, in accordance with NASA’s modate a sustained launch rate of one mission per year. current plans). NASA is unlikely to initiate competitive To address this issue comprehensively, it would be use- procurements or develop additional RPS-powered spacecraft ful to identify all constraints that the DOE and NASA must until the DOE begins construction of the facilities required overcome to increase the launch rate for RPS missions, and to produce the 238Pu needed by those additional missions. As how those constraints could be overcome. Relevant informa- shown in Figure 3.2, if the DOE receives funding in FY 2010 tion would include a comparison of historic and future launch for 238Pu production, the DOE should be able to begin con- rates for space nuclear systems and missions. For example, struction of new facilities and/or modification of existing facilities, as necessary, by the end of FY 2013, which would 11Letterfrom the NASA administrator Michael D. Griffin to secretary of enable the next set of RPS-powered missions (Discovery 14, energy Samuel D. Bodman, April 29, 2008 (reprinted in Appendix C). 

22 RADIOISOTOPE POWER SYSTEMS 2008 2010 2011 2012 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 Calendar Year 2009 2013 Pu DOE production 0.00 kg 0.00kg 0.00 kg 0.00 kg 0 .00 kg 0.00kg 0.00 kg 0.00 kg 0 .00 kg 0.0 0kg 0.00 kg 1.00 kg 2 .00 kg 5.0 0kg 5.00 kg 5.00 kg 5.00 kg 5.0 0kg 5 .00 kg 5.00 kg 5.00 kg NASA ESMD (Lunar Pressurized Rovers (Lunar Surface) Operations) #### 7.00 kg ## ## 7.00 kg #### 7.00 kg 7.00 kg 7.00 kg MSL Disc-12/ Scout OPF-1 NASA SMD (Planetary Science) Disc-14 NF-4 NF-5 Disc-16 3.50 kg OPF-2 Key DOE facility construction begins DOE facility preparation and NEPA compliance DOE DOE production ramp-up 238 DOE at full production (5 kg Pu/yr) Mission pre-phase A ( 238 Pu commitment required for RPS use) Competitive proposal period for NASA completed missions NASA Spacecraft development (Phases A-D) NEPA Compliance FIGURE 3.2  Time line for reestablishing domestic 238Pu production and NASA mission planning, 2010 through 2028, assuming the Depart- ment of Energy starts work in fiscal year 2010. 15 RPS missions were launched during a period of 8½ years National Security Council Memorandum 25 (PD/NSC-25, from April 1969 through September 1977. Those missions 1977) should also consider the demands of additional mis- included 31 RPSs of four different designs (see Table 2.1). It sions that use radioisotope heater units but not RPSs (e.g., the would be useful to know what it took to accomplish this feat Mars Pathfinder mission and the Mars Exploration Rover A in terms of staff, facilities, and facility usage at the DOE and and B missions).12 Also, not all launch reviews are equal. at NASA, especially at the Jet Propulsion Laboratory and the Kennedy Space Center. 12Radioisotope heater units (RHUs) provide small amounts of heat (on the Assessments of workforce issues related to radiological order of 1 W) to keep selected spacecraft components warm. They are used contingency planning associated with the Safety Review when mass and electrical power are at a premium for providing spacecraft thermal control. RHUs produce heat from the natural decay of radioactive and Launch Approval Process under Presidential Directive/ material, but they do not produce electricity. 

PLUTONIUM-238 SUPPLY 23 Although Galileo and Ulysses were launched one year DOE. 2001. Record of Decision for the Programmatic Environmental apart, and even though both used the same launch system and I ­ mpact Statement for Accomplishing Expanded Civilian Nuclear E ­ nergy Research and Development and Isotope Production Missions the same RPS design, the Ulysses review was just as involved in the United States, Including the Role of the Fast Flux Test Facility. as the Galileo review because the Ulysses GPHS-RTG was Federal Register 66(18): 7877-7887. Available at http://www.epa.gov/ oriented 90 degrees from those on the Galileo spacecraft. EPA-IMPACT/2001/January/Day-26/i2271.htm. In contrast, for the Apollo missions the first safety review GA (General Atomics). 2009. TRIGA Research Reactors. Available at was exhaustive, but subsequent Apollo safety reviews were http://triga.ga.com/45years.html. JHU (Johns Hopkins University). 2008. Solar Probe+ Mission Engineering abbreviated, focusing on mission and system differences. Study Report. Laurel, Md.: Johns Hopkins University Applied Physics Pioneer 10 and 11 were reviewed together, as were Viking 1 Laboratory. and 2, LES 8 and 9, and Voyager 1 and 2. NASA (National Aeronautics and Space Administration). Announcement Although the committee did not have the time or informa- of Opportunity: New Frontiers 2009. NNH09ZDA007O. Release date tion necessary to assess launch rate issues, the committee is April 20, 2009. NEPA (National Environmental Policy Act). 1970. National Environmental confident that the short supply of 238Pu is by far the most Policy Act of 1969, as amended, 42 USC Sections 4321-4347. Available urgent issue that must be addressed to carry out NASA’s at http://ceq.hss.doe.gov/Nepa/regs/nepa/nepaeqia.htm. plans for RPS missions. Still, a detailed investigation of NRC (National Research Council). 2003. The Sun to the Earth—and launch rate issues would be advisable because inattention Beyond: A Decadal Research Strategy in Solar and Space Physics. could eventually allow them to become a mission-limiting Washington, D.C.: The National Academies Press. NRC. 2004. Exploration of the Outer Heliosphere and the Local Inter­ factor. stellar Medium: A Workshop Report. Washington, D.C.: The National Academies Press. NRC. 2008. Opening New Frontiers in Space: Choices for the Next New REFERENCES Frontiers Announcement of Opportunity. Washington, D.C.: The DOE (Department of Energy). 2000. Final Programmatic Environmental N ­ ational Academies Press. Impact Statement for Accomplishing Expanded Civilian Nuclear PD/NSC-25 (Presidential Directive/National Security Council-25). 1977. E ­ nergy Research and Development and Isotope Production Missions Scientific or Technological Experiments with Possible Large-Scale in the United States, Including the Role of the Fast Flux Test Facility. Adverse Environmental Effects and Launch of Nuclear Systems into DOE/EIS-0310. December 2000. Washington, D.C.: U.S. Department Space. December 14, 1977 (as amended). of Energy.