Leveraging Commercial Nuclear Reactors to Power Space Exploration
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Leveraging Commercial Nuclear Reactors to Power Space Exploration Ben Johnson Brigham Young University, Provo, UT 84602, 970-822-7177, [email protected] This study is aimed at exploring the I. INTRODUCTION adaptation of commercial nuclear reactors as NASA has had a goal of a crewed an alternative to NASA’s current high-power 1 fission reactor systems, particularly with respect mission to Mars since the 1960s . Current to applications on the surface of Mars. The architecture for this manned mission study concludes that while the Kilopower recommends In Situ Resource Utilization architecture is brilliantly poised to provide (IRSU) on the surface of Mars and even the affordable, near-term power in the 1-10 Moon to produce fuel needed for travel to 2 kilowatts electric (kWe) range, the financial and from Mars. The power needed to barrier to higher power scaling of such systems convert the atmosphere and regolith into fuel is significant. This financial barrier adds risk to was initially estimated at 80 kWe, although the development of greater than 10kWe recent studies show that actual power systems and is likely to result in the failure to requirements for a 500 day mission with a successfully scale the technology to higher crew of six on Mars require at least 36 kWe powers for space exploration applications. To of energy.3 Producing consistent electricity investigate the feasibility of commercial reactor on Mars and the Moon is challenging in adaptation, the study first explores which some respects because the long lunar night general reactor concepts would be the most and dust storms on Mars’ surface make solar likely to succeed in space applications. The energy less feasible.4 This has driven NASA study’s analysis of current reactor concepts to investigate a fission power source for the concludes that solid core reactors scored the mission. best, although molten salt reactors also show potential for applications in space. A case study Fission power sources have also of AlphaTech’s ARC Reactor concept been investigated by NASA since the 1960s. demonstrates that a commercial reactor In fact, the only successful development and concept has potential to be adapted for NASA’s launch of a space reactor happened in 1965 5 purposes without sacrificing primary with the SNAP-10A reactor. Since then, requirements for reliability, safety, and power billions of dollars have been expended to density. Preliminary specific power estimates of develop space reactors, but the technical, the reactor concept demonstrate potential to political, and financial barriers to bring energy orders of magnitude greater than development have led to their ultimate the Kilopower concept to space exploration failure, until the Kilopower concept was while also mitigating financial barriers. This developed, a solid core reactor designed to study concludes that commercial reactor fulfill NASA’s energy needs in the 1-10kWe development merits further investigation as an range.6 This comparatively simple reactor alternative to NASA’s development for reactors concept was designed to leverage existing greater than 10kWe. facilities and technology. These attributes 1 allowed the reactor to be nuclear tested and flight testing of any commercial reactor under a budget of less than $20 million, design would certainly be more financially which is less than 20 times the budget of its and technically expensive than the progenitor, the SP-100.7 The 1-10 kWe Kilopower system in the 1-10 kWe range, potential electric output of the current since any commercial reactor in use would Kilopower concept opens many doors for merit the same technology readiness level space exploration, including deep space Kilopower has already achieved. exploration, as well as manned Moon and B. Commercial Reactors for Application Mars landings.6 Scaling the reactor concept to Power Mars ISRU and Crew Habitat to higher powers than its current 1-10 kWe range has also been considered, including 1. Technical Benefits and Challenges the resulting Westinghouse eVinci concept, of Applying Current Kilopower which scales the energy output to greater Technology to Mars Manned than 1 megawatt electric (MWe).8 Mission Architecture Intuitively, power systems greater than 10 kWe could open even more doors for space As previously stated, NASA’s goal exploration, including nuclear electric for a manned Mars mission requires more propulsion and permanent lunar and Mars than the 1-10kWe range the Kilopower bases.9 concept offers. Adapting a commercial reactor could be an alternative to scaling the II. ANALYSIS Kilopower system to the requisite 36 kWe power level or transporting four, 10 kWe A. Commercial Reactors for Application Kilopower reactors to Mars’ surface. NASA in the 1-10 kWe Range recently conducted a study on the benefits The Kilopower system is well poised and costs of a single 40 kWe reactor, versus to fill the 1-10 kWe gap in power four, 10 kWe Kilopower reactors for Mars availability in the near term. This surface power applications.3 According to technology was developed much faster and this study done by Rucker et al., application cheaper than its predecessors, taking 5 years of four, 10 kWe Kilopower systems on Mars and under 20 million for near prototypic has technical advantages, including the testing.5,10 Similar testing done on the SP- ability to test the system viability on Mars or 100 reactor from 1983 until the project was the Moon with a single, smaller and less canceled in 1994 cost about $500 million in massive reactor, lower cable mass, and 1994 dollars, which is $870 million in 2020 easier surface transportability.3 Rucker et al. dollars.7 Although there is no certain cost of also mentions challenges to scaling the further flight testing the reactor, a 2005 power up with this methodology: additional estimate for the cost to flight test a reactor surface delivery trips, increased operational was $100 million to $1 billion.9 The contrast complexity, and potentially lower overall between the SP-100 and Kilopower testing system reliability to the challenges with such costs gives some assurance that the 1-10 a trip. An important detail when considering kWe concept should fall in the lower ranges the effect of these challenges is that all the of that estimate, which would likely be connections made from the power system to financially feasible. The cost of adaptation the ISRU unit need to be made robotically, 2 before the crew arrives. A United States Air NNSA plans on spending $188 million on Force study also cited by Rucker et al. Naval Nuclear Laboratory facilites, determined that these connections are the compared to $23 million in the combined leading cause of aerospace reliability costs of all other research facilities. Perhaps problems. These challenges suggest that it a better evidence that the cost of upgrading may be desirable for the current Mars the facilities is substantial is that the 75 year manned mission architecture to scale the old COMET and FLATTOP critical Kilopower reactor to 40 kWe.2 assembly units are still in use after years of NASA fission power testing and Scaling this reactor also has development. technical challenges, including the bonding of the heat pipe heat rejection system to the The financial cost of the additional core, potential concerns about the solid research and development for a scaled UMo of the core creeping at high reactor is also a concern. It should first be temperatures, and the solid fuel swelling as noted that higher power Kilopower systems temperatures increased. The fuel swelling is already have a proof of concept, and the the primary reason attributed to the scaling technology is relatively simple compared to limit of 10 kWe, although NASA is previous designs. This must nevertheless be confident that this can be mitigated by a new balanced with the cost of overcoming the fuel pin design. This new design would technical challenges mentioned earlier. This however require additional testing.6 balance makes estimating the financial cost of scaling Kilopower to higher powers 2. Financial Barrier to Scaling the difficult. One potentially useful datapoint is Kilopower Concept to Greater the SP-100 reactor, which, as previously Than 10 kWe mentioned, cost $870 million in 2020 One potential advantage to dollars. Budget reports from the NNSA are commercial development and adaption is the also yield another potential datapoint.12,13 mitigation of the financial barrier to According to these reports, $2.7 billion is developing and testing a prototype. As appropriated to naval reactor research and previously mentioned, the Kilopower reactor development per novel reactor built in the concept was brilliantly designed to be tested last 20 years. An MIT publication also under a minimal budget, including using mentions that commercial nuclear energy existing reactor testing facilities. These tests spends an average of $10-15 billion in used critical assembly equipment that was research and development for each nuclear over 75 years old, FLATTOP and reactor design.14 These figures provide COMET.11 These old critical testing reasonable evidence that the financial cost of facilities would not be able to critical test a scaling Kilopower, including upgrading larger, scaled Kilopower reactor.6 It is facilities and flight testing, would likely cost difficult to estimate the cost of new facilities closer to NASA’s $1 billion estimate. For to accommodate the testing of a potential 40 comparison, NASA’s projected FY 2020 kWe Kilopower concept, but some data budget for Exploration Research & points come from the FY 2020 NNSA Technology is $178.6M, a category not budget reports.12 These reports show that the exclusive to developing space fission reactors.15 3 4000 3500 3000 2500 2000 1500 1000 500 Millions of 2020 USD 0 0 1 2 3 4 5 6 7 8 9 1011*1213 141516 1718 1920 Years of Development 1/3 of Average Naval R&D Spent per Reactor Average Naval R&D Spent per Reactor Design Built $60M per Year NASA Investment Total Exploration Research & Technology Budget Investment Fig.