View source for Kilopower

{{short description|NASA project aimed at producing a nuclear reactor for space}}
{{Use mdy dates|date=November 2017}}
{{Use American English|date=November 2017}}
{{Infobox nuclear reactor
| name        = Kilopower reactor
| image       = Kilopower experiment.jpg
| image_size  =
| caption     = Prototype NASA 1kW Kilopower nuclear reactor for use in space and planet surfaces
| location    =
| coordinates = <!-- Use {{coord}} -->
| concept     = [[Stirling engine]]
| generation  = Experimental
| reactor_line=
| type_label  =
| type        = <!-- Fertile material (if applicable, e.g. Th233) -->
| status      = In development
| fuel_type   = HEU
| fuel_state  = Solid (cast cylinder)
| spectrum_description    = <!-- Neutron energy spectrum (slow/fast) -->
| control     = [[Boron carbide]] control rod
| reflector   = [[Beryllium oxide]] radial reflector
| coolant     = [[Sodium]] heat pipes 
| moderator   =  
| electric    = {{val|1|-|10|u=kW}}
| thermal     = 4.3–43.3 kW<sub>th</sub>
| use         = Long-duration space missions
| website     = {{URL|www.nasa.gov/directorates/spacetech/kilopower}}
}}

'''Kilopower''' is an experimental [[U.S.]] project to make new [[nuclear reactor for space|nuclear reactors for space travel]].<ref name="DUFF-Gibson"/><ref name="Kilo_works">{{cite press release |last1=Jan Wittry |first1=Gina Anderson |title=Demonstration Proves Nuclear Fission System Can Provide Space Exploration Power |date=May 2, 2018 |url=https://www.nasa.gov/press-release/demonstration-proves-nuclear-fission-system-can-provide-space-exploration-power |publisher=NASA |access-date=May 2, 2018 |id=18-031 |archive-url=https://web.archive.org/web/20220418062638/https://www.nasa.gov/press-release/demonstration-proves-nuclear-fission-system-can-provide-space-exploration-power/ |archive-date=April 18, 2022 |url-status=live }}</ref> The project started in October 2015, led by [[NASA]] and the [[United States Department of Energy|DoE]]’s [[National Nuclear Security Administration]] (NNSA).<ref>{{cite web|title=Kilopower Small Fission Technology (KP)|url=https://techport.nasa.gov/view/14405|website=TechPort.nasa.gov|publisher=NASA|access-date=16 May 2018|date=2011-08-09 |archive-url=https://web.archive.org/web/20220418062844/https://techport.nasa.gov/view/14405 |archive-date=2022-04-18 |url-status=live }}</ref> As of 2017, the Kilopower reactors were intended to come in four sizes, able to produce from one to ten [[kilowatt]]s of electrical power (1–10&nbsp;kW<sub>e</sub>) continuously for twelve to fifteen years.<ref name="NASA_20171113">{{cite web |first1=Loura |last1=Hall |title=Powering Up NASA's Human Reach for the Red Planet |url=https://www.nasa.gov/directorates/spacetech/feature/Powering_Up_NASA_Human_Reach_for_the_Red_Planet |website=Space Tech |date=November 13, 2017 |publisher=NASA |access-date=November 15, 2017 |archive-url=https://web.archive.org/web/20220418063603/https://www.nasa.gov/directorates/spacetech/feature/Powering_Up_NASA_Human_Reach_for_the_Red_Planet/ |archive-date=2022-04-18 |url-status=live }}</ref><ref name="Space_Dev">{{cite journal|last1=McClure|first1=Patrick Ray|title=Space Nuclear Reactor Development|journal=Nuclear Engineering Capability Review|date=2017-03-06|volume=LA-UR-17-21904|page=16|url=http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-17-21904|access-date=16 May 2018 }}</ref> The [[fission reactor]] uses [[uranium-235]] to generate heat that is carried to the  [[Stirling engine|Stirling converters]] with passive sodium [[heat pipe]]s.<ref name="Media_event20180118">{{cite web |title=Kilopower Project media slides |url=https://www.nasa.gov/sites/default/files/atoms/files/kilopower-media-event-charts-final-011618.pdf |website=NASA.GOV |publisher=NASA and Los Alamos |access-date=January 26, 2018 |archive-url=https://web.archive.org/web/20211118075819/https://www.nasa.gov/sites/default/files/atoms/files/kilopower-media-event-charts-final-011618.pdf |archive-date=2021-11-18 }}</ref> In 2018, positive test results for the '''Kilopower Reactor Using Stirling Technology''' ('''KRUSTY''') demonstration reactor were announced.<ref name="Kilo_works" />

Potential applications include [[Nuclear electric rocket|nuclear electric propulsion]] and a steady electricity supply for crewed or robotic space missions that require large amounts of power, especially where sunlight is limited or not available. NASA has also studied the Kilopower reactor as the power supply for crewed Mars missions. During those missions, the reactor would provide power for the machinery necessary to separate and cryogenically store oxygen from the Martian atmosphere for ascent vehicle propellants. Once humans arrive the reactor would power their life-support systems and other requirements. NASA studies have shown that a 40&nbsp;kW<sub>e</sub> reactor would be sufficient to support a crew of between 4 and 6 astronauts.<ref name="DUFF-Gibson" />

==Description==
The reactor is [[nuclear fuel|fueled]] by an alloy of 93% [[uranium-235]] and 7% [[molybdenum]].<ref name="AIAA"/><ref>{{cite news |last1=Whittington |first1=Mark R. |title=NASA's Kilopower nuclear reactor would be a space exploration game changer |url=https://thehill.com/opinion/energy-environment/443068-nasas-kilopower-nuclear-reactor-would-be-a-space-exploration-game/ |work=The Hill |date=2019-05-10 |archive-url=https://web.archive.org/web/20220418064007/https://thehill.com/opinion/energy-environment/443068-nasas-kilopower-nuclear-reactor-would-be-a-space-exploration-game/ |archive-date=2022-04-18 |url-status=live }}</ref> The core of the reactor is a solid cast alloy structure surrounded by a [[beryllium oxide]] reflector, which prevents neutrons from escaping the reactor core and allows the chain reaction to continue. The reflector also reduces the emissions of [[gamma radiation]] that could impair on-board electronics.<ref>{{cite news |last1=Szondy |first1=David |title=NASA successfully tests next-generation space reactor |url=https://newatlas.com/nasa-krusty-reactor-nuclear/54465/|work=New Atlas |publisher=GIZMAG PTY LTD |access-date=12 June 2018  |date=May 2, 2018 |archive-url=https://web.archive.org/web/20220418064231/https://newatlas.com/nasa-krusty-reactor-nuclear/54465/ |archive-date=2022-04-18 |url-status=live }}</ref> A uranium core has the benefit of avoiding uncertainty in the supply of other radioisotopes, such as [[plutonium-238]], that are used in [[radioisotope thermal generator|RTGs]].<ref>{{cite web|last1=Foust|first1=Jeff|title=Plutonium supply for NASA missions faces long-term challenges - SpaceNews.com|url=https://spacenews.com/plutonium-supply-for-nasa-missions-faces-long-term-challenges/ |website=SpaceNews.com|access-date=16 May 2018|date=10 October 2017}}</ref>

The prototype KRUSTY 1&nbsp;kW<sub>e</sub> Kilopower reactor weighs 134&nbsp;kg and contains 28&nbsp;kg of {{SimpleNuclide|U|235}}. The space-rated 10&nbsp;kW<sub>e</sub> Kilopower for Mars is expected to have a mass of 1500&nbsp;kg in total (with a 226&nbsp;kg core) and contain 43.7&nbsp;kg of {{SimpleNuclide|U|235}}.<ref name="Space_Dev"/><ref name="Mars_Summit">{{cite web|last1=McClure|first1=Patrick Ray|title=A small fission reactor for planetary surface and deep space power|date=2019-07-08|url=http://fiso.spiritastro.net/telecon/McClure_7-31-19/McClure_7-31-19.pptx |access-date=16 July 2019 |archive-url=https://web.archive.org/web/20220418064559/http://fiso.spiritastro.net/telecon/McClure_7-31-19/McClure_7-31-19.pptx |archive-date=2022-04-18 |url-status=live}}</ref>

[[Nuclear reaction]] control is provided by a single rod of [[boron carbide]], which is a [[neutron absorber]]. The reactor is intended to be launched cold, preventing the formation of highly radioactive [[fission products]]. Once the reactor reaches its destination, the neutron absorbing boron rod is removed to allow the [[nuclear chain reaction]] to start.<ref name="AIAA">{{cite journal|last1=Gibson|first1=Marc A.|last2=Mason|first2=Lee|last3=Bowman|first3=Cheryl|last4=Poston|first4=David I.|last5=McClure|first5=Patrick R.|last6=Creasy|first6=John|last7=Robinson|first7=Chris|display-authors=3|title=Development of NASA's Small Fission Power System for Science and Human Exploration|journal=50th Joint Propulsion Conference|date=June 1, 2015|volume=NASA/TM-2015-218460|page=4|url=https://ntrs.nasa.gov/api/citations/20150011642/downloads/20150011642.pdf|access-date=16 May 2018 |archive-url=https://web.archive.org/web/20220418065151/https://ntrs.nasa.gov/api/citations/20150011642/downloads/20150011642.pdf |archive-date=2022-04-18 |url-status=live }}</ref> Once the reaction is initiated, [[radioactive decay|decay]] of a [[decay chain|series]] of fission products cannot be stopped completely. However, the depth of control rod insertion provides a mechanism to adjust the rate of the uranium fission, allowing the heat output to match the load.

Passive [[heat pipe]]s filled with [[liquid sodium]] transfer the reactor core heat to one or more free-piston [[Stirling engine]]s, which produce reciprocating motion to drive a linear [[electric generator]].<ref>{{cite news |last1=Patrascu |first1=Daniel |title=NASA KRUSTY Nuclear Reactor Could Power Outposts on Mars for Years |url=https://www.autoevolution.com/news/nasa-krusty-nuclear-reactor-could-power-outposts-on-mars-for-years-125424.html |work=autoevolution |publisher=SoftNews NET |access-date=12 June 2018 |date=3 May 2018 |archive-url=https://web.archive.org/web/20220418065258/https://www.autoevolution.com/news/nasa-krusty-nuclear-reactor-could-power-outposts-on-mars-for-years-125424.html |archive-date=2022-04-18 }}</ref> The [[melting point]] of sodium is {{convert|98|C|F}}, which means that liquid sodium can flow freely at high temperatures between about {{convert|400|and|700|C|F|sigfig=2}}. Nuclear fission cores typically operate at about {{convert|600|C|F|-2}}.

The reactor is designed to be [[intrinsically safe]] in a wide range of environments and scenarios. Several feedback mechanisms are employed to mitigate a [[nuclear meltdown]]. The primary method is passive cooling, which requires no mechanical mechanisms to circulate coolant. The reactor design is self-regulating through design geometry that creates a negative [[Fuel temperature coefficient of reactivity|temperature reactivity coefficient]].<ref name="Nerva">{{cite web|title=KRUSTY: First of a New Breed of Reactors, Kilopower Part II|url=https://beyondnerva.wordpress.com/2017/11/19/krusty-first-of-a-new-breed-of-reactors-kilopower-part-ii/|website=Beyond NERVA|publisher=beyondnerva|access-date=16 May 2018|date=19 November 2017 |archive-url=https://web.archive.org/web/20220418065430/https://beyondnerva.wordpress.com/2017/11/19/krusty-first-of-a-new-breed-of-reactors-kilopower-part-ii/ |archive-date=2022-04-18 |url-status=live }}</ref> In effect this means that as the power demand increases the temperature of the reactor drops. This causes it to shrink, preventing neutrons from leaking out. This in turn causes reactivity to increase and power output to increase to meet the demand. This also works in reverse at times of lower power demand.<ref name="Mars_Summit"/>

==Demonstration Using Flattop Fissions==
The development of Kilopower began with an experiment called '''DUFF''' or '''Demonstration Using Flattop Fissions''', which was tested in September 2012 using the existing [[Flattop (critical assembly)|Flattop]] assembly as a nuclear heat source. When DUFF was tested at the Device Assembly Facility at the [[Nevada Test Site]], it became the first Stirling engine powered by fission energy and the first use of a heat pipe to transport heat from a reactor to a power conversion system.<ref name="DUFF-Poston">{{Cite journal|last1=Poston |last2=McClure |first1=David|first2=Patrick|date=January 2013|title=The DUFF experiment - What was learned?|url=https://www.researchgate.net/publication/288297377|journal=Nuclear and Emerging Technologies for Space}}</ref> According to David Poston, the leader of the Compact Fission Reactor Design Team, and Patrick McClure, the manager for small nuclear reactor projects at [[Los Alamos National Laboratory]],<ref name="DUFF-Gibson"/> the DUFF experiment showed that "for low-power reactor systems, nuclear testing can be accomplished with reasonable cost and schedule within the existing infrastructure and regulatory environment".<ref name="DUFF-Poston"/>

==KRUSTY testing and first fission==
[[File:Kilopower DU core.jpg|thumb|The depleted uranium mockup core, manufactured at [[Y-12 National Security Complex|Y-12]] for the KRUSTY experiment.]]
[[File:KRUSTY heat pipes.png|thumb|Heat pipes of KRUSTY during an electrical-heating test]]

In 2017, the KRUSTY test reactor was completed. KRUSTY is designed to produce up to 1 kilowatt of [[electric power]] and is about 6.5 feet tall (1.9 meters).<ref name="Mars_20170629">{{cite news |last1=Irene Klotz |title=NASA to Test Fission Power for Future Mars Colony |url=https://www.space.com/37348-nasa-fission-power-mars-colony.html |access-date=November 15, 2017 |work=Space.com |date=June 29, 2017 |archive-url=https://web.archive.org/web/20220418070015/https://www.space.com/37348-nasa-fission-power-mars-colony.html |archive-date=2022-04-18 |url-status=live }}</ref> The goal of the test reactor is to closely match the operational parameters that would be required in NASA deep space missions.<ref>{{Cite web|url=https://ncsp.llnl.gov/sites/ncsp/files/2021-04/26_Sanchez_KRUSTY_MAR2017_R1.pdf |title=Kilowatt Reactor Using Stirling TechnologY (KRUSTY) Experiment Update Marcy 2017|last=Sanchez|first=Rene|date=March 2017|website=National Criticality Experiments Research Center|access-date=April 25, 2018 |archive-url=https://web.archive.org/web/20220418070215/https://ncsp.llnl.gov/sites/ncsp/files/2021-04/26_Sanchez_KRUSTY_MAR2017_R1.pdf |archive-date=2022-04-18 |url-status=live }}</ref> The first tests used a [[depleted uranium]] core manufactured by [[Y-12 National Security Complex]] in [[Oak Ridge, Tennessee|Oak Ridge]], Tennessee. The [[depleted uranium]] core is exactly the same material as the regular [[High-enriched uranium|high-enriched uranium (HEU)]] core with the only difference being the level of [[Enrichment of uranium|uranium enrichment]].<ref name="DUFF-Gibson"/>

The prototype Kilopower uses a solid, cast uranium-235 [[reactor core]], about the size of a paper towel roll. Reactor heat is transferred via passive sodium [[heat pipe]]s, with the heat being converted to electricity by [[Stirling engine]]s. Testing to gain [[technology readiness level]] (TRL) 5 started in November 2017 and continued into 2018.<ref name="NASA_20171113" /> The testing of KRUSTY represents the first time the [[United States]] has conducted ground tests on any space reactor since the [[SNAP-10A]] experimental reactor was tested and eventually flown in 1965.<ref name="DUFF-Gibson">{{Cite report|url=https://ntrs.nasa.gov/api/citations/20170002010/downloads/20170002010.pdf |archive-date=2022-01-23 |archive-url=https://web.archive.org/web/20220123085042/https://ntrs.nasa.gov/api/citations/20170002010/downloads/20170002010.pdf |url-status=live |title=NASA's Kilopower Reactor Development and the Path to Higher Power Missions|last1=Gibson |first1=Marc |last2=Oleson |first2=Steven |last3= Poston |first3=David |last4=McClure |first4=Patrick |website=NASA|date=March 4, 2017|access-date=March 25, 2018}}</ref>

During November 2017 through March 2018, testing of KRUSTY was conducted at [[Nevada National Security Site]]. The tests included thermal, materials, and component validation, and culminated in a successful fission trial at full-power. Various faults in the supporting equipment were simulated to ensure the reactor could respond safely.<ref name="Kilo_works"/>

The KRUSTY reactor was run at full power on March 20, 2018 during a 28-hour test using a {{val|28|u=kg}} uranium-235 reactor core. It reached {{convert|850|C|F}} was and generated about {{Val|5.5|u=kW}} of fission power. The test evaluated failure scenarios including shutting down the Stirling engines, adjusting the control rod, thermal cycling, and disabling the heat-removal system. A [[Scram]] test concluded the experiment. The test was considered to be a highly successful demonstration.<ref name="Nerva III">{{cite web|title=KRUSTY: We Have Fission! Kilopower part III|url=https://beyondnerva.wordpress.com/2018/05/02/krusty-we-have-fission-kilopower-part-iii/|website=Beyond NERVA|publisher=beyondnerva|access-date=16 May 2018|date=2 May 2018 |archive-url=https://web.archive.org/web/20220418070431/https://beyondnerva.wordpress.com/2018/05/02/krusty-we-have-fission-kilopower-part-iii/ |archive-date=2022-04-18 |url-status=live }}</ref>

==See also==
{{colbegin}}
*[[Advanced Stirling radioisotope generator]]
*[[Nuclear power in space]]
*[[Radioisotope thermoelectric generator]]
*[[RAPID-L]]
*[[Small modular reactor]]
*[[SNAP-10A]]
{{colend}}

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20180120144555/https://www.nasa.gov/directorates/spacetech/kilopower/ Kilopower NASA web site]
* {{YouTube|DcdfMcjUy_U|Kilopower: A Gateway to Abundant Power for Exploration}}
* {{YouTube|KobRfGqlpGc|Small Reactor for Deep Space Exploration - Los Alamos National Laboratory}}
* {{YouTube|NLE5YFuCmhw|Kilopower Reactor - public presentation in August 2018}}
* [https://www.nasa.gov/sites/default/files/atoms/files/ns_kilopower_fs_180111.pdf Kilopower - facts] 
* [http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-14-23402 KiloPower Space Reactor Concept - Reactor Materials Study]

[[Category:Nuclear power reactor types]]
[[Category:Nuclear power in space]]
[[Category:NASA programs]]
[[Category:Nuclear research reactors]]