Reactor On A Rocket (ROAR)
The Reactor On A Rocket (ROAR) program will develop and demonstrate a High-Assay Low-Enriched Uranium (HALEU) nuclear thermal propulsion (NTP) system. The capability afforded by NTP will expand the operating presence of the U.S. in space to the cislunar volume and enhance domestic operations to a new high-ground, which is in danger of being defined by the adversary. The program will initially develop the use of additive manufacturing (AM) approaches to print NTP fuel elements. In addition, the program will investigate on-orbit assembly techniques to safely assemble the individual core element subassemblies into a full demonstration system configuration, and will perform a technology demonstration.
DARPA's FY 2020 Plans:
- Demonstrate additive manufacturing techniques using surrogate materials, followed by proof-of-principle additive manufacturing of natural uranium reactor components.
- Initiate development of a modular nuclear propulsion system, including incorporation of additively manufactured fuel into a lowenriched uranium reactor and additive engine.
- Complete preliminary design of the demonstration integrated nuclear propulsion system.
Utilizing nuclear technology is not new. Nuclear Thermal Propulsion (NTP) research is part of NASA’s history. In 1961, NASA and the former Atomic Energy Commission jointly embarked on the Nuclear Engine for Rocket Vehicle Application (NERVA) program – an effort that over several years led to the design, building, and testing of reactors and rocket engines. But shifting priorities, political winds and space budget cutbacks led to curtailment of NASA’s nuclear propulsion work at the end of 1972. For decades therafter, the range of nuclear propulsion system designs involved reactors fueled by highly enriched uranium.
At the request of the Presidential Office of Science and Technology Policy (OSTP), a brief study was done by the Department of Energy's Space Reactor Power Systems Division of the impact of using other than highly enriched uranium (HEU) in the design of space nuclear reactor power systems. A presentation of the preliminary results was made to OSTP on February 10, 1994. Use of Uranium enriched to significantly less than 93% U-235 (medium-enriched uranium [MEU], defined as approximately 35% U-235, or low-enriched uranium [LEU], defined as < 20% U-235), always resulted in a mass penalty for the reactor core for a given power.
Recent studies, however, have shown that low-enriched uranium (LEU) can be used to create an NTP engine. Now NASA is looking at systems that use low-enriched uranium. This is consistent with US policy. “The United States is committed to eliminating the use of HEU in all civilian applications, including in the production of medical radioisotopes, because of its direct significance for potential use in nuclear weapons, acts of nuclear terrorism, or other malevolent purposes.” (2012 White House “Fact Sheet”).
One key benefit of this approach is that using low-enriched uranium may allow established rocket engine test facilities to be modified for use in qualifying NTP systems. Systems for capturing all potentially radioactive effluents from ground testing are also being developed and demonstrated, further increasing flexibility in test site location. Secondarily, using low-enriched uranium could be less impactful on budget and schedule due to the reduction of handling and security regulations. Low enriched uranium (LEU) lowers the security burden required to handle the nuclear material in the reactor components. Most nuclear thermal propulsion engine designs utilize uranium fuel enriched to 93 wt% 235U highly enriched uranium (HEU), which is over bomb-grade.
BWXT Nuclear Energy, Inc., headquartered in Lynchburg, Virginia was working with NASA on initial reactor conceptual trades and designs, initial fuel and core fabrication development, licensing support for initial ground testing, and engine test program development. By 2018 NTP fuel was being developed and fabricated by BWXT. Fuel samples were undergoing non-nuclear testing in NASA’s Compact Fuel Element Environmental Tester (CFEET) at NASA’s Marshall Space Flight Center in Huntsville, Alabama, helping to validate fabrication techniques and performance, Houts notes.
Non-nuclear testing of full-length fuel segments was planned for NASA’s Nuclear Thermal Rocket Element Environmental Simulator (NTREES), and potential follow-on projects may include fuel element testing at a Department of Energy facility, such as Idaho National Laboratory’s Transient Reactor Test Facility. Full utilization of NTP systems would also require an engine ground test facility. One option under review was use of the NASA’s Stennis Space Center’s A3 test stand to fully confine the hydrogen exhaust, and other options are being considered as well. Stennis was on track for a 2019 subscale demonstration of NTP exhaust capture.
CERMET is an acronym for CERamic METal composite, and was one of the first fuel forms tested as part of Project Rover. This fuel form offered increased temperature resistance, better thermal conductivity, and greater strength compared to the graphite fuel elements selected for NERVA, but unfortunately they also required much more development.
The Nuclear Energy Oak Ridge Site Office (NE-ORSO) of the Department of Energy (DOE) announced 07 January 2019 plans to contract with American Centrifuge Operating LLC (ACO), a subsidiary of Centrus Energy Corp., for the demonstration of high assay low enriched uranium (HALEU) production to support DOE research and development activities and programs. The HALEU Demonstration Program has two primary objectives: (1) Deployment of a 16 machine AC-100M HALEU Cascade producing a 19.75% U-235 enriched product by October 2020; and (2) Demonstration of the capability to produce HALEU with existing U.S.-origin enrichment technology, and provide DOE with a small quantity of HALEU beginning in 2020 for use in its research and development for the advancement of civilian nuclear energy and security, and other programmatic missions. The period of performance for this award was anticipated to be January 2019 - December 2020 with a one year option.
DOE's objective is to demonstrate the capability to produce HALEU by October 2020 utilizing U.S.-origin uranium enrichment technology. The use of existing U.S.-origin enrichment technology is needed in order to meet this schedule. Demonstrating the capability of U.S.-origin enrichment technology for the production of HALEU is the objective because only U.S.-origin technology would be capable of producing HALEU for use in any type of advanced reactor application, civilian or defense-related.
Many advanced commerical power reactors will require higher enrichments, and fuel forms very different from those manufactured for the current Light Water Reactors (LWRs). For example, the current generation of LWRs uses fuel enriched to less than 5% uranium-235. In contrast, many advanced non-LWR designs require enrichments between 5% and 20%, called High Assay Low Enriched Uranium (HALEU) fuel. In addition HALEU is also being considered for use in advanced fuels now being designed for the existing LWR fleet.
Advanced reactor concepts, such as advanced small modular reactors, offer the potential for step-change safety enhancements including walk-away safe reactor designs; unprecedented versatility including load-following capability, non-electric applications, and distributed power; dramatically improved financing; and the ability to consume waste as an energy resource. These design features, if proven and commercialized, could be truly transformational and game changing. The most mature, advanced U.S. designs could potentially be deployed as early as the mid-to-late 2020s by private industry, demonstrating U.S. leadership in this burgeoning area, as well as enhancing U.S. competitiveness in an emerging global market while supporting U.S. nonproliferation objectives. This is where the need for HALEU arises. Nearly all U.S. advanced reactors under development will require HALEU, including advanced micro reactors. The advanced reactor community has stressed the near-term need and importance of HALEU for advanced reactor fuel qualification testing and for potential demonstration reactors.
The U.S. Department of Energy (DOE) has determined that using DOE-owned high-assay low-enriched uranium (HALEU) stored at Idaho National Laboratory (INL) will not have a significant impact on the environment and is an important tool for advancing safe, economical, low carbon nuclear energy. In accordance with the National Environmental Policy Act (NEPA), DOE has issued a final Environmental Assessment for Use of DOE-Owned High-Assay Low-Enriched Uranium Stored at INL (DOE/EA-2087).
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