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Fusion Science and Technology
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How robust is HALEU from a nonproliferation perspective?
Shikha Prasad
High-assay low-enriched uranium (HALEU) has emerged as a popular fuel choice for advanced small modular reactors due to its long power production periods before refueling. It is currently being pursued by TerraPower, X-energy, BWX Technologies, Kairos, Oklo, and other reactor companies. HALEU has a uranium-235 enrichment ranging from 5 percent to 20 percent, whereas traditional LWRs use low-enriched uranium fuel enriched up to 5 percent.
HALEU will provide power for longer durations, compared with traditional LWRs. But could it also provide an opportunity for more rapid proliferation, as is speculated in a 2023 National Academy of Sciences report on advanced nuclear reactors (nap.nationalacademies.org/catalog/26630/)?
If a nuclear proliferator conspires to divert fresh nuclear fuel for weapons production when it has not been used in a reactor, the effort required in separative work units (SWUs) to enrich U-235 from 5 percent to 90 percent and that required to enrich from 20 percent to 90 percent are both very small, compared with the effort required to enrich U-235 from its natural abundance to the initial 5 percent.
Dennis L. Youchison
Fusion Science and Technology | Volume 68 | Number 3 | October 2015 | Pages 587-595
Technical Paper | Proceedings of TOFE-2014 | doi.org/10.13182/FST14-901
Articles are hosted by Taylor and Francis Online.
Due to a lack of prototypical experimental data, little is known about the off-normal behavior of recently proposed divertor jet cooling concepts. This article describes a computational fluid dynamics (CFD) study on two jet array designs to investigate their susceptibility to parallel flow instabilities induced by non-uniform heating and large increases in the helium outlet temperature. The study compared a single 25-jet helium-cooled modular divertor (HEMJ) thimble and a micro-jet array with 116 jets. Both have pure tungsten armor and a total mass flow rate of 10 g/s at a 600 °C inlet temperature. We investigated flow perturbations caused by a 30 MW/m2 off-normal heat flux applied over a 25 mm2 area in addition to the nominal 5 MW/m2 applied over a 75 mm2 portion of the face. The micro-jet array exhibited lower temperatures and a more uniform surface temperature distribution than the HEMJ thimble. We also investigated the response of a manifolded nine-finger HEMJ assembly using the nominal heat flux and a 274 mm2 heated area.
For the 30 MW/m2 case, the micro-jet array absorbed 750 W in the helium with a maximum armor surface temperature of 1280 °C and a fluid/solid interface temperature of 801 °C. The HEMJ absorbed 750 W with a maximum armor surface temperature of 1411 °C and a fluid/solid interface temperature of 844 °C. For comparison, both the single HEMJ finger and the micro-jet array used 5-mm-thick tungsten armor. The ratio of maximum to average temperature and variations in the local heat transfer coefficient were lower for the micro-jet array compared to the HEMJ device.
Although high heat flux testing is required to validate the results obtained in these simulations, the results provide important guidance in jet design and manifolding to increase heat removal while providing more even temperature distribution and minimizing non-uniformity in the gas flow and thermal stresses at the armor joint.