Shielding Analysis for a Moderated Low-Enriched-Uranium-Fueled Kilopower Reactor

• Published in: Nuclear technology 2022-07, Vol.208 (7), p.1137-1148
• Main Authors: King, Jeffrey C., de Holanda Mencarini, Leonardo
• Format: Article
• Language: English
• Subjects: dose assessment; low-enriched uranium; moderator; shielding; Space reactor
• ISSN: 0029-5450; 1943-7471
• DOI: 10.1080/00295450.2021.2004870

A low-enriched-uranium (LEU)-fueled space reactor could avoid the security and proliferation concerns inherent with highly enriched uranium (HEU)-fueled space nuclear reactors. Recent LEU-fueled space reactor designs include a moderator to reduce the size and mass of the reactor core. This paper considers shadow shield options for an unmoderated HEU-fueled space reactor and a moderated LEU-fueled space reactor. Both reactors are kilowatt-class reactors, producing 15 kW(thermal) of thermal power over a 5-year operational lifetime. Based on the shielding required to meet established dose limits [a neutron fluence of less than 10 14  n/cm 2 (1 MeV equivalent in silicon) and a gamma-ray dose of less then 1 Mrad in silicon], the moderated LEU-fueled space reactor will require a thicker shadow shield than the unmoderated HEU-fueled space reactor. The thinner reflector of the moderated LEU-fueled reactor results in more neutrons reaching the shadow shield at higher energies compared to the unmoderated HEU-fueled reactor. The presence of a significant reflector in most space reactor designs means that the core spectrum is relatively unimportant in terms of shadow shield design, as the reflector thickness has a much stronger impact on the neutrons and gamma rays reaching the shadow shield. Based on the results presented in this paper, the mass optimization of moderated LEU-fueled space nuclear reactors should always consider the coupled effects of the core, the reflector, and the shielding.