Full submersion criticality accident mitigation in the Carbide LEU-NTR

Abstract

The present study seeks to characterize how to implement neutron poisons in the active core in order to mitigate the full submersion criticality accident in the Carbide Low Enriched Uranium Nuclear Thermal Rocket (Carbide LEU-NTR). In previous work, it was found that the increase in reactivity in the case of the full submersion is largely due to two factors: increased self-shielding by the core and an infinite reflector on the outside of the core. The increased core self-shielding is addressed by exploring the possibility of implementing a neutron spectrum shift absorber, despite the significant difficulties involved in successfully implementing a thermal neutron absorber in a thermal spectrum reactor. This is studied by looking at the implementation of Gd-157 in the fuel matrix and characterizing different parameters which make its implementation possible such as the degree to which and how the spectrum is hardened and the amount of poison included in the fuel.