Sectored Compact Space Reactor (SCoRe) concepts with a supplementary lunar regolith reflector

Design concepts of the Sectored Compact Space Reactor for Small power (SCoRe-S) have been developed for the avoidance of single-point failures in reactor cooling and energy conversion and a wide range of thermal powers. These modular, fast neutron spectrum, lithium cooled reactors with 16.0 cm thick BeO radial reflector are designed for at least +$2.00 hot-clean excess reactivity, and with a sufficient reactivity shutdown margin. They employ (GdN)-Gd-157 additives in the UN fuel and a 0.10 mn thick coating of (Gd2O3)-Gd-157 on the outer surface of the reactor vessel to ensure that the bare reactors, when submerged in wet sand and flooded with seawater following a launch abort accident, remain at least -$1.00 subcritical. In addition to identifying the smallest SCoRe-S Concept that satisfies the design reactivity requirements, the benefit of using a lunar regolith as a supplementary reflector to decrease the thickness of the BeO radial reflector and hence, the launch mass of the SCoRe-S concepts for a lunar outpost is investigated. Calculations performed using MCNP5 confirmed that SCoRe-S-7 with a 16 cm thick BeO reflector is the smallest to satisfy the stated reactivity requirements. Results also show that a lunar regolith reflector alone is inadequate for this reactor to achieve a critical state at the beginning of life. However, when the regolith is used in conjunction with a BeO reflector of a reduced thickness, this reactor not only becomes critical. but also satisfies the reactivity design requirements at a significantly reduced launch mass. Using it supplementary reflector of regolith decreases the thickness of the BeO reflector for the SCoRe-S7 from 16 cm to 8.0 cm, and to 5.7 cm for the SCoRe-S of the largest core. The resulting decreases in the launch mass of the SCoRe-S concepts are similar to 34% or 150-200 kg. (c) 2009 Elsevier Ltd. All rights reserved.