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The 2004 NASA Vision for Space Exploration calls for the return of mankind to the moon by no later than 2020, in preparation for an adventure to Mars and beyond. An envisioned lunar outpost will provide living quarters for initially 5– 10 astronauts for up to 2 weeks, and latter for science experiments, and recovery of mineral and indigenous resources for the day-to-day operation and production of propellant. These activities would require electrical and thermal powers in the order of 10’s – 100’s of kilowatts 24/7. Potential power options include photovoltaic, requiring massive batteries or fuel cells for energy storage during the long nights on the moon, and nuclear reactor power systems, which are much more compact and operate independent of the sun. This paper examines the benefit of using the lunar regolith as a supplemental neutron reflector on decreasing the launch mass of the Sectored Compact Reactor (SCoRe-S), developed at the Institute for Space and Nuclear Power Studies. In addition to providing at least $2.00 of hot-clean excess reactivity at the beginning of life, various SCoRe-S concepts investigated in this paper are at least $1.00 sub-critical when shutdown, and when the bare reactor cores are submerged in wet sand and flooded with seawater, following a launch abort accident. Design calculations performed using MCNP5 confirmed that using lunar regolith as supplementary reflector reduces the launch mass of the SCoRe-S cores by ∼ 34% – 35%, or 150 – 200 kg, while satisfying the above reactivity requirements. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Fast neutron spectrum space reactors are an appropriate choice for high thermal powers, but for low powers, they need to be large enough to satisfy the excess reactivity requirement while remaining sub-critical when immersed in wet sand and flooded with seawater following a launch abort accident. All Sectored, Compact space Reactors (SCoRe) are fast spectrum reactors. They have a 0.1 mm thick 157Gd2O3 coating on the outer surface of the reactor vessel to reduce the effect of wet sand as a reflector, and 157GdN fuel additive to reduce the effect of thermal neutron fission on the criticality of the flooded reactor following a launch abort event. This paper identifies the SCoRe-S cores with the smallest BeO radial reflector thicknesses which satisfy the reactivity design requirements. These are a cold-clean and hot-clean excess reactivity > $4.00 and $2.00, respectively, at least $1.00 subcritical at shutdown, and when submerged in wet sand and flooded with seawater following a launch abort event. Reducing the radial reflector thickness increases the 157GdN fuel additive but decreases the diameter, and hence the shutdown margin, of the B4C/BeO control drums. The smallest reactor to satisfy the reactivity design requirements is SCoRe-S7, which has a thick BeO radial reflector (15.3 cm), and its mass (425.3 kg) is 21 kg heavier than the next larger SCoRe-S8 core with a thinner BeO reflector of 13.3 cm. The SCoRe-S7 is also 1.5 kg heavier than the SCoRe-S11, with the largest core, but the thinnest radial reflector thickness of 10.7 cm. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Fast neutron spectrum space reactors are an appropriate choice for high thermal powers, but for low powers, they may not satisfy the excess reactivity requirement while remaining sub-critical when immersed in wet sand and flooded with seawater following a launch abort accident. This paper identifies the smallest size fast spectrum, Sectored, Compact Reactor loaded with Single UN fuel pins (SCoRe-S7), which satisfy the requirements of cold clean excess reactivity > $4.00 and remains at least $1.00 subcritical at shutdown and in submersion conditions. Results indicate that increasing the diameter of the SCoRe-S core reduces its active height and the UN fuel enrichment, but increases the Spectrum-Shift Absorber (SSA) of 157GdN additive to the fuel. All SCoRe-S cores also have a 0.1 mm thick 157Gd2O3 SSA coating on the outer surface of the reactor vessel to reduce the effect of the wet sand reflector, while the SSA fuel additive reduces the effect on the criticality of the flooded reactor caused by thermal neutron fission. The active core height decreases from 42.4 cm for the smallest SCoRe-S7 to as much as to 37.4 cm for the largest core of SCoRe-S11. For a 1.8 MWth reactor thermal power the UN fuel specific power decreases from 17.0 in the SCoRe-S7 to 11.5 Wth/kg in the -S11. The corresponding reactor total mass, including the BeO reflector, increases from 440 kg to 512 kg. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Space nuclear Reactor Power Systems (SRPSs) are being developed to meet electrical power requirements for NASA’s planetary exploration missions early next decade. In addition to enjoying some degree of autonomy, these systems need to operate reliably through the end of the mission, which could not be realized solely through a redundancy in the reactor’s coolant loop. Besides increasing the total system mass, such hardware redundancy does not eliminate a single-point failure in the reactor and subsequent loss of coolant. This paper presents three concepts of the liquid metal cooled. Sectored, Compact Reactor (SCoRe) for the avoidance of single-point failure. The SCoRe-S, ScoRe-M, and SCoRe-L concepts are for small, medium, and large reactor cores, covering a wide range of electrical power requirements, from 10’s of kWe to a few MWe. As a common feature in all SCoRe concepts, the reactor core is divided into six sectors that are neutronically coupled but thermal-hydraulically decoupled. The dividers of the sectors are liquid metal heat pipes, which facilitate cooling a sector experiencing a Loss of Coolant (LOC) by passively transporting the fission power generated in it to the two adjacent sectors without losing the mission. At the same time, the fission power of the reactor is reduced to avoid overheating the fuel in the sector experiencing a LOC. The SCoRe concepts have compact, hexagonal cores surrounded by a relatively thick (10 cm minimum) BeO reflector and axial BeO reflector that is 4 cm thick. The SCoRe is placed directly in front of the radiation shield, thus reducing the shield mass and that of the power system. In SCoRe-S cores, the UN fuel pins are arranged in a triangular lattice while in the SCoRe-M and SCoRe-L cores, the UN fuel pins arranged in a triangular lattice are assembled in 19-pin and 37-pin shrouded bundles, respectively. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]