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Liquid Metal Cooled Reactor for Space Power
Abstract
The conceptual design is for a liquid metal (LM) cooled nuclear reactor
that would provide heat to a closed Brayton cycle (CBC) power conversion
subsystem to provide electricity for electric propulsion thrusters and
spacecraft power. The baseline power level is 100 kWe to the user. For
long term power generation, UN pin fuel with Nb1Zr alloy cladding was
selected. As part of the SP-100 Program this fuel demonstrated lifetime
with greater than six atom percent burnup, at temperatures in the range
of 1400-1500 K. The CBC subsystem was selected because of the
performance and lifetime database from commercial and aircraft
applications and from prior NASA and DOE space programs. The high
efficiency of the CBC also allows the reactor to operate at relatively
low power levels over its 15-year life, minimizing the long-term power
density and temperature of the fuel. The scope of this paper is limited
to only the nuclear components that provide heated helium-xenon gas to
the CBC subsystem. The principal challenge for the LM reactor concept
was to design the reactor core, shield and primary heat transport
subsystems to meet mission requirements in a low mass configuration. The
LM concept design approach was to assemble components from prior
programs and, with minimum change, determine if the system met the
objective of the study. All of the components are based on technologies
having substantial data bases. Nuclear, thermalhydraulic, stress, and
shielding analyses were performed using available computer codes.
Neutronics issues included maintaining adequate operating and shutdown
reactivities, even under accident conditions. Thermalhydraulic and
stress analyses calculated fuel and material temperatures, coolant flows
and temperatures, and thermal stresses in the fuel pins, components and
structures. Using conservative design assumptions and practices,
consistent with the detailed design work performed during the SP-100
Program, the mass of the reactor, shield, primary heat transport,
reactor instrument and control, and additional structure totaled
approximately 1100 kg.
... The LMRs have been considered as a potential technology for space power applications, specifically for long-duration space missions. The liquid metal coolant that the LMR transfers heat from the reactor core to a power conversion system, such as a Closed Brayton Cycle (CBC), to produce electricity [75]. Some conceptual designs and studies have been conducted by different organizations. ...
A small modular reactor (SMR) is a nuclear reactor that is characterized by its smaller size and capacity when compared to traditional large-scale nuclear reactors. An SMR is often categorized as having an electrical output of less than 300MW and is built to be more mobile, safe, and extensible to deploy. It has been established that SMRs can provide economic and flexibility advantages in a variety of industries thanks to the development, study, and use of multiple types of SMRs in recent years. The goal of this paper is to present a comprehensive overview of several SMR types, including light water reactors (LWRs), liquid metal-cooled reactors (LMRs), molten salt reactors (MSRs), and gas-cooled reactors (GCRs). Each type of reactor will be reviewed in terms of its structural design, modeling control implementation, applications, and impacts concerning the power system.
The National Aeronautics and Space Administration is considering nuclear power sources for space exploration. A series of critical mass experiments was designed to address the development, performance, and design of a space nuclear reactor being considered to support the Prometheus project. These experiments consisted of interlacing the refractory metals rhenium (Re), molybdenum (Mo), tantalum2.5 wt% tungsten (Ta-2.5W), and niobium-1 wt% zirconium (Nb-1Zr) with moderating materials (graphite or polyethylene) and were fueled by highly enriched uranium plates. These experiments are designed to assess the adequacy of and uncertainty in refractory metal neutron cross-section evaluations for use in Prometheus nuclear reactor design work. The critical experiments were designed in the energy spectrum closely resembling or bracketing that in the proposed space reactor. For each material (Re, Mo, Ta-2.5W and Nb-1Zr), four critical configurations were designed and performed to measure the sensitivity of keff to the material under four different and progressively softer neutron spectra (core center spectrum, harder than core average spectrum, softer than core average spectrum, and accident flooded spectrum). The thicknesses of the graphite or polyethylene moderator and reflector plates were adjusted to achieve the desired neutron spectrum. One critical and 18 subcritical experiments provided for measurements of material neutronic behavior in a simple cylindrical geometry configuration that was modeled in MCNP with ENDF/B-VI.6 cross-section data and compared to the extrapolated or predicted critical mass for all the experiments. These experiments were performed at the Los Alamos National Laboratory using the Planet vertical lift critical assembly at the Los Alamos Critical Experiment Facility.
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