Robert S. Reid

Small fission power systems for Mars

A Mars surface power system configuration with an output power of 3 kWe and a system mass of 775 kg is described. It consists of a heatpipe-cooled reactor with UN fuel coupled to a Stirling engine with a fixed conical radiator driven by loop heat pipes. Key to achieving this low mass is the use of a highly radiation-resistant multiplexer for monitoring and controlling the reactor, as well as radiation resistant generators and motors. Also key is the judicious placement of shields to prevent radiation scattered from the Martian surface and air from damaging the reactor controls. Several alternate configurations also are briefly looked at, including a moderated reactor with UZrH fuel and a reactor using 233U instead of 235U. The moderated reactor system has essentially the same mass as the baseline unmoderated UN system and yields the same radiation shielding requirements. The 233U reactor is significantly smaller and yields a system mass about 228 kg lighter than with 235U, but part of this weight reductio...

Review of liquid metal heat pipe work at Los Alamos

A survey of space‐power related liquid metal heat pipe work at Los Alamos National Laboratory is presented. Heat pipe development at Los Alamos has been on‐going since 1963. Heat pipes were initially developed for thermionic nuclear‐electrical power production in space. Since then Los Alamos has developed liquid metal heat pipes for numerous applications related to high temperature systems in both the space and terrestrial environments. Some of these applications include thermionic electrical generators, thermoelectric energy conversion (both in‐core and direct radiation), thermal energy storage, hypersonic vehicle leading edge cooling, and heat pipe vapor laser cells. Some of the work performed at Los Alamos has been documented in internal reports that are often little‐known. A representative description and summary of progress in space‐related liquid metal heat pipe technology is provided followed by a reference section citing sources where these works may be found.

Status Report on the Throhput Transient Heat Pipe Modeling Code

Improvements have been made to the throhput code which models transient thermohydraulic heat pipe behavior. The original code was developed as a doctoral thesis research code by Hall. The current emphasis has been shifted from research into the numerical modeling to the development of a robust production code. Several modeling obstacles that were present in the original code have been eliminated, and several additional features have been added.

Design of a heatpipe-cooled Mars-surface fission reactor

The next generation of robotic missions to Mars will most likely require robust power sources in the range of 3 to 20 kWe. Fission systems are well suited to provide safe, reliable, and economic power within this range. The goal of this study is to design a compact, low-mass fission system that meets Mars-surface power requirements, while maintaining a high level of safety and reliability at a relatively low cost. The Heatpipe Power System (HPS) is one possible approach for producing near-term, low-cost, space fission power. The goal of the HPS project is to devise an attractive space fission system that can be developed quickly and affordably. The primary ways of doing this are by using existing technology and by designing the system for inexpensive testing. If the system can be designed to allow highly prototypic testing with electrical heating, then an exhaustive test program can be carried out quickly and inexpensively, and thorough testing of the actual flight unit can be performed—which is a major b...

High-temperature self-circulating thermoacoustic heat exchanger

Thermoacoustic and Stirling engines and refrigerators use heat exchangers to transfer heat between the oscillating flow of their thermodynamic working fluids and external heat sources and sinks. An acoustically driven heat-exchange loop uses an engine’s own pressure oscillations to steadily circulate its own thermodynamic working fluid through a physically remote high-temperature heat source without using moving parts, allowing for a significant reduction in the cost and complexity of thermoacoustic and Stirling heat exchangers. The simplicity and flexibility of such heat-exchanger loops will allow thermoacoustic and Stirling machines to access diverse heat sources and sinks. Measurements of the temperatures at the interface between such a heat-exchange loop and the hot end of a thermoacoustic-Stirling engine are presented. When the steady flow is too small to flush out the mixing chamber in one acoustic cycle, the heat transfer to the regenerator is excellent, with important implications for practical use.

Small fission power systems for NEP

Two nuclear electric propulsion (NEP) power system configurations are presented, each with an output power of 50 kWe and a system mass of about 2500 kg. Both consist of a reactor coupled to a recuperated Brayton power conversion system with a fixed conical radiator driven by loop heat pipes. In one system the reactor is gas-cooled with the gas directly driving the Brayton power conversion system. In the other the reactor is heatpipe-cooled with a heat exchanger between the reactor and the Brayton system. Two variations are described briefly with powers of 100 k We and 150 kWe. The mass scales approximately with the square root of the power.

Sodium heat pipe module test for the SAFE-30 reactor prototype

Reliable, long-life, low-cost heat pipes can enable safe, affordable space fission power and propulsion systems. Advanced versions of these systems can in turn allow rapid access to any point in the solar system. Twelve stainless steel-sodium heat pipe modules were built and tested at Los Alamos for use in a non-nuclear thermohydraulic simulation of the SAFE-30 reactor (Poston et al., 2000). SAFE-30 is a near-term, low-cost space fission system demonstration. The heat pipes were designed to remove thermal power from the SAFE-30 core, and transfer this power to an electrical power conversion system. These heat pipe modules were delivered to NASA Marshall Space Flight Center in August 2000 and were assembled and tested in a prototypical configuration during September and October 2000. The construction and test of one of the SAFE-30 modules is described.

Experimental Evaluation of the Thermal Performance of a Water Shield for a Surface Power Reactor

Water based reactor shielding is being investigated for use on initial lunar surface power systems. A water shield may lower overall cost (as compared to development cost for other materials) and simplify operations in the setup and handling. The thermal hydraulic performance of the shield is of significant interest. The mechanism for transferring heat through the shield is natural convection. Natural convection in a 100 kWt lunar surface reactor shield design is evaluated with 2 kW power input to the water in the Water Shield Testbed (WST) at the NASA Marshall Space Flight Center. The experimental data from the WST is used to validate a CFD model. Performance of the water shield on the lunar surface is then predicted with a CFD model anchored to test data. The experiment had a maximum water temperature of 75 °C. The CFD model with 1/6‐g predicts a maximum water temperature of 88 °C with the same heat load and external boundary conditions. This difference in maximum temperature does not greatly affect the...

SAFE Alkali Metal Heat Pipe Reliability

Alkali metal heat pipes are among the best understood and tested of components for first generation space fission reactors. A flight reactor will require production of a hundred or more heat pipes with assured reliability over a number of years. To date, alkali metal heat pipes have been built mostly in low budget development environments with little formal quality assurance. Despite this, heat pipe test samples suggest that high reliability can be achieved with the care justified for space flight qualification. Fabrication procedures have been established that, if consistently applied, ensure long‐term trouble‐free heat pipe operation. Alkali metal heat pipes have been successfully flight tested in micro gravity and also have been shown capable of multi‐year operation with no evidence of sensitivity to fast neutron fluence up to 1023 n/cm2. This represents 50 times the fluence of the proposed Safe Affordable Fission Engine (SAFE‐100) heat pipe reactor core.

Analysis of the SAFE-30 resistance-heated test data

The Heatpipe Power System (HPS) is one possible system that could produce near-term, low-cost space fission power. One of the main ways that it achieves these goals is by designing the system for inexpensive testing. Nuclear testing is often a long and expensive process. The HPS utilizes electrical resistance heaters to simulate the nuclear heat, which if done correctly can reduce development time and cost. The purpose of the SAFE-30 testing is to verify core thermal performance and to evaluate the usefulness of this type of resistance heated testing. The Safe Affordable Fission Engine (SAFE) is a derivative of the HPS designed for producing electricity in space. A 30 kWt SAFE model was built by Los Alamos National Laboratory and recently tested at the NASA Marshall Space Flight Center. The SAFE-30 had 12 heatpipes and 48 electrical heaters to simulate the nuclear fuel. The SAFE-30 tests that were done were regulated and monitored using approximately 84 thermocouples. The heaters were controlled using variable current and voltage, which made it possible to obtain a specific input power. Attaching water-jacket calorimeters to the heatpipes made it feasible to obtain the power output from the core using simple heat transfer calculations. These actual temperatures and power values were then compared to a computational model that uses nuclear data and thermal properties. Near the completion of testing, a Stirling engine was attached to the core heatpipes to verify thermal coupling and produce electricity. This paper describes how the tests were conducted and what pieces of hardware were used to model potential environments. It also explains the results of the tests as well as the different conditions that they were tested under. Finally, it analyzes the overall data for the successful tests and confirms it to be comparable to the theoretical thermal calculations done by the computer code.The Heatpipe Power System (HPS) is one possible system that could produce near-term, low-cost space fission power. One of the main ways that it achieves these goals is by designing the system for inexpensive testing. Nuclear testing is often a long and expensive process. The HPS utilizes electrical resistance heaters to simulate the nuclear heat, which if done correctly can reduce development time and cost. The purpose of the SAFE-30 testing is to verify core thermal performance and to evaluate the usefulness of this type of resistance heated testing. The Safe Affordable Fission Engine (SAFE) is a derivative of the HPS designed for producing electricity in space. A 30 kWt SAFE model was built by Los Alamos National Laboratory and recently tested at the NASA Marshall Space Flight Center. The SAFE-30 had 12 heatpipes and 48 electrical heaters to simulate the nuclear fuel. The SAFE-30 tests that were done were regulated and monitored using approximately 84 thermocouples. The heaters were controlled using var...