David I. Poston

Design and analysis of the SAFE-400 space fission reactor

Ambitious solar system exploration missions in the near future will require robust power sources in the range of 10 to 200 kWe. Fission systems are well suited to provide safe, reliable, and economic power within this range. 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 benefit to reliability. Over the past 4 years, three small HPS proof-of-concept technology demonstrations have been conducted, and each has been highly successful. The Safe Affordable Fission En...

High-Thrust-High-Specific Impulse Gasdynamic Fusion Propulsion System

The gasdynamic fusion propulsion system utilizes a simple mirror magnetic geometry in which a highdensity plasma is cone ned long enough to generate fusion energy while ejecting charged particles through one end to generate thrust. At high densities the collision mean free path becomes much shorter than the length, making the plasma behave much like a continuous medium, a e uid. Under these conditions the escape of the plasma is analogous to the e ow of a gas into a vacuum from a vessel with a hole. With the mirror serving as a magnetic nozzle the plasma-charged particles are ejected at very high energies, giving rise to specie c impulses of well over 200,000 s, but at modest thrusts because of the smallness of their mass. We examine methods by which the thrust of this engine can be enhanced. On the one hand we explore the use of a hydrogen propellant that is heated by the radiation emanating from the plasma, which, upon exhausting through a nozzle, generates the additional thrust. On the other hand we focus purely on changing the properties of the injected plasma to achieve the same objectives. We e nd in the case of a deuterium‐ tritium plasma that the use of hydrogen results in a degradation of the propulsive capability of the system, but we e nd it quite suitable for an engine that burns a mixture of deuterium and helium 3. The same results can be achieved by simply increasing the density of the injected plasma without encountering major adverse consequences. Because of engineering considerations, however, the use of a hydrogen propellant may prove to be inevitable if no other means are found to protect the walls of the reactor chamber against large heat loads.

Nuclear safety calculations for heatpipe power system reactors

Misperceptions continue to exist about the safety of space nuclear systems—both with reactors and radioisotope systems. Frequently engineers do not bother to sufficiently explain the risk, because it is obvious to them that the risks are inconsequential and that their time can be spent in more productive ways. This paper attempts to quantify some of the nuclear risks associated with two space reactor concepts. The paper does not perform a detailed risk assessment; it merely provides information and data that serves as evidence that the risk to personnel and the public are minimal. The reactor concepts evaluated are Heatpipe Power System (HPS) reactors—the HOMER-15, a Mars surface reactor, and the SAFE-400, a space power reactor. The study concludes that these reactors do not pose any credible risk to personnel or the public.

The Heatpipe-Operated Mars Exploration Reactor (HOMER)

The Heatpipe Power System (HPS) is a near-term, low-cost, space fission power system that has been under development at Los Alamos National Laboratory (LANL) for 5 years. 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 inexpensively and quickly and thorough testing of the actual flight unit can be performed—which is a major benefit to reliability. Over the past 4 years, LANL has conducted three HPS proof-of-concept technology demonstrations—each has been highly successful. The Heatpipe-Operated Mars Exploration Reactor (HOMER) is a derivative of the HPS designed especially for producing electricity on the surface of Mars. The key attributes of the HOMER are described in this paper, as well as a 20-kWe point design, system scalability, and the current technology status.

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...

Design of a 25‐kWe Surface Reactor System Based on SNAP Reactor Technologies

A Hastelloy‐X clad, sodium‐potassium (NaK‐78) cooled, moderated spectrum reactor using uranium zirconium hydride (UZrH) fuel based on the SNAP program reactors is a promising design for use in surface power systems. This paper presents a 98 kWth reactor for a power system the uses multiple Stirling engines to produce 25 kWe‐net for 5 years. The design utilizes a pin type geometry containing UZrHx fuel clad with Hastelloy‐X and NaK‐78 flowing around the pins as coolant. A compelling feature of this design is its use of 49.9% enriched U, allowing it to be classified as a category III‐D attractiveness and reducing facility costs relative to highly‐enriched space reactor concepts. Presented below are both the design and an analysis of this reactor’s criticality under various safety and operations scenarios.

Phase 1 Space Fission Propulsion System Testing and Development Progress

Successful development of space fission systems requires an extensive program of affordable and realistic testing. In addition to tests related to design/development of the fission system, realistic testing of the actual flight unit must also be performed. If the system is designed to operate within established radiation damage and fuel bum up limits while simultaneously being designed to allow close simulation of heat from fission using resistance heaters, high confidence in fission system performance and lifetime can be attained through a series of non-nuclear tests. The Safe Affordable Fission Engine (SAFE) test series, whose ultimate goal is the demonstration of a 300 kW flight configuration system, has demonstrated that realistic testing can be performed using non-nuclear methods. This test series, carried out in collaboration with other NASA centers, other government agencies, industry, and universities, successfully completed a testing program with a 30 kWt core, Stirling engine, and ion engine configuration. Additionally, a 100 kWt core is in fabrication and appropriate test facilities are being reconfigured. This paper describes the current SAFE non-nuclear tests, which includes test article descriptions, test results and conclusions, and future test plans. INTRODUCTION AND BACKGROUND Successful development of space fission systems will require an extensive program of affordable and realistic testing. In addition to tests related to the design/development of the fission system, realistic testing of the actual flight unit must also be completed. Because heat from fission cannot be used for full-power testing of flight units (due to radiological activation), space fission systems must be designed such that heat from fission can be very closely mimicked by some other means. While some nuclear testing will be required, the system will ideally be optimized to allow maximum benefit from non-nuclear testing during the development phase. Non-nuclear tests are affordable and timely, and the cause of component and system failures can be quickly and accurately identified. The primary concern with non-nuclear tests is that nuclear effects are obviously not taken into account. To be most relevant, the system undergoing non-nuclear tests must thus be designed to operate well within demonstrated radiation damage and fuel burn up capabilities. In addition, the system must be designed such that minimal operations are required to move from non-nuclear testing mode to a fueled system operating on heat from fission. If the system is designed to operate within established radiation damage and fuel bum up limits while simultaneously being designed to allow close simulation of heat from fission using resistance heaters, high confidence in fission system performance and lifetime can be attained through a series of non-nuclear tests. Any subsequent operation of the system using heat from fission instead of resistance heaters would then be viewed much more as a demonstration than a test i.e. the probability of system failure from nuclear effects would be very low. These types of systems, along with any other nuclear propulsion system that can be tested with existing nuclear facilities, can be characterized as Phase 1 systems. https://ntrs.nasa.gov/search.jsp?R=20020050531 2020-01-31T05:03:31+00:00Z

A Stainless‐Steel, Uranium‐Dioxide, Potassium‐Heatpipe‐Cooled Surface Reactor

One of the primary goals in designing a fission power system is to ensure that the system can be developed at a low cost and on an acceptable schedule without compromising reliability. The Heatpipe Power System (HPS) is one possible approach for producing near‐term, low‐cost, space fission power. The Heatpipe Operated Moon Exploration Reactor (HOMER‐25) is a HPS designed to produce 25‐kWe on the lunar surface for 5 full‐power years. The HOMER‐25 core is made up of 93% enriched UO2 fuel pins and stainless‐steel (SS)/potassium (K) heatpipes in a SS monolith. The heatpipes transport heat generated in the core through the water shield to a potassium boiler, which drives six Stirling engines. The operating heatpipe temperature is 880 K and the peak fast fluence is 1.6e21 n/cm2, which is well within an established database for the selected materials. The HOMER‐25 is designed to be buried in 1.5 m of lunar regolith during operation. By using technology and materials which do not require extensive technology development programs, the HOMER‐25 could be developed at a relatively low cost. This paper describes the attributes, specifications, and performance of the HOMER‐25 reactor system.

A computational model for an open-cycle gas core nuclear rocket

A computational model of an open-cycle gas core nuclear rocket (GCR) is developed. The solution is divided into two distinct areas--thermal hydraulics and neutronics. To obtain the thermal-hydraulic solution, a computer code is written that solves the Navier-Stokes, energy, and species diffusion equations. The two-dimensional transport code TWODANT is used to obtain the neutronics solution. The thermal-hydraulic and neutronic models are coupled, and the solution proceeds in an iterative manner until a consistent power density profile is obtained. Various open-cycle GCR designs are evaluated. First, it is assumed that the fuel and propellant do not mix. In this ideal case, it is found that the limiting factor in determining thrust and specific impulse is the maximum allowable wall heat flux. Following this simplified study, the results from a complete thermal-hydraulic/neutronic solution are presented, and the use of alternate fuels and propellants is considered. Next, a parametric design study is conducted that examine the rocket performance of the open-cycle GCR as a function of various design and operational parameters. It is found that fuel containment is very adversely affected by high reactor power or rocket acceleration. Finally, some concepts are discussed that could help improve fuel containment.

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...