John J. Buksa

Selection of flowing liquid lead target structural materials for accelerator driven transmutation applications

The beam entry window and container for a liquid lead spallation target will be exposed to high fluxes of protons and neutrons that are both higher in magnitude and energy than have been experienced in proton accelerators and fission reactors, as well as in a corrosive environment. The structural material of the target should have a good compatibility with liquid lead, a sufficient mechanical strength at elevated temperatures, a good performance under an intense irradiation environment, and a low neutron absorption cross section; these factors have been used to rank the applicability of a wide range of materials for structural containment. Nb‐1Zr has been selected for use as the structural container for the LANL ABC/ATW molten lead target. Corrosion and mass transfer behavior for various candidate structural materials in liquid lead are reviewed, together with the beneficial effects of inhibitors and various coatings to protect substrate against liquid lead corrosion. Mechanical properties of some candida...

Reactor and shielding design implications of clustering nuclear thermal rockets

This paper examines design considerations in the context of engine-out accidents in clustered nuclear-thermal rocket stages, and an accident-management protocol is devised. Safety and performance issues are considered in the light of designs for the reactor and shielding elements of ROVER/NERVA-type engines. The engine-out management process involves: phase one, in which sufficient propulsive power is guaranteed for mission completion; and phase two, in which engine failure is isolated and not allowed to propagate to other engines or to the spacecraft. Phase-one designs can employ spare engines, throttled engines, and/or long-burning engines. Phase-two safety concepts can include techniques for cooling or jettisoning the failed engines. Engine-out management philosophies are shown to be shaped by a combination of safety and mission-trajectory requirements. 6 refs.

SP‐100 Heat Transport Technology Development

SP‐100 space reactor power system heat transport technology is reviewed, and progress to date is discussed in the key areas. Technical challenges, achievements, and the current status of the thermoelectric‐electromagnetic pump and gas separator/accumulator components are presented. Validation experiments, analytical models, and manufacturing processes developed for these components are summarized. Remaining components of the heat transport subsystems, including the auxiliary cooling and thaw subsystem are also discussed briefly.

Nuclear thermal rocket clustering I: A summary of previous work and relevant issues

Clustering of rocket engines refers to the parallel connection of two or more small engines so that the performance of the propulsion system is superior to that of a single large engine. A general review of the technical merits of nuclear thermal rocket clustering is presented. A summary of previous analyses performed during the Rover program is presented and is used to assess clustering in the context of projected Space Exploration Initiative missions. A number of technical issues are discussed including cluster reliability, engine‐out operation, neutronic coupling, shutdown core power generation, shutdown reactivity requirements, reactor kinetics, and radiation shielding.

Development of Nonfertile and Evolutionary Mixed-Oxide Nuclear Fuels for Use in Existing Water Reactors

Abstract Investigations of an advanced fuel form are currently under way. This new fuel form, referred to as evolutionary mixed oxide (EMOX), is a slight perturbation on standard mixed-oxide (MOX) fuel, and analyses show that it can be an effective plutonium management tool in existing light water reactors. The addition of a small fraction of calcia-stabilized zirconia to the uranium-plutonium oxide matrix allows for greater plutonium conversion while also providing a licensing path forward toward eventual implementation of higher-plutonium-destruction fuels. These fuels, referred to as nonfertile (NF) fuels, achieve their high destruction rates through the absence of uranium, which breeds plutonium, in the fuel composition. Extensive calculations have been performed to assess the feasibility of incorporating the EMOX fuel form into existing pressurized water reactor systems, and the results are given in detail. Specifically, calculations have been made to determine the plutonium consumption achievable by the EMOX concept, and comparisons have been made of this performance to that of typical MOX and NF fuels. The results indicate that EMOX and NF fuels can provide flexibility with regard to controlling plutonium inventories in spent fuel. In addition, fabrication experiments have been conducted to determine the feasibility of fabricating suitable EMOX and NF fuels. NF and EMOX fuels have been fabricated using the solid-state reaction method. Precursor powders were successfully blended and milled using a combination of ball milling and high-energy vibratory milling. Sintering data for EMOX fuel indicated that significant densification occurred at a temperature of 1700°C.

Assessment of an SP‐100 Bi‐Modal Propulsion and Power System

The attractiveness of using the SP‐100 space nuclear power system for both electric power production and direct thermal propulsion is discussed. A conceptual modification to the SP‐100 generic flight system that uses its hot, primary coolant to directly heat hydrogen propellant is presented. An analytical model of the system and its orbital‐mechanical behavior is presented and used to assess the benefits of a number of orbital transfer missions. Both a 500 kW and a 2.4 MW system are assessed. Preliminary results indicate that for LEO‐to‐GEO transfers, the SP‐100 bi‐modal system offers a 100 % increase in payload over conventional chemical‐only propulsion systems with transfer times on the order of days.

Neutronics and engineering design of the aqueous-slurry accelerator transmutation of waste blanket

A conceptual target and blanket design for an accelerator transmutation of waste system capable of transmuting the high-level waste stream from 2.5 light water reactors is described. Typically, four such target-blanket designs would be served by a single linear accelerator. The target consists of rows of solid tungsten rod bundles, cooled by heavy water and surrounded by a lead annulus. The annular blanket, which surrounds the target, consists of a set of actinide-oxide-slurry-bearing tubes, each 3 m long, surrounded by heavy water moderator. Heat is removed from the slurry tubes by passing the slurry through an external heat exchanger. Long-lived fission products are burned in regions that are separate from the actinides. Using the Monte Carlo codes LAHET and MCNP, a conceptual design for a beam current of 62.5 mA/target of 1.6-GeV protons has been developed. Preliminary engineering analyses on key system components have been performed. A preliminary layout of the concept and the associated primary-heat transport subsystems was developed, demonstrating a multiple-containment-boundary design philosophy.

Conceptual design of a thorium target for molten salt transmutation systems

A spallation target constructed of thorium metal has been designed for applications using molten‐salt as the target coolant. The design consists of an array of wire‐wrapped, hastelloy‐clad, thorium rods in which a parabolic void region is introduced in the upper regions. Each target rod is approximately 1 m in length, 3.1 cm in diameter, and has a clad thickness of 0.05 cm; 140 rods are arranged in a triangular lattice with a pitch of 3.2 cm, which results in a cylindrical target configuration with a radius of 20 cm and an estimated yield of 17 neutrons/proton for 800 MeV protons.

Kinetics of accelerator driven devices

Kinetic calculations were made to show that subcritical accelerator driven devices are robust and stable. The calculations show that large changes in reactivity that would lead to an uncontrollable excursion in a reactor would lead only to a new power level in a subcritical device. Calculations were also made to show the rate of power changes resulting from startup and shutdown, and that methods also exist for continuously monitoring the reactivity of a subcritical system.

Nuclear Power Supply for Early Lunar Bases

In recent years, numerous studies have been performed on the use of a nuclear power source for an early lunar base. These studies have shown that not only is using nuclear power feasible, but that it is also the best option for a reliable, long‐lived, compact power source. There are, however, several issues that need to be resolved concerning the radiation field created by the use of a reactor. These issues include such concerns as dose received by the astronauts, possible lunar soil activation, and the shutdown and disposal of the reactor. Using the MOHTR core concept developed at Los Alamos National Laboratory (LANL) as a baseline, this paper will describe the latest studies performed on these issues, and will resolve some of the more prevalent concerns regarding the use of a nuclear reactor for a lunar base.