G.J. Russell

Nuclear energy generation and waste transmutation using an accelerator-driven intense thermal neutron source

We describe a new approach for commercial nuclear energy production without a long-term high-level waste stream and for transmutation of both fission product and higher actinide commercial nuclear waste using a thermal flux of accelerator-produced neutrons in the 1016 n/cm2s range. Continuous neutron fluxes at this intensity, which is approximately 100 times larger than is typically available in a large scale thermal reactor, appear practical, owing to recent advances in proton linear accelerator technology and to the spallation target-moderator design presented here. This large flux of thermal neutrons makes possible a waste inventory in the transmutation system which is smaller by about a factor of 100 than competing concepts. The accelerator allows the system to operate well below criticality so that the possibility for a criticality accident is eliminated. No control rods are required. The successful implementation of this new method for energy generation and waste transmutation would eliminate the need for nuclear waste storage on a geologic time scale. The production of nuclear energy from 232Th or 238U is used to illustrate the general principles of commercial nuclear energy, production without long-term high-level waste. There appears to be sufficient thorium to meet the worlds energy needs for many millenia.

Introduction to spallation physics and spallation-target design

When coupled with the spallation process in appropriate target materials, high-power accelerators can be used to produce large numbers of neutrons, thus providing an alternate method to the use of nuclear reactors for this purpose. Spallation offers exciting new possibilities for generating intense neutron fluxes for a variety of applications, including: (a) spallation-neutron sources for materials science research; (b) accelerator-based production of tritium; (c) accelerator-based transmutation of waste; (d) accelerator-based destruction of plutonium; and (e) radioisotope production for medical and energy applications. Target design plays a key role in these applications, with neutron production/leakage being strongly dependent on the incident particle type and energy, and target material and geometry.

318 and 800 mev (p, xn) cross sections

Abstract Neutron yields from proton bombardment of elemental Pb and depleted U have been measured at bombarding energies of 318 and 800 MeV. Additionally, at 800 MeV, data were obtained for Al and C. The data were obtained at angles/flight-paths of 7.5deg/30m and 30deg/40m and were collected in two parameter histograms of tine-of-flight and pulse-height in order to select detector biases in the analysis and to permit comparison of calculated and experimental pulse height spectra in the calculation of detector efficiency. The data have been reduced to absolute double-differential cross sections and are in good agreement with INC calculations at 800 MeV but exceed calculation by a factor of three at the lower energy.

Long-pulse spallation source neutronic performance

Abstract There are potential gains of about a factor of seven in the time-average neutron brightness for a coupled liquid H2 moderator compared to a decoupled one, and a factor of around five for a H2O moderator. However, these gains come at the expense of putting “tails” on the neutron pulses. The particulars of the neutron pulses from a moderator (e.g., energy-dependent rise times, peak intensities, pulse widths, and decay constant(s) of the tails) are crucial parameters for designing instruments and estimating their performance at an LPSS. The spallation target system designer can alter moderator neutronic performance by: (a) the choice of target material and geometry; (b) proper selection of the moderator material and geometry; (c) varying the target—moderator geometry; (d) the choice of reflector material(s); (e) the presence/absence of decouplers and liners; and (f) the proton pulse width. A 1-MW Long-Pulse Spallation Source (LPSS) has world-class neutronic performance. We show that the calculated p...

Split-target neutronics and the MLNSC spallation target system

The Manuel Lujan, Jr., Neutron Scattering Center (MLNSC) at the Los Alamos National Laboratory is one of four operating Short-Pulse Spallation Sources worldwide. The MLNSC target system (composed of targets, moderators, and reflectors) was first installed in 1985. The target system employs a split tungsten spallation target with a void space in between (the flux-trap gap); this target system will be upgraded in 1998. The ability to efficiently split a spallation target allowed us to introduce the concept of flux-trap moderators and ultimately the notion of backscattering and upstream moderators. The upgraded MLNSC target system will employ both flux-trap and upstream/backscattering moderators to simultaneously service 16 neutron flight paths with high-intensity neutron beams for materials science research.

Determination of the absolute efficiency of an organic scintillator for neutrons with energies between 0.5 and 800 MeV

Abstract We have determined the absolute efficiency of an NE-213 scintillator for neutrons with energies from 0.5 to 800 MeV. The detector was 5.1 cm in diameter and 2.5 cm deep. The efficiencies were obtained for detector thresholds of 0.011, 0.48, 1.12, and 4.48 MeVee. Our results are compared to predictions of the STANTON computer code.

Target/blanket design for the Los Alamos Apt system

The Accelerator Production of Tritium (APT) concept proposes the production of tritium by means of an accelerator and target system. The Los Alamos APT design incorporates a high‐energy, high‐current proton accelerator, a tungsten neutron source, a lead neutron multiplier, and a moderating blanket that contains 3He for the production of tritium. This innovative system makes use of existing spallation neutron source technology, and proven design concepts. Inherent safety and environmental features include low decay heat, the absence of fissile or fertile material, no criticality concerns, no potential for overpower transients, and the fact that no high level waste is produced.

Thermal hydraulic study of the neutron production target at the Los Alamos Neutron Scattering Center

Abstract The Los Alamos Neutron Scattering Center (LANSCE) operates a pulsed neutron source for materials science research. The neutrons are produced by bombarding a tungsten target with the 800 MeV proton beam from the Los Alamos Meson Physics Facility (LAMPF). In an attempt to clarify the thermal hydraulics of the neutron production target, we performed a sequence of experiments aimed at determining temperature distributions in the target, as well as various heat transfer parameters. The results of these measurements were compared, and shown to agree, with radiation transport and heat transfer calculations. The information obtained from these tests was then used to determine other target properties, such as thermal stress, that are very difficult to measure directly.

FLAT TARGET NEUTRONICS

Abstract In this paper we will discuss the possibility of using a flat tungsten target as the target of a neutron spallation source. Therefore we investigated what influence the components of the target station, such as reflector material, moderator geometry, decoupler and target geometry, have on the neutronics of the target.

International Workshop on Cold Neutron Sources

The first meeting devoted to cold neutron sources was held at the Los Alamos National Laboratory on March 5--8, 1990. Cosponsored by Los Alamos and Oak Ridge National Laboratories, the meeting was organized as an International Workshop on Cold Neutron Sources and brought together experts in the field of cold-neutron-source design for reactors and spallation sources. Eighty-four people from seven countries attended. Because the meeting was the first of its kind in over forty years, much time was spent acquainting participants with past and planned activities at reactor and spallation facilities worldwide. As a result, the meeting had more of a conference flavor than one of a workshop. The general topics covered at the workshop included: Criteria for cold source design; neutronic predictions and performance; energy deposition and removal; engineering design, fabrication, and operation; material properties; radiation damage; instrumentation; safety; existing cold sources; and future cold sources.