William L. Myers

Comparison of active interrogation techniques

Active interrogation is necessary to detect highly enriched uranium in large cargo containers and trucks. To achieve sufficient penetration, most nuclear techniques first interrogate an object with high-energy photons or neutrons, to produce fission in any highly enriched uranium that may be present, and then detect the gamma rays or neutrons that are produced. Pulsed beams allow the detection of delayed gamma rays or neutrons from fission products between pulses. Many different systems have been proposed recently. This report presents the results for several techniques, both from measurements and from extensive simulations with the MCNPX code

Neutron detectors for active interrogation of highly enriched uranium

We describe the results of our effort to optimize three neutron detector systems for active interrogation of highly enriched uranium: 1) a large-area detector for maximum total efficiency, 2) modular detectors for maximum flexibility in configuring a detector system for an application, and 3) a portable detector. All three systems contained He tubes, polyethylene to moderate the neutrons, and cadmium to filter out room-return thermal neutrons. The back and sides of the detectors were shielded with additional polyethylene or borated polyethylene. The electronics gated off the data acquisition during the interrogating pulse, either bremsstrahlung photons from an electron linac or neutrons from a DT generator. The sensitivity of each detector system depends on the distance between the detector and nuclear material as well as on the intervening material. We present representative data for several configurations showing the performance of each system.

Linear Accelerator‐Based Active Interrogation For Detection of Highly Enriched Uranium

Photofissions were induced in samples of highly enriched uranium (HEU) with masses up to 22 kg using bremsstrahlung photons from a pulsed 10‐MeV electron linear accelerator (linac). Neutrons were detected between pulses by large 3He detectors, and the data were analyzed with the Feynman variance‐to‐mean method. The effects of shielding materials, such as lead and polyethylene, and the variation of the counting rate with distance for several configurations were measured. For comparison, a beryllium block was inserted in the beam to produce neutrons that were also used for interrogation. Because both high‐energy photons and neutrons are very penetrating, both approaches can be used to detect shielded HEU; the choice of approach depends on the details of the configuration and the shielding.

Photon and Neutron Active Interrogation of Highly Enriched Uranium

The physics of photon and neutron active interrogation of highly enriched uranium (HEU) using the delayed neutron reinterrogation method is described in this paper. Two sets of active interrogation experiments were performed using a set of subcritical configurations of concentric HEU metal hemishells. One set of measurements utilized a pulsed 14‐MeV neutron generator as the active source. The second set of measurements utilized a linear accelerator‐based bremsstrahlung photon source as an active interrogation source. The neutron responses were measured for both sets of experiments. The operational details and results for both measurement sets are described.

Criticality characteristics of mixtures of plutonium, silicon dioxide, Nevada tuff, and water

The major objective of this study has been to examine the possibility of a nuclear explosion (and evaluate this event if it is possible) should 50 to 100 kg of plutonium be mixed with SiO{sub 2}, vitrified, placed within a heavy steel container, and buried in the material known as Nevada tuff. To accomplish this objective we have created a survey of the critical states or configurations of mixtures of plutonium, SiO{sub 2}, tuff, and water and examined these data to isolate those configurations that might be unstable or autocatalytic. The survey of critical data now exists and is published herein. We identify regions of criticality instability with the possibility of autocatalytic power behavior (the existence of such autocatalytic phenomena is not new). Autocatalytic power behavior is possible for a very limited range of wet systems, but this behavior is improbable. A quantitative and conservative evaluation of the fission power behavior of these autocatalytic mixtures shows that no explosion should be expected.

Kilowatt Reactor Using Stirling TechnologY (KRUSTY) Demonstration. CEDT Phase 1 Preliminary Design Documentation

The intent of the integral experiment request IER 299 (called KiloPower by NASA) is to assemble and evaluate the operational performance of a compact reactor configuration that closely resembles the flight unit to be used by NASA to execute a deep space exploration mission. The reactor design will include heat pipes coupled to Stirling engines to demonstrate how one can generate electricity when extracting energy from a “nuclear generated” heat source. This series of experiments is a larger scale follow up to the DUFF series of experiments1,2 that were performed using the Flat-Top assembly.

Use of a COTS X-ray scanner for 2-D neutron activation analysis

Results from the use of a commercial, off-the-shelf X-ray scanner using storage phosphors to measure neutron activation in 1- and 2-D are presented. The technique consists of irradiating thin foils or wires of various elements, then placing the activated material on the storage phosphors to expose them. The amount of exposure is proportional to the activation obtained. Examples of wires, small foils, and large area foils with asymmetric irradiation using critical assemblies are presented. Combined with isotope-specific gamma counting of the entire foil or wire, the technique offers a simple way to obtain both qualitative and quantitative 2-D activation information.