Highly Enriched Uranium Metal Cylinders Surrounded by Various Reflector Materials

Conference · Mon May 28 04:00:00 EDT 2007

OSTI ID:912456

Jones, Bernard ^[1]; Briggs, J. Blair ^[2]; Monteirth, Leland M. ^[2]

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1. Georgia Institute of Technology, Atlanta, GA (United States)
2. Idaho National Lab. (INL), Idaho Falls, ID (United States)

A series of experiments was performed at Los Alamos Scientific Laboratory in 1958 to determine critical masses of cylinders of Oralloy (Oy) reflected by a number of materials. The experiments were all performed on the Comet Universal Critical Assembly Machine and consisted of discs of highly enriched uranium (93.3 wt.% ²³⁵U) reflected by half-inch and one-inch-thick cylindrical shells of various reflector materials. The experiments were performed by members of Group N-2, particularly K. W. Gallup, G. E. Hansen, H. C. Paxton, and R. H. White. This experiment was intended to ascertain critical masses for criticality safety purposes, as well as to compare neutron transport cross sections to those obtained from danger coefficient measurements with the Topsy Oralloy-Tuballoy reflected and Godiva unreflected critical assemblies. The reflector materials examined in this series of experiments are as follows: magnesium, titanium, aluminum, graphite, mild steel, nickel, copper, cobalt, molybdenum, natural uranium, tungsten, beryllium, aluminum oxide, molybdenum carbide, and polythene (polyethylene). Also included are two special configurations of composite beryllium and iron reflectors. Analyses were performed in which uncertainty associated with six different parameters was evaluated: namely, extrapolation to the uranium critical mass, uranium density, ²³⁵U enrichment, reflector density, reflector thickness, and reflector impurities. In addition to the idealizations made by the experimenters (removal of the platen and diaphragm), two simplifications were also made to the benchmark models that resulted in a small bias and additional uncertainty. First of all, since impurities in core and reflector materials are only estimated, they are not included in the benchmark models. Secondly, the room, support structure, and other possible surrounding equipment were not included in the model. Bias values that result from these two simplifications were determined and associated uncertainty in the bias values were included in the overall uncertainty in benchmark k_eff values. Bias values were very small, ranging from 0.0004 to 0.0007 Δk low. Overall uncertainties range from ± 0.0018 to ± 0.0030. Major contributors to the overall uncertainty include uncertainty in the extrapolation to the uranium critical mass and the uranium density. Results are summarized in Figure 1. Figure 1. Experimental, Benchmark-Model, and MCNP/KENO Calculated Results The 32 configurations described and evaluated under ICSBEP Identifier HEU-MET-FAST-084 are judged to be acceptable for use as criticality safety benchmark experiments and should be valuable integral benchmarks for nuclear data testing of the various reflector materials. Details of the benchmark models, uncertainty analyses, and final results are given in this paper.

• Research Organization: Georgia Institute of Technology, Atlanta, GA (United States); Idaho National Lab. (INL), Idaho Falls, ID (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• DOE Contract Number: AC07-99ID13727
• OSTI ID: 912456
• Report Number(s): INL/CON-06-11657
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
97 MATHEMATICS AND COMPUTING
ALUMINIUM
BERYLLIUM
COBALT
CRITICAL MASS
CRITICALITY
CROSS SECTIONS
DANGER COEFFICIENT
Evaluated Nuclear Data File (ENDF)
HIGHLY ENRICHED URANIUM
ICSBEP
MAGNESIUM
MOLYBDENUM CARBIDES
Monte Carlo N-Particle Transport (MCNP)
NATURAL URANIUM
NEUTRON TRANSPORT
Nuclear Criticality Safety Program (NCSP)
Oralloy
POLYETHYLENES
Reflector Cylinders
SAFETY
TITANIUM
TUNGSTEN
Tuballoy
URANIUM
Uranium
ZERO POWER REACTORS