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Title: Highly Enriched uranium Metal Spheres Surrounded by Various Reflectors

Abstract

A series of experiments was performed at the Los Alamos critical assembly facility in the early 1950s to determine the critical mass of highly enriched uranium spheres surrounded by thin reflectors of various materials. The objective of these experiments was to obtain a precision graph of the critical mass of highly enriched uranium metal as a function of reflector thickness and to generate transport cross sections for the reflector material. Thirteen configurations are described and evaluated under ICSBEP identifier, HEU-MET-FAST-085; two with 1.98-inch-thick and 4.158-inch-thick copper reflectors, two with 2- and 4-inch-thick cast iron reflectors, one with a 1.945-inch-thick nickel reflector, two with 1.88- and 2.02-inch-thick nickel-copper-zinc alloy reflectors, one with a 1.81-inch-thick thorium reflector, two with 2-inch-thick and 4-inch-thick tungsten alloy reflectors, two with 2-inch-thick and 4.075-inch-thick zinc reflectors, and one with a 2-inch-thick tungsten alloy reflector surrounded by a 2-inch-thick cast iron reflector. All configurations were slightly subcritical with measured multiplications ranging from 20 to 162. Analyses were performed in which uncertainty associated with six different parameters was evaluated; namely, extrapolation to uranium critical mass, uranium density, 235U enrichment, reflector density, reflector thickness, and reflector impurities were considered. Uncertainty in cast-iron alloying elements was also considered when appropriate.more » In addition to the idealizations made by the experimenters, 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 keff values. Bias values range from 0.0021 ?k low to 0.0016 ?k high. Overall uncertainties range from ? 0.0023 to ? 0.0064. Major contributors to the overall uncertainty include uncertainty in the extrapolation to the uranium critical mass and the uranium density. Results are summarized in the following figure. The 3 configurations described and evaluated in HEU-MET-FAST-085 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.« less

Authors:
; ;
Publication Date:
Research Org.:
Idaho National Laboratory (INL)
Sponsoring Org.:
DOE - NE
OSTI Identifier:
912457
Report Number(s):
INL/CON-06-11656
TRN: US200801%%887
DOE Contract Number:
DE-AC07-99ID-13727
Resource Type:
Conference
Resource Relation:
Conference: Conference on Nuclear Criticality Safety,St. Petersberg, Russia,05/28/2007,06/01/2007
Country of Publication:
United States
Language:
English
Subject:
73 - NUCLEAR PHYSICS AND RADIATION PHYSICS; ACCURACY; ALLOYS; BENCHMARKS; CAST IRON; COPPER; CRITICAL MASS; CRITICALITY; CROSS SECTIONS; EXTRAPOLATION; HIGHLY ENRICHED URANIUM; IMPURITIES; NICKEL; SAFETY; THICKNESS; THORIUM; TUNGSTEN ALLOYS; URANIUM; ZINC; 235U; HEU-MET-FAST-085; ICSBEP

Citation Formats

Jessica Feener, J. Blair Briggs, and Leland Montierth. Highly Enriched uranium Metal Spheres Surrounded by Various Reflectors. United States: N. p., 2007. Web.
Jessica Feener, J. Blair Briggs, & Leland Montierth. Highly Enriched uranium Metal Spheres Surrounded by Various Reflectors. United States.
Jessica Feener, J. Blair Briggs, and Leland Montierth. Tue . "Highly Enriched uranium Metal Spheres Surrounded by Various Reflectors". United States. doi:. https://www.osti.gov/servlets/purl/912457.
@article{osti_912457,
title = {Highly Enriched uranium Metal Spheres Surrounded by Various Reflectors},
author = {Jessica Feener and J. Blair Briggs and Leland Montierth},
abstractNote = {A series of experiments was performed at the Los Alamos critical assembly facility in the early 1950s to determine the critical mass of highly enriched uranium spheres surrounded by thin reflectors of various materials. The objective of these experiments was to obtain a precision graph of the critical mass of highly enriched uranium metal as a function of reflector thickness and to generate transport cross sections for the reflector material. Thirteen configurations are described and evaluated under ICSBEP identifier, HEU-MET-FAST-085; two with 1.98-inch-thick and 4.158-inch-thick copper reflectors, two with 2- and 4-inch-thick cast iron reflectors, one with a 1.945-inch-thick nickel reflector, two with 1.88- and 2.02-inch-thick nickel-copper-zinc alloy reflectors, one with a 1.81-inch-thick thorium reflector, two with 2-inch-thick and 4-inch-thick tungsten alloy reflectors, two with 2-inch-thick and 4.075-inch-thick zinc reflectors, and one with a 2-inch-thick tungsten alloy reflector surrounded by a 2-inch-thick cast iron reflector. All configurations were slightly subcritical with measured multiplications ranging from 20 to 162. Analyses were performed in which uncertainty associated with six different parameters was evaluated; namely, extrapolation to uranium critical mass, uranium density, 235U enrichment, reflector density, reflector thickness, and reflector impurities were considered. Uncertainty in cast-iron alloying elements was also considered when appropriate. In addition to the idealizations made by the experimenters, 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 keff values. Bias values range from 0.0021 ?k low to 0.0016 ?k high. Overall uncertainties range from ? 0.0023 to ? 0.0064. Major contributors to the overall uncertainty include uncertainty in the extrapolation to the uranium critical mass and the uranium density. Results are summarized in the following figure. The 3 configurations described and evaluated in HEU-MET-FAST-085 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.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}

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