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Title: Neutron Assay System for Confinement Vessel Disposition

Abstract

Waste will be removed from confinement vessels remaining from 1970s-era experiments. Los Alamos has 9+ spherical confinement vessels remaining from experiments. Each vessel contains {approx} 500 lbs of radioactive debris such as actinide metals and oxides, metals, powdered silica, graphite, and wires and hardware. In order to dispose of the vessels, debris and contamination must be removed. Neutron assay system was designed to assay vessels before and after cleanout. System requirements are: (1) Modular and moveable; (2) Capable of detecting {approx}100g {sup 239}Pu equivalent in a 2-inch thick steel sphere with 6 foot diameter; and (3) Capable of safeguards-quality assays. Initial design parameters arethe use of 4-atm {sup 3}He tubes with length of 6 feet, and {sup 3}He tubes embedded in polyethelene for moderation. This paper describes the calibration of the Confinement Vessel Assay System (CVAS) and quantification of its uncertainties. Assay uncertainty depends on five factors: (1) Statistical uncertainty in the assay measurement; (2) Statistical uncertainty in the background measurement; (3) Statistical uncertainty in the isotopics determination - This should be much smaller than the other uncertainties; (4) Systematic uncertainty due to position bias; and (5) Systematic uncertainty due to fluctuations in cosmic ray spallation. This one can bemore » virtually eliminated by performing the background measurement with an empty vessel - but that may not be possible. We used modeling and experiments to quantify the systematic uncertainties. The calibration assumes a uniform distribution of material, but reality will be different. MCNPX modeling was used to quantify the positional bias. The model was benchmarked to build confidence in its results. Material at top of vessel is 44% greater than amount assayed, according to singles. Material near 19-tube detector is 38% less than amount assayed, according to singles. Cosmic ray spallation contributes significantly to the background. Comparing rates with and without a vessel showed that spallation adds an average of 27.27 singles/s and 5.45 doubles/s to background. Errors in the background rates were estimated at 20%.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Los Alamos National Laboratory
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
DOE/LANL
OSTI Identifier:
1046510
Report Number(s):
LA-UR-12-22981
TRN: US1203780
DOE Contract Number:  
AC52-06NA25396
Resource Type:
Conference
Resource Relation:
Conference: Institute of Nuclear Materials Management Annual Meeting 2012 ; 2012-07-16 - 2012-07-16 ; Orlando, Florida, United States
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 36 MATERIALS SCIENCE; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 42 ENGINEERING; ACTINIDES; CALIBRATION; CONFINEMENT; CONTAMINATION; DESIGN; DISTRIBUTION; FLUCTUATIONS; GRAPHITE; NEUTRONS; NUCLEAR MATERIALS MANAGEMENT; OXIDES; SILICA; SPALLATION; STEELS; WASTES

Citation Formats

Frame, Katherine C, Bourne, Mark M, Crooks, William J, Evans, Louise, Mayo, Douglas R, Miko, David K, Salazar, William R, Stange, Sy, Valdez, Jose I, and Vigil, Georgiana M. Neutron Assay System for Confinement Vessel Disposition. United States: N. p., 2012. Web.
Frame, Katherine C, Bourne, Mark M, Crooks, William J, Evans, Louise, Mayo, Douglas R, Miko, David K, Salazar, William R, Stange, Sy, Valdez, Jose I, & Vigil, Georgiana M. Neutron Assay System for Confinement Vessel Disposition. United States.
Frame, Katherine C, Bourne, Mark M, Crooks, William J, Evans, Louise, Mayo, Douglas R, Miko, David K, Salazar, William R, Stange, Sy, Valdez, Jose I, and Vigil, Georgiana M. Fri . "Neutron Assay System for Confinement Vessel Disposition". United States. https://www.osti.gov/servlets/purl/1046510.
@article{osti_1046510,
title = {Neutron Assay System for Confinement Vessel Disposition},
author = {Frame, Katherine C and Bourne, Mark M and Crooks, William J and Evans, Louise and Mayo, Douglas R and Miko, David K and Salazar, William R and Stange, Sy and Valdez, Jose I and Vigil, Georgiana M},
abstractNote = {Waste will be removed from confinement vessels remaining from 1970s-era experiments. Los Alamos has 9+ spherical confinement vessels remaining from experiments. Each vessel contains {approx} 500 lbs of radioactive debris such as actinide metals and oxides, metals, powdered silica, graphite, and wires and hardware. In order to dispose of the vessels, debris and contamination must be removed. Neutron assay system was designed to assay vessels before and after cleanout. System requirements are: (1) Modular and moveable; (2) Capable of detecting {approx}100g {sup 239}Pu equivalent in a 2-inch thick steel sphere with 6 foot diameter; and (3) Capable of safeguards-quality assays. Initial design parameters arethe use of 4-atm {sup 3}He tubes with length of 6 feet, and {sup 3}He tubes embedded in polyethelene for moderation. This paper describes the calibration of the Confinement Vessel Assay System (CVAS) and quantification of its uncertainties. Assay uncertainty depends on five factors: (1) Statistical uncertainty in the assay measurement; (2) Statistical uncertainty in the background measurement; (3) Statistical uncertainty in the isotopics determination - This should be much smaller than the other uncertainties; (4) Systematic uncertainty due to position bias; and (5) Systematic uncertainty due to fluctuations in cosmic ray spallation. This one can be virtually eliminated by performing the background measurement with an empty vessel - but that may not be possible. We used modeling and experiments to quantify the systematic uncertainties. The calibration assumes a uniform distribution of material, but reality will be different. MCNPX modeling was used to quantify the positional bias. The model was benchmarked to build confidence in its results. Material at top of vessel is 44% greater than amount assayed, according to singles. Material near 19-tube detector is 38% less than amount assayed, according to singles. Cosmic ray spallation contributes significantly to the background. Comparing rates with and without a vessel showed that spallation adds an average of 27.27 singles/s and 5.45 doubles/s to background. Errors in the background rates were estimated at 20%.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2012},
month = {7}
}

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