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Title: Assessment of the potential for criticality in the far field of a used nuclear fuel repository

Abstract

This study aims to assess the likelihood for criticality in the far field of a repository for direct disposal of commercial light water reactor used nuclear fuel. Two models are used in combination: (1) a neutronics model to estimate the minimum critical masses of spherical, water-saturated depositions of fissile material; (2) a transport model to simulate the dissolution of waste packages arranged in an array and the subsequent transport of fissile solutes through fractured bedrock to a single accumulation location. The neutronics model shows that heavy metals from different types of used fuel present the same minimum critical mass behavior in the parameter space of initial enrichment and burnup, dictated largely by the fissile content. However, the magnitude of the minimum critical mass varies significantly within that parameter space, and secondary effects like the presence of absorbing nuclides play a minor role. Here, the transport model employs various subsurface transport scenarios, and for each scenario the mass of each isotope and the overall fissile content of the accumulation is reported from the time of canister failure up to one hundred million years at various distances from the repository edge. Taking the results of the two models in concert, it ismore » shown that even if the accumulation of a critical mass is possible under conservative conditions, these conditions are unlikely to be present in the vicinity of a carefully engineered repository. Based on the results of each model, recommendations for risk mitigation in terms of waste characteristics and repository design are given.« less

Authors:
 [1];  [1];  [2];  [1];  [1]
  1. Univ. of California, Berkeley, CA (United States)
  2. Japan Atomic Energy Agency, Ibaraki (Japan)
Publication Date:
Research Org.:
Univ. of California, Berkeley, CA (United States). Nuclear Science and Security Consortium
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation (NA-20)
OSTI Identifier:
1545538
Grant/Contract Number:  
NA0003180
Resource Type:
Accepted Manuscript
Journal Name:
Annals of Nuclear Energy (Oxford)
Additional Journal Information:
Journal Name: Annals of Nuclear Energy (Oxford); Journal Volume: 124; Journal Issue: C; Journal ID: ISSN 0306-4549
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
Nuclear waste disposal; Criticality safety assessment; Geologic repository; Radionuclide transport

Citation Formats

Atz, Milos, Salazar, Alex, Hirano, Fumio, Fratoni, Massimiliano, and Ahn, Joonhang. Assessment of the potential for criticality in the far field of a used nuclear fuel repository. United States: N. p., 2018. Web. doi:10.1016/j.anucene.2018.09.028.
Atz, Milos, Salazar, Alex, Hirano, Fumio, Fratoni, Massimiliano, & Ahn, Joonhang. Assessment of the potential for criticality in the far field of a used nuclear fuel repository. United States. doi:10.1016/j.anucene.2018.09.028.
Atz, Milos, Salazar, Alex, Hirano, Fumio, Fratoni, Massimiliano, and Ahn, Joonhang. Mon . "Assessment of the potential for criticality in the far field of a used nuclear fuel repository". United States. doi:10.1016/j.anucene.2018.09.028. https://www.osti.gov/servlets/purl/1545538.
@article{osti_1545538,
title = {Assessment of the potential for criticality in the far field of a used nuclear fuel repository},
author = {Atz, Milos and Salazar, Alex and Hirano, Fumio and Fratoni, Massimiliano and Ahn, Joonhang},
abstractNote = {This study aims to assess the likelihood for criticality in the far field of a repository for direct disposal of commercial light water reactor used nuclear fuel. Two models are used in combination: (1) a neutronics model to estimate the minimum critical masses of spherical, water-saturated depositions of fissile material; (2) a transport model to simulate the dissolution of waste packages arranged in an array and the subsequent transport of fissile solutes through fractured bedrock to a single accumulation location. The neutronics model shows that heavy metals from different types of used fuel present the same minimum critical mass behavior in the parameter space of initial enrichment and burnup, dictated largely by the fissile content. However, the magnitude of the minimum critical mass varies significantly within that parameter space, and secondary effects like the presence of absorbing nuclides play a minor role. Here, the transport model employs various subsurface transport scenarios, and for each scenario the mass of each isotope and the overall fissile content of the accumulation is reported from the time of canister failure up to one hundred million years at various distances from the repository edge. Taking the results of the two models in concert, it is shown that even if the accumulation of a critical mass is possible under conservative conditions, these conditions are unlikely to be present in the vicinity of a carefully engineered repository. Based on the results of each model, recommendations for risk mitigation in terms of waste characteristics and repository design are given.},
doi = {10.1016/j.anucene.2018.09.028},
journal = {Annals of Nuclear Energy (Oxford)},
number = C,
volume = 124,
place = {United States},
year = {2018},
month = {10}
}

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