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51317--9590-Assessment of Aging Mechanisms for Steels in Spent Nuclear Fuel Dry Storage Systems

Aging mechanisms - including general corrosion, pitting/crevice corrosion, galvanic corrosion, microbiologically influenced corrosion, stress corrosion cracking (SCC), creep, fatigue, thermal aging, radiation embrittlement, stress relaxation, and wear - based on literature and operating experience from nuclear and nonnuclear applications.

 

Product Number: 51317--9590-SG
ISBN: 9590 2017 CP
Author: Xihua He
Publication Date: 2017
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Assessment of Aging Mechanisms for Carbon Steel Low-Alloy Steel and Stainless Steel Components Exposed to Outdoor and Sheltered Environments in Spent Nuclear Fuel Dry Storage SystemsXihua He1 Yi-Ming Pan1 John Wise2 Darrell Dunn2 Greg Oberson2 and M. Hiser21Center for Nuclear Waste Regulatory Analyses (CNWRA®)Southwest Research Institute®San Antonio Texas 782382U.S. Nuclear Regulatory Commission (NRC)Washington DC 20555-0001ABSTRACTDry storage systems (DSSs) store spent nuclear fuel at many operating and decommissioned power reactor sites in the United States. Carbon steel low-alloy steel and stainless steel components are commonly used to construct DSSs. These components are exposed to outdoor and sheltered environments in which the materials may be susceptible to degradation. Potential environmental thermal mechanical and irradiation-induced aging mechanisms include general corrosion pitting and crevice corrosion galvanic corrosion microbiologically influenced corrosion stress corrosion cracking (SCC) (including hydrogen embrittlement) creep fatigue thermal aging radiation embrittlement stress relaxation and wear. This paper presents an assessment of these degradation mechanisms based on review of literature and operating experience from nuclear and nonnuclear applications and their long-term effects on the integrity of DSSs.The results of this study indicate that the following mechanisms be considered to continue safely storing spent nuclear fuel during a 60-year timeframe: (i) general corrosion pitting and crevice corrosion galvanic corrosion stress relaxation and wear of carbon steel and low-alloy steel (ii) wear of stainless steel (iii) galvanic corrosion of stainless steel in contact with graphite (iv) SCC of stainless steel welds and (v) pitting and crevice corrosion of stainless steel as a precursor or initiation site for SCC. For weld-free austenitic stainless steel components or regions away from welds such as the storage canister body atmospheric SCC could be a credible aging mechanism provided sufficient tensile stresses exist. The results of this work are being used to inform recommendations for monitoring inspection and other activities to manage the aging of DSSs.This abstract is an independent product of the CNWRA and does not necessarily reflect the view or regulatory position of the NRC. The NRC staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of any licensing action that may be under consideration at the NRC.

Key words: carbon steel, low-alloy steel, stainless steel, outdoor air, sheltered environment

Assessment of Aging Mechanisms for Carbon Steel Low-Alloy Steel and Stainless Steel Components Exposed to Outdoor and Sheltered Environments in Spent Nuclear Fuel Dry Storage SystemsXihua He1 Yi-Ming Pan1 John Wise2 Darrell Dunn2 Greg Oberson2 and M. Hiser21Center for Nuclear Waste Regulatory Analyses (CNWRA®)Southwest Research Institute®San Antonio Texas 782382U.S. Nuclear Regulatory Commission (NRC)Washington DC 20555-0001ABSTRACTDry storage systems (DSSs) store spent nuclear fuel at many operating and decommissioned power reactor sites in the United States. Carbon steel low-alloy steel and stainless steel components are commonly used to construct DSSs. These components are exposed to outdoor and sheltered environments in which the materials may be susceptible to degradation. Potential environmental thermal mechanical and irradiation-induced aging mechanisms include general corrosion pitting and crevice corrosion galvanic corrosion microbiologically influenced corrosion stress corrosion cracking (SCC) (including hydrogen embrittlement) creep fatigue thermal aging radiation embrittlement stress relaxation and wear. This paper presents an assessment of these degradation mechanisms based on review of literature and operating experience from nuclear and nonnuclear applications and their long-term effects on the integrity of DSSs.The results of this study indicate that the following mechanisms be considered to continue safely storing spent nuclear fuel during a 60-year timeframe: (i) general corrosion pitting and crevice corrosion galvanic corrosion stress relaxation and wear of carbon steel and low-alloy steel (ii) wear of stainless steel (iii) galvanic corrosion of stainless steel in contact with graphite (iv) SCC of stainless steel welds and (v) pitting and crevice corrosion of stainless steel as a precursor or initiation site for SCC. For weld-free austenitic stainless steel components or regions away from welds such as the storage canister body atmospheric SCC could be a credible aging mechanism provided sufficient tensile stresses exist. The results of this work are being used to inform recommendations for monitoring inspection and other activities to manage the aging of DSSs.This abstract is an independent product of the CNWRA and does not necessarily reflect the view or regulatory position of the NRC. The NRC staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of any licensing action that may be under consideration at the NRC.

Key words: carbon steel, low-alloy steel, stainless steel, outdoor air, sheltered environment

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