51316-7670-Degradation of Stainless Steel- and Aluminum-Based Neutron Absorbers Used in Spent Fuel Dry Storage

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Product Number: 51316-7670-SG

ISBN: 7670 2016 CP

Author: Xihua He

Publication Date: 2016

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At operating and decommissioned reactors in the United States spent nuclear fuel (SNF) can be stored in sealed dry cask storage systems. Criticality of the SNF in the systems can be prevented in part by the placement of neutron absorbing materials (NAMs) around the spent fuel assemblies. NAMs include borated stainless steel borated aluminum alloys aluminum matrix composites (such as Metamic and Boralyn) and aluminum boron carbide laminate composites (such as Boral). The cask systems are licensed by the Nuclear Regulatory Commission (NRC) for an initial term of 20 years after which the license may be renewed for another 40 years. NRC is evaluating aging-related degradation mechanisms that could affect the NAMs to ensure that these components will continue to provide adequate criticality control for initial and extended licensing periods. NAMs’ integrity could potentially be affected by fatigue boron depletion thermal aging general corrosion creep and radiation embrittlement. Boral is also susceptible to wet corrosion and blistering. The results of this evaluation indicate that the degradation mechanisms should have little or no effect on the NAMs’ integrity with the possible exception of wet corrosion and blistering of Boral caused by reactions between aluminum and water trapped in the porous matrix above 200 °C [392 °F]. Because the system temperature decays over time and it is a dry and inerted system the progression of the corrosion and blistering is likely to be arrested within 60 years. These findings will be used by NRC to develop generic guidance for aging management of NAMs in dry cask storage systems. The paper will present an assessment of these degradation mechanisms relating to the dry storage system internal environment and their effects on NAMs’ integrity.This abstract is an independent product of the Center for Nuclear Waste Regulatory Analyses and does not necessarily reflect the view or regulatory position of the U.S. Nuclear Regulatory Commission (NRC). 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 NRC.