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Product Abstract

Technical Bases for Extended Dry Storage of Spent Nuclear Fuel

Product ID:1003416
Date Published:29-Dec-2002
Sector Name:Nuclear
Document Type:Technical Results
Price:No Charge

This Product is publicly available

   514.41 KB - Adobe PDF (.pdf)

Independent spent fuel storage installations (ISFSIs) are currently licensed for 20 years. However, delays in developing permanent spent fuel disposal capability require continued ISFSI storage beyond the 20-year term. This report provides a technical basis for demonstrating the feasibility of extended spent fuel storage in ISFSIs.


ISFSIs use storage systems in which spent fuel is placed in a dry gas environment (typically helium) inside a metal container, which is sometimes placed inside a concrete cask. Because the Nuclear Regulatory Commission (NRC) limits the license term for an ISFSI to 20 years from the date of issuance and no final solution for spent fuel disposition is available, utilities must prepare for license extension.


To summarize potential dry storage system degradation issues that may affect the maintenance of ISFSI safety functions for time periods beyond 20 years, along with approaches for managing these potential degradation issues.


Investigators examined documents containing information on long-term aging of ISFSIs (beyond 20 years). These documents included existing regulations governing extended spent fuel storage, 10 CFR Part 72, several documents that discussed specific aging issues, reports that provided data on the potential importance of aging issues, a summary of the first ISFSI license extension application to be filed with the NRC, and a discussion of possible aging management options. Investigators next evaluated the license renewal application for the ISFSI at Dominion Generation's Surry nuclear plant, focusing on approaches to identifying, evaluating, and managing aging issues associated with extended storage. In addition, a review of prior work provided data to evaluate the relative importance of degradation issues. This review focused primarily on the Dry Cask Storage Characterization (DCSC) Project, during which a metal cask that had stored spent fuel for approximately 14 years was opened, and the cask and stored fuel assemblies were examined for signs of aging. Finally, investigators reviewed aging management practices to determine if current monitoring and inspection programs would be adequate for extended storage.


This report reviews specific aging issues related to extended storage in ISFSIs. Among the aging issues discussed are the following: degradation of the spent fuel assemblies (including, for example, cladding creep, diffusion-controlled cavity growth, hydride reorientation, radiation embrittlement, and thermal annealing), corrosion of metals inside the sealed spent fuel canister, corrosion of metals outside the canister, radiation damage to metals and concrete, neutron shielding irradiation and thermal damage, and concrete degradation. These aging issues have already been identified, evaluated, and managed as part of the initial 20-year ISFSI licenses granted by the NRC. Only a few aging issues associated with continued dry storage beyond 20 years need to be revisited.

Data collected in the DCSC project showed no evidence of significant degradation of metal cask systems important to safety from the time of initial cask loading in 1985 to testing in 1999. DCSC project examinations of the spent fuel in this cask after approximately 15 years of storage suggested that there was little to no cladding creep or significant hydride reorientation, and no rod failure. Residual creep testing on the spent fuel cladding suggested that there was significant residual creep available such that maintenance of spent fuel integrity well beyond 20 years is likely. The surveillance and monitoring programs ISFSI licensees currently use appear sufficient for extended storage as well.

EPRI Perspective

The NRC has not fully developed a license extension approach for ISFSI licensees, and there has been some concern that aging issues associated with continued dry storage beyond 20 years will prevent ISFSI storage for several more decades. A summary of aging issues related to extended dry storage -- and how to manage them -- is needed to ensure the safety of long-term spent fuel storage, either at the surface or underground.

2002 Program 41.03.01   Used Fuel and High-Level Waste Management Program
  • Aging (Materials)
  • Casks
  • Spent Fuel Storage
  • Licensing
  • Fuel Assemblies
  • Material Degradation

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