Inspection and Maintenance of Spent Nuclear Fuel Canisters

There are two dry fuel storage systems at the San Onofre Nuclear Generating Station. The original storage system is the Orano TN-NUHOMS system, which is a horizontal storage system. SCE began loading spent nuclear fuel into this system in 2003 and there are 50 canisters located there now.

In 2014, SCE selected Holtec for its expanded dry fuel storage system. The Holtec UMAX system contains 73 canisters of spent nuclear fuel. We completed the loading process of this system in August 2020.

Aging Management Programs for Dry Fuel Storage

Dry fuel storage systems are initially licensed for 20 years, and then in 40-year intervals. After the first 20 years, an aging management program (AMP) is required by the Nuclear Regulatory Commission (NRC). This program "evaluates known aging degradation mechanisms to determine if they could affect the ability of dry storage system components to fulfill their safety functions in the 20- to 60-year period of extended operation," according to the NRC. SCE has developed an AMP for the TN-NUHOMS system, which is approaching its post-20 year license renewal period.

More information about that program is available in this white paper produced for the Community Engagement Panel.

In November, 2021, SCE and system manufacturer Orano conducted a baseline inspection for the TN-NUHOMS dry fuel storage system. The inspections found no signs of degradation of the inspected canisters, which have been in storage 17 and 18 years, respectively.

See the video below to learn more.

Inspection and Maintenance Program

For the Holtec system, SCE agreed to an accelerated Inspection and Maintenance Program, which will be implemented long before the eventual aging management program for the system. Key elements of the program include:

  1. Periodic canister inspections
  2. A test canister program (using a canister without spent fuel)
  3. Other ongoing inspections of the dry storage system and radiation monitoring
  4. Response and remediation plans including a demonstrated repair method
  5. Reporting requirements

On June 12, 2020, the California Coastal Commission posted notice of its intent to consider SCE's proposed Inspection and Maintenance Program during its July virtual meeting. A Commission staff report includes a recommendation for the Commissioners to approve the IMP. The notice is available on the Commission’s website here and includes links to SCE’s proposed Inspection and Maintenance Program, the Commission’s staff report, and an independent evaluation of the Inspection and Maintenance Program performed by the Commission’s consultant, Lucius Pitkin, Inc.

The IMP is modeled on NRC requirements for AMPs and guidance from the American Society of Mechanical Engineers (ASME), as well as research by the Electric Power Research Institute (EPRI) and the nuclear industry on MPC performance and potential degradation.

A potential challenge for the long‐term service life of stainless-steel spent fuel canisters is chloride-induced stress corrosion cracking (SCC) initiated on the outer surface of the canisters. Although this type of degradation is highly unlikely for SONGS MPCs, the IMP provides an effective program to monitor, detect, and mitigate any canister surface degradation.

Additional SCE information regarding the Inspection and Maintenance Program is available here.

SCE supported the Commission’s July 2020, approval of the Inspection and Maintenance Program, which SCE believes represents the industry’s most advanced and comprehensive spent fuel management program.

Watch the video below to learn more about SCE's industry leading effort on canister inspection and repair.