By John Stang
Holtec International has determined that scratches and abrasions on spent nuclear fuel storage canisters do not represent a safety danger at a closed nuclear power plant in California, executives told U.S. Nuclear Regulatory Commission officials on Wednesday.
However, Holtec critics at the same meeting argued that today’s scratches could lead to major defects in the future.
The New Jersey-based energy technology firm requested the meeting at NRC headquarters near Washington D.C., to discuss concerns about scratches and abrasions found on canisters used in its HI-STORM UMAX underground dry storage system at the retired San Onofre Nuclear Generating Station (SONGS) in San Diego County, Calif. Also in attendance at the open meeting, by telephone, were a number of citizens and watchdog groups.
Beyond affirming the safety of its storage system for the radioactive spent fuel assemblies, Holtec representatives did not provide much detail on its study. The company in 2014 secured the fuel-transfer contract from SONGS majority owner and licensee Southern California Edison, a year after the utility closed the plant’s two remaining operational reactors following installation of faulty steam generators.
The issue ripples out from the August 2018 suspension of used-fuel transfers from wet storage at SONGS after a mishap of inserting one canister into its dry-storage slot. In a YouTube video posted this week, the NRC administrator for the region covering California, Scott Morris, noted the potential for canisters to be scratched as they are lowered with little spare space into storage slots.
“This scratching issue is the principal reason why the NRC is not yet comfortable with or confident that the licensee can resume spent fuel handling,” said Scott Morris, administrator for NRC Region 4.
The nuclear-industry regulator wants to determine whether the scratches create a future potential for radiation leaks from the canisters. Morris noted that the final safety analysis submitted to the NRC as part of the certification for the Holtec spent fuel storage pad said there was no risk of scratching. But that proved not to be the case.
Southern California Edison also has a general license from the NRC to employ the Holtec spent fuel storage pad. In that document, the regulator acknowledges that the American Society of Mechanical Engineers boiler and pressure vessel code accepts some incidental scratches on the canisters during production and operations.
Even if the situation is found to be safe, Morris said in the video, Southern California Edison must reconcile the inconsistencies in the various documents on whether scratching is permitted.
“It’s yet to be determined whether that process … can be done without prior NRC approval or whether prior NRC approval is required, the latter of which could take several weeks or potentially months to resolve,” he said. It is now up to the utility to provide the agency with a technical basis demonstrating why the identified scratching does not create a safety threat.
Southern California Edison is using a robotic camera system to examine the 29 canisters that have been placed into SONGS’ HI-STORM UMAX system, Morris said. As of Monday, three canisters had been examined. The NRC will evaluate the data from the utility in determining whether fuel loading can resume.
The resumption of fuel loading at SONGS is also dependent on the federal agency reviewing and signing off on the steps taken by Southern California Edison and Holtec to overhaul their equipment and procedures. The timetable for restarting fuel movement is up in the air.
Southern California Edison has already said it will accept a $116,000 penalty assessed by the NRC for two violations of federal regulations linked to the incident.
So far, the scratches and abrasion issue has been raised solely at SONGS, according to the NRC. HI-STORM UMAX is also used at the Callaway nuclear power plant in Missouri. The HI-STORM canisters are deployed at the shuttered Vermont Yankee facility and other sites.
The scratches and abrasions do not threaten the safety of the canisters, said Chuck Bullard, director of engineering mechanics at Holtec: “They are a common occurrence.”
The scratches come from inevitable scraping from moving the canisters and inserting them into tight holes in the storage pads, Bullard said. The scratches on the canisters are shallow, he added. The deepest scratch found on a SONGS canister was 0.026 inch in depth, compared to the thickness of the canister wall –five-eighths of an inch.
Some callers into the meeting remained unpersuaded.
Architect Torgen Johnson, of the California-based Samuel Lawrence Foundation, said the canisters face the prospect of being scratched multiples times when they are withdrawn from their storage slots at SONGS and potentially transported to an interim storage site for U.S. spent fuel, then again to a permanent repository.
The nonprofit Samuel Lawrence Foundation has been particularly critical of plans for spent fuel storage at SONGS, which have been a concern for locals given the seismic activity and population density in Southern California. Its criticisms have been so pointed that Southern California Edison has responded directly in newspaper editorials.
Also during the meeting, caller Marvin Lewis said: “Maybe the scratches didn’t go deep. But they are starting blotches of pitting and corrosion.”
Holtec and NRC officials did not respond to those concerns Wednesday.
The HI-STORM UMAX system is a combination of canisters and tailor-made system of modules for underground dry storage. It is a version of the Holtec HI-STORM system that holds at least 52,500 used fuel assemblies in 1,025 casks at 34 dry storage sites across the nation, according to a 2018 Ux Consulting Co. report.
At the time of the August 2018 incident, SCE and Holtec had placed 29 of 73 canisters into dry storage via the HI-STORM UMAX system. Roughly one-third of SONGS’ spent reactor fuel was already held in 51 canisters in an on-site independent spent fuel storage installation. That radioactive waste is from the plant’s reactor Unit 1, which shut down in 1992.
