By John Stang
Holtec International is philosophically at ease with accepting a pair of potential violations being considered by the U.S. Nuclear Regulatory Commission, but contended Wednesday there was no safety threat in procedural glitches in modifying the design of a storage container for spent nuclear fuel.
During a meeting at NRC headquarters, Holtec President and CEO Kris Singh said the regulator’s May inspection of the company’s New Jersey headquarters showed only a flaw in the design update process.
“This, to quote Shakespeare, is much ‘Ado About Nothing,’” Singh said. However, he added that Holtec is prepared to accept the NRC’s final decision on two apparent violations of agency regulations that could lead to fines or other forms of escalated enforcement.
The inspection led from the discovery last March of a loose bolt in a Holtec container being filled with spent fuel assemblies at the San Onofre Nuclear Generating Station (SONGS) in California. By that point four canisters of the same design had been loaded with spent fuel for on-site dry storage at the retired nuclear plant. Holtec subsequently switched to an older-design cask for its contract to transfer SONGS’ used fuel from wet to dry storage.
Canisters of the same design are used for spent fuel storage at seven other nuclear power plants around the country. One, the shuttered Vermont Yankee facility, also briefly halted fuel transfers following finding at SONGS.
Those canisters present no danger to the public, Michael Layton, director of spent fuel management at the NRC’s Office of Nuclear Material Safety and Safeguards, said during Wednesday’s meeting.
Not all observers appeared convinced. Ray Lutz, of El Cajon-based watchdog Citizens Oversight, called on the NRC to check all canister design changes made by Holtec. “How many other things changed in the designs that Holtec has not told us about,” he said.
This was a pre-decisional enforcement conference, a public discussion of the potential violations and mitigating circumstances that will lead to the NRC’s enforcement decision. The agency expects in 30 to 60 days to issue its final decision addressing whether violations occurred, their severity, and what action it will take.
The proceeding began with a May 14-18 site visit in Camden, N.J., to evaluate the adequacy of Holtec’s activities related to federal regulations on licensing for storage of spent nuclear reactor fuel. Specifically, officials looked at factors that could have affected the March 5 discovery of the loose bolt at SONGS.
The interior of the newest model of Holtec’s spent fuel canister has 37 long rectangular chambers that each hold up to 37 spent fuel assemblies. “Basket shims” are placed around the interior of a canister’s walls to keep the long rectangular chambers in place and enable circulation of helium used to cool the fuel assemblies. The broken bolt was one of 88 in each canister to hold the shims in place.
The first potential violation is Holtec’s failure to look at the ripple effects of a change in the shims in the canisters involved in the SONGS incident. “The NRC determined Holtec, when it changed the shim to the pin design in 2016, failed to establish adequate design control measures for selecting and applying materials, parts, equipment and processes essential to the function of safety-related structures, systems and components,” the agency said in a Jan. 2 press release.
The second potential violation is Holtec’s failure to perform a written evaluation of the design changes in canister design, focusing on the new shim. This includes not applying to the NRC for an amendment to the certificate of compliance for the canister.
Singh acknowledged the design change in the shims did not address how the manufacturing process would affect them. However, he contended Holtec conducted the written evaluation on the changed design.
The design change in question involved hollowing out the shim to improve the helium flow around the inside of the cask. Singh said loss of one or more shims would not affect criticality countermeasures in the cask, and would have a minor effect in eliminating heat in the canister.
Singh, though, said Holtec stumbled in the “laser peening” process, which strikes metal such as the bolt holding the shim with shock waves from a high-energy laser to strengthen it. This process is suspected in loosening a bolt in the canister, which caused the shim to break loose. When Holtec redesigned its canister, it did not account for the effects of laser peening on the bolts and redesigned shims, he said.
“The nexus between manufacturing and design is weak. … We need to fix it,” Singh said.
Holtec has now studied the situation, revamped design and manufacturing procedures, improved training on meshing the design work with the manufacturing processes, and separated the design and quality assurance teams.
Holtec’s spent fuel canisters each have 76 to 88 shims, depending on the model. Singh said the company examined 4,200 shims within two existing models in New Jersey, SONGS, and. Vermont Yankee. It found 0.12 percent to the shims were broken, and 1.22 percent were bent, which Singh said were dramatically smaller percentages than what Holtec’s quality assurance obligations allow. He contended all the shims could actually fail without significant effects on the safety of the fuel within the canister.
In the public comment portion of the pre-decision conference, Gary Frederick of the San Clemente, Calif., area wanted the NRC to examine whether Holtec has financial incentives rush its work on the canisters and on spent fuel transfers. “You should be concerned about contractual matters that create incentives for errors,” Frederick said.
Layton said the NRC focuses on safety matters and not on contractual issues.
SONGS majority owner Southern California Edison permanently retired the plant’s last two operational reactors in 2013. The following year, it hired Holtec to provide “pool to pad” services for 2,668 spent fuel assemblies.
The fuel transfer has been suspended since an Aug. 3 mishap in placing a canister into its storage slot. Southern California Edison is scheduled for its own pre-decisional enforcement conference with the NRC on Jan. 24 ahead of possible enforcement action linked to that incident.
