A few brows furrowed when Southern California Edison announced that a scratch on a nuclear waste canister at San Onofre was re-assessed — and is actually less than half as deep as originally estimated.

How very convenient! Edison skeptics said. How’s that again?

Edison, actually, announced this bit of news in March, and has been reiterating its explanation ever since. Doubters, however, remain, so we’ll do what we can here to suss it out — though we hold no illusions that it will satisfy all.

Q. How the heck does a scratch in a nuclear waste canister suddenly shrink?!

A. It doesn’t. But technology evolves, Edison said.

We’re talking about Canister 72 here, which was scratched in 2018 by seismic restraints as it journeyed into its steel-and-concrete vault in the Holtec dry storage system.

In 2019, Edison sent robots and remote cameras inside that vault to inspect 72’s scratch. The camera system had some trouble locking on to it — flagged by a red dot beside the image, like trying to take a picture before autofocus has engaged, said San Onofre’s head of engineering. At that time, the tech estimated the scratch to be about 0.026 inches deep. That’s not deep enough to require any sort of remediation, but it was by far the deepest of several scratches observed on the canisters.

Engineering head Jerry Stephenson had his doubts about the measurement. It looked like bad data. But tossing it out would be “nonconservative,” he said, and he knew Edison would be criticized if it ignored the bigger number. It’s best to err on the side of caution anyway, so he decided to keep the measure and to check again at the next opportunity.

That came in March 2024, at the five-year inspection mark required by the state (not the Nuclear Regulatory Commission, mind you; the NRC doesn’t require inspections until the 20-year-mark). This time, Edison sent the camera back and forth over the area, giving it time to take a solid reading and make a good map. This time, 72’s scratch was found to to be less than half as deep as the original estimate — just 0.011 inches.

Puh-lease! some of Edison’s critics groaned.

Stephenson explained that, by 2024, the software locking in on the scratches and recording data to measure depth had improved. You can see it in the image of the scratch, he said — the dot that was red in 2019 was green in 2024. The scratch, it turns out, is actually small, about as thick as three or four human hairs, or one-third as thick as a credit card, he said.

Overall, last year’s inspection found the three canisters in good condition, with no corrosion in any of the scratched areas. Visible scuff marks caused by the shield ring — a radiation barrier — had minimal or no depth, Edison said.

Q. Do folks believe this?

A. The NRC declined comment on the remeasurement issue (thanks!), but David Lochbaum, retired director of the nonprofit Union of Concerned Scientists’ Nuclear Safety Project, said he had no reason to doubt it.

Improved tech has worked similar miracles when nuclear plant operators were required to monitor actual cracks — not just scratches — in steam generators and steel containment liners. As cracks got closer to the threshold requiring plugging or replacement, the industry developed more sensitive detection methods to more accurately measure them (and stave off expensive remediation, at least for a while).

Lochbaum, for his part, thinks Edison had ample justification for tossing the 2019 measure, and isn’t sure he would have kept it had he been in Stephenson’s shoes. Edison’s explanation for the change between 2019 and 2024 is, indeed, plausible, Lochbaum said.

Gary Headrick, founder of San Clemente Green and a regular thorn in Edison’s side, doesn’t buy it. On Canister 72, “Our photos show a large gouge the length of the canister and a patch of corrosion which can lead to ‘Chloride Induced Stress Corrosion Cracking’, the Achilles heel of nuclear waste storage containment throughout the United States,” Headrick wrote. “Their photo shows a shallow, shiny scuff mark with no corrosion, not requiring any sort of remediation.”

Edison responds: That picture of the long scratch on 72 is not trying to measure depth. The blotch on 72 is from a paint defect on the transfer cask (used to get waste out of spent fuel pools and into dry storage canisters). That allowed iron oxide to affix to 72. It was photographed in 2019 and reinspected in 2024, and the pictures are identical, Edison said.

Here’s the situation, according to spokeswoman Liese Mosher: The American Society of Mechanical Engineers code allows a defect up to 0.062” deep before requiring any analysis.

The deepest scratch identified on any San Onofre canister is far shallower — 0.016” deep — and most are less than 0.010” deep.

While a scratch deeper than 0.062” would require engineering analysis, it would not challenge the safety and integrity of the canister because of its robust design, Mosher said. “Edison added 0.125” of extra thickness beyond what is credited in the design analysis. We have tremendous margin.”

Q. Edison is inspecting the “oldest and coldest” waste canisters in its dry storage systems, not necessarily the hottest or scratchiest. Why?

This isn’t an Edison edict, but NRC and industry guidance.

Here’s the logic: The hottest and/or scratchiest canisters could well be the most recently loaded ones, which you’d expect to show the least degradation and wear-and-tear. The oldest canister, obviously, has had the most time to develop issues.

The coldest canister is likely to be among the oldest as well, but is of interest for another reason: Moisture won’t evaporate off cooler canisters the way it does off hotter canisters. That means condensation can accumulate, making the cooler canisters more susceptible to chloride-induced stress corrosion cracking. Over time, those cracks could present issues.

Q. Issues?! 

A. Breathe. Sixty spent fuel canisters at 25 sites nationwide have been inspected to date, Edison said, and all were in good condition, with none showing precursors to chloride-induced stress corrosion cracking.

Right here at San Onofre, we have canisters that are more than 20 years old. San O was among the nation’s first to be licensed by the NRC to build a dry storage system (because feds don’t have a disposal site yet). The Orano TN-NUHOMS sits a bit inland from the Holtec pad, and started loading waste in 2003. It holds 50 canisters.

As its 20th birthday approached a few years ago, the NRC’s aging management requirements kicked in. Two canisters were inspected in 2021. “Not only did it look fine, but it was shiny,” Stephenson said. “It looked brand new. We were giggling at how good it looked.”

The NRC relicensed the NUHOMS for 40 more years.

Q. How do we head off problems over the coming decades?

By looking for them. Some, however, think inspections don’t happen frequently enough, and/or don’t examine enough canisters when they do.

As we mentioned, the NRC doesn’t require inspections — or an aging management plan — for dry storage systems until they’re approaching 20 and must be relicensed. San Onofre’s more rigorous inspection protocol is required by the California Costal Commission, not the feds.

Edison peers at two loaded canisters every 5 years, and examines the test canister — weighted and heated to mimic a real nuclear waste canister, though devoid of radioactive waste — every 2.5 years. The test canister can be easily pulled out and pored over for defects; is positioned closest to the harsh ocean conditions; and serves as the canary in the coal mine, said Edison. If problems arise, officials expect to see them in the test canister first.

And they haven’t. “Scratches are still bright and shiny, no evidence of corrosion or chloride-induced stress corrosion cracking precursor activity,” Edison reported out of last year’s inspection. “Scratches are all shallow and not a challenge to the integrity of the canisters. No action required.”

Edison will inspect the test canister again in 2027, and will inspect the test canister and two more loaded canisters in 2029.

Of course, there are more than 70 canisters in the Holtec system.

Q. Should we be inspecting more?

Lochbaum isn’t a big fan of current protocols, which are less a “safety spotlight” than an “infrequent safety strobe light,” flashing every once in a while, he has said.

Rather than picking just a couple canisters, inspections should focus on flawed canisters and a “reasonable subset” — say, 10-15% — of the total. If results show that some are less susceptible to degradation than others, “that knowledge can be used to responsibly reduce the scope of canisters inspected,” he wrote.

You want the “Goldilocks” spot — not too much, and not too little, but just right. Lochbaum’s not sure we’re there now.

Edison’s Stephenson heartily disagrees. “All of the assessments, nationally and worldwide, have never found anything,” Stephenson said. “Not corrosion. Not precursors to corrosion.”

To wit: Scientists at the Argonne National Laboratory examined spent fuel rods that were in dry storage at the Surry nuclear plant in Virginia for more than 15 years. They examined fuel pellets and fuel rods, finding that 15 years of dry storage caused no discernible degradation.

“We’re doing more than what’s required,” Stephenson said.

Q. But we’re talking decades before a permanent repository is built. If problems are found, then what?

Nature will degrade all canisters sooner or later, Lochbaum has said. The good news is that a dry cask experiencing a through-wall crack isn’t like a balloon popping — all the contents would not be swiftly ejected. But the safety margins protecting the public would be reduced, and that would be bad.

The industry’s solution: Repair robots — sort of like high-tech St. Bernards — aiming to find and fix defects long before they become serious.

In a test run in 2019, robots were set upon a Holtec canister with two “mock” defects, like pock marks on its outer skin. One robot carried inspection cameras. The other, a nozzle mounted on a movable arm. Using magnetic wheels to crawl around, they found the trouble spots and applied a metallic overlay of nickel, effectively sealing them, Edison said.

Q. What now?

A. Activists want Edison to release all the inspection images, which are technically not public documents, to the public, as other plants have. But Edison has no plans to do that.

Why? Because when technical questions arise at other plants, experts explain and folks move on; while here, expertise is often rejected and misinformation often spreads, officials said.

Environmental activists like Headrick of San Clemente Green fear that, by the time the feds are ready to take possession of the waste (if that day ever comes), the canisters will be too degraded to safely move. “We need a plan to repair or repackage the waste before it can be shipped even a short distance,” he said. “Edison would rather deny the problem even exists.”

There is no problem, officials have said repeatedly. The tech to repair damaged canisters exists and could be easily employed if it were ever necessary (hot cells — heavily shielded enclosures — allow folks to handle radioactive materials remotely and could be set up pretty quickly, they’ve said).

People aren’t keen to trust industry or the government these days. The bottom line, we can all agree, is that nuclear waste should not be kept on a bluff in an earthquake zone a couple of hundred feet from the ocean and near 8 million people. The only way to change that, though, is to demand that the federal government finally find the permanent home it has promised us, and get nuclear waste the heck out of here. The Spent Fuel Solutions coalition, including Edison, lawmakers and officials, is dedicated to doing just that.

“Spent fuel on beach is the symptom. The problem is far greater. We’ve lacked a robust policy to address this,” said U.S. Rep. Mike Levin, D-San Juan Capistrano.

Levin has introduced numerous bills to push the ball forward, and several communities have expressed interest in hosting a permanent disposal site and reaping the economic benefits. “I don’t think we need to sound the alarm immediately,” he said of dry storage. “I always say I want to get this done before I qualify for Medicare.”

Levin, incidentally, is 46.