Robert J. Budnitz, a career nuclear power safety expert, didn't mince words when describing the potential risk that Diablo Canyon Power Plant's spent fuel poses as it's been stored at the site for years, and likely will be for decades.

"That stuff's hazardous," Budnitz said in his March 13 presentation on the subject to the Diablo Canyon Decommissioning Engagement Panel. "Even though a whole lot of it has decayed, it's full of radioactive stuff."

In one disaster scenario that Budnitz outlined, a massive earthquake knocks out the plant's electricity, including its six backup generators. As a result, the instrument that helps cool down the ultra-hot spent fuel assemblies, stored in two pools, shuts off. Those pools eventually get so hot that they boil over and spill their water—leaving the radioactive material exposed to the atmosphere for leaks and fires.

"That's a really nasty accident," Budnitz explained. "The principal engineering challenge is working to ensure, with very high assurance, that that stuff doesn't get out. That's what engineers do. That's the challenge."

Spent fuel is a key concern for Budnitz as the chair of the Diablo Canyon Independent Safety Committee, a body formed back in 1990 to provide analyses and recommendations to the state about plant safety. Spent fuel is going to become his and the committee's No. 1 focus when Diablo's nuclear reactors are shut off in 2024 and 2025.

With nowhere else to take the spent fuel, PG&E will have to store and monitor it on-site indefinitely, first in the cooling pools, and then in large concrete and steel containers called dry casks.

The Diablo Canyon Decommissioning Engagement Panel—a committee of 12 local community members created "to foster open and transparent dialogue" about the plant's shutdown, per PG&E's website—tackled the hot-button topic at its latest meeting on March 13.

In his presentation, Budnitz assured the panel that a catastrophe occurring like the one he described was "very unlikely." The facility was built to withstand powerful earthquakes and, even if it were compromised by one, the pools would take days to boil, giving responders ample time to devise solutions.

"I'm not worried," he said.

Nevertheless, it's events like these that PG&E and San Luis Obispo County must protect against while the nuclear waste is stored at the site—which will continue long after the plant goes out of production.

PG&E's most recent plan to handle the spent fuel has drawn some scrutiny. It targets 2032 for the transfer of material from cooling pools to dry casks. Safety advocates and regulators had hoped that process, which in the past has taken about 10 years, would start a lot sooner, since spent fuel is more secure in the dry casks than it is in the cooling pools.

"There's no equipment that could fail," Budnitz noted about the dry casks. "It's safer and certainly more secure."

Budnitz said the Independent Safety Committee hadn't reviewed PG&E's latest proposal yet, but said, "whether there's a safety issue, we're going to look at it very soon."

In recent years, PG&E has slowed down its transferring of spent fuel assemblies from pools to dry casks. Engagement panel member Alex Karlin pointed this out at the March 13 meeting, echoing criticisms from the local group, Alliance for Nuclear Responsibility, which recently filed a scathing response to PG&E's spent fuel plan.

"PG&E has unilaterally decided to halt that offloading campaign," Karlin, a former administrative judge with the Nuclear Regulatory Commission, said. "Instead, they are proposing to let the [spent fuel] build up and stay there until the closure. I think this is a problem."

PG&E officials at the meeting responded that storing the remaining spent fuel assemblies in the pools would increase flexibility as they map out a plan for the final transfer phase. PG&E plans to purchase a new fleet of dry casks that may have a higher heat capacity, which could help facilitate a faster transfer time from the pools to casks, company reps said at the meeting.

Whether in pools or casks, the hazardous byproduct of Diablo Canyon's production will remain in SLO County for the foreseeable future. Without a remote, federally managed site to transport the material to—despite decades-old assurances of one—local residents will have to grapple with the risks.

"I just want to keep that in our minds," panel member Linda Seeley said. "This is March 13, 2019. On March 11, 2011, Fukushima melted down in an earthquake that was unanticipated. Things happen that we don't anticipate. ... The consequences can be immense." Δ

Assistant Editor Peter Johnson can be reached at [email protected].