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How Diablo Canyon’s likely delayed decommissioning will be extremely costly and comes with risks

California's last operational nuclear power plant is perched on the ocean’s edge near the City of San Luis Obispo on the Central Coast. Diablo Canyon was due to close in 2025 – it’s unlikely that’s going to happen. But, ultimately one day it will be decommissioned. We look at the costs and risks for the local community.

The story comes from KCLU’s podcast The One Oh One. You can listen to the full episode here.

California’s largest single source of electricity, about 10% of it, comes from Diablo Canyon Nuclear Power Plant. And that electricity is carbon free.

This plant sits on the edge of the Pacific Ocean, west of San Luis Obispo and south of Morro Bay.

A lot of power plants loom large in the communities they reside – this one – not so much. The plant is miles from the closest community and perhaps the only reason you’d be traveling in that direction is to hike the beautiful nature trails of the state park that neighbors the plant.

“Diablo Canyon’s tucked away seven miles down a road, out of sight to a large number of people out of mind,” said Bruce Gibson, the current Chair of the San Luis Obispo County Board of Supervisors. He’s been a supervisor since 2007.

“My guess is that 85 to 90% of the population hardly ever think of it,” said Gibson.

It’s not on the radar of many people – even the locals.

So why should we care about this plant?

Even if it's not going to happen on its original schedule, Diablo Canyon will eventually be decommissioned.

And, that decommissioning process will not be quick. It could take decades; cost billions of dollars; with the end product possibly being a hundred plus canisters of spent nuclear waste stored at the site in perpetuity.

That impacts San Luis Obispo County and its residents of course, but the cost and risks to decommissioning should be something we all pay attention to.

We need a case study

To fully understand what this process will be like, it helps to have a case study of sorts.

Luckily there is something like that – the now decommissioned Humboldt Bay Nuclear Power Plant, located over 500 miles north of Diablo Canyon, also on the California coast.

Humboldt Bay Nuclear Power Plant.jpg
Mike Manetas
After operating for only 13 years, Humboldt Bay Nuclear Power Plant went offline in 1976, after the discovery of an earthquake fault below it. From the moment it went offline to the end of the decommissioning, the process took 45 years.

“I've been here since 1966 and I've been living in the same place for the last 50 years actually,” said Mike Manetas, a longtime Humboldt Bay resident and a retired professor from Humboldt Bay State University, now known as Cal Poly Humboldt.

As part of the Environmental Engineering Department for over 20 years he taught a class on the decommissioning of the Humboldt Bay Nuclear Power Plant and was appointed to the community advisory board following that decommissioning – which meant many trips to the plant over the years.

“Because nobody knew anything about what was going on. And so I learned a lot myself. And I brought in all kinds of expertise to examine what the process was,” said Manetas.

Why is Humboldt Bay a good case study for us to use? 

Well, firstly that decommissioning has been completed. The whole process is done. It’s also – like Diablo Canyon – right on the ocean’s edge with some of the same concerns like earthquake faults and marine impacts. And lastly, they’re both operated by Pacific Gas and Electric or PG&E.

A note here: despite multiple requests to PG&E for an interview for this episode, I never heard back.

So by studying Humboldt Bay’s decommissioning we can get an idea of what to expect.

With everyone I spoke to for this story, the two most important factors about decommissioning came down to the costs and the risks.

Let’s start with the costs.

After operating for only 13 years, Humboldt Bay Nuclear Power Plant went offline in 1976, after the discovery of an earthquake fault below it.

“Everything in the facility is to be removed and the site will be restored back to what it naturally was before the plant was built there,” explained Manetas.

So it went offline in the mid-1970s. Actual decommissioning only started in 2009. The site was completely decommissioned last year – 2021 – meaning from the moment it went offline to the end of the decommissioning, the process took 45 years.

Manetas kept a tab on the money being spent to decommission.

“The cost of decommissioning is something that's enormous and it's really incalculable,” said Mike Manetas.

The total projected cost was originally put at $95 million, he says, but ended up being just over a billion dollars.

Before decommissioning began – 1976 to 2008 – Manetas estimates another half a billion dollars was spent caretaking the plant after it went offline.

And the costs aren’t over. There are six casks on the site today – these are huge canisters of the spent high-level nuclear waste left over after decommissioning. They have to be kept safe and that costs money.

“The PUC, the Public Utilities Commission, has authorized PG&E to collect $150 million to safeguard that waste to the year 2035,” said Manetas.

And those canisters could be there for a very, very long time. There’s been talk for years about a federal site for high-level nuclear waste – spent fuel – but that hasn’t happened yet so like many sites across the U.S., Humboldt Bay is stuck with its nuclear waste.

And that waste stays highly radioactive for thousands of years.

“The waste that literally is going to stay with us in the environment for 10,000 years,” said Manetas.

He says they have been told these storage vessels are sufficient for up to 80 years.

“The industry says originally they told us, ‘Oh, it's good for 40 years’ now they're saying, ‘Oh, they're good for 60 years’, gee, maybe 80 years,” said Manetas. “Okay, that's beside the point. The point is, is that at the end of 80 years or 60 years or 40 years, what happens to these casks? They're going to degrade.”

So they have to keep an eye on what to do with the aging canisters storing waste that lasts for thousands of years.

The safe storage of the waste adds up to a lot of money for taxpayers for a plant that ran for just over a decade a long time ago.

“The analogy I use is you buy an automobile, you buy a Cadillac, and ten years later, it's run its course and you either sell it or take it to the junkyard,” said Manetas. “And then for the rest of your life, you're going to get a bill, $1 or $2 a month, because you owned that Cadillac to take care of the muffler that is highly radioactive and has to be watched over for 10,000 years. I mean, it's mind boggling.”

Ok, so those are the mind-boggling costs, as Manetas puts it.

In our case study let’s move onto risks.

During decommissioning there are risks to dismantling a plant – you know, the actual buildings and everything in it.

“They have to go in and very carefully remove that either robotically or with people with suits,” said Manetas.

HB divers.jpg
Mike Manetas
As a member of the community advisory board following the decommissioning of Humboldt Bay Nuclear Power Plant, Mike Manetas was able to visit the site many times and take photographs. He says divers had to scrape the walls of the spent fuel pool as part of the process. These are the suits they would wear.

16,000 truckloads of the low-level waste from reactor operations were transported offsite, Manetas says.

“It's a very, very expensive, difficult technology to take this stuff apart and then to package it and then to ship it someplace wherever it's going to go,” said Manetas.

Then there are the environmental and external risks. What happens if there’s an earthquake or tsunami – think Fukushima in Japan. What about war – Europe's largest nuclear plant – Zaporizhzhia – wasn’t on many people’s radar until Russia invaded Ukraine.

And then there’s the more likely and imminent threat to the Humboldt Bay site specifically – sea level rise.

Jennifer Marlow is the assistant professor of Environmental Law at Cal Poly Humboldt.

“The bluff upon which the spent nuclear fuel at Humboldt Bay is stored – it's 115 feet away from the shoreline and 44 feet above sea level. And so it used to be 96 feet about high and now it's 44 feet high,” said Marlow. “And so it's a particularly erosive part of Humboldt Bay. Over time, as erosion accelerates, as sea level rises, and as that seawall currently protecting the bluff might be breached.”

Marlow explains what this means for the rip rap retainer wall, also known as a seawall, currently protecting the site and shoreline.

“With 1.5 meters of sea level rise, there would be chronic or monthly overtopping of that rip rap wall,” said Marlow. “And with 2 meters of sea level rise, that rip rap wall would be overtopped daily at high tide, and it would make the spent nuclear fuel site, an island with everything around it submerged by the rising sea.”

Before bluff.jpg
Lloyd Stine
An image taken in 1952, of the coastline and protective seawall close to the site of the Humboldt Bay Nuclear Power Plant, where the high-level nuclear waste leftover after decommissioning is stored today.
After bluff.jfif
Abigail Lowell
And image taken in 2020 of the seawall close to the Humboldt Bay Nuclear Power Plant site. Researchers have looked into how sea level rise could overtop that seawall and affect the site storing leftover high-level nuclear waste.

Marlow said credible tsunami risks have also been looked into, and reports suggest the maximum tsunami run up level is 43 feet – dangerously close to where the site sits currently at 44 feet.

“What we don't know is how sea level rise is going to impact this tsunami run up estimates into the future,” said Marlow.

So how does this all compare to Diablo Canyon? 

Of course, we can’t do a complete apples to apples comparison, but we can make some educated assumptions.

Let’s first look at the size and lifespan of the plants for comparison and what that means for the leftover nuclear waste.

Humboldt Bay was a 65-megawatt nuclear power plant. Diablo Canyon is over 30 times bigger at over 2,000 megawatts.

Humboldt Bay operated for 13 years. Diablo Canyon has been operating for 37.

Essentially this all means a lot more nuclear waste. Far more than the six canisters at Humboldt Bay. Mike Manetas has done some math and he puts the eventual number at Diablo Canyon at around 300 canisters.

I put this eye-popping number to another one of my sources – David Weisman, the legislative director for the Alliance for Nuclear Responsibility.

The alliance opposes nuclear power because it says it’s too expensive and cumbersome for what it delivers. It has been actively involved in the decommissioning plans.

So, how many nuclear waste canisters would be stored on the site after decommissioning? Weisman lives in Morro Bay, just north of Diablo Canyon.

His estimate is a lot less than Manetas’ 300.

“My number was like 138. In other words, if the plant runs to the end of its life, that has planned – 2025, they have 70 up there now and they’ve ordered another 68, 70 from this new vendor,” said Weisman.

Either way, it’s a huge number compared to Humboldt Bay. A lot more highly radioactive waste to keep an eye on and store safely for those thousands of years.

“The biggest question we would have also of the longevity of the canisters is – it's the marine environment. It may not be immediately impacted by tsunami or erosion. But you've got the fog, the cold air, the mist. And they're absolutely going to have to maintain a vigilant program to make sure that rust and corrosion…”

… Doesn’t affect the canisters.

And Diablo Canyon, because of its size and how long it's been operating, has a ton of that low-level waste as well.

“All the toxics involved in the building have to be carefully wrapped and transported away,” said Weisman.

Weisman says at first the plan was to transport thousands of loads of this waste off site by truck – like they did at Humboldt Bay.

“Avila Valley roads, a little winding road that leads from the plant. There were going to be thousands of truckloads and the local people are like, ‘What?’ So a decision was made for most of the bulky stuff – we're going to build a dock where the intake is, load it on a barge and send it down to Port Hueneme or something like that,” said Weisman.

Low-level waste on barges or trucks – all of this, as with the theme of this piece, has risks and costs a lot of money.

Let’s now turn to environmental and external factors. Weisman has already pointed to one of them – marine impacts. Let’s look at some others.

Sea Level rise is not as much of a concern for Diablo Canyon as in Humboldt Bay, Weisman says. The canisters are stored up the hill 200 feet above sea level.

What about earthquakes? Well PG&E has long maintained that the plant could withstand an earthquake. But the plant is located close to several earthquake faults and many locals have voiced concern about its safety for decades.

One of the main factors in the original plans to shut down Diablo Canyon was the high cost of retrofitting it to meet updated environmental regulations.

Talking about money. Let's look at the total cost of decommissioning. In 2021, the California Public Utilities Commission approved an estimated $3.9 billion needed to safely decommission the plant.

But remember our professor from Humboldt Bay – Mike Manetas – and how he kept an accounting of that decommissioning. He believes the costs will go up.

“Diablo Canyon right now they're saying, ‘Oh, we're going to do it for $4 billion’. Well, if you look 30 years down the road, that $4 billion could easily become $10 billion. $20 billion,” said Mike Manetas.

And finally let’s turn to the timeline.

Compared to Humboldt it seems decommissioning at Diablo Canyon, when it does actually start, will be a lot quicker.

PG&E has details on their website about their plans for decommissioning – on its page dedicated to the process, it says, after the plant is shut down… “Decommissioning will begin promptly and the process will take approximately ten years.”

David Weisman and I discussed what this would look like if shutdown plans were still going ahead on the original timeline

David Weisman: In theory, by about 2035 the soil would be flat. The domes in the structures are gone. They’d regrade the hillside planted with native vegetation. And so by the mid to late 2030s, it should have looked like nothing had ever been there.  

Michelle Loxton: Except for the waste that's sitting in the canisters?  

David Weisman: Two football fields or three football fields up on the hill. But again, the benefit is the entire security perimeter shrinks to just that area. That opens up the land, which is what the REACH people and these others were looking at, or the native tribes and indigenous tribes are now looking at it as well. 

The REACH people Weisman is referring to there, is a regional economic group that has put forward a plan to turn the fully decommissioned site into a Clean Energy Innovation Tech Park with desalination, battery storage, wind energy and a community center. This was a plan that many local political leaders and community groups had signed on to.

What it all means for San Luis Obispo County

I wanted to end this piece with the reason why I decided to tell the story of Diablo Canyon in the first place – why we should care.

Beyond the cost to rate and taxpayers across the state, the risks associated with having a nuclear power plant and its left-over waste nearby, is mostly on the local community.

DIABLO 1 credit PG&E.jpg
California’s largest single source of electricity, about 10% of it, comes from Diablo Canyon Nuclear Power Plant. This plant sits on the edge of the Pacific Ocean, west of San Luis Obispo and south of Morro Bay.

Bringing Bruce Gibson back in here, the San Luis Obispo County Supervisor.

“The risk of those things, the impact of an accident, a bad outcome, and any of those issues rests physically on San Luis Obispo County,” said Gibson.

Gibson has a background in geophysics and has been involved in monitoring Diablo Canyon’s operations for many years.

“Diablo Canyon has been a big deal in San Luis Obispo County for a very long time, and there's a great diversity of view about it,” said Gibson. “There are those who have long objected to its construction and its operation, and there are those who are extremely supportive of it because of its impact on our economy. It is easily the single largest private employer in our county and has provided a great number of well-paying head of household jobs.”

Despite the polarizing local opinions about the plant, he says he understands why it needs to stay open a little longer.

“I am comfortable with its operation. And I certainly understand the case to be made that extending its life for a certain amount of time in the time we are transitioning to renewable energy could provide some benefits to the entire state of California,” said Gibson.

He says he tries to stay neutral when representing the overall interests of his community.

“I see my job as holding PG&E and the other regulatory bodies accountable for doing the best possible job of mitigating those impacts,” said Gibson. “There's the risk of an accident while the plant’s operating – that's obviously very much top of everybody's mind. But more than that, there's the issue, for instance, of the spent fuel that's still stored on that site. And so far as we can see, it is going to be there for the rest of my life.”

“I can't be one of those folks that just lets it go. I have to be thinking about it,” said Bruce Gibson.

I asked him about how he approaches an issue that will remain relevant far beyond the lifespan of his political career.

“But that whole business of burdening generations for 10,000 years to take care of something that cannot escape into the environment is a huge ethical question. So we benefited from this. And ‘Hey, kids, here's your legacy’. Right? We talk all the time about the programs we have to put in place for that are much longer than terms in office,” said Gibson.

For Gibson, in the end it all comes down to never being able to disengage from what is happening at Diablo Canyon.

“I can't be one of those folks that just lets it go. I have to be thinking about it,” Gibson said. “Never lose sight of its benefit and risk… I think we can get successfully to the next phase. And I'm certainly hopeful for that.”


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Michelle Loxton joined KCLU in June 2021 as Podcast and Digital Content Producer.