Inside the shutdown of California's last nuclear plant

SAN FRANCISCO -- A nuclear power plant doesn't just shut down.

It gets taken apart piece by piece, until almost nothing remains. The process requires billions of dollars, hundreds of workers and more than a decade to complete.

It's a fate Pacific Gas and Electric Co. is now planning for California's last nuclear plant, Diablo Canyon, set to close in 2025. Every step must be carefully scripted.

Fuel rods full of uranium pellets are pulled from the reactor, cooled in pools of water laced with boric acid, then transferred to giant concrete casks.

Deep in the heart of the plant, metal components made radioactive by decades of use must be disassembled or carved into chunks -- often by remote-controlled tools. The hazardous scrap gets hauled to four specially designed landfills scattered across the country, with some machinery buried in concrete sarcophagi.

``It's not dangerous to handle this stuff if done properly,'' said Victor Dricks, senior public affairs officer with the Nuclear Regulatory Commission. ``There are specialized crews, limiting their exposure, working in short periods of time.''

Buildings are razed, foundations removed. Fresh rock and dirt take their place.

And once done, radiation at the site is not supposed to exceed natural background levels. By federal standards, the site must be safe for any use. Although PG&E has not yet given state regulators a formal plan for decommissioning Diablo Canyon, located on the Central Coast near San Luis Obispo, a 2016 study commissioned by the utility estimated the process could wrap up as soon as 2039 or as late as 2071.

``Fortunately, Diablo Canyon isn't the first plant to go through this process, so there's plenty of lessons learned to make this go more right than wrong,'' said Dave Lochbaum, a former nuclear plant engineer and director of the nuclear safety project at the Union of Concerned Scientists.

It's a process likely to be repeated often in the coming years as more nuclear plant operators decide to shut down their facilities, which have been undercut by cheap electricity from natural gas plants.

In March, FirstEnergy Solutions announced it would close three nuclear plants in Ohio and Pennsylvania unless state or federal authorities devise a new way to compensate them. In the past five years, 18 nuclear reactors at 14 U.S. plants have either shut down or been scheduled for closure by their owners, according to the Nuclear Energy Institute, a lobbying group.

The decommissioning process varies from plant to plant, and it isn't foolproof.

Last month, at the shuttered San Onofre Nuclear Generating Station north of San Diego, crews loading used fuel rods into concrete casks for long-term storage found a loose bolt inside a new cask and stopped work for 10 days to investigate. When loading resumed, workers used casks with a different design while trying to determine whether the bolt represented a larger problem.

In 2017, crews decommissioning a nuclear plant in Wisconsin spilled 400 gallons of radioactive water into the Mississippi River. Given the vast volume of water in the river, federal regulators said the incident did not threaten public health.

When planning for a plant's end, the owners must start with a basic choice -- whether to do all the work as early as possible or to wait.

The first option is known as ``decon,'' short for decontamination. In it, the first steps of taking the plant apart begin as soon as the fuel is removed. Work continues in a steady stream until the buildings are gone. The 2016 report commissioned for PG&E estimated this process would take until 2039 to complete and cost just under $3.8 billion.

The second option -- called ``safstor,'' for safe storage -- takes much longer. After the fuel is removed, the plant is mothballed. Its owner keeps it that way for years, possibly decades, allowing time for the irradiated metal and concrete to become less radioactive and therefore easier to handle.

PG&E took this approach at its Humboldt Bay Power Plant near Eureka. The plant's sole reactor shut down for seismic upgrades in 1976. The utility decided six years later to scrap it for good, while keeping in operation two fossil-fuel generators at the plant. Dismantling the reactor and related structures didn't begin until 2009.

``If you defer, the level of radioactivity drops markedly once it's shut down,'' Dricks said. ``It remains radioactive, but less so over time.''

The 2016 report on Diablo gave one possible safstor timeline for the plant. It showed a flurry of work in the first 10 years after closure, then decades of dormancy, with activity picking back up in 2062. The total cost for this option: $3.9 billion.

While mothballed, the plant is not abandoned. It remains under armed guard and subject to periodic inspections by the commission. The owner must monitor its condition and conduct radiation surveys to make sure nothing goes awry.

Safstor has the advantage of lowering radiation levels in the plant's machinery, but Lochbaum argues against it. While the country now has four landfills for radioactive machinery, there's no guarantee they all will be open a half century from now, or that they won't raise their rates. And there's the question of how closely the plant's owner will monitor and guard the facility over time.

``During those 50 years, are you going to give the plant the same care and attention, the same level of safety?'' Lochbaum said. ``Are you going to keep the ISISes and the Timothy McVeighs away?''

Many plant operators choose a combination of the decon and safstor methods. A third decommissioning option, appropriately known as ``entomb,'' is almost never used. At least some of the equipment is left on site and encased in long-lasting materials, such as concrete and steel. The 2016 Diablo report dismissed it as not viable and didn't include a cost estimate for it.

No matter which option a plant operator chooses, the process is expensive. San Onofre's decommissioning is expected to cost $4.4 billion. PG&E's Humboldt Bay Power Plant had just one small reactor, and yet its decommissioning is expected to cost $1.1 billion when it wraps up next year.

For Diablo, much of the money that will be needed to take the plant apart is already in the bank.

PG&E customers have been paying into a decommissioning fund, bit by bit, since the plant opened in 1985. The fund now has $2.7 billion, according to the utility, and is continuing to grow. If PG&E decides the fund won't be big enough to cover the final cost, it must ask the California Public Utilities Commission to boost the amount customers pay into the fund. A typical PG&E residential customer currently pays about 11 cents per month for decommissioning both Diablo Canyon and Humboldt Bay.

PG&E expects to file an updated decommissioning cost estimate with the California Public Utilities Commission either late this year or in 2019. The company also is assembling a community advisory panel that will provide input both on decommissioning Diablo Canyon and what to do with the 12,820 acres of undeveloped coastal hills that PG&E owns around the plant. More than 100 people have applied to serve on the panel, according to PG&E.

Although the panel will have strictly an advisory role, its members and PG&E will have much to discuss.

Should all the components and rubble be hauled out via narrow Diablo Canyon Road, a prospect that could require upgrading the road? The seaside power plant has a small harbor, so should larger components exit by barge? Diablo also has a desalination plant capable of producing up to 1.5 million gallons of water per day, and local officials have in the past expressed interest in tapping into it. Should it stay after the rest of the plant is gone?

One element of decommissioning that will almost certainly cause friction is the fate of the nuclear waste.

Even after the rest of Diablo Canyon has been demolished, the used fuel may remain, stored in rows of 20-foot-tall concrete-and-steel canisters bolted to a 7-foot-thick slab of concrete on a hillside above the site. The federal government in 1982 promised to open a centralized repository for the long-term storage of radioactive waste. That still hasn't happened.

``The federal government made a commitment to take the fuel, and we expect them to keep it,'' said PG&E spokesman Blair Jones. ``In the interim, we'll continue safely storing the fuel.''