Science
Earthquake risks and rising costs: The price of operating California's last nuclear plant

Under two gargantuan domes of thick concrete and steel that rise along California’s rugged Central Coast, subatomic particles slam into uranium, triggering one of the most energetic reactions on Earth.
Amid coastal bluffs speckled with brush and buckwheat, Diablo Canyon Nuclear Power Plant uses this energy to spin two massive copper coils at a blistering 30 revolutions per second. In 2022, these generators — about the size of school buses — produced 6% of Californians’ power and 11% of their non-fossil energy.
Yet it comes at almost double the cost of other low-carbon energy sources and, according to the federal agency that oversees the plant, carries a roughly 1 in 25,000 chance of suffering a Chernobyl-style nuclear meltdown before its scheduled decommissioning in just five years — due primarily to nearby fault lines.
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As Gov. Gavin Newsom’s administration looks to the aging reactor to help ease the state’s transition to renewable energy, Diablo Canyon is drawing renewed criticism from those who say the facility is too expensive and too dangerous to continue operating.
Diablo is just the latest in a series of plants built in the atomic frenzy of the 1970s and ’80s seeking an operating license renewal from the federal Nuclear Regulatory Commission as the clock on their initial 40-year run ticks down. As the price of wind and solar continues to drop, the criticisms against Diablo reflect a nationwide debate.

Tom Jones, right, a regulatory and environmental senior director at PG&E, and Jerel Strickland, a senior licensing and spent nuclear storage consultant, walk past one of two massive turbine-generator units inside the turbine building at Diablo Canyon Nuclear Power Plant recently.
(Genaro Molina/Los Angeles Times)
The core of the debate lives in the quaint coastal town of San Luis Obispo, just 12 miles inland from the concrete domes, where residents expected Diablo Canyon to shut down over the next year after its license expired.
Instead, Newsom struck a deal on the last possible day of the state’s 2021-22 legislative session to keep the plant running until 2030, citing worries over summer blackouts as the state transitions to clean energy. The activists who had negotiated the shutdown with PG&E and the state six years prior were left stunned.
Today, the plant is still buzzing with life: Nuclear fission, in the deep heart of the plant, continues to superheat water to 600 degrees at 150 times atmospheric pressure. Generators continue to whir with a haunting and deafening hum that reverberates throughout the massive turbine deck.
Left untouched, nuclear fission erupts into a runaway chain reaction that can heat the core of a nuclear plant to thousands of degrees, liquifying the metal around it into radioactive lava.
So, operators have to constantly stifle the reaction to keep it under control.
In the event of an earthquake, they need to stop the reaction as quickly as possible. But if the shaking is so rapid and intense that the plant is critically damaged before it can shut down, operators could become helpless in preventing a meltdown.

Tom Jones, senior director of Regulatory Environmental and Repurposing at PG&E, talks about how the Diablo Canyon Nuclear Power Plant operates.
(Genaro Molina/Los Angeles Times)

Tom Jones, senior director of Regulatory Environmental and Repurposing at PG&E, is reflected in a display that explains the fission process at Diablo Canyon Nuclear Power Plant recently.
(Genaro Molina/Los Angeles Times)
Diablo Canyon is built to endure specific intensities and speeds of shaking — but predicting how likely an earthquake is to exceed those specifications is no easy task. Earthquakes are the result of deeply complex underground motion and forces, and they’re notoriously chaotic.
In order to start estimating the seismic safety of the plant, geophysicists have to understand: first, where the faults are; second, how much they’re slipping to trigger earthquakes; and finally, when those quakes hit, how much shaking they cause.
Earthquakes account for about 65% of the risk for a worst-case scenario meltdown. Potential internal fires at the plant make up another 18%. The last 17% is made up of everything from aircraft impacts and meteorites to sink holes and snow.
In assessing the likelihood of all these threats, the Nuclear Regulatory Commission estimates that in any given year, each of Diablo Canyon’s two reactor units has a roughly 1 in 12,000 chance of experiencing a nuclear meltdown similar to Japan’s Fukushima disaster.
Likewise, there’s about a 1 in 127,000 chance a failure will cause the plant to release exorbitant amounts radioactive material into the atmosphere before residents could evacuate, creating a Chernobyl-style disaster.
This means that, every year, nearby residents have roughly the same chance of seeing a nuclear meltdown as dying in a car crash. Also, in any given year, they’re about 50 times more likely to face a mass-casualty radioactive catastrophe than get struck by lightning.
Diablo Canyon employees work around the clock to ensure the risk is as small as possible. “Our safety culture, it’s always on the top of my mind,” said Maureen Zawalick, the vice president of business and technical services at Diablo. “It’s in my DNA.”

Maureen Zawalick, PG&E Business and Technical Services vice president, in her office at the Diablo Canyon Power Plant.
(Genaro Molina/Los Angeles Times)
The plant is the only one in the U.S. with a dedicated geoscience team that studies the region’s seismic landscape. And like other nuclear facilities, Diablo has done countless tests on its equipment, hosted walkthroughs with regulators to identify possible points of failure and generated thousands of pages of analysis on the facility’s ability to withstand the largest earthquake possible at the site.
Earthquake precautions include massive metal dampers that are fixed to essential infrastructure, such as the duct carrying the control rooms’ air supply. In the event of a tremor, monstrous concrete pillars penetrate deep into the bedrock to keep the building and essential infrastructure grounded. The hefty concrete walls reinforced with steel rebar as thick as a human arm safely distribute the forces throughout the structure to prevent critical cracks or collapses.
If the plant loses power, there are backup generators for the backup generators.

A worker pushes a utility cart past a billboard that lists employee goals at Diablo Canyon Nuclear Power Plant recently.
(Genaro Molina/Los Angeles Times)
Operators spend a fifth of their time on the job training for every possible nightmare. Diablo has a simulator on site that’s an exact replica of the Unit One control room. It’s capable of putting operators through the worst conditions imaginable. It shakes with the vigor of a real earthquake. The lights flicker and the analog dials spin back up as emergency power comes online.
For everyone working on site — including the senior leadership team — safety is personal. Should something go wrong, their lives are on the line.
“With any source of energy, there is risk,” said Zawalick. “All the independent assessments, all the audits, all the third party reviews, all of that …. is what gives me the confidence and the security and the safety of why I’ve been out here almost 30 years.” Her office is no more than 500 feet from the reactors.
“If there ever was an earthquake of any magnitude in this community,” she said, “I would grab my two daughters and we’d come here.”

Maureen Zawalick, PG&E Business and Technical Services vice president, looks out her office window at Diablo Canyon Nuclear Power Plant recently.
(Genaro Molina/Los Angeles Times)
Many critics charge that the risks are understated — due in part to a cozy relationship between industry and regulators. (Some scientists involved with one of Diablo Canyon’s two independent review organizations have collaborated on scientific papers with PG&E staff and funding.)
The Nuclear Regulatory Commission also oversees the plant and conducts its own investigations. In July, the government agency dismissed all three formal criticisms against Diablo’s seismic safety in the plant’s license renewal process.
Sam Blakeslee, a San Luis Opispo geophysicist and former state senator and Assembly member, has a list of technical concerns — primarily the lack of shaking data close to fault lines, which are used to inform the models that predict earthquake motion at the plant — but he likens the core of his concern to the NASA Challenger disaster.
NASA publicly touted a strong safety culture and low chances of things going wrong. Yet, the investigation found political and public pressures had corrupted the safety from the top down.
He argues this is a possibility for any large organization dealing with complex and potentially dangerous systems. Therefore, people need to constantly hold the plant accountable.
“That’s why I tend to try to make sure that the community voice is present,” he said, “ because we are the ones that will pay the price.”
In 2022, Newsom introduced a proposal to keep Diablo Canyon open past its two reactors’ 2024 and 2025 shutdown dates. His proposal, distributed to lawmakers just three weeks before the end of the legislative session, set off a flurry of negotiations among PG&E, the governor and the Legislature.
After discussion drew on past midnight, the Legislature passed the bill.
But it comes at a cost.
While the average price of solar and wind have dropped dramatically over the past 15 years, nuclear’s has been steadily rising. In 2009, solar cost three times what nuclear did, and wind was about even with it. Now, nuclear is over two times the cost of both renewables.
Technical advancements have slashed the price of renewable energy, but nuclear power has faced more outages, equipment replacements and increasingly stringent and expensive safety requirements in the wake of the Fukushima disaster.
One study from MIT researchers found that about a third of the increasing cost could be attributed to safety requirements from the Nuclear Regulatory Commission. They attribute another third to research and development projects for efficiency, reliability and safety improvements, and they assign the final third to a decrease in worker productivity — perhaps in part due to lower morale.

Twin containment domes rise above the facility as seen through a windshield on the drive to the Diablo Canyon Nuclear Power Plant.
(Genaro Molina/Los Angeles Times)
PG&E is estimating that Diablo Canyon will produce energy at $91 per megawatt-hour during its extension. (The average U.S. household buys about 10 megawatt-hours every year.)
However, the Alliance for Nuclear Responsibility argues the plant’s cost is even higher. David Weisman, the legislative director at the alliance, said PG&E is using optimistic predictions of its energy output for the extended period — 5% higher than previous years.
On top of that, the state gave PG&E a $1.4-billion loan to alleviate the initial costs of extended operations. But Wiesman said the funds don’t necessarily need to go toward offsetting the cost of running Diablo. The federal government agreed to reimburse the state up to $1.1 billion — depending on whether the plant meets specific operating criteria — and PG&E is expected to pay off the rest of the loan with profits.
While the loan isn’t a cost that consumers would see on their energy bills, taxpayers across the country could foot the bill. Weisman argued that it brings Diablo’s cost to a maximum of $115 per megawatt-hour — roughly double the cost of solar.
Yet Newsom argues that if California is to meet its goals of 60% renewable energy by 2030, Diablo needs to stay online in the meantime to ensure the state has reliable power amid heatwaves and wildfires.
Diablo Canyon essentially runs 24/7, providing constant power to the state (assuming it doesn’t have any issues, which it sometimes does). For solar to provide similarly constant power, the electric grid will require a massive expansion of its battery infrastructure to store the energy between the midday peak of energy production and the evening peak of energy use.
However, new studies are finding that energy storage is a feasible approach to grid reliability — and that even when adding the price of that infrastructure, solar still costs less than nuclear.

Tom Jones, a regulatory and environmental senior director at PG&E, talks about the number of days that Turbine Unit One has operated to bring power to California while inside the turbine building at Diablo Canyon Power Plant recently.
(Genaro Molina/Los Angeles Times)
Since Diablo’s extension was signed into law, California has almost doubled its battery storage. The state now has enough to supplement about a quarter of the state’s power needs for about half an hour during peak energy usage (although, in practice, it would likely supplement much less for much longer).
“That’s four or five Diablo Canyons,” said Weisman. Newsom should “save the people of California [billions of dollars] thrown down PG&E’s rat hole, declare triumphant victory in the renewable race and accept the laurels.”
Instead, at a recent press event announcing California had reached a fifth of its storage capacity goal, Newsom laughed off the idea that Californians will no longer have to worry about blackouts.
“We have a lot of work to do still in moving this transition, with the kind of stability that’s required,” he said. “So no, this is not today announcing that blackouts are part of our past.”
Diablo Canyon’s leaders and advocates view the plant as supporting California through this challenging transition period: It’s not perfect, but it provides the state with much-needed reliable, clean power, they say.
In a conference call shortly after Diablo’s initial 2024 shutdown date was negotiated, then-chief executive of PG&E Tony Earley acknowledged the plant would eventually become too expensive to operate.
“As we make this transition, Diablo Canyon’s full output will no longer be required,” he said.

Steam rises from the Pacific Ocean where an outfall of heated water from the Diablo Canyon Nuclear Power Plant pours into coastal waters.
(Genaro Molina/Los Angeles Times)
Zawalick said the Diablo team is ready to continue operating as long as the state needs it to. “Thinking about electrification, [electric vehicle] demand, continued drought, the temperatures we’re seeing, wildfires … tariffs — I mean, the list goes on,” she said. “That’s making the equation a bit challenging to see exactly when Diablo will shut down versus how long Diablo will be needed by the state.”

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Science
Lawmakers ask Newsom and waste agency to follow the law on plastic legislation

California lawmakers are taking aim at proposed rules to implement a state law aimed at curbing plastic waste, saying the draft regulations proposed by CalRecycle undermine the letter and intent of the legislation.
In a letter to Gov. Gavin Newsom and two of his top administrators, the lawmakers said CalRecycle exceeded its authority by drafting regulations that don’t abide by the terms set out by the law, Senate Bill 54.
“While we support many changes in the current draft regulations, we have identified several provisions that are inconsistent with the governing statute … and where CalRecycle has exceeded its authority under the law,” the lawmakers wrote in the letter to Newsom, California Environmental Protection agency chief Yana Garcia, and Zoe Heller, director of the state’s Department of Resources Recycling and Recovery, or CalRecycle.
The letter, which was written by Sen. Catherine Blakespear (D-Encinitas) and Sen. Benjamin Allen (D-Santa Monica), was signed by 21 other lawmakers, including Sen. John Laird (D-Santa Cruz) and Assemblymembers Al Muratsuchi (D-Rolling Hills Estates) and Monique Limón (D-Goleta).
CalRecycle submitted informal draft regulations two weeks ago that are designed to implement the law, which was authored by Allen, and signed into law by Newsom in 2022.
The lawmakers’ concerns are directed at the draft regulations’ potential approval of polluting recycling technologies — which the language of the law expressly prohibits — as well as the document’s expansive exemption for products and packaging that fall under the purview of the U.S. Department of Agriculture and the Food and Drug Administration.
The inclusion of such blanket exemptions is “not only contrary to the statute but also risks significantly increasing the program’s costs,” the lawmakers wrote. They said the new regulations allow “producers to unilaterally determine which products are subject to the law, without a requirement or process to back up such a claim.”
Daniel Villaseñor, a spokesman for the governor, said in an email that Newsom “was clear when he asked CalRecycle to restart these regulations that they should work to minimize costs for small businesses and families, and these rules are a step in the right direction …”
At a workshop held at the agency’s headquarters in Sacramento this week, CalRecycle staff responded to similar criticisms, and underscored that these are informal draft regulations, which means they can be changed.
“I know from comments we’ve already been receiving that some of the provisions, as we have written them … don’t quite come across in the way that we intended,” said Karen Kayfetz, chief of CalRecycle’s Product Stewardship branch, adding that she was hopeful “a robust conversation” could help highlight areas where interpretations of the regulations’ language differs from the agency’s intent.
“It was not our intent, of course, to ever go outside of the statute, and so to the extent that it may be interpreted in the language that we’ve provided, that there are provisions that extend beyond … it’s our wish to narrow that back down,” she said.
These new draft regulations are the expedited result of the agency’s attempt to satisfy Newsom’s concerns about the law, which he said could increase costs to California households if not properly implemented.
Newsom rejected the agency’s first attempt at drafting regulations — the result of nearly three years of negotiations by scores of stakeholders, including plastic producers, package developers, agricultural interests, environmental groups, municipalities, recycling companies and waste haulers — and ordered the waste agency to start the process over.
Critics say the new draft regulations cater to industry and could result in even higher costs to both California households, which have seen large increases in their residential waste hauling fees, as well as to the state’s various jurisdictions, which are taxed with cleaning up plastic waste and debris clogging the state’s rivers, highways, beaches and parks.
The law is molded on a series of legislative efforts described as Extended Producer Responsibility laws, which are designed to shift the cost of waste removal and disposal from the state’s jurisdictions and taxpayers to the industries that produce the waste — theoretically incentivizing a circular economy, in which product and packaging producers develop materials that can be reused, recycled or composted.
Science
U.S. just radically changed its COVID vaccine recommendations: How will it affect you?
As promised, federal health officials have dropped longstanding recommendations that healthy children and healthy pregnant women should get the COVID-19 vaccines.
“The COVID-19 vaccine schedule is very clear. The vaccine is not recommended for pregnant women. The vaccine is not recommended for healthy children,” the U.S. Department of Health and Human Services said in a post on X on Friday.
In formal documents, health officials offer “no guidance” on whether pregnant women should get the vaccine, and ask that parents talk with a healthcare provider before getting the vaccine for their children.
The decision was done in a way that is still expected to require insurers to pay for COVID-19 vaccines for children should their parents still want the shots for them.
The new vaccine guidelines were posted to the website of the U.S. Centers for Disease Control and Prevention late Thursday.
The insurance question
It wasn’t immediately clear whether insurers will still be required under federal law to pay for vaccinations for pregnant women.
The Trump administration’s decision came amid criticism from officials at the nation’s leading organizations for pediatricians and obstetricians. Some doctors said there is no new evidence to support removing the recommendation that healthy pregnant women and healthy children should get the COVID vaccine.
“This situation continues to make things unclear and creates confusion for patients, providers and payers,” the American College of Obstetricians and Gynecologists said in a statement Friday.
Earlier in the week, the group’s president, Dr. Steven Fleischman, said the science hasn’t changed, and that the COVID-19 vaccine is safe during pregnancy, and protects both the mom-to-be and their infants after birth.
“It is very clear that COVID-19 infection during pregnancy can be catastrophic,” Fleischman said in a statement.
Dr. Susan Kressly, president of the American Academy of Pediatrics, criticized the recommendation change as being rolled out in a “conflicting, confusing” manner, with “no explanation of the evidence used to reach their conclusions.”
“For many families, the COVID vaccine will remain an important way they protect their child and family from this disease and its complications, including long COVID,” Kressly said in a statement.
Some experts said the Trump administration should have waited to hear recommendations from a committee of doctors and scientists that typically advises the U.S. Centers for Disease Control and Prevention on immunization recommendations, which is set to meet in late June.
California’s view
The California Department of Public Health on Thursday said it supported the longstanding recommendation that “COVID-19 vaccines be available for all persons aged 6 months and older who wish to be vaccinated.”
The changes come as the CDC has faced an exodus of senior leaders and has lacked an acting director. Typically, as was the case during the first Trump administration and in the Biden administration, it is the CDC director who makes final decisions on vaccine recommendations. The CDC director has traditionally accepted the consensus viewpoint of the CDC’s panel of doctors and scientists serving on the Advisory Committee on Immunization Practices.
Even with the longstanding recommendations, vaccination rates were relatively low for children and pregnant women. As of late April, 13% of children, and 14.4% of pregnant women, had received the latest updated COVID-19 vaccine, according to the CDC. About 23% of adults overall received the updated vaccine, as did 27.8% of seniors age 65 and over.
The CDC estimates that since October, there have been 31,000 to 50,000 COVID deaths and between 270,000 and 430,000 COVID hospitalizations.
Here are some key points about the CDC’s decision:
New vaccination guidance for healthy children
Previously, the CDC’s guidance was simple: everyone ages 6 months and up should get an updated COVID vaccination. The most recent version was unveiled in September, and is officially known as the 2024-25 COVID-19 vaccine.
As of Thursday, the CDC, on its pediatric immunization schedule page, says that for healthy children — those age 6 months to 17 years — decisions about COVID vaccination should come from “shared clinical decision-making,” which is “informed by a decision process between the healthcare provider and the patient or parent/guardian.”
“Where the parent presents with a desire for their child to be vaccinated, children 6 months and older may receive COVID-19 vaccination, informed by the clinical judgment of a healthcare provider and personal preference and circumstances,” the CDC says.
The vaccine-skeptic secretary of Health and Human Services, Robert F. Kennedy Jr., contended in a video posted on Tuesday there was a “lack of any clinical data to support the repeat booster strategy in children.”
However, an earlier presentation by CDC staff said that, in general, getting an updated vaccine provides both children and adults additional protection from COVID-related emergency room and urgent care visits.
Dr. Peter Chin-Hong, a UC San Francisco infectious diseases expert, said he would have preferred the CDC retain its broader recommendation that everyone age 6 months and up get the updated vaccine.
“It’s simpler,” Chin-Hong said. He added there’s no new data out there that to him suggests children shouldn’t be getting the updated COVID vaccine.
A guideline that involves “shared decision-making,” Chin-Hong said, “is a very nebulous recommendation, and it doesn’t result in a lot of people getting vaccines.”
Kressly, of the American Academy of Pediatrics, said the shared clinical decision-making model is challenging to implement “because it lacks clear guidance for the conversations between a doctor and a family. Doctors and families need straightforward, evidence-based guidance, not vague, impractical frameworks.”
Some experts had been worried that the CDC would make a decision that would’ve ended the federal requirement that insurers cover the cost of COVID-19 vaccines for children. The out-of-pocket cost for a COVID-19 vaccine can reach around $200.
New vaccine guidance for pregnant women
In its adult immunization schedule for people who have medical conditions, the CDC now says it has “no guidance” on whether pregnant women should get the COVID-19 vaccine.
In his 58-second video on Tuesday, Kennedy did not explain why he thought pregnant women should not be recommended to get vaccinated against COVID-19.
Chin-Hong, of UCSF, called the decision to drop the vaccination recommendation for pregnant women “100%” wrong.
Pregnancy brings with it a relatively compromised immune system. Pregnant women have “a high chance of getting infections, and they get more serious disease — including COVID,” Chin-Hong said.
A pregnant woman getting vaccinated also protects the newborn. “You really need the antibodies in the pregnant person to go across the placenta to protect the newborn,” Chin-Hong said.
It’s especially important, Chin-Hong and others say, because infants under 6 months of age can’t be vaccinated against COVID-19, and they have as high a risk of severe complications as do seniors age 65 and over.
Not the worst-case scenario for vaccine proponents
Earlier in the week, some experts worried the new rules would allow insurers to stop covering the cost of the COVID vaccine for healthy children.
Their worries were sparked by the video message on Tuesday, in which Kennedy said that “the COVID vaccine for healthy children and healthy pregnant women has been removed from the CDC recommended immunization schedule.”
By late Thursday, the CDC came out with its formal decision — the agency dropped the recommendation for healthy children, but still left the shot on the pediatric immunization schedule.
Leaving the COVID-19 vaccine on the immunization schedule “means the vaccine will be covered by insurance” for healthy children, the American Academy of Pediatrics said in a statement.
How pharmacies and insurers are responding
There are some questions that don’t have immediate answers. Will some vaccine providers start requiring doctor’s notes in order for healthy children and healthy pregnant women to get vaccinated? Will it be harder for children and pregnant women to get vaccinated at a pharmacy?
In a statement, CVS Pharmacy said it “follows federal guidance and state law regarding vaccine administration and are monitoring any changes that the government may make regarding vaccine eligibility.” The insurer Aetna, which is owned by CVS, is also monitoring any changes federal officials make to COVID-19 vaccine eligibility “and will evaluate whether coverage adjustments are needed.”
Blue Shield of California said it will not change its practices on covering COVID-19 vaccines.
“Despite the recent federal policy change on COVID-19 vaccinations for healthy children and pregnant women, Blue Shield of California will continue to cover COVID-19 vaccines for all eligible members,” the insurer said in a statement. “The decision on whether to receive a COVID-19 vaccine is between our member and their provider. Blue Shield does not require prior authorization for COVID-19 vaccines.”
Under California law, health plans regulated by the state Department of Managed Health Care must cover COVID-19 vaccines without requiring prior authorization, the agency said Friday. “If consumers access these services from a provider in their health plan’s network, they will not need to pay anything for these services,” the statement said.
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