When nuclear operator Heather Hoff started hearing rumors that Pacific Gas and Electric Company (PG&E) would not be renewing their license at the Diablo Canyon Power Plant back in 2016, she knew she had to speak up and share what she had learned during her time working at the plant.
She has been speaking out ever since.
“This is my role in life,” Hoff said, who has since teamed up with coworker Kristin Zaitz to create Mothers for Nuclear, a nonprofit that functions as a way to share their stories and begin a dialogue with others who want to protect nature for future generations.
Hoff has worked at the plant for 17 years and describes her job at the power plant as what Homer Simpson does from “The Simpsons.”
The Diablo Canyon Power Plant, California’s last remaining nuclear plant, is currently set to close by 2025, and in the years following the 2016 decision, the debate went quiet.
Last month, Hoff’s platform gained a significant boost last month when a report published by Stanford, the Massachusetts Institute of Technology (MIT) and LucidCatalyst renewed public debate about whether to move forward with plans to shut down the plant.
“It’s great to see with the new information that people are talking about this issue,” Hoff said at the “Save Clean Energy” rally Mothers for Nuclear hosted on Dec. 4. “New people are coming out that have not before — people are here to learn, not just to support.”

Key findings from the study suggest delaying the retirement of Diablo Canyon to 2035 could reduce California power sector carbon emissions by more than 10% from 2017, as well as reduce reliance on gas, save $2.6 billion in power system costs and bolster system reliability to mitigate brownouts.
If operated until 2045 and beyond, the study said, Diablo Canyon could save up to $21 billion in power system costs and spare 90,000 acres of land from use for energy production, while meeting coastal protection requirements.
In addition, researchers explored the idea of converting the plant into a polygeneration facility, which would produce electricity, desalinated water and clean hydrogen for a lower financial cost.
“We wanted to really turn every stone and we were curious, so we started asking ourselves; what if, in addition to just providing electricity to the grid, you use part of the energy output of the system to do other interesting things,” co-author and MIT Nuclear science and engineering professor Jacopo Buongiorno said.
In September 2020, Buongiorno initiated the study with Stanford energy resources engineering professor Sally Benson because, according to him, aspects have changed since the California Public Utilities Commission (CPUC) made the decision to close down the plant.
“It’s those changes that have motivated us to take a fresh look at the value of this facility,” Buongiorno said.
According to Buongiorno: this is what has changed in the three and a half years since the decision was made:
California now has very aggressive targets for decarbonization for the power grid and economy in the form of CA Senate Bill (SB) 100, which mandates the state to be net-carbon zero by 2045.
Separate studies have come to the conclusion that, in addition to renewables such as solar and wind, there also needs to be a clean, firm energy source — Diablo Canyon being one such generator.
California experienced a lot of reliability changes on its grid in 2020, including rolling blackouts in some areas of the state and more are expected to be moving forward.
California is experiencing a severe drought and, the overall trend is that, the state is continuing to become drier over the years.
Lastly, the Nuclear Regulatory Commission (NRC), the federal agency that ensures and monitors that nuclear power plants are designed and operated safely, determined that the Diablo Canyon site and the Diablo Canyon design can withstand even the most extreme types of seismic hazards or earthquakes that could occur at that site.
“What motivated the study at Stanford and MIT is really the observation that so many things have changed since that decision was made,” Buongiorno said. “And they all now sort of go in the direction of say, well wait a minute, maybe this facility has a lot higher value than people thought.”
The Diablo Canyon Power Plant currently powers 8% of California’s electricity and 15% of the state’s carbon-free emission electricity, although Buongiorno said that nothing is truly zero-carbon.
“If you account for construction of the plant, transportation or the fuel decommissioning, then you should appreciate that there is no such thing as a zero carbon energy source,” Buongiorno said.
That being said, if life cycle carbon footprints are calculated for all forms of energy technologies, nuclear and wind are the two lowest in carbon emission, according to the professor.
To replace the 2.2 gigawatts of nuclear energy that Diablo Canyon is constantly producing on 140 acres of land, it would take 18 gigawatts of solar energy, which would occupy 90,000 acres of land in solar panels.
When the landmass required to replace Diablo Canyon is superimposed onto a map, it covers the whole of the San Francisco Peninsula.
Every time a nuclear power plant is shut down, data shows that carbon emissions go up, Buongiorno said. When a plant is decommissioned, the power output is typically replaced with natural gas or a mix of renewable energy and natural gas, which increases carbon emissions, he said.
“We wanted to make sure people understand that there is a very clear environmental value for these plants, because if it goes down, the emissions in California will go up — that’s a mathematical certainty,” Buongiorno said.
For Buongiorno, it is not a question of Diablo or renewables, but rather a combination of the two.
Buongiorno wants to make it clear that their study was purely academic, and does not seek to make any policy recommendations, although he personally supports the continued operation of the plant past the 2025 close date.
Following the publication of the report, SLO County Supervisor and Democrat Dawn Ortiz-Legg teamed up with Republican and former State Assemblyman Jordan Cunningham to bring attention to the study.
“Together we believe in carbon-free energy, we believe in jobs, we believe in science,” Ortiz-Legg said. “The report really talks about the importance of all these items, and the potential of the facility itself and that’s where we come together.”
In 2016 when the decision was made to close the plant, Ortiz-Legg said there was information that made it seem that the energy from the plant would not be needed — renewables were moving forward and energy efficiencies were coming.
“But that calculation, I believe, hasn’t borne out to be accurate,” Ortiz-Legg said.
The “100 Percent Clean Energy Act of 2018,” Senate Bill 100 outlines California’s energy goal of powering all retail electricity sold in California and state agency electricity needs with renewable and zero-carbon resources by 2045.
In order to reach that goal, Ortiz-Legg said, it is going to require a significant investment in stabilizing the grid and an enormous outlay of storage and renewable projects to go forth very quickly.
In addition, Ortiz-Legg said San Luis Obispo county has been an energy-exporting county for a number of years, which has brought benefits and created a good standard of living for a large portion of the population, feeding directly off of the Diablo Canyon power plant.
“I’m just really encouraging people to think long and hard about and to review and to educate themselves on energy generation, and delivery,” Ortiz-Legg said. “It’s more about promoting good science, and really addressing carbon.”
To create any “real movement” Ortiz-Legg said the state hold all of the keys.
“Meaning, permitting, coastal and lands commissions would have to weigh in or the Governor’s office would too,” Ortiz-Legg said. “It’s out of local hands at this point.”
According to Cal Poly physics professor Jennifer Klay, the most recent report published by the The Intergovernmental Panel on Climate Change (IPPC) said that warming the earth’s climate by 1.5 degrees, even if all carbon emissions were stopped immediately, is unavoidable.
“If we don’t want it to go any higher than that, we have to come off of fossil fuels as fast as possible,” Klay said.
The most viable option for doing that is keeping nuclear power plants open and investing in more nuclear power plants innovation, research and development, Klay said.
For Klay, nuclear waste is not something to be concerned about.
“The fact is that it’s solid, it’s compact and it’s manageable,” Klay said. “If you took all of the high level radioactive waste from commercial power generation in the United States from the last 70 years, it would all fit inside of a football stadium on the field, stacked 10 meters high, but it doesn’t even fill an entire football stadium.”
If fossil fuel practices remain or increase from the level they are at, Klay added, she does not know if there will be generations 100,000 years from now who will need to worry about it.
“As a scientist who studies nuclear reactions and trying to improve our understanding of nuclear reactions, I think that we won’t have to worry about it for hundreds of thousands of years, because we’ll find a different solution for it,” she said.
When it comes to concerns about nuclear energy, Klay said she understands and shares in the fears that come from past incidents such as Chernobyl, Fukushima and Three Mile Island.
“But when we look at the total loss of life and compare it to the annual loss of life from air pollution globally, nuclear is actually the safest form of energy generation per amount of energy generated of all sources of power,” Klay said.
Klay compared fears around nuclear energy to that of airplanes.
Airplanes can be scary and traumatic and can even lead to mass casualties in some cases, she said. However, the number of people who die annually in car crashes dwarfs that of airline accidents, and people still get in their cars and drive every day.
“Yet that fear is visceral when we feel it, and we have to talk ourselves down from it,” Klay said. “I think that the same thing is true of nuclear power — we have to talk ourselves down from that visceral fear that we experience from major accidents that are scary.”
Klay, who is a member of Mothers for Nuclear, said it is important to recognize that people have questions about nuclear power and whether it is safe, whether the waste is something to worry about and whether they should be worried about radiation and earthquakes.
“I think all of those questions have answers,” Klay said. “My own path, from almost indifference about nuclear energy to advocacy, came about because I asked the questions about the things people are concerned about, sought the answers and was satisfied by what I read.”
Klay said emotions surrounding nuclear energy are generational.
“The threat to our generation felt like nuclear World War III with the Soviet Union,” Klay said.
The existential threat for today’s generation, Klay said, is climate change.
“There’s actually more younger people who are supporting nuclear because they see it as the way to get us to our climate goals,” Klay said. “Fifty years ago, we didn’t know as much, so maybe it didn’t come out ahead. Now, I think the tides have turned and we know enough about what we’ve done to our climate, and if we don’t stop emitting carbon, we’re putting our future generations at risk.”
In one of her environmental engineering classes, senior Sierra Withers learned about nuclear power and Diablo Canyon, and how much of a gray issue it can be.
“I’ve often been only exposed to the black and white arguments that people make,” Withers said. “I had been exposed to a lot of what I would kind of call fear mongering about nuclear power.”
When it comes to learning about nuclear power, Withers said it would be easy to say that it is a personal responsibility, although she does not think that is a feasible answer.
“I don’t think you’re ever going to be able to get a completely unbiased source, I don’t think that’s possible,” Withers said. “Especially in an industry that requires this amount of money and has this amount of fear response.”
According to Withers, fear is a powerful motivator to not listen to fact.
Withers feels that she does not have the qualifications to make the decision to keep the Diablo Power plant open or not, but she does have the qualifications to learn and listen to real scientists.
“It doesn’t really get better in the environmental engineering community than MIT and Stanford,” Withers said.
If Withers would want Cal Poly students to know one thing, it would be that nuclear power is not all good and not all evil, there is truth that lies between those two things.
“If there is a middle ground between good and evil, the scientists are going to find where that’s at,” Withers said.
As of Nov. 17, no proposal has been made to directly revisit the 2018 decision to allow the plant to close down, according to the California Public Utilities Commission (CPUC).
Sofia Silvia and Tessa Hughes contributed to this story.