The Diablo We Know

The Case for Keeping California’s Last Nuclear Plant


California’s last remaining nuclear power plant – and the lynchpin of the state’s clean energy production –– Diablo Canyon faces a number of threats from both antinuclear environmentalists and state regulators, whose bill of particulars against the plant gives a distorted picture of its impacts on the natural world and on human well-being. But by fixating on largely groundless scenarios of risk, antinuclear advocates ignore the far worse problems that nuclear power solves with its enormous production of low-carbon electricity. The plant’s premature closure could add hundreds of million of tons of greenhouse emissions to the atmosphere and set back the task of making the state’s energy supply cleaner and healthier by many years. The struggle over Diablo Canyon raises questions about whether the environmental movement and the regulatory state it has created are up to the task. –– Photo by Marya Figueroa

August 4, 2015 | Will Boisvert,

Diablo Canyon is California’s last nuclear power plant. It has been the state’s most famous and most controversial plant ever since it divided Sierra Club members in the late 1960s. Perched amidst spectacular natural beauty on the California coast, Diablo faces threats on many fronts. State regulators are demanding that it build expensive cooling towers to ease its impact on marine life. Harsh claims are being made about its vulnerability to earthquakes. And there are lawsuits filed by environmental groups aimed at shutting it down.

The 30-year-old Diablo Canyon reactors, despite the “aging nuclear plant” tag from opponents, are in their prime: the Nuclear Regulatory Commission (NRC) is preparing to vet reactors for license renewals in 20-year increments, which may allow Diablo to run for another 50 years and spare the climate 350 million more tons of carbon dioxide.1

Shuttering Diablo Canyon would have the same impact on carbon emissions as tearing down every wind turbine and rooftop PV panel in California.4 If Diablo Canyon is closed it will be replaced mainly by fossil fuels because replacing the nuclear power plant with an equivalent capacity of wind and solar would cost upwards of $15 billion compared to about $2.5 billion for a comparable natural gas plant.

The high cost of solar and wind is why, after Friends of the Earth and other antinuclear environmentalists forced the closure of California’s San Onofre nuclear power plant in 2013, Southern California’s power became dirtier, with most of the replacement power coming from natural gas.

Diablo is the workhorse of California’s low-carbon power sector. Its output last year exceeded the electricity produced by the state’s wind turbines by 31 percent and California’s solar electricity by 24 percent.2 Coming on top of San Onofre’s closure, the loss of the state’s nuclear fleet would wipe out low-carbon generation equal to the output of California’s entire wind, solar, and biomass sectors combined, thus nullifying decades of climate efforts.3

Diablo Canyon data from NRC. Wind and solar data based on average land requirements for existing wind and solar power facilities from a Breakthrough Institute analysis. 

Graphic Credit: Jessica Lovering

Moreover, the environmental impacts of replacing Diablo Canyon with solar would be massive. California would have to pave a whopping 90 square miles of land to equal Diablo’s output. Environmentalists point to a modest fish kill as an environmental crime, but a comparable bird kill is a necessary sacrifice for the cause of clean wind power and a much larger fisheries harvest is an economic boon; meanwhile the state builds low-carbon renewable power with its right hand while threatening low-carbon nuclear power with its left.

The public health science on nuclear is clear: generating nuclear power is one of the safest activities in the human repertoire, accidents and all. As such, the effort by antinuclear groups to close Diablo Canyon has been forced to prey on public ignorance, fear, and irrationality.

In their crusade to shutter nuclear plants like Diablo Canyon, antinuclear environmentalists betray almost every value they claim to uphold. They are sacrificing their concern for the land, the climate, and a healthy human environment upon the altar of unreasoning dogma.

Fear of the Devil

Antinuclear activists have used Fukushima to mislead the public into thinking there is new evidence of earthquake risk. But the plant was already upgraded to withstand very strong quakes. Moreover, Fukushima survived an earthquake far larger than the one it was rated for. Where Fukushima’s problems arose from a tsunami, at Diablo Canyon the tsunami threat is virtually nil. The reactors sit 85 feet above sea level, almost twice the height of the Fukushima wave.

Radiation is such a weak carcinogen that even in the Fukushima exclusion zone the cancer risks are substantially lower than the risks of driving a car. The vast majority of the evacuation zone can be reinhabited. The radioactive release from the second worst nuclear disaster ever will produce no measurable public health consequences at all. Today, the children of Fukushima actually have lower rates of thyroid cancer than the rest of the Japanese population.

Fears of “the big one” reignited last year when a report by an NRC official called into question Diablo Canyon’s seismic vulnerability. The “Differing Professional Opinion” by Michael Peck, a former NRC resident inspector at the plant, concerned a new fault discovered a few hundred yards offshore in 2008 and the damage an earthquake might cause.

PG&E’s studies estimated the maximum shaking from a quake on the Shoreline fault at 0.62 g (seismologists measure ground motion as a fraction of the acceleration from the force of gravity – g) and put potential shaking at other nearby faults at up to 0.75 g. But the plant’s original operating license, Peck contended, was based on a hypothetical quake, called the “Double Design Earthquake” (DDE), that would produce ground motion of only 0.4 g. His conclusions were ominous: Diablo Canyon could face much harder earthquake shaking than its operating license allowed for, and should be shut down until PG&E could prove it was safe against stronger seismic shocks.

Antinuclear groups pounced on these revelations. Friends of the Earth spokesman Damon Moglen declared that Diablo Canyon was “surrounded by dangerous earthquake faults that were unknown at the time of construction, and these faults are capable of far stronger shaking than the plant was designed and built to withstand.” FOE filed a motion with the NRC to shut the plant down pending a license amendment proceeding, a drawn-out process with public hearings. When NRC refused, the group appealed to a federal court, alleging a “cover-up of Diablo Canyon quake risks.”

Plant opponents paint this episode as a criminal instance of lax regulation, but on closer examination the case falls apart. An NRC panel rejected Peck’s Differing Professional Opinion — and declared, “The safety of the [plant] is not in question” — for a simple reason: Diablo Canyon was indeed designed, and certified by the NRC, to withstand much harder shaking than the DDE’s 0.4 g.

The Shoreline fault was not the first seismic surprise at the plant. In 1973, the Hosgri fault, three miles offshore, was discovered and assessed for maximum shaking of 0.75 g. The plant, then under construction, was retrofitted with expensive upgrades — buttresses to outside walls, steel bracings for floors, and equipment — as a condition of its licensing by the NRC.

After it opened in the 1980s, PG&E instituted a Long Term Seismic Program to further vet vulnerabilities. That project concluded that the plant might encounter earthquake shocks up to 0.83 g but would withstand them with a 35 percent margin of safety, a result the NRC analyzed and accepted in 1991. The plant had thus been operating for decades under the NRC-approved understanding that it could stand up to the shaking scenario Peck flagged.

Rather than uncovering new facts about seismic risks, Peck simply reinterpreted the regulatory strictures governing old facts in a way that other NRC staffers found unwarranted. The case thus turns not on safety hazards but on lawyerly technicalities about exactly what a “license amendment” is.

There are still scientific and engineering issues at play. Peck argued that the Hosgri evaluation was less conservative than the original DDE evaluation — it assumed better damping of tremors by plant buildings — but the NRC panel defended “the use of more modern insights (eg, damping values) because the use of these more conservative DDE values was no longer technically justified.”

PG&E has since done new seismic evaluations, based on what it says are better data and methodologies, that lower previous estimates of shaking from the web of faults surrounding the plant, but these are contested. An expert Independent Peer Review Panel for the California Public Utilities Commission questioned some of PG&E’s assumptions concerning the possible size of quakes, the speed of seismic waves through rock, and the relevant “ground motion prediction equations.” Different assumptions, they contend, yield shaking estimates stronger than the LTSP’s maximum of 0.83 g (though still within the 35 percent safety margin PG&E claims). 

Seismologists can disagree on whether Diablo Canyon pushes the envelope of seismic risk or stays comfortably inside it. The final say belongs to the NRC, which is now doing a comprehensive post-Fukushima seismic review of all reactors and may require safety upgrades and licensing changes. But the NRC’s verdict won’t allay all doubts. Seismology is an inexact science, and while an earthquake big enough to challenge Diablo Canyon is a once-in-ten-thousand-years long shot, the possibility can’t be entirely ruled out. The key question, then, becomes how we should parse that risk — the trade-off between the infinitesimal odds and the seemingly vast harm of a nuclear accident.

The answer is to put the risk in perspective. Californians are used to doing that, especially when it comes to earthquakes. The whole state is dedicated to the proposition that mankind should live under constant threat of seismic catastrophe — and indeed court it by inhabiting flimsy bungalows, soaring apartment towers, and precarious hillside villas rather than low-rise reinforced-concrete bunkers (like nuclear plants). Californians do that because the benefits of living in harm’s way outweigh the unlikely costs.

Unfortunately, a broad perspective is exactly what eludes the debate over nuclear power. That owes much to the aura of dread surrounding its association with nuclear weapons. But it’s also a product of the Manichaeism of the environmental movement, which has organized itself around passionate campaigns to save cherished species and landscapes and to demonize ill-favored polluters and technologies.

Birds and Fish, Land and Sea

The destruction of aquatic life by “once-through” cooling systems (OTC) is an important issue facing nuclear reactors and other power plants. Diablo Canyon is a large baseload plant that sucks up 2.5 billion gallons per day of ocean water, shunts it through heat exchangers, and then spits it back out, 20 degrees warmer, into the Pacific Ocean, with usually fatal consequences for anything dragged along.

In line with EPA guidelines, California ruled in 2010 that coastal plants with OTC must drastically reduce their water intake, which in practice means either closing or switching to massively expensive cooling towers that draw much less water.

State cooling-tower mandates are a focus of campaigns against older nuclear plants elsewhere, including New York State’s effort to shutter the Indian Point plant. California’s rules allow leeway to nuclear power plants if the costs of compliance seem exorbitant, and the Water Resources Control Board empanelled a Nuclear Review Committee to study the matter.

As usual in the world of nuclear regulation, the process became highly politicized. The 10-member committee included a representative for PG&E and one for Southern California Edison, owner of the now-closed San Onofre nuclear plant.

The committee also includes a rep from the antinuclear group Alliance for Nuclear Responsibility (A4NR), and another from the Center for Energy Efficiency and Renewable Technologies, a non-profit partly funded by renewable energy companies that could be commercial competitors of Diablo Canyon. Its board also includes people from Iberdrola Renewables, the California Energy Efficiency Industry Council, SunPower Corp. and NRG Solar.

The committee’s deliberations polarized around the cost of cooling towers. An independent report commissioned from Bechtel estimated a price tag anywhere from $6 billion to $14 billion and an excavation that might rival the Panama Canal dig.

The environmental group Friends of the Earth (FOE) and its consultants, in well-prepared public comments that influenced the committee, floated an alternative cooling tower proposal that they said would only cost $1.62 billion.

When FOE and Bechtel weren’t fencing over siting and construction details, antinuclear grandstanding sometimes took over: at one hearing A4NR attorney John Geesman asked, “Is PG&E the type of institution that an advanced civilization entrusts its single most lethal non-military activity to?”

A decision is pending while the SWRCB sifts through the minutiae and posturing in the Review Committee’s proceedings. But there are larger questions about the plant’s environmental impact that the Board’s focus on marine ecology may not register.

On one side is the plant’s substantial, but not overwhelming, effect on nearby marine life. Diablo Canyon’s impact on adult fish is trivial: about 5,000 a year, weighing all of 710 pounds, are “impinged” against the screens on the water intake pipes — barely enough for a busy weekend at a seafood restaurant. “Entrainment” is another matter; about 1.5 billion fish eggs and larvae pass through the screens into the plant’s maw each year.

That sounds like a piscine holocaust, but almost all those small fry would have died soon anyway; it is the fate of little fish to be eaten by bigger fish, so a species is doing well if one in a thousand offspring survives to maturity. Diablo Canyon’s toll isn’t negligible. Studies suggest that hundreds of thousands of baby fish that would have made it to adulthood are killed by the plant each year. But it pales beside the tens of millions of adult fish killed each year by California’s coastal fishing industry.

On the other side of the ledger are the billions that cooling towers would cost, a price that may not prove feasible. A red flag for Diablo is that New Jersey’s Oyster Creek nuclear plant will close in 2019 to avoid building state-mandated cooling towers. If a cooling-tower requirement prompts Diablo Canyon’s closure, the environmental impact will be serious even if the plant is replaced entirely by renewable generators, as its opponents insist it can be. Wind turbines, for example, are noted killers of flying creatures.

One study estimates that in 2012 the nation’s 51 gigawatts of wind power killed 880,000 bats and 573,000 birds, including 83,000 raptors, so the 8 gigawatts of wind turbines needed to replace Diablo Canyon’s output would likely kill hundreds of thousands of bats and birds each year. California’s Ivanpah concentrating solar plant has won notoriety for roasting birds in mid-air with focused sunlight from its mirrors.

That doesn’t mean we should ban wind turbines — other man-made hazards inflict a much higher feather-count — but it does mean that ecological considerations don’t necessarily favor wind over nuclear.

Electricity is fungible: every kilowatt-hour of renewable electricity devoted to replacing the 8.6 percent of California’s generation that Diablo Canyon supplies is a kilowatt-hour that’s not available to displace fossil-fueled generation.

That gap in potential clean energy won’t close soon. California’s electricity generation is still almost two thirds fossil-fueled and it would take decades for renewables to displace it all. Assuming they ever can, given their reliance on fossil-fueled backup power and their short service lives; most of the wind turbines and PV panels California has in 2020 will have to be replaced by 2050.

The Diablo We Know

The bill of particulars against Diablo is long and gives a distorted picture of its impacts on the natural world and on human well-being. Breathless news stories—and environmentalists’ legal challenges—have misstated the facts about the plant’s earthquake defenses, which meet stringent regulatory standards and can cope with all the seismic risks scientists have identified (and then some).

That owes much to the aura of dread surrounding its association with nuclear weapons, a potent strategy for mobilizing support and transforming policy. But this strategy also has tendencies towards anathema, tunnel vision, and biased perceptions that make it a dangerous approach to more complex problems. Following the cue of their most vocal constituents, regulators translate those doctrinal rigidities into legal strictures that sometimes defy common sense.

By fixating on far-fetched scenarios, antinuclear environmentalists ignore the far worse problems that nuclear power solves with its enormous production of low-carbon electricity. Worse, that blinkered viewpoint is enshrined in a regulatory establishment that lacks the vision to weigh Diablo’s modest environmental and safety risks against its reliable production of clean energy, its abatement of carbon emissions and pollution and its tiny land footprint.

Low-carbon energy of any kind is a precious asset that should be husbanded, but nuclear plants, because of their prodigious output, reliability and longevity, are irreplaceable. The green program of boosting renewables while attacking nuclear power isn’t a blueprint for sustainable progress, it’s a formula for running in place.

While the cooling-tower issue is Diablo Canyon’s chief regulatory challenge, it’s the risk to humans, not fish, which drives public opposition — especially the specter of a mega-quake causing a meltdown. For instance, Mothers For Peace has gotten traction with its claim that a sufficiently biblical rainfall could swamp the plant. (PG&E argues that no such deluge has ever occurred at the site, and that sandbags could handle it.)

Contradictions like these are hobbling energy policy in California and across the country, and environmentalists and regulators alike need to rethink the mindset that produces them. Nuclear plants shouldn’t get a pass on environmental and safety regulations. But they also deserve supportive policy that recognizes their extraordinary contributions to a healthy, sustainable economy.

Will Boisvert writes on energy, environmental, and urban policy for The New York ObserverDissent, and other publications. He lives in New York.

Graph Credit: Breakthrough Institute analysis

Photo Credit: Wikipedia Commons


1. Assuming the alternative is combined cycle nat gas at 400 grams carbon dioxide per kwh; with 17 TWh per year of electricity, that’s 6.8 million tons carbon dioxide avoided per year by Diablo Canyon. Those numbers are slight underestimates, so 7 million tons of avoided carbon dioxide is a good ballpark estimate, times 50 years is 350 million tons.

2. To utility-scale solar production, I added my estimate of 3.4 TWh from 2.29 GW of rooftop solar panels (US DOE Energy Information Agency) assuming a 17 percent capacity factor

3.  My estimate of 3.4 TWh from 2.29 GW of rooftop solar panels (US DOE Energy Information Agency) assumes a 17 percent capacity factor

4. Last year Diablo Canyon generated 17 TWh of electricity while California’s wind turbines generated a total of 12.997 TWh. Utility-scale PV generated 4.639 TWh, but that doesn’t include rooftop PV, and I specify rooftop solar panels. Without finding any hard data on specifically rooftop PV generation in California, I had to estimate it from capacity and capacity factor data. EIA gives a figure of 2.29 GW of rooftop solar in California at the end of 2014, while this California state government source gives a figure of 2.4 GW of distributed solar as of July 29, 2015. This state report on distributed rooftop solar from 2013 puts average capacity factor at about 17 percent, by eyeball from figure 3. So 2.4 GW of rooftop solar with a capacity factor of 17 percent gives total annual generation from California’s current rooftop solar panels of 3.57 TWh. The 12.997 TWh of wind generation plus 3.57 TWh of rooftop solar generation is 16.567 TWh combined, a bit shy of Diablo Canyon’s last-year generation of 17 TWh. (Diablo Canyon averages about 17.5 TWh per year.)