Diablo Canyon faces state deadlines to change its cooling system

This rendering shows what cooling towers might look like at Diablo Canyon nuclear power plant.
This rendering shows what cooling towers might look like at Diablo Canyon nuclear power plant. Courtesy photo

An important milestone looms for Diablo Canyon nuclear power plant.

Plant manager PG&E and state officials will decide soon whether the plant will spend up to $12 billion to change its cooling system, which damages the ocean ecosystem by killing fish larvae and discharging billions of gallons of unnaturally warm seawater.

Some options, such as building 600-foot-tall cooling towers, would permanently alter the landscape around Diablo Canyon and certainly face stiff local opposition.

PG&E has until the end of 2024 to make required changes to the plant, but on Monday a review committee will hold a public meeting in Sacramento to discuss the issue. Then in December, that committee will make its final recommendations to the state Water Resources Control Board.

PG&E says the cost of any required changes will be passed on to its customers.

What’s at stake

Every day, Diablo Canyon nuclear power plant circulates 2.5 billion gallons of seawater through its cooling system.

This system, called once-through cooling, does significant damage to marine ecosystems. Biologists have estimated that Diablo Canyon sucks in more than 1.5 billion fish larvae a year, most of which do not survive.

Once the water has circulated through the cooling system, it is discharged back into the ocean 20 degrees warmer. This influx of warm water creates an artificial ecosystem in the discharge cove, damaging kelp, other forms of algae and small fish.

“The marine life that is killed is mainly at the base of the food chain, and that can adversely affect the future of certain species and adversely impact recreational and commercial fishing,” said George Kostyrko, spokesman for the state Regional Water Quality Control Board.

Diablo Canyon isn’t alone in needing to make costly changes.

On May 4, 2010, the state Water Resources Control Board adopted a policy requiring all 19 coastal power plants in California to reduce by 93 percent the amount of damage their once-through cooling systems cause. State regulators have given PG&E until the end of 2024 to comply with the new rule.

That process is reaching an important juncture.

On Dec. 16, a specially appointed nuclear review committee will issue comments and recommendations to state water authorities about the feasibility of the best technologies available for reducing Diablo Canyon’s impact on the ocean.

PG&E commissioned engineering firm Bechtel to study technology options to assist state regulators in their decision. It will be up to the state water board to make a final ruling on which technology PG&E will be required to install, probably late next year, Kostyrko said.

Timing is everything

These costs come at a time when the utility already faces considerable expense.

Federal regulators are requiring about $50 million in safety equipment at Diablo Canyon in the aftermath of the Fukushima nuclear disaster in Japan.

PG&E is also finishing up a series of detailed onshore and offshore seismic surveys of the earthquake faults surrounding the plant, which could indicate that further retrofitting is necessary.

At the same time, PG&E is pondering whether to move ahead with its application to renew Diablo Canyon’s two operating licenses for an additional 20 years. The company has put on hold its applications to renew the permits that expire in 2024 and 2025.

Although the once-through cooling issue is a state requirement and relicensing is a federal process, the cost of revamping its cooling system is one of many factors the utility will consider as it makes its relicensing decision.

“We have to wait for the process to play out,” PG&E spokesman Blair Jones said. “PG&E will comply with the once-through cooling policy, but it is premature to speculate on what the state water board will recommend.”

Cost and power disruption

The state water board and PG&E face several daunting problems as they ponder the once-through cooling issue.

The most effective methods for reducing the impacts of once-through cooling, such as cooling towers, would cost PG&E ratepayers billions of dollars. They would also cause their own severe environmental impacts.

The towers would require major excavation of a mountain behind Diablo Canyon.  This option would involve the installation of two to four towers 100 to 600 feet tall, depending on which tower cooling system was chosen.

PG&E and others do not think this option is workable.

“Based on our review, cooling towers do not appear to be feasible at our location due to the extreme engineering, environmental and permitting challenges as well as the expected cost for our customers,” Jones said.

The state water board anticipated this difficulty and created a separate set of rules for nuclear power plants that allows for consideration of alternatives to the most expensive and disruptive options in order to ensure reliability of the state’s electrical power supply.

Diablo Canyon supplies about 10 percent of the state’s power. PG&E estimates retrofitting the plant to replace once-through cooling could cause a shutdown of 17 months while work is done.

“Cost and grid reliability are both factors the board considers in approving a compliance option,” Kostyrko said. “Hypothetically, if grid reliability becomes a great concern for specific compliance options such as installing cooling towers, the board may not approve that option.”

However, the available alternatives that Bechtel evaluated are not as effective and may not achieve the goal of a 93 percent reduction in cooling system damage. These alternatives include additional screens, intake pipes buried below the sea floor or other modifications to the plant’s water intake structure that would reduce the number of larvae that enter the system.

The board could also decide that additional studies are needed before it makes a decision, Kostyrko said.

PG&E would not comment on the feasibility of these other alternatives until the state water board makes its decision. It also would not say what influence once-through cooling modifications would have on its decision whether to pursue renewal of the plant’s two operating licenses.

Other possibilities

Other options not outlined in the Bechtel report have also been suggested.

These include various environmental projects that could allow once-through cooling to continue but offset the damage by replacing the larvae killed by the plant.

On previous occasions, the Central Coast Regional Water Quality Control Board has looked at the once-through cooling problem and suggested several kinds of environmental enhancements as possible solutions, said Peter von Langen, an environmental scientist with the regional board. Von Langen also sits on the state board’s once-through cooling nuclear review committee.

“The expense of modifying the once-through cooling system seems just enormous, and the environmental costs seem very high as well,” he said.

Von Langen said he will recommend that the state board look at having PG&E fund a range of environmental projects. All of them would increase the overall health and productivity of the ocean and could offset the harm once-through cooling does to the ocean.

One option is permanently preserving land around Point Buchon owned by PG&E. This area of coastline has many rocky intertidal reefs that are fertile breeding grounds for larvae.

Others include building artificial rocky reefs off the Morro Bay sand spit to increase larvae production, or providing additional funding for the state’s network of marine reserves that enhance fish stocks and increase marine biodiversity.

Rochelle Becker, executive director of the San Luis Obispo-based anti-nuclear Alliance for Nuclear Responsibility, also sits on the state’s once-through cooling nuclear review committee.

Short of shutting down the plant or reducing its power output, there is no good solution to the once-through cooling problem, she said.

Her group recommends that the state allow the continued use of once-through cooling at Diablo Canyon until the end of 2025, then require the plant to shut down when its license expires.

“Many of the recommendations outlined in the Bechtel report are untried, and there’s a lot of time and money involved here,” she said. “I have grave concerns about underestimating the cost of doing any engineering project on the coast.”


The engineering firm Bechtel has released a 217-page report analyzing technologies available for replacing Diablo Canyon’s once-through cooling system. The report focuses on three main technologies:

• Cooling towers. The study looked at two types of towers to eliminate the use of ocean water. Radiation or evaporation would be used to cool and condense steam that has passed through the plant’s turbine generators. Large segments of hills north of the plant would be removed to make room for the towers. 

Estimated cost: $8 million to $12 billion.

• Mesh screens on the intake structure. This option installs a series of fine screens on the cooling water intake system to reduce the number of larvae drawn into and killed by the cooling system.

Estimated cost: $371 million to $493 million.

• Offshore pipes. These would take cooling water from offshore, filter it through wire screens and pump it into the existing cooling water intake cove that has been enclosed to create a shoreline basin. A tunnel or buried piping could be used to transport the water into the intake cove.

Estimated cost: $261 million to $407 million.