7/28/2019 PGE FactSheet OncethroughCooling

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Corporate AffairsDiablo Canyon Power Plant

415-973-5930Fax 805-546-5232

diablocanyon@pge.com

For more information visiwww.diablocanyonpge.com

Diablo Canyon Power PlantOnce-through coolingFor nearly three decades, Diablo Canyon Power Plant has remainedone of the safest and most efcient commercial nuclear powerplants in the United States. When operating at full power, DiabloCanyon Power Plant generates enough electricity to cleanly andreliably power nearly 3 million Northern and Central Californiahomes. This is done by creating heat through the process ofsplitting uranium atoms (ssion) that heats water to create steam.The steam then forces the turbine, connected to an electricalgenerator to spin, creating electricity.

In order to safely and efciently operate the plant, Diablo Canyonuses upwards of 2.5 billion gallons of water from the Pacic Oceanto condense steam after it has passed through the two electricalgenerators in a process known as once-through cooling.

A Prime LocationDiablo Canyon is located on 12,000 acres of one of the most scenicand habitat-rich coastlines in the country. Pacic Gas and ElectricCompany preserves roughly 11,000 acres of land in a natural stateas a home to many species of plant and animal wildlife. Like manylarge, utility-scale power plants in the U.S. built along rivers, oceansand other bodies of water, Diablo Canyon uses the abundant supplyof ocean water to ensure the plants reactors continue operatingsafely. The ocean water never touches the nuclear reactor itself. Thewater is separated by Diablo Canyons system of three, independentwater loops.

Primary Water SystemPure water in the rst loop is pushed through the nuclear reactors

to absorb heat and carry the heat to the steam generators. Apressurizer keeps the water at a high pressure to prevent boiling,

allowing the water to reach over 600 degrees Fahrenheit and 2,200pounds per square inch of pressure. This water is radioactive so it enclosed inside the protective reactor containment dome.

Secondary Water SystemWithin the steam generators, pure water in the second loop isheated to create steam. The pressure from the steam spins aturbine, which drives a generator that produces electricity. Thesteam is then condensed when it comes into contact with the thirdsystem and is pushed back through the steam generators to bereheated into steam, continuing the process. This water does notcome into contact with the reactor and is not radioactive.

Tertiary Water System

The third loop carries ocean water that condenses the steam in theturbine back into water. The ocean water is then returned to theocean and more water is brought into the plant. Because each loopis separate, water in one loop cannot mix with water in other loops

Revisions to California LawIn May 2010, the California Water Resources Control Boardadopted a new policy mandating that power plants across the stateupdate their once-through cooling systems. The policy providesa variance approach for nuclear power plants, recognizing theirunique contribution to the states electric generation capacityand greenhouse emission reduction goals. Under this policy, anuclear review committee will be established to oversee a studyof the feasibility and cost of a retrot at Diablo Canyon. The studywill be completed by 2013. Based on the results of the study, if

the Board determines that the costs to install cooling towers arewholly out of proportion to the costs considered by the Board indeveloping its policy or if the installation of cooling towers would bewholly unreasonable after considering non-cost factors such asengineering and permitting constraints and adverse environmentaimpacts, Diablo Canyon would be granted a variance and allowedto continue operating its once-through cooling system and mitigateits impacts. Pacic Gas and Electric Company estimates the cost toretrot Diablo Canyon at over $4.5 billon dollars. A retrot at DiabloCanyon would also have signicant negative environmental impact.

About PG&EPacic Gas and Electric Company, a subsidiary of PG&E Corporatio(NYSE: PCG), is one of the largest combined natural gas and electrutilities in the United States. Based in San Francisco, with 20,000

employees, the company delivers some of the nations cleanestenergy to 15 million people in northern and central California. Formore information, visit www.pge.com/about.

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