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Once-Through Cooling Power Plant Phase Out in Progress

By Media Office Staff

The use of once-through cooling (OTC) has been phased out at three more power plants since 2016, according to a tracking progress report from the California Energy Commission.

OTC has been eliminated at 10 power plants equating to 10,400 megawatts (MW). OTC power plants with 6,300 MW of capacity is expected to retire by 2020 and the remaining 3,800 MW by 2029. Renewable energy will replace the lost energy capacity from retired power plants.

OTC technology in power plants diverts marine water to cool the steam after passing through a turbine to create power, destroying and dislocating billions of aquatic organisms and habitats in the process. In 2010, the State Water Resources Control Board (SWRCB) began a phase out process at 19 OTC power plants to address state coastal and estuarine waters damages.

The California Independent System Operator, Energy Commission, and California Public Utilities Commission works with the SWRCB to implement the OTC policy to improve water quality and ensure electricity grid reliability. The policy is aimed at the intake of marine water or using operational/structural controls to reduce organisms and objects being trapped in the screens.

Many of the OTC power plants are critical for local energy reliability, which is why the Statewide Advisory Committee on Cooling Water Intake Structures works with SWRCB to maintain grid reliability while implementing the policy.

That means that compliance dates may need to be changed. The SWRCB approved deferring the compliance date for the Encina Power Plant Units 2 to 5 to December 31, 2018. The one-year extension for those units, which were retired December 11, 2018, was needed because of delays in the completion of its replacement project, the Carlsbad Energy Center.

Nuclear power plants also are phasing out OTC. In 2012, the San Onofre Nuclear Generating Station shut down because it would have been more costly to repair steam generator tube leaks. The Diablo Canyon Power Plant’s nuclear regulatory license ends in 2024 at Unit 1 and 2025 at Unit 2, but the compliance date for both units is December 31, 2024. Pacific Gas &Electric’s implementation plan would require a compliance date delay for Unit 2.

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