California water officials have proposed a set of stringent new rules that are intended to eliminate or greatly reduce a harmful type of ocean-water cooling at power plants such as Diablo Canyon nuclear plant and Morro Bay.

It is unclear what effect the new rules would have on Diablo Canyon. They contain two exemptions for which nuclear plant operators could apply for reasons of safety or cost.

Known as once-through cooling, the process involves pumping massive amounts of ocean water through the cooling system to condense steam after it has passed through the electrical generators. It damages ocean life in a number of ways including killing millions of larvae and, in some cases, sucking in and drowning seals.

The new rules are intended to force plant owners to use less damaging cooling methods by reducing intake of ocean water by at least 93 percent or finding other ways to reduce damage to ocean life.

Options available to plant owners include the use of giant radiators to condense the steam, called dry cooling, or using evaporation towers or other wet-cooling techniques that use substantially less water.

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