Waterford — The Millstone Power Station is being asked to provide additional information to the Nuclear Regulatory Commission before it decides whether to allow the nuclear power plants to use intake water from Long Island Sound that is 5 degrees warmer than its current permit specifications.

In a letter this week, the NRC asked Millstone for 10 areas of safety information on the heat exchangers at Millstone Units 2 and 3. It also asked for a diagram on the piping and instrumentation system for its service water system, and whether the plants’ emergency diesel generators will still be able to produce sufficient electricity if warmer water is used. The information is requested by July 3.

“It’s a very complicated application we’ve made, and we’re responding to the request,” Ken Holt, spokesman for Millstone owner Dominion, said Thursday.

In May, the company submitted an application to use intake water that is up to 80 degrees, along with a 48-page engineering analysis of how the warmer water would affect Unit 2 operations, and a 56-page analysis of how it would affect Unit 3.

The company’s permit sets the maximum water temperature the plants can use at 75 degrees.

The company is seeking the change because of a long-term trend of warming water in the sound that peaked last summer, when Unit 2 had to shut down for three weeks when the water temperature exceeded 75 degrees.

The cooling water intake pipes for Unit 3 draw water from a colder, deeper part of the sound that did not exceed the current temperature limit.

The NRC expects to make a decision on the application next year.