HARTFORD, Conn. – Connecticut’s nuclear plant is preparing to ask federal regulators for permission to use water that’s even warmer than the temperature that forced it to shut a unit last August.

Regulators were cool to at least two other suggestions by Millstone Power Station in Waterford to operate with rising water temperatures, according to emails among Nuclear Regulatory Commission officials obtained by The Associated Press through an open records request.

One of the plant’s two operating units was forced to shut down for nearly two weeks last year because the water in the Long Island Sound was warmer than the limit of 75 degrees that’s in place to keep the plant operating safely.

The partial shutdown at Millstone was the first in the United States to be caused by rising water temperatures, and the head of the NRC has asked for a review of climate change impacts on nuclear plants nationwide.

Nuclear plants require large amounts of water to cool equipment and buildings, and federal regulators impose water temperature limits so plants are safely cooled even with water temperatures that are warmer than normal.

Millstone provides half of all power in Connecticut and 12 percent in New England.

Its two units produce 2,100 megawatts of electricity, which shrank 40 percent with its unit down.

As temperatures rose in the hottest July on record, Millstone, a subsidiary of Dominion Resources Inc., proposed a number of options to get around the temperature requirement.

The other Millstone unit, which reaches deeper into the sound, remained open.

The NRC gave Millstone permission to use an average of readings, which brought the measurement down but not enough to avoid the shutdown.

Temperatures in the sound were on average 1.7 degrees above the limit.

Millstone also discussed with regulators the possibility of using equipment that more precisely measures water temperature to push the margins out by a few tenths of a degree, according to emails.

The NRC said that was not a long-term solution.