WASHINGTON (Reuters) - The U.S. Nuclear Regulatory Commission (NRC) said on Friday it has not yet gotten an application from Constellation Energy ( CEG ) on restarting the Three Mile Island nuclear reactor.

Constellation and Microsoft ( MSFT ) have signed a data center deal to help resurrect a reactor by 2028 at Three Mile Island in Pennsylvania. It has been shut since 2019.

"At this point there's nothing in front of us in terms of an application. It's up to Constellation to lay out its rationale for justifying restart, so we're prepared to engage with the company on next steps," said NRC spokesperson Scott Burnell.

Constellation said it had plans to file a permit application but did not immediately specify a timeline for doing so. "We anticipate the NRC review to be complete in 2027," a company spokesperson said.

Nuclear proponents complain that NRC takes too long to review licenses, and a law signed by President Joe Biden this year is meant to help address that. But as demand for power soars for the first time in decades, the NRC is mulling a host of applications from new high-tech nuclear reactors and an application from a decommissioned reactor, in Michigan called Palisades, which if approved could be the first U.S. reactor to come back from restart.

Burnell said the NRC will use existing review processes to consider any licenses for TMI. Some opponents of quickly reopening shuttered nuclear plants have filed a petition at NRC saying the agency should adopt a new rule-making for such cases, as no closed U.S. nuclear power plant has ever been resurrected.