It might take as long as six months for the regulatory impacts of the Japan nuclear crisis to be felt in the United States, executives whose company operates one of the largest U.S. nuclear fleets said today.

But one thing is certain, Exelon Corp. President and Chief Operating Officer Christopher Crane told reporters: The industry's costs are going up.

What happens to regulations depends on the results of the Nuclear Regulatory Commission's safety review of 104 U.S. reactors as well as what international regulators learn in reviews launched after the March 11 earthquake and tsunami that crippled the Fukushima Daiichi nuclear station in northeast Japan.

"Wish we could nail it, but we can't," Exelon CEO John Rowe said of potential regulatory changes.

While Chicago-based Exelon cannot say what new costs will be incurred during the next three to five years as a result of the Japan disaster, Rowe said he can be sure that they will be "significant."

The "most likely places of additional investigation" for regulators, he said, include:

• The 10-mile "emergency planning zones" or evacuation areas around reactors.

• The maintenance of spent fuel in pools beyond the required five-year period.

• Nuclear plants' preparation for earthquakes and other catastrophic events, including terrorist attacks.

• The general adequacy of containment at General Electric Co.'s Mark 1 nuclear reactors. Exelon operates seven Mark 1 boiling water reactors, which are similar to one at the crippled Fukushima reactors.

Exelon is already feeling ripple effects from the Japan disaster. This week, a federal appellate court in Philadelphia asked Exelon and NRC to appear before the court to review the agency's 2009 decision to grant a 20-year license extension to the company's 40-year-old Oyster Creek nuclear plant in Forked River, N.J. (Greenwire, March 22).

The court asked that NRC attorneys advise whether events at Japan's Fukushima Daiichi plant have any effect on the commission's granting the license renewal application for the reactor. The Oyster Creek plant uses the Mark I reactor.

The nuclear industry faces the challenge of reviewing all the potential disaster that reactors could face, and at some point it comes down to how operators will deal with the "infinitesimal" unforeseen disasters, Rowe said, adding that the magnitude 9.0 earthquake and tsunami in Japan "weren't supposed to happen."

The company does not expect regulatory changes to affect the permitting or relicensing of its nuclear plants. Exelon operates about 20 percent of the U.S. nuclear industry's capacity with 10 power plants and 17 reactors in Illinois, Pennsylvania and New Jersey.

Rowe did cast doubt on the ability of the U.S. nuclear industry to expand, but he pointed to the costs as opposed to safety concerns.

"I believe there is little opening for new nuclear plants in the near future," Rowe said, adding that his view is based on economics, not safety.