Lessons about reactor safety that can be learned from the Japan nuclear crisis would lead to a call for immediate changes at U.S. nuclear plants but they won't affect ongoing license-renewal reviews, a top nuclear regulatory official told lawmakers today.

"There is no technical reason that I'm aware of that this would impact the license-renewal process for the remaining plants in the U.S.," said Bill Borchardt, executive director for operations at the Nuclear Regulatory Commission.

"It is our intent through the lessons-learned programs and our continuous operational oversight of the operating fleet that if there was a design change necessary in order to adapt the plants to what we're learning from Japan, we would take that action absent or outside the license-renewal review process."

He added, "We would take that without hesitation."

His testimony to the Senate Energy and Natural Resources Committee comes as officials are scrambling to understand the problems and impacts of the ongoing crisis at the Fukushima Daiichi power plant, which was crippled by a March 11 earthquake and tsunami.

Some congressional Democrats have called for a moratorium on license-renewal and new license reviews until the problems in Japan are better understood. But the Obama administration is opposed to halting the license reviews.

About half of the U.S. reactors have already received a license renewal for an additional 20 years of operation. Borchardt said he expects the rest will continue with their license-renewal applications or will pursue them in the future.

"The decision on whether or not a utility applies for a license renewal is their decision -- partially a business decision, partially a technical decision," Borchardt told reporters. "The way the NRC would do our review of license-renewal reviews, I don't anticipate it changing."

NRC is currently conducting a 90-day review of information coming out of Japan to provide a snapshot of U.S. reactor safety and to evaluate the U.S. fleet's ability to respond to emergencies.

Borchardt said that if that review reveals the need for design changes to improve safety at U.S. reactors, NRC would call for those changes immediately.

"If we believe that there is a design change that's necessary that we think needs to be imposed, we're not going to do that as part of the license-renewal review," Borchardt said. "We'll do that based for the 104 operating reactors right now. We won't wait.

"From that aspect, I see them as different issues to some extent."