(CNN) -- A call for stiffened safety rules at American nuclear plants after the March disaster in Japan got mixed reviews from both the industry and its critics Wednesday.
A task force set up by the Nuclear Regulatory Commission after the triple meltdown at Japan's Fukushima Daiichi power plant urged owners of the 104 U.S. commercial reactors to rethink their worst-case scenarios. It said the prospect of a similar accident in the United States is unlikely, but the effects would be "inherently unacceptable" if one occurred.
The panel delivered 12 recommendations to the NRC, including one to require plants to be able to run cooling systems for up to 72 hours during a blackout. And it said a "patchwork" of existing regulations should be replaced with a "logical, systematic and coherent" set of rules.
The 96-page report found that the industry's voluntary steps are useful to set standards, "but should not take the place of needed regulatory requirements."
"We're still digesting the contents of the report," said Tony Pietrangelo, senior vice president of the Nuclear Energy Institute, the industry's trade association. But Pietrangelo told reporters that the NRC needed additional input from the industry before approving any new regulations.
"I might have done it a little bit differently in separating out what the near-term Fukushima lessons learned are versus a sweeping review of the entire regulatory framework," Pietrangelo told reporters Wednesday. "I think we can do it more efficiently, more effectively, more holistically, but that takes time."
And Edwin Lyman, a physicist at the Union of Concerned Scientists, said the nuclear watchdog group had a mixed first impression of the report.
"We think some of the changes in the framework they've proposed are potentially very useful," Lyman said. But he added, "The devil is in the details of how thoroughly it's done."
Pietrangelo said the U.S. nuclear industryis likely to see higher costs in the aftermath of Fukushima Daiichi, but "It remains to be seen which recommendations will be implemented and how they'll be implemented."
"At this point, I think the entire report should be vetted with not only the commission, as it will be, but with the broader spectrum of stakeholders across the board to sort it out and get added perspective to the table about how to proceed," he said.
The industry already has stepped up safety measures at its plants since the disaster, on top of new regulations imposed after the September 11, 2001, terrorist attacks on New York and Washington, Pietrangelo said. He disputed the task force's characterization of current rules as a "patchwork," and called its finding that the concept of defense-in-depth was undervalued "indefensible."
Meanwhile, Lyman said the task force should have widened the NRC's requirements for emergency plans for residents living beyond 10 miles of the plant. Fukushima Daiichi, the worst nuclear accident since Chernobyl, has displaced more than 100,000 people living more than 25 miles away.
"We think that lessons still need to be learned from Japan," he said. The Union of Concerned Scientists has put out its own list of two dozen recommended regulations, including stepped-up defenses against terrorist attacks and additional measures to protect spent fuel rods.
The Fukushima Daiichi disaster occurred when a 15-meter (48-foot) tsunami inundated the coastal plant after northern Japan's historic March 11 earthquake. The flooding knocked out the cooling systems for the three operating reactors and their associated spent fuel pools, causing the reactors to overheat and hydrogen gas explosions that blew apart the building housing reactors No. 1 and 3. Another hydrogen blast is believed to have damaged the inside of the No. 2 reactor, while engineers are struggling to manage an estimated 100,000 tons of highly contaminated water that was used to cool the reactors during the emergency.
Tokyo Electric Power Company projects the situation won't be fully over until sometime between October and January. The disaster has caused Japan to rethink its commitment to nuclear energy, and Germany has since announced plans to abandon atomic power entirely by 2022.
The NRC task force also called for requiring vent systems that could limit the buildup of steam and gas in boiling-water reactors like the ones at Fukushima Daiichi. There are 23 operating U.S. reactors with the same basic containment design, the General Electric Mark 1.
CNN's Mike M. Ahlers contributed to this report.