By Eileen O'Grady
(Reuters) - As the first anniversary of Japan's Fukushima nuclear disaster approaches, U.S. nuclear regulators have moved to issue the first new rules to deal with safety issues raised by the world's worst nuclear accident in 25 years, according to agency filings.
On March 11, 2011, an earthquake and tsunami overwhelmed the Fukushima Daiichi plant on Japan's northeast coast, knocking out critical power supplies that resulted in a nuclear meltdown and the release of radiation.
This week, a majority of the U.S. Nuclear Regulatory Commission voted to issue the first three proposed rules recommended by the agency staff, although the commissioners differ on some important details.
The staff said its recommendations, based on eight changes identified by the NRC's Fukushima task force, could move forward without significant delay, with implementation by the end of 2016.
Reactor design modifications and operating changes based on lessons from Fukushima are expected to add millions of dollars in costs for nuclear operators, including Exelon Corp, Entergy Corp, Southern Co and others.
The orders, subject to review and commission action, call for all U.S. nuclear operators to develop plans to deal with extreme situations, such as earthquakes, floods and other natural disasters that could affect multiple reactors operating at a single site.
The NRC staff also proposed that all plants improve instrumentation in the pools used to store spent nuclear fuel.
A third proposal would address containment "vent" structures at plants similar in design to the crippled Daiichi nuclear plants, according to the staff memo posted late last month.
NRC Chairman Gregory Jaczko and commissioners William Magwood and George Apostolakis have approved issuance of the proposed orders, but only Jaczko said all the changes should be mandatory and not subject to further cost-benefit analysis.
While the combination of events - an earthquake and tsunami - would be unlikely in the United States, "the events at Fukushima have reinforced that any nuclear accident with public health and safety or environmental consequences is inherently unacceptable to society," Jaczko said in filed comments.
The NRC chairman also urged a speedier timeline for the industry to complete the re-evaluation of seismic risk for reactors in the central and eastern United States.
"I still strongly believe that all Fukushima-related enhancements should be complete within five years," Jaczko said.
Magwood and Apostolakis repeated earlier opinions that more analysis is needed to determine if Fukushima-related changes should be required at all nuclear stations, regardless of cost.
Apostolakis said the proposed rule calling for additional spent-fuel pool instrumentation, while beneficial, should not be deemed mandatory due to the low likelihood of a catastrophic event affecting spent fuel.
"If we are to remain a predictable, reliable and credible regulator, we must base our decisions - especially those as important as those before us today - on careful, sober, detailed technical analyses," Magwood wrote.
(Reporting By Eileen O'Grady; editing by David Gregorio and Andre Grenon)