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Nuclear Industry Will Reassess Safety Systems

http://online.wsj.com/article/SB10001424052748704296604576197354007005470.html

›MARCH 14, 2011
By REBECCA SMITH

The accident at the Fukushima Daiichi nuclear-power plant involved multiple system failures that cast doubt on the guiding principle of the nuclear power industry: that engineers can build enough redundancy into safety systems to overcome any threat.

In Fukushima prefecture, Tokyo Electric Power Co. found that the layers of redundancy in the plant's electricity-supply and cooling systems weren't sufficient to nullify the power of nature, which took the form of a massive earthquake followed by aftershocks and tsunami waves.

After the plant lost grid electricity, diesel generators kicked in but reportedly were knocked out by the tsunami. Batteries weren't able to power critical instrumentation and controls and keep functional the reactor cooling system, which relies on massive water pumps.

Plant operators finally used seawater in a desperate attempt to cool reactors No. 1 and 3 that suffered enough heat buildup to damage the nuclear fuel that's inside the reactor pressure vessel in each unit. Operators said Monday they weren't sure they could trust their readings from several key instrument panels.

Thousands of evacuees from areas around Japan's Fukushima nuclear power plant were scanned for radiation exposure, though the Japanese government insists radiation levels are low. Video courtesy of Reuters

Thus, the failures spanned the electrical system, cooling system and control and instrumentation systems at the plants. What didn't fail, at last report, was the series of physical barriers in the form of steel and concrete that keep radioactive materials from being freely released into the environment.

Richard Meserve, a physicist and former NRC chairman from 1999 to 2003, said the Japanese reactors experienced a "one-two punch of events beyond what anyone could expect or what was conceived." A reassessment of safety threats to boiling-water reactors, in particular, and also to coastal reactors at risk of tsunamis will result, he said.

Peter Bradford, a member of the U.S. Nuclear Regulatory Commission at the time of the Three Mile Island accident in Pennsylvania in 1979, said the accident exposes shortcomings in risk analysis as well as engineering.

"The redundancy, such as it was, obviously was inadequate to the event that actually happened," he said. He said the problem is that certain risks always are discounted in the licensing process as "so highly unlikely that you don't have to plan for them."

It isn't known if operator error played a role, as it did three decades ago at Three Mile Island, but it's clear the earthquake exceeded the level for which the plant was designed.

"The really important question," Mr. Bradford said, "is to ask how different licensing bodies decide what risks have to be guarded against and see if that analysis was adequate."

Operators of similar early-vintage General Electric Co. boiling-water reactors in the U.S. said they are trying to understand events in Japan. Two kinds of nuclear plants are most likely to be affected by the accident—those of similar reactor type and those that also are located in coastal areas near earthquake faults.

In earthquake-prone California, attention immediately turned to PG&E Corp.'s Diablo Canyon nuclear plant and Southern California Edison's San Onofre plant, both of which are on the Pacific Ocean, near fault zones.

Companies with boiling-water reactors similar to the ones in Japan include Exelon Corp., Entergy Corp. and Xcel Energy Inc. There are nearly two dozen such plants in the U.S.

Marshall Murphy, spokesman for Exelon's nuclear business, said his company "is not in a position to talk about" the Japan accident or its similar units, a list that includes its Quad Cities plant in Cordova, Ill., its Dresden plant in Morris, Ill., and its Oyster Creek plant in Forked River, N.J. Entergy has several similar units, including its Pilgrim plant in Plymouth, Mass., its Vermont Yankee plant in Vernon, Vt., and its FitzPatrick plant in Scriba, N.Y. Xcel's Monticello plant in Monticello, Minn., also is similar.

Xcel and Entergy referred calls to an industry association.

The Japanese nuclear accident has come at a delicate time for the nuclear-power industry, growing globally, for the first time in decades as a new generation of "passive" designs is being embraced as offering more safety. The passive feature means they rely less on electrically driven pumps and valves, for safety, and more on systems designed to shut down plants safely in emergencies and to prevent operator error.

For example, the Westinghouse AP 1000 reactor places cooling water at a level above the reactor—unlike the Fukushima design—so that it would naturally flow down. Older reactors often pump water up.

A spokesman for the Nuclear Energy Institute, the trade organization that represents U.S. nuclear utilities, said it is too early to tell what changes in the industry could result from the accident. "I'm sure there will be lessons learned," said Tom Kauffman, at the institute in Washington.

The industry hopes it will be nothing like what happened after the Pennsylvania accident in 1979. That basically stopped planning for new reactors, and utilities lost billions of dollars as design criteria were strengthened. Half of today's U.S. reactors were built after that landmark event, but all were projects proposed before the accident.‹