U.S. reactor retrofits in works to avoid blasts. (May 25th)

Thursday, May 26, 2011

U.S. reactor retrofits in works to avoid blasts
Bloomberg
New York/New Delhi — Entergy Corp., the second-biggest nuclear operator in the U.S., and Duke Energy Corp. said the industry may need to retrofit reactors or bolster safety systems after a pressure-relief system failed at the Fukushima No. 1 plant, contributing to the disaster.

Venting systems at reactors there were designed to allow engineers to release pressurized gas into the atmosphere to avoid dangerous hydrogen explosions. The systems were installed in the U.S. and Japan after the partial core meltdown at Three Mile Island unit 2 in 1979.

The vents were built into General Electric Co. boiling- water reactors, including at the Fukushima plant that was rocked by at least two blasts blamed on trapped, exploding hydrogen. A conclusion that the vents were at fault may add costs for nuclear-power generators as politicians from Germany to India question the safety of atomic energy.

The hydrogen explosions in Fukushima "call the modification into question," said Tony Roulstone, who directs the University of Cambridge's master's program in nuclear technology in England. "If these vents don't work, then the design looks wrong. Fixing it will take some design work, but won't be wildly expensive."

The U.S. Nuclear Regulatory Commission is "looking at effectiveness of containment venting strategies," Charlie Miller, head of the post-Fukushima safety review, said at a May 12 agency meeting. The vent system is "worthy of a look" after the disaster, he said.

Entergy "fully expects" the NRC to order new equipment installed and new procedures to be adopted as a result of the accident in Fukushima, said Jim Steets, a spokesman for the New Orleans-based company, which owns 11 reactors.

Operator error or lack of power at the facility may explain why venting systems didn't work at Fukushima. "There are multiple explanations for failure of venting systems in Japan to prevent hydrogen explosions," Michael Burns, another Entergy spokesman, said last week.

After the Fukushima plant was damaged by the March 11 quake and the tsunami took out the primary power supply, diesel generators either worked only briefly or also were flooded, according to a May 18 interim review of the incident by the U.K.'s Office for Nuclear Regulation.

Because loss of the power needed to open valves may have contributed to the hydrogen explosions, "one of the things we expect to be testing with our own units is, do we have adequate auxiliary power, could it withstand fire or flood?" said Jim Rogers, chairman and chief executive officer of Duke Energy.

It's still unclear whether Tepco engineers opened the vents to release pressure in the containment building, according to the U.K. report.

"It is certainly possible that inadequacies in the venting routes may have featured in the devastating explosions that were seen in reactor units 1 and 3," the review found. "This may indicate that more attention should have been given in the design and safety assessment to the robustness of the venting routes."

The hardened-vent systems were designed by a consortium of reactor owners advised by GE. U.S. regulators recommended installation of the systems in a September 1989 letter to owners.

"At this point, we still believe that under design-basis conditions, the hardened-vent system would operate as designed and meets the current regulatory requirements," said Jim Klapproth, chief consulting engineer for GE Hitachi, the nuclear-power joint venture of GE and Hitachi Ltd.

"We are evaluating the situation in Japan to determine if there's any difference in the design or operator actions."

Scott Burnell, a spokesman for the NRC, declined comment on any similarities between the venting and suppression systems at Fukushima and U.S. reactors.

It's "still too early to be drawing conclusions on either events at Fukushima or possible recommendations from our task force" that's leading a safety review of U.S. reactors, Burnell said in a recent email.

U.S. reactor operators are able to decide for themselves whether to vent radioactive gas when reactor pressure is high, said Carrie Phillips, a spokeswoman for Atlanta-based Southern Co., which operates two GE reactors with containment systems similar to the Fukushima plant.

Southern and U.S. regulators tested the venting system at its GE-designed Hatch reactors in Georgia in March and they worked as intended, Phillips said.

More information is needed about the explosions at the Fukushima plant, including a still unexplained blast at reactor 2, said David Lochbaum, the director of the nuclear safety project at the Union of Concerned Scientists, a nonprofit group.

"We haven't yet heard what the most likely scenario is," said Lochbaum, adding, "There are some signs that the vents may not have worked."