Engineers at Monticello plant warned of problem that struck Japanese plant.
WASHINGTON - Five years before the crucial emergency vents at the Fukushima Daiichi nuclear power plant in Japan were disabled by an accident they were supposed to help handle, engineers at the Monticello nuclear plant in Minnesota warned U.S. regulators about that very problem.
Anthony Sarrack, one of the two engineers, notified staff members at the Nuclear Regulatory Commission that the design of venting systems was seriously flawed at his reactor and others in the United States similar to those in Japan. He later left the industry in frustration because managers and regulators did not agree.
Sarrack said that the vents, which are supposed to relieve pressure at crippled plants and keep containment structures intact, should not be dependent on electric power and workers' ability to operate critical valves because power might be cut in an emergency and workers might be incapacitated. Part of the reason the venting system in Japan failed -- allowing disastrous hydrogen explosions -- is that power to the plant was knocked out by a tsunami that followed a major earthquake.
Sarrack's memo was found in the archives of the Nuclear Regulatory Commission by David Lochbaum, an expert on boiling-water reactors who works for the Union of Concerned Scientists, a nonprofit group based in Cambridge, Mass., that is generally cautious of nuclear power.
'Cannot claim ignorance'
"The Nuclear Regulatory Commission cannot claim ignorance about this one," he said.
Plant managers and nuclear regulators are warned about far more problems each year than actually occur, but in this case, the cautionary note was eerily prescient and could rekindle debate over whether automatic venting systems are safer.
While staff members at the Nuclear Regulatory Commission considered Sarrack's suggestion, they decided against it. On Wednesday, NRC spokesman Scott Burnell said the commission still believed that existing venting systems were a "reasonable and appropriate means" of dealing with a rise in pressure after an accident. But he also said that the commission's staff members are studying the events at Fukushima for "lessons learned" and that they had identified means of "reducing risk even further" by making the vents "more passive." He said the staff had not yet chosen a way to do that.
One way would be using rupture disks, relatively thin sheets of steel that break and allow venting when the pressure reaches a specified level without any operator command or moving parts. But many in the industry argue that using such a disk requires that there be a way to close the vent once pressure is relieved to hold in radioactive materials.
Sarrack, reached by telephone, said that his proposal was opposed by the operations department officials at his company, who wanted direct control over the reactor rather than employing automatic systems.
He said he continued to believe that a passive system, like one using a rupture disk, would work better and could be set to rupture at a pressure just slightly less than the pressure at which the containment would rupture.