Concern is in reactors’ design
Originally published on March 27, 2011 by Omaha World-Herald
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By Nancy Gaarder
Midlanders don’t have to look far to find the type of nuclear reactors that are in crisis in Japan.
Nebraska and Iowa each has one similar to the Japanese reactors that released significant radiation after being damaged by an earthquake and tsunami.
Are the Midlands’ reactors — Nebraska’s largest and Iowa’s only one — vulnerable to similar releases during an extraordinary crisis?
The two Midlands reactors that rely on the design in question are Cooper Nuclear Station and Duane Arnold Energy Center.
Cooper sits along the Missouri River in southeast Nebraska, about 70 miles from Omaha and Lincoln. Duane Arnold is about nine miles from Cedar Rapids, Iowa.
The general design of this kind of reactor has been dogged by criticism for more than 30 years — criticism that has prompted significant safety retrofits.
But subsequent concerns have arisen. Research by Sandia National Laboratories has found a “high probability” that a prolonged, complete loss of power at this type of plant would result in fuel melting through the reactor’s thick shell.
Also of concern: Many of the U.S. reactors like this, including Duane Arnold, are substantially boosting output. They’re doing that on the basis of calculations that have determined the reactors’ safety margins are more robust than was believed 30 years ago.
The boosting of output has been authorized by the Nuclear Regulatory Commission, but over objections by the agency’s own advisory panel on safeguards.
One thing is certain, a former nuclear regulator said as the Japan crisis unfolded.
“There’s no way that the Nuclear Regulatory Commission won’t be taking a very close look at those plants,” said Peter Bradford, a former commissioner of the NRC.
Of the nation’s 104 reactors, 35 have the general design of those in crisis in Japan and 23 of those, including the two in the Midlands, are most similar.
At issue with this type of plant’s original design: the system to contain radiation in event of an accident.
For all reactors, the containment system is the final defense against high amounts of radiation being released into the atmosphere.
There are different types of containment, and each has its strengths and weaknesses. The General Electric Mark 1 reactor at Duane Arnold and Cooper is smaller and more complex than the completely different type of reactor found at Fort Calhoun Nuclear Station north of Omaha.
At Cooper and Duane Arnold, a highly reinforced tank around the reactor is the vessel that would contain radiation. The building around the reactor vessel is considered secondary.
At Fort Calhoun, the entire building around the reactor is reinforced and considered the primary means to contain releases of radiation.
Both types of nuclear plants have additional equipment that kicks in to help contain radiation.
But at Cooper and Duane Arnold, this extra equipment is more complex because it compensates for the smaller size. As a result there are more moving parts and thus more points of vulnerability.
Back in the early 1970s, regulators debated banning new plants of this type. The idea didn’t get off the ground, in part because it was feared doing so would stop nuclear power in its tracks.
Cooper came on line in 1974 and Duane Arnold in 1975.
Alan Dostal, corporate nuclear business manager for Nebraska Public Power District, which owns Cooper, said the criticisms made in the past are no longer relevant.
From the 1980s forward, the Nuclear Regulatory Commission has required significant safety retrofits of these reactors, he said.
The criticism “might have been appropriate 30 years ago, but things change, and we’ve changed,” Dostal said. “The industry stepped up and addressed those issues.
“Where it’s appropriate to make modifications, we’ve made those and until we see something that’s significant, we’ll just have to wait and see,” Dostal said. “We’re confident in the equipment, systems and people we have.”
Those modifications include:
>> Bolting down the containment vessel, an enclosed steel moat at the base of the reactor. The water in this moat cleanses radiation from steam that is being created.
As originally designed, the moat, known as a torus, rested in supports that sat on concrete. Now those supports have been bolted 10 feet into concrete so that the torus doesn’t bounce and rupture from the tremendous forces unleashed by a problem at a reactor.
>> Installing screens to catch debris created by an accident. The screens are intended to keep pumps from clogging, which otherwise would prevent the free movement of water.
>> Building a hydrogen vent to prevent a buildup of explosive gas. Cooper’s stack is 325 feet tall.
General Electric has defended the design of its plants.
“The Mark 1 meets all regulatory requirements and has performed well over 40 years,” GE said in a statement. Since no one knows the full chain of events at the Japanese reactors, GE says, it’s too early to draw conclusions.
Edwin Lyman, senior scientist for global security at the Union of Concerned Scientists, said plant modifications don’t mean “the problem’s over.”
Specifically, he cited the Sandia report.
Bill Borchardt, executive director of the NRC, told his commissioners last Monday that he sees no reason to change the way the 104 U.S. reactors are regulated.
“We have a sufficient basis to believe, to conclude, that the U.S. plants continue to operate safely,” said Borchardt, who also briefed a U.S. House committee on the Japan situation.
Borchardt said the United States drew lessons from the Three Mile Island partial meltdown in 1979 and the Sept 11, 2001, terrorist attacks and significantly improved nuclear safety.
Dostal said nuclear reactors are individually designed to withstand — and then some — the worst expected natural disasters that could strike the plant.
At Cooper, that includes a 1 in 1-million-years flood, which takes into account a burst dam upstream on the Missouri River; 300 mph winds, which are the equivalent of an EF 5 tornado; and earthquakes of 6.0 magnitude.
Duane Arnold likewise is designed to withstand 300 mph winds, an earthquake and flooding well beyond what Iowa has experienced in its recorded history, said Renee Nelson, a spokeswoman for the plant.
Duane Arnold is jointly owned by NextEra Energy Resources, Central Iowa Power Cooperative and Corn Belt Power Cooperative.
Nelson said this much is clear: The plant’s design didn’t initiate the problem.
“The Japanese event was caused by extraordinary natural forces that could not likely happen in Iowa,” she said.
The loss of emergency backup power — as a result of the earthquake and tsunami — is believed to be the primary reason the Japanese safety systems were overwhelmed.
President Barack Obama has ordered a review of U.S. reactors, and the Nuclear Regulatory Commission will do a two-phase review. The first is a quick 90-day review to see if something requires immediate action. The second and more thorough review will take much longer.
One question for U.S. regulators is whether a different set of circumstances could trigger a similar loss of safety systems in American reactors. If so, what reasonable steps can be taken to be better prepared?
David Lochbaum, director of nuclear safety at the Union of Concerned Scientists, said the answer is clear. Lochbaum will testify this week before a Senate committee on the nuclear plant safeguards.
“If our reactors were faced with a similar challenge, the outcome would be similar,” he said.
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