Warning was issued in ’70s on GE-designed reactors
NEW YORK — The warnings were stark and issued repeatedly as far back as 1972: If the cooling systems ever failed at a Mark 1 nuclear reactor, the primary containment vessel surrounding the reactor would probably burst as the fuel rods inside overheated. Dangerous radiation would spew into the environment.
Now, with one Mark 1 containment vessel damaged at the embattled Fukushima Daiichi nuclear plant and other vessels there under severe strain, the weaknesses of the design — developed in the 1960s by
When the ability to cool a reactor is compromised, the containment vessel is the last line of defense. Typically made of steel and concrete, it is designed to prevent — for a time — melting fuel rods from spewing radiation into the environment if cooling efforts fail.
In some reactors, known as pressurized water reactors, the system is sealed inside a thick steel-and-cement tomb. Most nuclear reactors around the world are of this type.
But the type of containment vessel and pressure suppression system used in the failing reactors at the Fukushima Daiichi plant is physically less robust, and it has long been thought to be more susceptible to failure in an emergency than competing designs. In the United States, 23 reactors at 16 locations use the Mark 1 design, including Pilgrim 1 in Plymouth, Mass.; Vermont Yankee in Vernon, Vt., and the Oyster Creek plant in central New Jersey.
GE began making the Mark 1 boiling-water reactors in the 1960s, marketing them as cheaper and easier to build — in part because they used a comparatively smaller and less expensive containment structure.
US regulators began identifying weaknesses very early on.
In 1972, Stephen Hanauer, then a safety official with the Atomic Energy Commission, recommended that the Mark 1 system be discontinued because it presented unacceptable safety risks. Among the concerns cited was the smaller containment design, which was more susceptible to explosion and rupture from a buildup in hydrogen — a situation that may have unfolded at the Fukushima Daiichi plant.
Later that same year, Joseph Hendrie, who would later become chairman of the Nuclear Regulatory Commission, a successor agency to the atomic commission, said the idea of a ban on such systems was attractive. But the technology had been so widely accepted by the industry and regulatory officials, he said, that “reversal of this hallowed policy, particularly at this time, could well be the end of nuclear power.’’
In an e-mail yesterday, David Lochbaum, director of the Nuclear Safety Program at the Union for Concerned Scientists, said those words seemed ironic now, given the potential global ripples from the Japanese accident.
“Not banning them might be the end of nuclear power,’’ said Lochbaum, a nuclear engineer who spent 17 years working in nuclear facilities, including three that used the GE design.
Questions about the design escalated in the mid-1980s, when Harold Denton, an official with the NRC, asserted that Mark 1 reactors had a 90 percent probability of bursting should the fuel rods overheat and melt in an accident.
Industry officials disputed that assessment, saying the chance of failure was only about 10 percent.
Michael Tetuan, a spokesman for GE’s water and power division, staunchly defended the technology this week, calling it “the industry’s workhorse with a proven track record of safety and reliability for more than 40 years.’’
Tetuan said there are currently 32 Mark 1 boiling-water reactors operating safely. “There has never been a breach of a Mark 1 containment system,’’ he said.
Several utilities and plant operators also threatened to sue GE in the late 1980s after the disclosure of internal company documents dating to 1975 that suggested the containment vessel designs were either insufficiently tested or had flaws that could compromise safety.
The Mark 1 reactors in the United States have undergone modifications since the initial concerns were raised. Among these, according to Lochbaum, were changes to the doughnut-shaped torus — a water-filled vessel encircling the primary containment vessel that is used to reduce pressure in the reactor.