As Susan Schwartz of the Press Enterprise reports from Salem Twp., PA, three senior reactor operators at the Susquehanna nuclear power plant (see NRC file photo, left) have been temporaily suspended, pending retraining:
Three senior reactor operators have been temporarily disqualified after they took a safety system offline before shutting down a reactor at the Susquehanna nuclear plant in May, regulators confirm. A nuclear watchdog believes the operators did it in an effort to avoid shutting down the unit, an expensive move for the plant.
Susquehanna has two reactors, both Fukushima Daiichi sibling designs. Susquehanna Units 1 and 2 are General Electric Mark II boiling water reactors.
The article, which reports the incident took place at Unit 2, quotes Dave Lochbaum of UCS:
But David Lochbaum, nuclear safety project director for the Union of Concerned Scientists, said he suspects the operators disabled the safety system to buy themselves time in the hope of avoiding the shutdown.
If the high pressure coolant injection system is triggered, it can cause the unit to shut down automatically, said Lochbaum. He’s a nuclear engineer who worked 17 years in the industry and also a former reactor technology instructor with the Nuclear Regulatory Commission.
He believes the operators hoped that by delaying the automatic scram, they would give workers time to fix the electrical fault and restore proper cooling and ventilation so the reactor wouldn’t need to be shut down.
But before they took the safety system offline, they didn’t check to make sure nothing was happening that might require it to work.
“They breezed through that step,” he said. “They put the operation of the plant ahead of safety. They took some shortcuts.”
‘Mistakes were made’
That attitude contributed to the accident at Three Mile Island in 1979, he said.
Operators there misdiagnosed a problem with the reactor and shut off the safety systems, explained Lochbaum. If they had left them alone, he says the safety systems as designed would have saved the day.
The Susquehanna Steam Electric Station was nowhere near such dire straits, Lochbaum stressed.
“It’s unfortunate mistakes were made, but the system is pretty robust,” he said. “It would have taken several more miscues before this event would have resulted in meltdown or core damage.”
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 General Electric — could be contributing to the unfolding catastrophe.
A fuel storage pool in the Fukushima plant reactor building. Surrounding this and reactors like it is a containment vessel, the last line of defense if cooling fails.Credit Jiji Press/Agence France-Presse — Getty Images
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 completely 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 Japan’s 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 the Oyster Creek plant in central New Jersey, the Dresden plant near Chicago and the Monticello plant near Minneapolis.
G.E. 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.
American regulators began identifying weaknesses very early on.
In 1972, Stephen H. 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 on Tuesday, 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 Mr. Lochbaum, a nuclear engineer who spent 17 years working in nuclear facilities, including three that used the G.E. design.
Questions about the design escalated in the mid-1980s, when Harold Denton, an official with the Nuclear Regulatory Commission, 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 G.E.’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.”
Mr. Tetuan said there are currently 32 Mark 1 boiling-water reactors operating safely around the globe.
“There has never been a breach of a Mark 1 containment system,” he said.
Several utilities and plant operators also threatened to sue G.E. in the late 1980s after the disclosure of internal company documents dating back to 1975 that suggested that 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 a variety of modifications since the initial concerns were raised. Among these, according to Mr. Lochbaum, were changes to the torus — a water-filled vessel encircling the primary containment vessel that is used to reduce pressure in the reactor. In early iterations, steam rushing from the primary vessel into the torus under high pressure could cause the vessel to jump off the floor.
In the late 1980s, all Mark 1 reactors in the United States were also retrofitted with venting systems to help reduce pressure in an overheating situation.
It is not clear precisely what modifications were made to the Japanese boiling-water reactors now failing, but James Klapproth, the chief nuclear engineer for General Electric Hitachi, said a venting system was in place at the Fukushima plants to help relieve pressure.
The specific role of the G.E. design in the Fukushima crisis is likely to be a matter of debate, and it is possible that any reactor design could succumb to the one-two punch of an earthquake and tsunami like those that occurred last week in Japan.
Although G.E.’s liability would seem limited in Japan — largely because the regulatory system in that country places most liability on the plant operator — the company’s stock fell 31 cents to $19.61 in trading Tuesday.