Japan's Nuclear Crisis: Regulators Warned of Reactor Risks

Government regulators knew of a heightened risk of explosion in the type of nuclear reactors used at the Fukushima plant in Japan from the moment they went into operation.

Safety inspectors at America's Atomic Energy Commission (AEC) warned as early as 1972 that the General Electric reactors, which did away with the traditional large containment domes, were more vulnerable to explosion and more vulnerable to the release of radiation if a meltdown occurred.

Michael Mariotte, director of the Nuclear Information and Resource Service, said: "The concern has been there all along that this containment building was not strong enough and the pressure containment system was not robust enough to prevent an explosion."

The ageing GE reactors are regarded as less resilient then newer models. Dr Arjun Makhijani, president of the Institute for Energy and Environment Research, said: "They are not designed to contain these explosions. They are not designed to contain an aircraft crashing into it. Modern reactors are significantly different. Designs built from the 1980s onwards don't have the vulnerabilities of mark one reactors."

All six of the reactors at the Fukushima Two plant, which has suffered two explosions, are GE-designed boiling water reactors. Five are the original mark one design and went on line from 1971 to 1979.

Mariotte's group has made public a 1972 letter from an AEC inspector, Stephen Hanauer, recommending the design be discontinued.

Environmental campaign groups say that the boiling water reactors are more vulnerable to explosion because human intervention is needed to vent radioactive steam in the event of a core meltdown.

They are also now reaching the end of their operational life.

Mariotte said damage to the containment structures in the explosion raised an additional risk of a radiation leak from the spent fuel pools, a part of the facility where spent fuel rods are stored under liquid. Like the reactor cores, the pools require constant cooling.

Robert Alvarez, a senior policy expert at the institute of Policy Studies, said satellite pictures of the Fukushima plant showed evidence of damage to the spent fuel pool. "There is clear evidence that the fuel cask cranes that haul spent fuels to and from the reactor to the pool both fell. They are gone," he said. "There appears to be copious amounts of steam pouring of the area where the pools is located."

He said there was no evidence of fire but described the situation as "worrisome".

"What we don't know is whether or not explosions or the quake or the tsuanmi or a combination of things might have damaged support structures or compromised the pool," Alvarez said.

He warned that it could take years to repair the damage to the upper decks of the reactor and to move the discharged fuel into a safer area of storage.

The early warning about the reactor design was reinforced in 1986 when Harold Denton, then the top safety official at the Nuclear Regulatory Commission (NRC), warned of a high risk of failure of the mark one containment system.

"Mark one containment, especially being smaller with lower design pressure, in spite of the suppression pool... you'll find something like a 90% probability of that containment failing," he told an industry trade group at the time.

"Any reactor in this situation would be in a world of hurt. These designs are even more problematic because should you get core melt according to the nuclear regulatory commission the containment is 90% likely to fail," said Jim Riccio, a nuclear expert at Greenpeace. "In essence, the public's last line of defence in case of a meltdown really doesn't exist at all."

Mariotte said damage to the containment structures in the explosion raised an additional risk of a radiation leak from the spent fuel pools, which are sited above each reactor.

There is growing concern about the status of irradiated fuel pools at all of the Fukushima reactors. The pools are located inside the outer containment building above the core and, like the reactor cores, require constant cooling. Pictures from the site show that at least the top third of two containment buildings have been blown off, so the integrity of the fuel pools is unclear.

Japanese campaign groups have also warned of problems at the Fukushima 2 plant including a failure of the generator when the plant lost power in June last year.

In addition to the Fukushima 2 plant, eight reactors of the same design are in use in Japan at nuclear facilities at Tsuruga, Hamaoke and Shimane. Like the Fukushima plants, all three are also on Japan's main Honshu island.

Nuclear reactors of the same design are in widespread use in America.Of the 104 reactors currently in use, 23 are of the same GE mark two design, according to the US Nuclear Regulatory Commission. Twelve more are a modified version of the boiling water reactor.

A number of those reactors are now reaching the end of their original 40-year lifsepan, and campaigners have been fighting attempts by the nuclear industry to extend their operation. One such GE mark one plant in contention is the Vermont Yankee. The NRC renewed the plant's lease for 20 years last week. However, the state government has moved to shut down the plant.