While the world watches anxiously to see if Japan’s nuclear crisis can be brought under control soon enough to prevent larger explosions and the release of intensely radioactive, cancer-causing material across the countryside, a new cloud of doubt stemming from the crisis is already settling over the global energy landscape. It has raised old questions about both the safety of the General Electric Mark 1 boiling water reactors used in the Fukushima plant’s six nuclear reactor units and in similar reactors elsewhere in the world. And it has raised broader questions about the safety and future of the nuclear industry in general.
There is ample reason for concern over GE’s Mark 1 reactors and similar reactors. Twenty-three Mark 1 reactors are used in 16 plants in the United States, including several along the ocean, and there are 17 similar boiling water reactors in the European Union. TVA’s nearby Browns Ferry plant in the north Alabama town of Athens is one of the American plants that uses the Mark 1 system.
Warnings were raised repeatedly by Atomic Energy Commission officials after 1972 about the ability of the Mark 1’s primary containment vessel to resist rupture in the event of a loss of electrical power to the reactor and the resulting overheating of the uranium fuel rods due to a loss of cooling-water circulation, and the likelihood of subsequent explosions. That is precisely the crux of the crisis at reactor units 1, 2 and 3 in Fukushima, where explosions have occurred due to loss of cooling in the primary containment vessel in No. 2, and in the reactor buildings in Nos. 1 and 3.
In addition to the perceived weakness of the boiling water reactor system of Mark 1 type reactors, the reactor building itself is considered the secondary containment system in the event of an overheating crisis and a resulting explosion. In the Fukushima plant, the reactor buildings also contain spent fuel rods, which are stored in separate pools of cooling water adjacent to the reactor itself.
Reactors 4, 5 and 6 had been shut down for maintenance, but the power loss and resulting heat build-up in the spent-fuel pools also led to an explosion which damaged the No. 4 reactor building, and similar damage is believed possible in reactors 5 and 6.
A report by The New York Times published Wednesday noted that an AEC safety official, Stephen H. Hanauer, recommended as early as 1972 that the Mark 1 system be discontinued because its weaker containment vessel in the event of a coolant loss represented an unacceptable safety risk. The preference was for a pressurized water reactor, in which the fuel-rod system is encased in much thicker steel and concrete tomb.
The AEC concerns continued into the 1980s, The Times reported, after Harold Denton, an official with the Nuclear Regulatory Commission asserted there was a 90 percent probability of failure of the reactor in the event of a crisis due to overheating and fuel melt. Industry officials, who liked the cheaper reactors, disputed that contention, saying there was just a 10 percent chance of failure.
With fuel melts causing four damaged reactors or reactor buildings at the Fukushima plant, that dispute bears new scrutiny.
The Japanese crisis raise further questions about the potential, in crisis situations, of explosions in spent fuel stored on site. A report by this paper’s reporter, Pam Sohn, on TVA’s on-site storage of spent fuel is pertinent to this issue. TVA’s Sequoyah plant has 1,094 metric tons of spent fuel — 812 in pool storage inside the plant, and 282 outside the plant in casks. At 2,200 pounds per metric ton, that’s more than 2.4 million pounds of spent fuel lying around, mainly for lack of a national depository for spent fuel.
TVA has 315 metric tons (693,000 pounds) in pool storage inside Watts Bar, and 1,604 metric tons of spent fuel (more than 3.5 million pounds) at Browns Ferry, with 1,405 metric tons inside the plant and 189 tons in casks outside. This is the plant where a reactor was shut down years ago for a long period after an electric fire knocked out power at the plant. The reactor was later rebuilt.
The potential for a nuclear calamity, to be sure, has been managed well over the decades of the use of nuclear power. But there is scant margin for error, and certainly none for complacency. With TVA planning to use a more highly potent form of fuel — mixed oxide fuel, or MOX — by 2018, the safety margin would be even narrower. Japan’s present crisis is ample evidence of the fallacy of assuming that nothing can go wrong.