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.