Japan nuclear plant’s tortured road to stability
Each time workers at the Fukushima Daiichi nuclear power plant make some headway in their attempts to get the damaged facility under control, a new problem seems to arise. This week, for instance, observers celebrated when electrical power was partially restored. But by Friday, the discovery of highly radioactive water led to fears that radiation was leaking from a damaged reactor core.
This one-step-forward, one-step-back routine could continue for days or even weeks before the situation is fully under control, experts said. But they can already see what it will take to get the plant stable enough to handle unexpected problems in stride.
The key is to reestablish a dependable cooling system capable of keeping the volatile nuclear fuel at safe temperatures inside all six reactors and their adjacent storage pools. Without proper cooling, the fuel heats up and runs the risk of releasing radiation into the environment.
Photos: Japan’s earthquake, tsunami and nuclear crisis
Once workers regain control over cooling, further damage to the plant and its fuel supply would be unlikely, said David Lochbaum, director of the Nuclear Safety Project at the Union of Concerned Scientists. Getting to that point “is more likely days than weeks,” he said Friday.
That means securing a reliable source of electrical power and making sure at least some of the facility’s monitoring and control systems still work — no mean feat at a complex that has been hit by an earthquake, a tsunami, fires and hydrogen-fueled explosions and further troubled by the very emergency cooling measures that warded off a meltdown.
Successful cooling would involve transitioning the reactors into “cold shutdown” — a stable state in which water circulating around the fuel in the core remains below 200 degrees Fahrenheit at normal atmospheric pressure, experts said. Only reactors No. 5 and 6 — which were not in service at the time of the earthquake and did not sustain fuel damage — were in cold shutdown as of Friday.
Engineers would also need to make sure that the spent-fuel ponds remain cool.
Workers cleared a significant hurdle Tuesday night, when they finished connecting new power lines to all of the reactors.
But that was just the beginning. Tokyo Electric Power Co., the plant’s operator, also known as TEPCO, was still working on getting electricity flowing Friday.
And delivering power to the entire site may not be enough to ensure quick recovery of the cooling system, since it probably sustained severe damage from the earthquake and tsunami and their aftermath.
Once the power is back on, TEPCO officials will have a chance to find out which equipment is working properly — and which machines, instruments and controls sustained serious damage, said Michael W. Golay, a professor of nuclear science and engineering at MIT.
With the facility badly scarred, such progress may be slow. Hydrogen explosions from overheating in reactors No. 1, 3 and 4 scattered debris and damaged buildings.
Efforts to avert catastrophe may have added to problems at the plant. With cooling pumps knocked out, TEPCO enlisted firetrucks and truck-mounted concrete pumps to spray seawater in an attempt to keep temperatures down in the reactors and spent-fuel pools.
That’s fine as an emergency measure, said Edward Morse, a professor of nuclear engineering at UC Berkeley. But seawater is corrosive, so using it for cooling could have caused some plumbing or other equipment to fail, or could have weakened the structural support around the reactor core.
What’s more, salt could have built up on the fuel in the reactors, preventing efficient cooling, he said.
TEPCO reported that it began pumping freshwater into reactor No. 1 on Friday afternoon.
Radioactivity at the site has complicated matters too, preventing workers from entering crucial areas, assessing damage and making repairs, Golay said. High levels of radiation forced workers to evacuate the plant Thursday. Two have been taken to the hospital.
But Morse said radiation worries would subside as the fuel decays. “The first day is the hardest, and then the first week, and then the first month,” he said.
Eventually, he suggested, the situation should begin to “spiral” — in a good way. Radiation levels will drop, allowing workers to remain in the plant longer to make repairs. Additional repairs will push radiation levels down further, allowing more people to complete still more repairs, and so on.
But however many days or weeks it takes to get to a stable state, it will be years before conditions at the plant are truly safe.
“This will be a full-time job for at least as many people as ran that plant for at least six months to two years,” Morse said.
At Three Mile Island, workers spent 14 years cleaning up the reactor that suffered a partial meltdown when its cooling system malfunctioned one morning in 1979.
Thomas Kauffman, who was a plant systems operator there at the time, recalled that he and his coworkers knew by nightfall that the moment of critical danger had passed.
“We had our electrical supplies, we had our roads, we had our backup systems functioning,” he said. “It’s quite a different story in Japan.”
