At two reactors, a race to contain meltdowns

By Steven Mufson

Tokyo Electric Power Co. entered Day 4 of its battle against a cascade of failures at its two Fukushima nuclear complexes, using fire pumps to inject tens of thousands of gallons of seawater into two reactors to contain partial meltdowns of ultra-hot fuel rods.

Japanese officials say they believe a hydrogen explosion occurred at the Fukushima Daiichi nuclear plant, similar to an earlier one at a different facility. TV footage shows a wide plume of white smoke shrouding the base of the entire plant.

Government spokesman Yukio Edano said that based on initial reports, the explosion did not damage the container vessel. Radiation level near the plant will go up, as happened with Saturday’s explosion. There are no initial reports of injuries.

Pumping seawater into the plants produced high pressures and vapors that the company vented into its containment structures and then into the air, raising concerns about radioactivity levels in the surrounding area where people have already been evacuated. The utility said that at one of the huge, complicated reactors, a safety relief valve was opened manually to lower the pressure levels in a containment vessel.

But the limited vapor emissions were seen as far less dire than the consequences of failure in the fight against a more far-reaching partial or complete meltdown that would occur if the rods blazed their way through the reactor’s layers of steel and concrete walls.

The potential size of the area affected by radioactive emissions could be large. A state of emergency was declared briefly at another nuclear plant called Onagawa after elevated radioactivity levels were detected there. Later Japanese authorities blamed the measurement on radioactive material that had drifted from the Fukushima plant more than 75 miles away, according to the International Atomic Energy Agency.

The IAEA noted that forecasts said winds would be blowing to the northeast, away from the Japanese coast, over the next three days.

Tokyo Electric said that radioactivity levels both inside the plant and at its nearby monitoring post were higher than normal. The Nuclear Energy Institute, an industry group in the United States, reported that the highest recorded radiation level at the Fukushima Daiichi site was 155.7 millirem at 1:52 p.m. on March 13; radiation levels fell to 4.4 millirem by the evening. The Nuclear Regulatory Commission’s radiation dose limit for the public is 100 millirem per year.

In addition to one worker hospitalized for radiation exposure, two others felt ill during stints in the control rooms of Fukushima Daiichi units 1 and 2.

While Tokyo Electric said it also continued to deal with cooling system failures and high pressures at half a dozen of its 10 reactors in the two Fukushima complexes, fears mounted about the threat posed by the pools of water where years of spent fuel rods are stored.

At the 40-year-old Fukushima Daiichi unit 1, where an explosion Saturday destroyed a building housing the reactor, the spent fuel pool, in accordance with General Electric’s design, are placed above the reactor. Tokyo Electric said that it was trying to figure out how to maintain water levels in the pools, indicating that the normal safety systems there had failed too. Failure to keep adequate water levels in a pool would lead to a catastrophic fire, said nuclear experts, some of whom believe that unit 1’s pool may now be outside.

“That would be like Chernobyl on steroids,” said Arnie Gundersen, a nuclear engineer at Fairewinds Associates Inc. and a member of the public oversight panel for the Vermont Yankee nuclear plant, which is identical to the Fukushima Daiichi unit 1.

Gundersen said the unit 1 pool could have as much as 20 years of spent fuel rods, which are still radioactive.

At Fukushima Daiichi unit 3, Tokyo Electric said the government ordered a halt to the pumping of seawater for a time as pressures and hydrogen levels rose in the containment structure, causing fears of an explosion like the one that destroyed the building around unit 1.

Victor Gilinsky, a former commissioner at the Nuclear Regulatory Commission, said that in order to produce hydrogen, temperatures inside the reactor core had to be well over 2,000 degrees and as high as 4,000 degrees Fahrenheit. He said a substantial amount of fuel had to be exposed at least at some point.

The Fukushima Daiichi unit 3, built by Toshiba, is 37 years old. Last year, the unit began using some reprocessed fuel known as “mox,” a mixture of plutonium oxide and uranium oxide, produced from recycled material from nuclear weapons as part of a program known as “from megatons to megawatts.” Anti-nuclear activists have called mox more unsafe than enriched uranium. If it escapes the reactor, plutonium even in small quantities can have much graver consequences on human health and the local environment for countless years, much longer than other radioactive materials.

Kyodo news agency cited Tokyo Electric as saying that more than three yards of a mox nuclear-fuel rod had been left above the water level, raising concerns that bits of plutonium or its byproducts may already be mixed into vapors or molten material.

The Fukushima Daiichi unit 3, once capable of generating 784 megawatts of power, is substantially bigger than unit 1, which generated about 460 megawatts. As a result, getting temperatures in its reactor core could prove a much tougher task, experts said.

Japanese officials were also trying to figure out whether Friday’s earthquake, or the subsequent high pressures and temperatures in the reactors, had caused other cracks or leaks in reactors in the region. So far officials have not said that they have found any, though they have noted still unexplained losses of water in some reactor vessels.

Though Fukushima Daiichi units 1 and 3 posed the gravest dangers for now, Tokyo Electric said it was still working on its other units. At Fukushima Daiichi unit 2, initially thought to be worst affected by the earthquake, cooling water levels were lower than normal but stable, the company said.

Tokyo Electric also said it had released vapors with some radioactive materials at all four of the reactors at its second Fukushima complex — Fukushima Daini — on March 12. After injecting water into the reactors, the company said that water levels were stable, off-site power restored and shutdowns complete or in progress. Nonetheless, Japan’s Nuclear and Industrial Safety Agency said Monday that Fukushima Daini units 1, 2 and 4 remained in a nuclear state of emergency.

The crisis at the Japanese nuclear reactors began when the earthquake last Friday disabled the power grid that the reactors use to run cooling systems. Backup diesel generators at the seaside plants were later disabled by the tsunami. Backup batteries lasted only a few hours. For a period of time, the Fukushima Daiichi complex is believed to have been completely blacked out. During that time, the cooling systems failed to prevent a steep rise in temperatures in the reactor core.