Nuclear update: Leak stopped. Why is Japan injecting nitrogen into reactor?

Workers plugged a leak of highly radioactive water into the ocean from Japan's Fukushima Daiichi nuclear power plant Wednesday, even as they tried to prevent another hydrogen explosion in reactor No. 1 by injecting nitrogen gas.

There was a bit of good news Wednesday from the stricken Fukushima Daiichi nuclear plant, as workers managed to plug a crack in a concrete pit which had been leaking highly radioactive water into the ocean.

Does this mean the Pacific is now safe from further contamination by the Fukushima complex? Probably not. For one thing, Tokyo Electric Power Company (TEPCO) workers are not sure if there are more leaks. For another, TEPCO continues to pump water with low levels of radioactivity into the sea, to clear tank space for storage of more dangerous wastewater.

“Right now, just because the leak has stopped, we are not relieved yet,” said Chief Cabinet Secretary Yukio Edano at a press conference Wednesday.

Preventing another hydrogen explosion

Meanwhile, TEPCO was also preparing to inject nitrogen into Fukushima’s reactor No. 1 in an attempt to prevent a hydrogen explosion.

Reactor No. 1 has suffered extensive damage to its fuel rods, with upwards of 70 percent melting, according to TEPCO. Scientists have become increasingly concerned that radiation from the damaged fuel could split water into oxygen and hydrogen. The injection of nitrogen, an inert gas, is intended to displace a potentially combustible oxygen-hydrogen mix.

The move does not mean that the reactor is in “immediate danger” of explosion, said Hidehiko Nishiyama, a spokesman for Japan’s Nuclear and Industrial Safety Agency, on Wednesday.

Seawater radiation levels improving

TEPCO’s success in sealing the water leak from the concrete pit did appear to be making a difference in radiation levels near Fukushima. On Wednesday, a seawater sample taken from about 360 yards offshore contained about 280 times the legal limit of radiation. Previous samples from the same point had contained upwards of 4,000 times the legal radiation level.

TEPCO workers had been sure that the hole they plugged was a major problem. Tracer coloring dropped in the water of the concrete pit had shown up offshore.

The irony of the situation is that while stemming one source of water radioactivity, TEPCO was actively opening the spigot on another. With the approval of Japan’s government, TEPCO is pumping into the ocean about 10,000 tons of water from Fukushima’s radioactive waste treatment plant and 1,500 tons of water from the drain pits of reactors No. 5 and No. 6, according to a report from the International Atomic Energy Agency.

The water being released has about 100 times the legal limit of radiation. Since the legal limit is quite low, the released water would be a health concern for local residents only if they ate seaweed and seafood from the affected area every day for a year, said the IAEA.

Conflicting radiation reports cause confusion

In past weeks, there have been so many reports of different radiation readings in different places from the sea and in the air around Fukushima that many Japanese – and Americans – are confused about whether the surrounding environment is safe.

“At this time, this event has not become a national health disaster for Japan,” said Michael Corradini, chairman of the engineering physics department at the University of Wisconsin in Madison, at a House hearing in Washington on Wednesday.

Airborne radiation doses outside of a 60-kilometer (35-mile) radius from Fukushima now are close to normal, Dr. Corradini testified before the House Energy and Commerce Committee, on behalf of the American Nuclear Society.

However, at the same hearing Dr. Edwin Lyman, senior scientist in the Global Security Program at the Union of Concerned Scientists, said that the Austrian Central Institute for Meteorology has estimated that the Fukushima complex has released 80 percent as much of the long-lived radioactive isotope cesium-137 as was emitted by the devastating Chernobyl nuclear accident.

Yet the amount that has escaped so far is only about one-tenth of the total amount of cesium-137 contained in the three most damaged Fukushima reactor cores, said Dr. Lyman.

“Further damage to the fuel, reactor vessel, and containment could result in far greater releases,” he said.