Some spent rods from No. 4 reactor tainted

TOKYO, April 13 (UPI) -- The operator of the crippled nuclear power plant in northeastern Japan confirmed some of the spent nuclear fuel rods stored in the No. 4 reactor were damaged.

Tokyo Electric Power Co., operator of the Fukushima Daiichi nuclear power plant also said Wednesday most of the spent rods should be sound, Kyodo News reported. The utility has estimated 25 percent to 70 percent of the nuclear fuel rods in the Nos. 1, 2 and 3 reactors have been damaged.

Tokyo Electric said a water sample taken Tuesday from the No. 4 unit's spent nuclear fuel pool indicated damage to some fuel rods for the first time, detecting higher-than-normal levels of radioactive iodine-131, cesium-134 and cesium-137.

The roof and the upper walls of the No. 4 reactor building were blown off by a hydrogen explosion and damaged by fires since the plant was damaged by the March 11 9-magnitude earthquake and tsunami. Officials said they think the water level in the reactor's spent fuel pool temporarily dropped.

Also Wednesday, the government's nuclear regulatory agency ordered TEPCO to check the earthquake resistance of reactor buildings at the Fukushima plant and consider reinforcing the buildings if they weren't determined to be sufficiently quakeproof.

Besides the No. 4 unit, the Nos. 1 and 3 reactor buildings were severely damaged by hydrogen explosions as the crisis first unfolded.

"As strong aftershocks occur almost daily, we have to consider what will happen to buildings already damaged by blasts," said Hidehiko Nishiyama, a spokesman for the nuclear agency.

Early Wednesday a 5.8-magnitude quake jolted Ibaraki prefecture and its vicinity but no tsunami warning was issued, Kyodo News reported. There were no immediate reports of damage.

Yoko Komiyama, senior vice minister of health, labor and welfare, told lawmakers Wednesday 22 workers at the plant were exposed to radiation exceeding 100 millisieverts as of midnight Tuesday. Normally, exposure to 100 millisieverts is the legal limit for nuclear plant workers during an emergency, but the upper limit was raised to 250 millisieverts for the crisis, Kyodo News said.

Also Wednesday, TEPCO workers were removing highly radioactive water in the plant, pumping it from an underground trench to a nearby storage area inside the No. 2 reactor building. Officials said they planned to transfer 700 tons of polluted water by Thursday.

About 60,000 tons of the contaminated water have collected in the basements of the reactors. Some has been leaking into the Pacific Ocean, raising concerns about contamination of seafood but that leak has since been sealed.

Japanese Prime Minister Naoto Kan said Tuesday the situation at the troubled reactors was "improving step by step" with falling levels in the release of radioactive particles, while other officials said much of the emissions occurred immediately after March 11, which also caused hydrogen explosions, Kyodo reported.

In other developments, the Japanese government Wednesday announced a ban on shipments of shiitake mushrooms grown outdoors in some areas near the crippled nuclear plant because of radioactivity, Kyodo News reported.

The ban includes mushrooms grown in five cities, eight towns and three villages in Fukushima prefecture, Chief Cabinet Secretary Yukio Edano told reporters. Mushrooms grown indoors in the prefecture are safe.

Also on Wednesday, the government, citing the impact from the "Great East Japan Earthquake," downgraded its assessment of the economy. Earlier the International Monetary Fund cut its 2011 growth forecast for Japan to 1.4 percent from its 1.6 percent forecast in January.