JAPAN NEWS_Japan tightens rules for nuclear plant backups

Japan tightens rules for nuclear plant backups By Matt Smith, CNN April 9, 2011 -- Updated 0847 GMT (1647 HKT)


Tougher contingency plans have been ordered for Japanese nuclear power stations in light of the Fukushima Daiichi disaster

Tokyo (CNN) -- Japanese regulators issued tougher standards for emergency power at nuclear plants Saturday in response to the 4-week-old crisis at the Fukushima Daiichi power station.

Power stations will be required to have two diesel generators as backup power for each reactor unit, said Hidehiko Nishiyama, the chief spokesman for Japan's Nuclear and Industrial Safety Agency. Current regulations require only one generator per unit.

The move comes as workers for the Tokyo Electric Power Company kept up the battle to cool down three damaged reactors at Fukushima Daiichi, on the Pacific coast about 240 kilometers (150 miles) north of Tokyo. The plant's coolant and backup power systems were knocked out by the March 11 earthquake and tsunami that devastated northern Japan, leaving engineers scrambling to avert a bigger disaster.

The No. 2 reactor is believed to be leaking highly radioactive water, some of which had been leaking into the Pacific until Wednesday. Now officials are keeping a close eye on water levels inside the basement of the reactor's turbine plant, and Tokyo Electric reported Saturday that water levels were rising in the steam condenser of reactor No. 3 as well. The source of the water remained unknown Saturday afternoon.

Workers are pouring hundreds of tons of water a day into the reactors in an effort to keep them cool and have been adding nitrogen into the primary containment shell around reactor No. 1, a move aimed at countering a buildup of flammable hydrogen in the unit. The non-flammable nitrogen displaces oxygen that could fuel an explosion like the hydrogen blast that blew apart the buildings surrounding units 1 and 3 in the days following the earthquake.

Hydrogen buildup is a symptom of overheated fuel rods in the cores of the reactors, which plant workers have been struggling to keep under control since the earthquake and tsunami. The nitrogen injections are aimed at displacing oxygen in the reactor shell, reducing the possibility of an explosion -- a chance the plant's owner, the Tokyo Electric Power Company, called "extremely low."

New equipment allowed engineers to raise the concentration of nitrogen from 98 percent to 99 percent Saturday, Nishiyama said.

Workers returned to the plant Friday following a magnitude 7.1 aftershock late Thursday night that forced them to evacuate for about eight hours, Japanese authorities said. The aftershock is not believed to have inflicted any further damage to the plant, Tokyo Electric and the Nuclear and Industrial Safety Agency reported Friday.