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Increased water injection cooling No 1 reactor faster

world Updated: Apr 29, 2011 15:01 IST

The operator of the crippled Fukushima Daiichi nuclear plant said that the injection of more water is helping to cool the No 1 reactor core faster and there appears to be no major leakage so far from the No 4 unit's spent fuel storage pool.

To reduce the radiation exposure of engineers working at the plant and improve the efficiency of restoration work, Tokyo Electric Power Co also revealed a plan to introduce new types of remote-controlled robots, including a Japanese-made one, to gauge radiation levels at the site.

"Remote-controlled technologies are contributing significantly to resolving the accident... We would like to continue using this kind of technology," Goshi Hosono, special adviser to Prime Minister Naoto Kan on the ongoing crisis at the plant, told a joint press conference with the utility and government officials, Friday.

The utility known as Tepco is aiming to restore stable cooling of the reactors and spent fuel pools of the Nos 1 to 4 units in about three months. It raised the amount of water Wednesday injected into the No 1 reactor from 6 tons per hour to 10 tons as a temporary measure.

Tepco official Junichi Matsumoto told the press conference, "We think the water injection must be having an effect as the temperature of the primary container and pressure vessel is falling faster."

But he and the government's nuclear agency said pressure inside the primary container must not be allowed to drop too much, which happens as the container cools, to avoid oxygen entering the container, which could increase the risk of a hydrogen explosion.

Reactor fuel is placed inside a pressure vessel, which is contained in a round-bottom, flask-shaped primary containment vessel. Each reactor building houses the vessels as well as a spent nuclear fuel tank.

Matsumoto dismissed concerns that there could be a serious leak in the No 4 unit's spent fuel pool, citing data taken from the latest examination.

The No 4 reactor, halted for regular checks prior to last month's quake and tsunami disaster, had all of its spent fuel rods and unused fuel rods stored in the pool for the maintenance work.

He said new types of robots are being prepared to work at the plant, in addition to a pair of remote-controlled robots called PackBot from iRobot Corp of the United States, which have entered the plant's reactor buildings to check radiation levels and take photographs of rubble.

As for Quince, Matsumoto said it is capable of operating in places where rubble is scattered and can climb wet and slippery steps, but it has to be checked to see if it can cope with a situation in which a system failure occurs due to the high radiation levels at the plant.