30/03 Balancing act at reactors / Water vital for cooling, but drainage poses new set of problems

The Yomiuri Shimbun

Work to remove radiation-contaminated water from the turbine buildings of reactors at the Fukushima No. 1 nuclear power plant moved into full gear Tuesday, while efforts continued to cool the reactors with water.

Plant operator Tokyo Electric Power Co. earlier confirmed radioactive water that spilled out of the reactors had collected in underground trenches connected to them.

Workers were scrambling to prevent the contaminated water in the trenches from leaking into the sea. For instance, work was continuing around the clock to transfer water from the first basement floor of the No. 1 reactor's turbine building to a condenser.

The condensers at the Nos. 1 and 4 reactors still had room for more water as of Tuesday, but the condensers at the Nos. 2 and 3 reactors were already full to capacity.

At the No. 3 reactor, there were renewed efforts to transfer water in the condenser to a tank outside the building, and then to other tanks.

The top priority at the plant is to cool the reactors, but the dilemma facing workers is that the cooling process produces more contaminated water, which is time-consuming and troublesome to clear.

To minimize the amount of leaking water, water used to cool the reactors must also be kept as small as possible. But if too little cooling water is used, reactor temperatures will rise.

At the No. 2 reactor, water became contaminated with radioactive material during the cooling process, and is believed to have then leaked into the turbine building from the reactor containment vessel.

Late Sunday night, TEPCO reduced the amount of water being injected into the No. 2 reactor, from around 17 tons per hour to 7 tons per hour.

The temperature in the reactor pressure vessel, which had been about 125 C, increased to 148 C by 7 p.m. Monday and 152 C by 2 a.m. Tuesday.

Also at 2 a.m. Tuesday, at the No. 1 reactor, the temperature and pressure inside the pressure vessel were unstable. The amount of cooling water being injected has increased since Monday night in an attempt to suppress the rise in temperature that began Saturday.

As of 6 a.m. Tuesday, the temperature was stable at 323.3 C, slightly lower than it had been four hours earlier.

TEPCO is carefully monitoring conditions to assess whether the temperature had been brought under control.

At the No. 3 reactor, where the condenser is already full, the focus was on removing water from a makeup water tank--an outdoor tank for temporarily storing water from the reactor--and transferring it to empty water-storage tanks for storing water for pressure suppression chambers. These empty tanks, also located outdoors, are situated south of the No. 4 reactor.

Emptying the makeup tank will allow TEPCO to remove water from the condenser in the turbine building, and then transfer contaminated water from inside the building into the condenser.

Chief Cabinet Secretary Yukio Edano said a scenario where nuclear fuel is not being cooled by water has to be prevented by any means.

"A situation where fuel is burning without any water must be avoided. The cooling work should be prioritized," Edano said. He also stressed the importance of using as little water as possible.

(Mar. 30, 2011)