TEPCO may use 'shower spray' on troubled reactor

August 05, 2011

By TAKASHI SUGIMOTO / Staff Writer

Tokyo Electric Power Co. is considering changing the method of injecting water into the No. 3 reactor at its hobbled Fukushima No. 1 nuclear power plant as the current system isn't cutting it.

The No. 3 reactor is consuming nearly three times the coolant water that the No. 1 and No. 2 reactors are taking to cool down their fuel rods, as a considerable amount is missing the target.

TEPCO said that the pressure vessels in the No. 1 through No. 3 reactors, where fuel meltdowns have occurred, currently have temperatures at the bottom between about 90 and 120 degrees. In the meantime, the amount of water pumped in daily to maintain the temperatures at these levels is about 216 tons for the No. 3 reactor, as opposed to 84 tons for the No. 2 reactor, which is about the same size and contains roughly the same number of fuel rods, and 91 tons for the No. 1 reactor, which is smaller.

The question is, why is this discrepancy occurring?

TEPCO said that in all three reactors, coolant water is being injected from outside the shroud, a major component covering the core.

Analysis conducted so far has hinted at the possibility that, unlike in the No. 1 and No. 2 reactors, part of the melted fuel in the No. 3 reactor did not fall through to the bottom of the pressure vessel but has stayed on the grid-like core support plate. The current injection method cannot pump water into there, resulting in inefficient cooling and increasing the amount of radioactive water.

The new water injection method under consideration is based on the use of an emergency cooling system called a "core spray." It can pour water down like a shower above the fuel rods, resulting in more efficient cooling and the use of less coolant water, TEPCO said.

Much has been learned about the state of the cooling pipe systems since workers regained access to the reactor buildings.

On Aug. 3, TEPCO conducted tests on the operability of valves along the piping.

"We plan to make decisions in two or three weeks," a TEPCO official said.

By TAKASHI SUGIMOTO / Staff Writer
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