Japan Crisis: Possible Change in Nuke Cooling

Tuesday, August 9, 2011 @ 02:08 PM gHale

Tokyo Electric Power Co. (TEPCO) is eying a change in how they will inject water into the No. 3 reactor at the beleaguered Fukushima nuclear power plant as the current system isn’t working very well.

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

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TEPCO said 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 issue is TEPCO really doesn’t know why there is such a large difference between the reactors.

In all three reactors, coolant water is coming from outside the shroud, a major component covering the core, TEPCO officials said.

Analysis conducted so far shows there is a possibility, 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 the 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.

Officials learned quite a bit about 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.

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