Tepco to try core cooling system (unit #3 shift from feedwater to core spray)

[FBaggins]

The temperature of the reactor core of unit 3 of the damaged Fukushima Daiichi plant is expected to drop significantly with the commissioning of a more efficient cooling system, according to Tokyo Electric Power Company (Tepco). The company said that it plans to put into operation a system for spraying cooling water directly into the core of the reactor. This core spray system - which is positioned above the fuel - would be used in parallel with the feed water system currently in use, which injects water into the bottom of the reactor pressure vessel (RPV). Some six cubic metres per hour of water is currently being injected into the RPV using this system.

Tepco said that operating the core spray system would offer "efficient cooling potential." It said that it had confirmed that the injection valve of the existing system could be operated electrically. The company also said that a gauge would be installed to allow the flow of water through the jet pump to be measured. The core spray system is set to be commissioned on 25 August.

Tepco said that, while the feed water system continues to inject 6m3/h of water into the RPV, the flow of water through the core spray system will be increased incrementally to 3m3/h over the first three days of operation. This total level of water injection - 9m3/h - would then be maintained over two days and the temperature of the RPV monitored. Then, over the next four days, the flow of water through the feed water system would be gradually reduced to 3m3/h, again with the RPV temperature being monitored. After that, both systems would be injecting 3m3/h of water into the reactor, for a total flow of 6m3/h of cooling water.

http://www.world-nuclear-news.org/RS-Tepco_to_try_core_cooling_system-2408115.html

I find this interesting because it should provide some clues re: how much of the core remains in the RPV. The fact that they're trying it implies (IMO) that they think a large percentage of it remains there (rather than at the floor of the primary containment). The text of the article implies that they are even more optomistic than this (with most of the fuel still on the support plate rather than even at the bottom of the RPV).

It may be years before we know by direct evidence.

[dtexdem]

1. For future cooling tasks, do they have a pipe long enough ...

to extend to the center of the earth? ;-)

[SpoonFed]

3. It is all about the temperature differential...

once it is deep enough to come close to matching the temperature inside the molten core of the earth, they will declare it official cool and case closed.

[Steepler0t]

2. They are crazy

They might as well start spraying all over northern Japan and the pacific. Because that's where the core of #3 went, spraying the "fuel" in the RPV? The more correct term (for those who do not speak TEPCO as a first language) is closer to "remnants of melted fuel" or just good old plain corium it a lot more accurate.