Stabilisation after Fukushima cooling change

[wtmusic]

Water injection from the dark blue feedwater line was reduced, while the light blue core spray was increased by the same amount


Readings from the three sensors in the reactor vessel bottom head of Fukushima Daiichi 2

"Cooling of Fukushima Daiichi unit 2 has been upset by a change in injection rates, leading to a rise in temperature that Tokyo Electric Power Company (Tepco) is working to gradually correct.

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Two of the three temperature sensors at the bottom of the reactor vessel edged up by about 2ºC. The third, however, rose by around 20ºC to hit 72.2 degrees 5.00am today. Tepco acted to stem this increase by injecting an extra cubic metre of water per hour through the feedwater line, and this stabilised the sensor at about 70ºC. It has since decreased to 68.5ºC, while the other two sensors were at a new low of around 41ºC.

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The majorty of unit 2's core is thought to have melted and slumped to the bottom of the reactor vessel, but its configuration there is unknown. What Tepco's experience indicates is that one portion of the deformed core relies on a certain flow from the feedwater pipe for cooling. While the core spray complements feedwater input and was significant in the push to bring the temperature below 100 degrees C, the two are apparently not interchangeable for one specific area of unit 2's core."

http://www.world-nuclear-news.org/RS_Stabilisation_after_Fukushima_cooling_change_0702121.html

[Yo_Mama]

1. It suggests

That more of the core remains in the reactor vessel than previously believed, and perhaps more of it isn't in the bottom of the reactor, but globbed above.

An interesting sequence.

[FBaggins]

2. I'd say that it's likely that some fuel that was still above the support plates...

...has falled to the bottom of the RPV.

A far cry from the burningdowntothewatertablechinasyndrome!!!!!! that some still cling to.

[Yo_Mama]

5. Possible

Still you'd expect the feedwater injection to work better than the spray in that case. Maybe a breakaway exposed a much more heated surface. Maybe this is a natural evolution and it was due to cool down anyway.

Whatever it was, it was clearly localized.

No matter how I turn this over in my head, I can't make it not end up being good news. Perhaps this is due to my limited understanding.

[wtmusic]

6. It was the result of a change by Tepco

"This stability of unit 2 was disturbed for a few days, however, when Tepco tried to improve cooling further by tuning the rates of water injection. On 2 February, feedwater injection was reduced by two cubic metres per hour and the core spray was stepped up by the same amount."

They've switched back to the old way.

[Fledermaus]

3. But we were told the it was in cold shutdown!?!?!?

[wtmusic]

4. It's the temperature of your morning coffee now

By nuke standards, that's cold.

[AtheistCrusader]

7. It still is. And still was during the temp spike.

These terms have meaning. It helps if you know what they mean.