#Fukushima I Nuke Plant Reactor 2: Another Thermocouple on Pressure Vessel Dies

Another thermocouple goes kaput on the Reactor 2 Pressure Vessel.

From Jiji Tsushin (4/15/2012):

瞬時に６度上昇、異常と判断＝２号機圧力容器温度計で－東電

Reactor 2 Pressure Vessel thermocouple deemed abnormal after jumping 6 degrees Celsius instantly, says TEPCO

　東京電力は１５日、福島第１原発２号機圧力容器下部に設置された温度計が１４日夜、瞬間的に６．１度の上昇を記録したと発表した。上がり方が異常だったため調査したところ、温度計の電流が流れにくくなっており信頼性に疑問が生じたと判断。１５日未明に監視計器からは外すことを決めた。

TEPCO announced on April 15 that one of the thermocouples installed at the bottom of the Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant jumped 6.1 degrees Celsius in an instant on April 14 night. TEPCO investigated, as the rise in temperature was abnormal. The resistance was found to be too high, and on early April 15 TEPCO decided to exclude the thermocouple from the list of instruments that are regularly monitored because there was a doubt on the reliability of the thermocouple.

　東電によると、異常とされた温度計は圧力容器底から高さ約２．９メートルの外壁に設置されており、１４日午後９時ごろ突然、それまでの５３．８度から５９．９度に上昇した。同じ高さにある別の温度計では４５度前後で大きな変化はなかった。

According to TEPCO, the thermocouple in question is installed on the outer wall of the Reactor Pressure Vessel, about 2.9 meters from the bottom of the RPV. At 9PM on April 14, the temperature suddenly jumped from 53.8 degrees Celsius to 59.9 degrees Celsius. The other thermocouple at the same height but at a different position stayed at about 45 degrees Celsius, showing no marked difference.

So, at this location, there will be only one thermocouple monitoring the temperature. Originally there were three, at the measurement location called "vessel wall above bottom head", but the first one, 69H1, died back in February after shooting up above 250 degrees Celsius. Now the second one has died, which must be 69H2, looking at TEPCO's temperature data on Reactor 2:

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Temperature at Reactor 2 RPV Thermocouple (69H1) Slowly Coming Down

It doesn't look like the behavior of a thermocouple that has been broken, but what would I know?

From TEPCO's plant parameter, Reactor 2 RPV temperatures, hourly (latest: 2/15/2012 10AM):



In the meantime, the temperature at the CRD (control rod) Housing has been rising again. Again, instrument failure. (Brown line in the graph. 69H1 is light green.)

From TEPCO's plant parameters, Reactor 2 RPV temperature (2/15/2012):

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