#Fukushima I Nuke Plant Reactor 2: Temperature Gauges Go Haywire

Some of the temperature gauges for the Reactor 2 Suppression Chamber and the Containment Vessel seem to be malfunctioning.

In each case, only one gauge out of several seems to be affected. Cause unknown, according to TEPCO. Countermeasures: closer monitoring of gauges.

From TEPCO's own words in the press handout on November 28 (page 3):

Gas temperature of Suppression Chamber of Unit 2:

・11/26 17:00, read 52.7℃, but at 11:00 pm on the day we confirmed that it read “Overscaled” (digital recorder).

・11/27 5:00, it read 102.6℃. Though the readings were not stable, as there were no significant changes or variations in the temperatures of the same types of 2 thermometers and the pool water in Suppression Chamber, we have been investigating the causes for this event including the possibility of malfunction of the measuring instruments. Later, we inspected the measuring instruments and estimated that the readings were overscaled due to certain impacts on the signal detection line seeing that signal from the temperature detector is not stable. We will keep monitoring readings of this instrument and also monitor the temperature using instruments close to it.

Temperature inside the Primary Containment Vessel (Drywell) of Unit 2 (base line temperature of the air conditioning unit, local cooling equipment):

・11/27 5:00, read 78.2℃

・11/27 6:50, it was confirmed that it read approximately 84 , increasing in a staircase pattern. On the other hand, it was also confirmed that the temperature changes of the bottom of the Reactor Pressure Vessel and the water in the pool of the Suppression Chamber were smaller than that of the inside of the Primary Containment Vessel (Drywell) and that there was no significant change in the temperature. Now we have been decreasing the flow rate of water injection as stated below and therefore it is expected that the temperature inside the Primary Containment Vessel will rise, but, as the line temperature of which rose in a staircase pattern was only one line of the five lines and the rest of the lines did not show the same changes, we have been investigating the causes for this event, including the possibility of malfunction of the measuring instruments.

- At 7:11 pm on November 24, we adjusted the flow rate of water injection from Core Spray
System from approx. 7.2 m3/h to approx. 5.6m3/h (for feed water system, the flow rate is kept
at 2.9 m3/h).
- On November 26 (from 10:18 am to 11:02 am), we adjusted the flow rate from Core Spray
System from approx. 5.5 m3/h to approx. 4.5m3/h (for feed water system, the flow rate is kept
at 3.0 m3/h).

Later we inspected the instrument but got no data indicating malfunction, and the readings after the inspection are not different from those before. Therefore, we estimated that the signal detection line was somehow affected, which raised the temperature indicated. We will keep monitoring this instrument and also monitor the temperature using instruments close to it.

Another instrument malfunctioning apparently occurred in front of Main Anti-Earthquake Building on November 28, necessitating the workers to wear full-face masks. From the same handout (also page 3)

Approx. 14:28 [on November 28], the alarm went off from an indicator installed in front of Main Anti-Earthquake Building to continuously measure airborne radiation dose (continuous dust monitor).
14:38, in response to the alarm, we instructed to put full face masks on at 2:38 pm accordingly.
16:04, we measured the airborne radiation dose in front of Main Anti-Earthquake Building. As the result, we confirmed that it read below detection limit. It was announced that the workers did not have to wear a full face mask as per normal. We are investigating the cause of the alarm.

Some terminal feeling at Fuku-I, where all they could do is to monitor the gauges.

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