From Yomiuri Shinbun (2/13/2012):
TEPCO announced on February 13 that the thermocouple on the bottom of the Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant, which had been showing the rising temperature, exhibited the abnormal temperatures after the inspection in the afternoon on February 13, at one time going overscale over 400 degrees Celsius which is the limit.
TEPCO thinks it is "most certainly broken". The thermocouple had been exposed to high temperature from the core meltdown, and has been in the high humid condition [inside the Reactor 2 Containment Vessel].
TEPCO conducted the test of the electric circuit of the thermocouple from the central control room from 2PM. The electrical resistance was higher than normal, which would result in the temperature indicated by the thermocouple higher [than the actual temperature]. Right after the test, the temperature showed 342 degrees Celsius, and it rose sharply at one time and went overscale.
The thermocouple is a bi-metal sensor to detect temperature. It produces a voltage when it is heated. It is possible that an abnormality occurred in the circuit which caused the voltage to change, resulting in the extreme measurements displayed.
In the press conference yesterday, TEPCO's Matsumoto said it was a copper-constantan thermocouple. Constantan is a copper-nickel alloy.
I was watching the press conference live, and was quite amused that TEPCO's Matsumoto and the junior PR manager were rather put off and irritated at some of the senior journalists who kept asking tough questions. They are not the usual fixture these days at TEPCO's press conferences.
These journalists, unlike the regulars (dwindling number, these days) who are mostly young boys and girls in their 20s and early 30s at most who hunch over their laptops and ask questions from behind the laptop display screen while they type, looked straight into Matsumoto, and ask questions with a pen in hand and a notebook on the desk.
Old fashioned way of journalism, which I thought was refreshingly effective. You have to knock TEPCO's PR people out of their kilter to get an edge and draw answers which TEPCO didn't intend to give.
As I mentioned in my post reporting the press conference, Matsumoto was particularly announced by the 2 questions:
One was posed by a reporter from Yomiuri Shinbun (he's a regular). The reporter asked if the test itself broke the thermocouple. (Bingo...) Matsumoto denied the possibility, saying the test was conducted distantly from the central control room, not at the thermocouple (no way, as it is inside the CV).
The other was posed by an independent journalist who kept asking Matsumoto if TEPCO was consulting the manufacturer of the thermocouple for insight and technical assistance. That really set off Matsumoto, who immediately said TEPCO was fully capable of the maintenance of the thermocouples at the plant. Despite repeated questions, Matsumoto refused to give the name of the manufacturer or whether the representative of the manufacturer was on hand at Fukushima I Nuke Plant.
Never mind that this is not an ordinary maintenance of the thermocouples in a functioning reactor.