TEPCO has stopped monitoring two more thermometers at the crippled Fukushima nuclear plant. In Unit 1, TEPCO admitted that one of the thermometers measuring the reactor vessel temperatures has been found to be inoperable due to a wiring mistake over 10 years old.
The faulty wire connections were made 11 years ago, and during a regular inspection the thermometer was judged to be short-circuited and inoperable. On Thursday TEPCO found that one of the other thermometers was connected to the data recorder (by way of a jumper) instead of the failed thermometer, so the readings taken by the data recorder were actually duplicates.
Tepco is removing this thermometer from the reactor surveillance data, and is inspecting the detailed sequence of events through which this [jumper] connection remained overlooked until now.
On Thursday TEPCO also announced that another temperature gauge at Unit 2 has failed. Currently only 14 of 21 thermometers measuring temperatures of the reactor pressure vessel at Unit 2 remain in service, forcing TEPCO to begin looking for alternate locations to install new thermometers.