One of the two remaining thermometers at the bottom of the pressure vessel of reactor No. 2 at the Fukushima power plant is broken, Tokyo Electric Power Co. said Sunday.
The finding follows the discovery of a broken thermometer in the same unit in February and means only 18 of its 36 temperature sensors are working, magnifying concerns about the utility’s long-term ability to monitor the crippled facility.
Tepco said that the sensor’s reading instantaneously jumped 6 degrees to hit 60 around 9 p.m. Saturday.
After checking the equipment, engineers found that the electric resistance of the device had greatly increased and concluded it was broken.
As of 11 a.m. Sunday, the reading of the only operational thermometer at the bottom of the reactor read 46.7 degrees, which is well below the “cold shutdown” threshold of 100 degrees, when water starts boiling and radioactive materials are released.
“We are able to check the temperatures at the vessel’s bottom with the remaining one and assess whether a cold shutdown was being maintained by monitoring all the thermometers, including those at other locations,” a Tepco spokesman said.