Tokyo Electric Power Co. reported a spike in temperature in the No. 2 reactor at the crippled Fukushima No. 1 nuclear power plant on Feb. 5, forcing it to increase the volume of cooling water there as a precautionary step.
Tokyo Electric Power Co. reported a spike in temperature in the No. 2 reactor at the crippled Fukushima No. 1 nuclear power plant on Feb. 5, forcing it to increase the volume of cooling water there as a precautionary step.
TEPCO said cooling water may not have reached part of the fuel in the reactor’s pressure vessel while it switched to different piping for injecting water and changed the volume of water.
According to TEPCO, a thermometer at the bottom of the pressure vessel measured 71.7 degrees as of 4 p.m. Feb. 5, up from 52 degrees on Feb. 1.
However, readings at two other thermometers installed at the same height in the reactor have remained stable at around 45 degrees.
Radiation levels have shown no changes within the Fukushima No. 1 plant.
The amount of cooling water was increased by 1 ton per hour to 9.6 tons, and the temperature fell to 69.4 degrees as of 5 p.m.
In December, the government said the reactors at the Fukushima No. 1 plant, damaged by the Great East Japan Earthquake, achieved cold shutdown, meaning temperatures are maintained below 100 degrees.
However, thermometer readings can sometimes be out by as much as 20 degrees. Therefore, a reading exceeding 80 degrees could mean that conditions for cold shutdown have been compromised.
New safety regulations were introduced at the Fukushima No. 1 plant after it was disabled last March. If the thermometer at the bottom of the pressure vessel shows a temperature reading of 80 degrees or more, or the volume of cooling water is increased by more than 1 ton per hour in a single day, TEPCO is required to notify local governments of such changes.
TEPCO will analyze gas in the reactor within a few days to check whether a chain of nuclear fission has occurred again in the melted fuel.