The operator of the crippled Fukushima No. 1 nuclear plant could be forced to reconsider the plant’s decommissioning process after lethal radiation levels equivalent to those of melted nuclear fuel were detected near one of the lids covering a reactor.
The Nuclear Regulation Authority said Sept. 14 that a radiation reading near the surface of the lid of the No. 2 reactor’s containment vessel was 1.2 sieverts per hour, higher than the level previously assumed.
The discovery came on Sept. 9 during a study by the NRA and Tokyo Electric Power Co., the operator of the plant.
When operators work on the decommissioning, the shield plug will be removed to allow for the entry into the containment vessel.
The NRA said a huge amount of radioactive cesium that was released during the meltdown of the No. 2 reactor in March 2011 remained between the uppermost lid and middle lid.
In the Sept. 9 study, workers bored two holes measuring 7 cm deep each on the surface of the uppermost lid to measure radiation doses there by deploying remotely controlled robots.
One radiation reading was 1.2 sieverts per hour at a location 4 cm down from the surface in a hole near the center of the lid.
While it is expected to be a huge challenge to dismantle the lids, TEPCO has yet to decide what to do with them during the decades-long cleanup work.
The NRA also mentioned the possibility that radioactive cesium is also concentrated between the middle lid and the lowermost lid.
But there is no way at the moment to confirm whether that is the case, according to NRA officials.