TEPCO probes nuclear debris in containment vessel of No.2 reactor

February 13, 2019

Tepco carries out examination of melted Fukushima reactor fuel by remote-controlled probe

https://www.japantimes.co.jp/news/2019/02/13/national/tepco-completes-physical-examination-probe-melted-reactor-fuel/#.XGXAEqBCeos

Kyodo

The operator of the disaster-hit Fukushima No. 1 nuclear power plant said Wednesday it has completed its first attempt to use a remote-controlled probe to manipulate melted fuel accumulating at the bottom of one of the crippled reactors.

During the nearly eight-hour operation, Tokyo Electric Power Company Holdings Inc. inserted the probe that is equipped with a camera, radiation meter and tong-like grips into the primary containment vessel of the No. 2 reactor.

Of the six locations that were surveyed, the probe, which is 30 cm tall and 10 cm wide, successfully lifted several centimeters of deposits at five locations, a Tepco official said at a news conference. The deposits in many of those areas resembled gravel.

But in the remaining area, where deposits resembled clay, the probe could not pick up any of the deposited material, indicating it was relatively solid.

The findings from the operation will provide important information to help in the decommissioning of the Nos. 1 to 3 reactors at the plant that suffered core meltdowns in the nuclear crisis that began in March 2011, according to Tepco.

The No. 2 reactor was in operation when the crisis began and some fuel is believed to have melted through the reactor pressure vessel, a container that is supposed to hold the fuel, and accumulated at the bottom of the outer primary containment vessel.

In the latest examination, Tepco focused on checking the nature of the deposits and did not plan to remove samples. The extraction of samples is expected to be carried out in the second half of the fiscal year starting in April, the plant operator said.

The probe was inserted through a penetration hole that provides access to the primary containment vessel. It is capable of holding an object weighing up to 2 kilograms.

The probe had to be remotely controlled due to the extremely high radiation levels inside the reactor.

If the fuel debris is in an extractable condition, Tepco will have a better chance of removing the deposits. But if it is too hard to pick up, Tepco may have to consider developing tools capable of cutting the debris for removal.

Under the decommissioning road map, Tepco and the central government will decide from which reactor to start removing fuel as well as the method for extraction within fiscal 2019. The actual removal is expected to start in 2021.