February 10, 2018
Tokyo Electric Power Company Holdings Inc. plans to use a small unmanned aerial vehicle to closely inspect conditions inside the No. 3 reactor building of the Fukushima No. 1 nuclear power plant as early as this month.
TEPCO will use the drone to examine the location of scattered debris and the level of radiation inside the reactor building, among other things.
It will be the first drone-based research conducted inside the plant’s Nos. 1, 2 and 3 reactor buildings, in which nuclear meltdowns occurred.
The drone, called Riser, was developed by a British company. It measures 83 centimeters by 93 centimeters and weighs about four kilograms.
Riser is equipped with cameras and a dosimeter that can measure up to 2.5 sieverts of radiation per hour.
Even in indoor spaces inaccessible to GPS signals, the drone is capable of determining its position and avoiding obstacles using lasers.
The same model was used for decommissioning work at the Sellafield nuclear facility in Britain.
TEPCO’s plan is for the drone to enter the No. 3 reactor building through a bay for large cargo on the first floor, then fly upward through a series of openings from the first to the fifth floor.
The drone will check areas including the building’s third floor, which has not been sufficiently monitored because radiation levels are too high.
According to TEPCO, key equipment such as that used to cool spent nuclear fuel pools are located on the third floor.
Confirming the location of possible obstacles and the level of radiation is necessary before decommissioning work can progress.
Riser also has a mapping function that enables it to produce three-dimensional graphic images of its surroundings using lasers.
Combining these images with measurements of radiation levels allows for the production of maps outlining contamination levels inside the reactor buildings. TEPCO will consider making this kind of distribution map in the future.
A hydrogen explosion inside the No. 3 reactor building on March 14, 2011, destroyed the building’s upper structures.
Work is currently under way to construct a dome-shaped roof over the building to facilitate the removal of fuel that remains in the spent fuel storage pools.