Officials of Tokyo Electric Power Co., the operator of the crippled Fukushima No. 1 nuclear power plant, are considering a plan to remove spent fuel rods from storage pools at its reactors, sources said.
Officials of Tokyo Electric Power Co., the operator of the crippled Fukushima No. 1 nuclear power plant, are considering a plan to remove spent fuel rods from storage pools at its reactors, sources said.
TEPCO workers began collecting samples of water from a storage pool at the plant on Tuesday to help assess the condition of the spent fuel rods and the feasibility of the plan.
Under normal conditions, spent fuel rods are kept for many years in the storage pools to cool. They are then placed in airtight steel casks for removal.
But TEPCO is having to improvise a method of moving spent fuel rods that may have been severely damaged by explosions at the reactors.
The buildings housing the Fukushima plant's No. 1, No. 3 and No. 4 reactors have all been damaged, leaving storage pools exposed, and equipment normally used in the removal process may also have been knocked out by the explosions.
High levels of radiation are also likely to prove a major obstacle to the removal effort, which sources said TEPCO has been formulating since March.
Water was collected from the No. 4 reactor storage pool on Tuesday to check on the condition of the spent fuel rods. The No. 4 reactor is of particular concern to TEPCO officials.
It was not operating when the Great East Japan Earthquake struck on March 11 because it was being inspected. About 1,300 fuel rods had been moved to its storage pool for that inspection, and that large number of fuel rods means the pool is now the hottest of the storage pools at the plant.
The water from the pool was collected using a special vehicle normally used to spray liquid concrete onto construction projects. A container was attached to the end of a 62-meter arm on the vehicle and was lowered into the storage pool to collect the sample.
Experts will assess the condition of the rods from the radioactive material in the water.
According to internal TEPCO documents outlining the plan to remove the spent fuel rods, metal structures will be constructed around the buildings housing the No. 1, No. 3 and No. 4 reactors and huge cranes will be set up on those frames.
The cranes would be used to lower airtight casks into the storage pools. Once the spent fuel rods were moved into the casks, the cranes would the move the casks outside of the reactor buildings.
The casks could weigh as much as 100 tons, and TEPCO officials are unsure if the cranes will be powerful enough to move them safely. Alternatively, TEPCO officials are considering constructing a temporary storage pool outside of the reactor buildings. The spent fuel rods would be moved to that temporary pool and then placed into the casks.
Sources said TEPCO officials were using the experience of the Three Mile Island nuclear accident in the United States in 1979 as a model. At Three Mile Island, melted fuel rods in the reactor core could not be removed using ordinary procedures and had to be shifted in small batches. Cranes were operated by remote control to reduce exposure to radiation among the workers.
The U.S. company that developed the remote-control technology and handled the processing of fuel rods at Three Mile Island is now part of the Toshiba Corp. group. TEPCO officials are considering drawing on that expertise.
A major difference between the two accidents, however, is that the reactor building at Three Mile Island was not damaged. The wrecked buildings at Fukushima have led to high radiation levels on the plant site.
A TEPCO executive said, "It will be impossible to conduct the work now because of the high radiation levels."
An official with the Nuclear and Industrial Safety Agency said of the plan: "It cannot be carried out unless radiation levels fall to a point that ensures the safety of the workers."
Some TEPCO officials say the removal of the spent fuel rods could take several years.