The Nuclear and Industrial Safety Agency (NISA) for the first time presented a plan to secure the safety of the reactors at the Fukushima No. 1 nuclear power plant after cold shutdown is achieved.
The Nuclear and Industrial Safety Agency (NISA) for the first time presented a plan to secure the safety of the reactors at the Fukushima No. 1 nuclear power plant after cold shutdown is achieved.
In the plan released by NISA officials on Oct. 3, four major objectives were laid out: limiting and managing the emission of radioactive materials; removing decay heat from the nuclear fuel; preventing criticality in which a nuclear chain reaction continues; and preventing hydrogen explosions.
The agency included 57 measures that must be implemented to achieve those objectives, covering such areas as cooling the reactors and fuel storage pools while maintaining stable operations of purification equipment processing water contaminated with high levels of radiation.
A major reason for the plan is that many current facilities being used to achieve cold shutdown are temporary ones, raising concerns about whether a state of cold shutdown can be continued in a stable manner.
Under the government's road map to settle the Fukushima nuclear accident, the target date for achieving cold shutdown, in which temperatures in the reactors are under 100 degrees and no radioactive materials are being emitted, is next January. That would mark the conclusion of the second step of the road map.
Three additional years are needed between the end of the second step and the start of work to decommission the four reactors at the Fukushima plant, officials said.
Learning a lesson from the nuclear accident triggered by the March 11 Great East Japan Earthquake, the NISA plan calls for at least two different sources of external electric power as well as alternative equipment in the event emergency power sources are lost.
The plan also calls for backup measures to cool the reactors and fuel storage pools.
A recycling cooling system at the Fukushima plant is purifying highly radioactive water and returning it to cool the reactors. However, much of the equipment is temporary and for emergency use, raising doubts about whether the system can continue operating stably if another earthquake or tsunami causes a blackout.
Officials of Tokyo Electric Power Co., the operator of the Fukushima plant, will have to submit a report to NISA by Oct. 17 on how they plan to continue operating the recycling cooling system.
NISA officials will have to verify the safety of the system before determining if a state of cold shutdown has been achieved.
"There will be a need for an appraisal of the TEPCO report that can reassure the public," Goshi Hosono, the state minister in charge of the Fukushima nuclear accident, said at an Oct. 3 news conference.
NISA's plan also includes steps to be taken when removing nuclear fuel from the storage pools as well as installing a temporary fuel storage facility. Such measures are needed because the nuclear fuel rods are believed to have been damaged.
The plan calls for careful work to prevent the spewing of radioactive materials when the fuel rods are removed from the storage pool.