Fukushima Daiichi : the three phases of dismantling

March 11, 2013

Fukushima plant decommissioning may last until 2051

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201303110084

THE ASAHI SHIMBUN

In a monumental undertaking the likes of which has never been attempted, it could take up to four decades to complete the decommissioning and dismantling of the four damaged reactors at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear power plant.

The entire process will be composed of three phases, according to the road map toward the decommissioning of the No. 1 to No. 4 reactors at the plant announced in December 2011 by the government and TEPCO. Phase 1 will last until the end of 2013, followed by Phase 2, which is likely to continue until around 2021. The third and final phase should conclude sometime between 2041 and 2051.

PHASE 1:

In Phase 1, the cooling water circulation loops will be curtailed step by step while cooling of nuclear fuel is continued. A method of establishing a closed and independent cooling system for each reactor building will be devised. Research and development efforts will be started for removing fuel and disposing of radioactive waste.

In addition to the fuel assemblies inside the reactors, totals of 392-1,533 assembly units are left in the spent fuel storage pools of the four reactor buildings. Full-scale operations to remove spent fuel from the No. 4 reactor will start in November 2013, one month earlier than initially scheduled.

PHASE 2:

In Phase 2, operations to remove fuel assemblies from the spent fuel storage pools of the No. 1 to No. 3 reactors will be launched and completed. The removed fuel assemblies will then be placed in the shared storage pool within the plant, which is relatively less damaged. After nuclear fission and resultant generation of heat have declined to certain levels, the fuel assemblies will be put in dry casks for storage within the compound.

Flooding of the reactors will also be done in Phase 2. Flooding the reactors is important not only for scaling down the cooling water circulation loops but also for the subsequent removal of melted fuel from the reactors. Removal of nuclear fuel must be done in water in order to ensure that radiation is contained and the fuel keeps being cooled. TEPCO tried but failed to flood the reactors immediately after the nuclear disaster broke out on March 11, 2011, following the Great East Japan Earthquake and resulting tsunami. That’s probably because the reactor containment vessels had been damaged, resulting in leakage of water.

Repair of the containment vessels will begin around 2016 so that a closed and independent cooling system can be installed in each of the reactor buildings, which are currently connected with each other with pipes and other equipment.

PHASE 3:

In Phase 3, which will begin around 2021 and last until around 2051, at the latest, the main task will be removal of the melted fuel from the reactors. If the flooding of the reactors to be done in Phase 2 goes as planned, work to remove melted fuel will start around 2021 and be finished for all the reactors around 2031 – 2036. The removed fuel will be stored for a certain period within the plant and then moved to a disposal site.

In the meantime, decontamination and monitoring of radioactive materials will continue in the surrounding sea and within the plant itself. After all the fuel is removed, operations to dismantle the facilities will start. The work will begin with areas, such as the turbine buildings, where levels of radiation are lower. The reactor pressure vessels will be the last to be dismantled. The whole process of dismantling the vessels is expected to require some 15 years.

No decision has yet been made on how the site of the damaged reactor buildings will be used after the facilities are dismantled. Since the land will remain contaminated, the possible options will be quite limited.