Tokai-1 Decommissioning Project: The First Challenge in Japan

Tokai-1 is the oldest and historical commercial Magnox reactor in Japan, which had started commercial operation in 1966. The unit had helped introduction and establishment of the construction and operation technologies regarding nuclear power plant at early stage in Japan by its construction and operating experiences. However, The Japan Atomic Power Company (JAPC), the operator and owner of Tokai-1, decided to cease its operation permanently because of a fulfillment of its mission and economical reason. The unit was finally shut down in March 1998 after about 32 year operation. It took about three years for removal of all spent fuels from the site, and then decommissioning started in 2001. JAPC, always on the forefront of the nation’s nuclear power generation, is now grappling Japan’s first decommissioning of a commercial nuclear power plant, striving to establish effective, advanced decommissioning. The decommissioning for Tokai-1 was scheduled as 20 years project. At the beginning, the reactor was started to be in a static condition for ten years (“safe storage period”). While the reactor had been safely stored, the phased decommissioning works started from non-radioactive or low radioactive equipments toward high radioactive equipments. First five years of the project, JAPC concentrated to drain and clean spent fuel cartridge cooling pond and to remove conventional equipments such as turbine, feed water pump and fuel charge machine as planed and budgeted. From 2006, the project came into new phase. JAPC has been trying to remove four Steam Raising Units (SRUs). The SRUs are huge component (750ton, φ 6.3m, H24.7m) of the Gas Cooling Reactor (GCR) and inside of the SRUs are radioactively contaminated. Major concerns are workers safety and minimizing contamination areas during SRU removal. Therefore, JAPC is developing and introducing Jack-down method and remote control multi-functional dismantling system. This method is to cut and remove the SRUs in turn from the bottom to top remotely while lifting the SRU by a large jack system. The system enables cutting and holding not only the SRU body but also internals. This technology and experiences would be useful for the reactor removal in the near future.