Tokai-1

Tokai-1 NPP (GCR) is a graphite-moderated, gas-cooled reactor. Tokai-1 NPP started commercial operation in 1966. However, it has disadvantages from an economic standpoint because the carbon dioxide GCR has a rela­tively low power output for the volume of the reactor. This raises the cost of electricity generation compared with light water reactors. Tokai-1 NPP was finally shut down in 1998 after it was defuelled and all fuel elements were shipped off-site for reprocessing by 2001. The reactor area was stored in a safe condition for 10 years after final shutdown to reduce radioactivity. During safe storage, conventional facilities outside the reactor area are removed to secure a transportation route for dismantling wastes, and also to create space for new waste conditioning facilities. Starting with periph­eral equipment outside the reactor area, Tokai-1 NPP is being demolished in stages. Equipment in the reactor area will be dismantled and removed after being securely stored until radioactivity has decayed to an allowable level. Finally, the site would be able to be re-used for a new NPP. Disman­tling activities initiated in 2001 and during the first five years, conventional facilities, such as the turbine system were removed. Cartridge cooling pond (CCP) water was also drained and the CCP was cleaned up for clearance activities.

Four steam raising units (SRUs) have been removed since 2006. The SRUs are 24.7 m in height, 6.3 m in diameter and within the SRUs are radio­actively contaminated and complicated structures. Jack-down methods and a remote dismantling system were developed for workers’ safety and to minimize the extent of the contaminated areas. The SRUs are removed with the system remotely in turn from bottom while lifting them with large jacks. The system enables cutting and holding not only of the SRU body but also other internal parts of the SRUs. Figure 23.2 shows images of cutting work on the SRU. The jack-down method prevents the need to work in high places and restricts the radiation controlled area to the bottom area of the SRU.

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