Fugen

Fugen NPP (ATR, 165 MWe) is a heavy water-moderated, boiling light water-cooled, pressure tube-type reactor. Fugen NPP began operating in March 1979, finally shut down in March 2003, and its decommissioning plan was approved in February 2008. Fugen NPP dismantling was separated into the following four periods.

1. Spent fuel transfer period. SF will be transported to Tokai reprocessing plant, and heavy water will be transported to Canada for re-use at

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Tier transfer Secondary cutting

23.2 Cutting working images of the SRU.

CANDU reactors. Less contaminated equipment such as turbines will be dismantled, while some related systems for SF storage remain operational.

2. Peripheral facilities dismantling period. After SF transportation is com­plete, the related SF storage systems are dismantled and the peripheral reactor equipment will be dismantled to enable installation of remotely operated dismantling machines.

3. Reactor core dismantling period. The reactor core by dismantled by remote operation underwater, and it is expected that the exposure dose in the dismantling activities will be minimized to the equivalent dose of an annual inspection during the plant operation. In this period, both dismantling of all contaminated equipment and decontami­nation of buildings will be carried out to release the radiation-controlled area.

4. Building demolition period. In this period, both released buildings and non-contaminated buildings will be demolished by conventional methods.

After the approval of the programme, decommissioning was initiated. SF has been transferred to the Tokai reprocessing plant, and heavy water has been transported to Canada. Dismantling of the turbine facility was started in parallel. Two of five feedwater heaters and main steam lines were dis­mantled. Experience of cutting technologies and relevant data such as total manpower have been accumulated for future work.

The reactor core of Fugen NPP has a complicated configuration arising from its pressure tube-type structure. The pressure tube and the calandria tube are made of zirconium alloy which can be combustible in powder form. Also, they have been highly activated during operation. It is thus planned to dismantle the core structure underwater for shielding radiation, to prevent airborne dust and for fireproof cutting.

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