Abstract

A plutonium-contaminated waste incinerator facility (PWIF) was operated from 1983 to 1989 to demonstrate the treatment of combustible plutonium-contaminated wastes from MOX fuel production facilities in Tokai works of the former Power Reactor and Nuclear Fuel Development Corporation (PNC). PWIF has following features: 1) Silicon carbide cakes (approximately 300kg) were filled in the incinerator. 2) The incinerator had the multi-layer structure, and the plutonium-contaminated ashes adhered on the inner surface of the incinerator. 3) The space for dismantling was not maintained sufficiently because the clearances between equipments and walls were very small. It is necessary for decommissioning of PWIF in safety and with rationality to choose optimum dismantling methods and procedures in which these features are considered. Key principles in decommissioning of this facility are 1) Dismantling the main process equipments and gloveboxes in the greenhouses to prevent the scattering of contaminated particles 2) Working with airline suit in the greenhouse to prevent workers from inhaling alpha radioactive nuclides 3) Decreasing the generation of secondary waste. Following methods and procedures were adopted:

• Step I Creating the space for dismantling of equipments;

• Step II Performing the pre-treatment for the dismantling of the incinerator;

• Step III Dismantling the glovebox for throwing the wastes into the incinerator, the glovebox for exchanging the high-temperature filter material, and four small gloveboxes for sampling;

• Step IV Dismantling the incinerator and the upper part of the high-temperature filter;

• Step V Dismantling the lower part of the high-temperature filter and two gloveboxes for extracting the ashes and for the absorbing device for sampling;

• Step VI Dismantling the ventilation process.

It was planned that this facility is dismantled from the beginning of May 2000 to the end of December 2001. An absorbing device for extracting the silicon carbide cakes from the incinerator and a remote-controlled device for decontamination of the inner surface of the incinerator were developed. The pre-treatment work was performed by using these devices successfully. The dose rate and the density of radioactive materials in the incinerator were decreased from 180μSv/hr to 90μSv/hr and from 30 Bq/cm2 to 0.5 Bq/cm2 respectively by the pre-treatment. Dismantling of the gloveboxs was carried out in the greenhouse using popular tools (band saws, disk grinders and etc.). Dismantling the incinerator and the high-temperature filter is being carried out from the beginning of December 2000. The whole dismantling works will be accomplished by the end of December 2001.

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