The Tokai NPP decommissioning technique

Tokai power station was closed down in March 1998 and started decommissioning from December 2001 as a pioneer of NPP decommissioning. This article presented current state of Tokai NPP decommissioning technique. As the second stage of decommissioning works, removal works of steam raising unit (four units of heat exchangers) were started from 2006 by jacking down method with decommissioning data accumulated. Each heat exchanger was divided into top head, seven 'tears' of shell and bottom head. Each 'tear' was out and separated into a cylinder, and then divided into two by remote-operated cutting equipment with manipulators for gas cutting and motor disk cutting under monitoring works by fixed and mobile cameras. Divided 'tear' was further cut into center baffle plate, heat transfer tubes and fine pieces of shell. Cutting works would produce radioactive fine particles, which were filtered by temporary ventilation equipment with exhaust fan and filters. Appropriate works using existing technique combined and their rationalization were important at this stage. (T. Tanaka)