Disassembly and defueling of the TMI-2 [Three Mile Island Unit 2] reactor vessel lower core support assembly

Planning for the disassembly and defueling of the Three Mile Island Unit 2 (TMI-2) reactor lower core support assembly (LCSA) began early in 1985. Evaluations of methods of defueling were performed based on various assumed LCSA conditions. Tooling was conceptualized and various defueling sequences were evaluated. As defueling of the core region progressed, information and data were obtained that clearly showed that a large amount of fuel was located within the LCSA and an even larger amount was located below the LSCA in the lower head of the vessel. It became apparent that it would be impractical to defuel this area of the reactor without massive cutting of the structural steel internal components. A plan was developed to defuel the LCSA by using two techniques: (a) core-boring LCSA components that had a round configuration (support posts and in-core instrument guide tubes) and (b) plasma arc cutting of components, which required linear cutting (plates and forgings). This paper describes the approach to LCSA disassembly, including the design basis of the equipment and sequence of in-vessel operations