Three Mile Island Unit 2 dry-canal defueling water cleanup system: an update

During the defueling phase of the Three Mile Island Unit 2 (TMI-2) cleanup effort, the reactor vessel (RV) with internals indexing fixture (IIF), the refueling canal, and the spent fuel pool will be partially filled with water to enable the fuel transfer operation to occur safely. This water must be maintained at a Cs-137 concentration of 0.01 to 0.02 μCi/ml and a clarity level of approximately 1 nephelometric turbidity unit (NTU). These criteria were selected to ensure that radiation dose rates to workers one foot above the defueling platform are maintained as low as reasonably achievable (ALARA), and to maintain sufficient water clarity to allow workers to see underwater components in the vessel, refueling canal, and spent fuel pool during the defueling operation. A defueling water cleanup system (DWCS) has been designed to meet these objectives. Two subsystems constitute the DWCS. One subsystem processes water within the vessel/internals indexing fixture (a cylindrical extension of the vessel) with a 400 gallons-per-minute (gpm) design basis flowrate for filtration and a 60 gpm flowrate for ion exchange. The other subsystem processes refueling/spent fuel pool water with a 400 gpm filtration system and a 30 gpm ion-exchange system