Controlling Rdiation Fields in CANDU Reactors using Chemical Decontamination Technologies

Abstract

Radiation dose to personnel during major maintenance and reactor refurbishment of CANDU reactors can be controlled using chemical decontamination technologies. Technologies that have, and can be applied in CANDU reactors include; sub- and full-system decontaminations of the heat transport system using the CAN-DECON, CAN-DEREM and CAN-DEREM Plus processes; and removal of Sb-122 and Sb-124 from the reactor core using hydrogen peroxide. CAN-DECON is a dilute chemical decontamination process that employs ion-exchange technology to continuously remove dissolved metals and radionuclides and regenerate the components of the CAN-DECON formulation. Qualification of the CAN-DECON process, equipment requirements, process effectiveness, recent process improvements and future directions are discussed. Radioantimony deposited on in-core surfaces can be released into the HTS coolant by air ingress during maintenance. At Gentilly-2, where large amounts of in-core antimony are present, these releases have resulted in increased radiation fields around the reactor, making outage dose planning difficult and contributing significantly to the radiation exposure of maintenance personnel. An antimony removal process developed by KWU for PWR's and adapted to meet CANDU specific conditions, has been successfully applied at Gentilly-2. Optimization of process conditions, and improvements in the in-core antimony removal process are described.