Contamination Control During 4A-7 Pickering Units 1 and 2 LSFCRP

Abstract

Removal and replacement of the fuel channel assemblies in Pickering Units 1 and 2 was hindered by a source of loose and extremely mobile contamination. Neutron irradiation of the nitrogen annulus gas in these units had created a Carbon-14 deposit over the inner surfaces of the annulus gas system. Various retubing operations; but most notably the rapid induction heating of the east Pressure Tube to End Fitting rolled joints caused the expulsion of Carbon-14 particulate into the fueling machine vaults. To control this contamination spread it was necessary to make some significant changes to the retubing program. Process logic was modified, tooling was redesigned and operating procedures were revised to ensure that adequate control was maintained over the contamination spread. Regular monitoring of Reactor Building contaminaton conditions and pre-set action levels for surface decontamination were instituted to prevent the build up and spread of contamination. Rehabilitation of the reactor building following completion of fuel channel installation included extensive decontamination of the fuelling machine vaults. Most accessible surfaces were cleaned by wiping with detergent soaked mops and rags. Prior to removal from the reactor building, the shield cabinets were thoroughly decontaminated by a high pressure wash down and rinse. Floors and walls were painted to fix residual contamination. An exception to this manual approach to decontamination was made in the case of the feeder cabinet internals. During reactor operation the temperature within the feeder insulation cabinets reaches 250 to 300 degrees C. At these temperatures the carbon material oxidizes rapidly to form carbon dioxide gas. This gaseous product was continuously drawn out of the cabinet containment, and vented into the monitored unit exhaust stack.