Stack Effluent Monitoring for an Operating Four Reactor Unit Candu Nuclear Station

Gaseous effluents from an operating four reactor unit CANDU power station are monitored for radioactive particulates, iodines, noble gases and tritium to ensure compliance with approved derived emission limits. The four types of stack effluent monitors used on each of ten stacks are described. The total stack flow at a four reactor unit station is about 10 times that at a single unit station, hence there is the need for monitors with an order of magnitude greater sensitivity at the four unit stations. This need has been met by optimizing standard measurement techniques for particulate and iodine detection, and by introducing a novel technique for noble gas loss determination that provides several orders of magnitude increased sensitivity over traditional methods of detection. In addition, the use of a simple silica-gel desiccant to extract moisture from the sample stream has proven highly accurate and reliable for tritium monitoring purposes.