CANDU reactor channel temperature measurement problems and solutions at the Pickering nuclear generating station

It is a requirement of the CANDU nuclear reactor that many non-penetrating temperature measurements be made of channel inlet and outlet temperatures. This paper discusses two problems associated with the surface measurement of feeder temperatures using resistance temperature detectors (RTDs). The problem of silver migration within an RTD, causing calibration drift and failure, was solved by reducing the excitation voltage on the earlier Pickering units, and using bridge methods on the later units. Error caused by not thermally insulating RTDs was investigated, and it was decided to insulate them individually on the later units