Evaluation of Effect of Temperature Variation on Pressure Tube to Calandria Tube Gap Measurements

Abstract

Eddy current (EC) based pressure tube (PT) to calandria tube (CT) gap measurement in the fuel channels of CANDU reactors relies on calibration under nominal temperature conditions, but in-reactor measurements may be performed at temperatures up to 50°C. The effects of temperature variation on PT to CT gap measurement were investigated using a semi-analytical model and laboratory measured temperature coefficients for resistivity of the PT and resistance of the EC coils. Modeled gap responses showed an increased sensitivity to changes in gap with increasing temperature, the result of increasing PT resistivity, which would provide a conservative estimate of gap.