Conditions Contributing to Radiation-Induced Thermocouple Decalibration

Chromel/Alumel thermocouples were calibrated at the temperatures of boiling water and melting tin and lead before, during, and after exposure to several cycles of nuclear radiation. A temporary calibration shift of up to 50 µ V was observed at all three calibrating temperatures persisting for at least one hour following cessation of exposure. Comparison with corresponding data from a previous experiment indicates that the relative location of flux and temperature gradients along the thermocouple leads has a major influence on the magnitude of decalibration encountered. The effect is attributed to radiation-produced scattering centers subject to self-annealing processes. For in-pile thermocouple installations, temperature gradients should be restricted to locations outside high-flux regions to minimize potential radiation-dependent, decalibrating effects.