Testing of a Prototype PWR Design Gamma Thermometer for Use as a Local Power Monitor in the Thimble Tube of a Nuclear Reactor

Out-of-pile tests were performed on a 0.185-in. OD gamma thermometer (GT) designed for insertion in existing thimble tubes of W¿ pressurized water reactors (PWR). The experimental measurements were conducted with the GT inserted in a simulated thimble tube. The measurements were performed to examine the effect on the sensitivity, response time, and repeatability of the GT output signal when surrounded by an ai r-and a water-filled thimble tube with random and controlled physical contact between the two units. The results showed that the linearity of the instrument is not affected when operated in an air- or water-filled thimble tube. However, the response time of the GT to a step change in power increased from 9 s to about 30 s for water and dry thimble tube conditions respectively. Results are also presented which show that the sensitivity, mV/W/cm3, of the GT with and without controlled physical contact between the inner surface of the simulated thimble tube and the outer surface of the GT did not vary significantly.