Measurements of critical heat flux in CANDU 37-element bundle with a steep variation in radial power profile

An experiment has been performed to obtain dryout power measurements with a 37-element bundle string simulating radial power profiles of high-enriched fuel (which contains slightly higher enrichment than the CANDU fuel and is not the same as the traditional highly enriched uranium) and natural-uranium fuel. The electrically heated bundle string was cooled with Refrigerant-134a and installed vertically inside the test station. Occurrences of CHF were detected using sliding thermocouples installed inside each element. Measurements showed that the dryout power for the high-enriched fuel bundle is lower than that for the natural-uranium fuel bundle by 26%, on average. Similarly, the corresponding critical heat flux (CHF) values for the high-enriched fuel power profile are lower than those for the natural-uranium fuel power profile by about 48%. A correlation previously proposed for the effect of radial power profile on CHF underpredicts considerably the CHF for the high-enriched fuel power profile. The correlation has been revised to improve the prediction accuracy. The revised correlation represents closely the available database. It exhibits a correct asymptotic trend and hence can be extended to bundles with more severe variation in radial power profile than those covered in the current experiment.