ABSTRACT
The bulk temperature stays below the saturation temperature, but near the top of the core small bubbles start to form in the hotter channels. However, the coolant continues to remain subcooled. Normally, the values of the nuclear hot channel factor differ from the values we calculated earlier due to statistical uncertainties in the values of the core components over which the designer of the core has little or no control. The value of the critical heat flux (CHF) also depends on whether grid spacers or wire wraps are used. In general, the CHF increases for a short distance downstream of a grid spacer or wire wrap. Correlations for the critical heat flux in reactor fuel assemblies have existed since the 1950s. The first correlations to calculate the CHF for pressurized water reactors were developed in the 1950s, and there have been many improvements to these correlations since that time.
