An analytical study of azimuthal temperature distribution in pressurized water reactor fuel rods under steady-state and blowdown conditions

An analytical study was conducted to quantify the azimuthal temperature variations that might occur around a light water reactor nuclear fuel rod under steady-state and loss-of-coolant accident (LOCA) blowdown conditions. Significant azimuthal temperature variations on the cladding surface will result in a reduction of the total circumferential elongation of the cladding deforming in the alpha phase of the Zircaloy and thus a reduction in coolant channel blockage. Power skewing across the fuel rod and off-center location of the fuel pellet within the cladding are considered as possible causes for an asymmetrical temperature distribution on the cladding. The conclusions reached were as follows. Off-center location of a fuel pellet produces significant azimuthal temperature variations in the fuel during steady-state operation and small circumferential temperature differences in the cladding during the LOCA blowdown. Highly localized small strains-to-failure in Zircaloy out-of-pile ballooning experiments may not be representative of in-pile results where cladding temperatures are calculated to be relatively uniform