Thermal and flow behavior of coolant through 19-pin fuel bundle with special emphasis on eccentricity.

Under prolonged working of the nuclear reactor, swelling of the pressure tube (PT) may lead to increases in its diameter and thus generates a little eccentricity with respect to PT. In this study, the effect of eccentricity on the thermal and hydraulic behavior of the coolant through 19-pin nuclear bundle has been numerically carried out. With eccentricity, whole 19-pins of the bundle shifts downwards with respect to pressure tube and disturbs the flow distribution through the different subchannels. For maximum eccentricity, the mass flux in the bottom subchannel decreased by 17.6% and hot streak (maximum temperature) point was also found at 285° on the surface of the rod R3_6. Huge circumferential temperature variation was noticed for bottom fuel rods and has a big concern and might lead to the critical situation, where the integrity of the fuel bundle may fail. Parameters like temperature, velocity, turbulent kinetic energy and heat transfer coefficient have also been studied.