Analysis of processes in nuclear fuel during refueling of WWER reactors at the Kozloduy NPP using the PIN-Micro code

The necessity of modeling the fuel behaviour during the core reloading and accompanying uncertainties are discussed. The results from numerical analysis of thermomechanical processes in fuel rods of WWER-440 (with expended core life) and WWER-1000 (with highest burnup) in the Kozloduy NPP units are reported. The quasi-two-dimensional PIN-micro code based on the GAPCON-THERMAL-2, for steady state and slow transients, has been used. The results from calculations show large thermo-mechanical operational resources for the Kozloduy NPP units: maximal fuel temperature <1000 grad C - 1100 grad C, fission gas release <1-3%, gas pressure <80 bar, which are in the prediction capabilities of the PIN-micro code. 18 fig., 8 ref