Determination of the allowable range of the relative power coefficient distribution in the VVER1000 for a blockage accident

As we know, accident analysis is one of the most important field in the study and assessment of the nuclear reactor safety performance. Failure occurrence in the heat transfer system (such as LOCA and LOFA) are formed the group of the possible accidents in nuclear reactors. Including these transient states due to failure of the heat transfer system is the flow path blockage accident by crashing and falling some external pieces (knots and so on) into first loop and reactor core which could be decreased the coolant flow in one or more fuel assemblies. In this study the flow path blockage accident at the entrance of a hot fuel assembly in the various relative power distribution coefficient using COBRA-EN and developed program with MATLAB software for the analysis of the blockage in a hot fuel assembly in hollow center fuel rods. Firstly, for evaluating COBRA-EN code and developed program, the VVER-1000 reactor core is modeled and the results are compared for evaluating the accuracy of the modelling using two methods. In the following, the blockage at the various intensities for different relative power distribution coefficients has been modeled. The results have been shown that with considering the other effective neutronic parameters such as PPF and multiplication factor, the fuel assemblies must be arranged until the relative power distribution coefficient are between 1.28±0.57. Therefore the blockage accident in a fuel assembly does not have certain effect on the performance of the reactor.