A Space–Time-Dependent Study of Control Rods Withdrawal in a Large-Size Pressurized Water Reactor

This work focuses on the safety analysis of a typical pressurized water reactor (PWR) for reactivity-initiated transients. These transients result from withdrawal of six sets of groups of control rods that may occur under control systems or other faults. NEA/OECD PWR benchmark is considered for the study. A 3D space–time kinetics code, “TRIKIN” (neutronic and thermal-hydraulics coupled code) is used to account for local changes in the neutron flux. These local changes in the neutron flux affect the total reactivity, local power, and temperature distribution. The safety parameters are the usual 3D radial power distribution, flux tilt, axial heat flux for the peak channel, and radial peak central line temperature profiles over the horizontal plane. These safety parameters studied in the incident progression up to reactor SCRAM level. The minimum departure from the nucleate boiling ratio (MDNBR) has been investigated quantitatively for all six cases. The case that gives maximum drop in MDNBR at SCRAM level is identified and its consequences are discussed. The study is of high importance in revealing the importance of grouping of control rods’ configurations, providing insight in developing strategy for designing the configuration and reactivity worth of groups of control rods and local/global reactor control systems for large-size PWRs.