This work presents the development and testing of some thermal hydraulic models designed to address the limitations of using the Homogeneous Equilibrium Model (HEM) in predicting and simulating the hydraulic response of the positive reactivity-initiated power excursion accidents in small light water reactors. The neutronic response of such accidents has been investigated based on the neutron diffusion method. Most of the power reactors have a code system to analyse such accidents. Unfortunately, the training and research of Budapest University of Technology (BME) has to build its own code system. In this sense, a number of different 3D space–time-dependent neutron diffusion models with thermal hydraulic feedback have been introduced, compared and tested together and with the point-kinetic REMEG model for this purpose. The results show that the fuel parameters are maintained below specified limits during the accident so that fuel failure and release of radioactivity will not occur.
Keywords: hydraulics, critical, accidents, HEM, diffusion, reactivity, point-kinetic