Time History of Performance Parameters of WWR-K Reactor during Gradual Replacement of the Water Reflector by a Beryllium One

The water-cooled WWR-K research reactor has been operating since 2016 using low-enrichment uranium fuel. In order to maintain high levels of generated power and reactivity margin sufficient for a 21-day operation cycle, the water-cooled core reflector of neutrons was gradually, depending on the fuel burnup, replaced by a beryllium one in order to prevent decreasing of the reactor performance. A series of calculation studies are performed with a simulation of the core region of the WWR-K reactor using an MCNP transport code including determination of neutron flux density, reactivity, efficiency of the control rods of the control and protection systems, as well as kinetic parameters critical for ensuring safe reactor operation. The calculated curves of the principal performance characteristics of the WWR-K reactor are presented and analyzed in terms of their use in scientific research and their effect on the reactor operation safety.