Design of annular fuels for a typical VVER-1000 core: Neutronic investigation, pitch optimization and MDNBR calculation

In this work, an internally and externally cooled annular fuel was investigated and adapted to a typical VVER-1000 reactor. In order to achieve this goal, ordinary solid pins as well as annular pins are fully investigated using MNCP5 code to find many neutronics parameters of the core. A comprehensive calculation has been performed on the possible configurations of the annular fuel rods applicable to VVER-1000 type reactors. In due course, many investigations are carried out to make under-moderated core of the annular fuel pins, and then the pitch optimization was performed for each annular case (which are described herein) to obtain the best configuration and dimension. Moreover, using the neutronic calculations for the selected annular cases, power peaking factors of the fuel assemblies and the heat flux of hottest annular fuel rods were determined and based on the results, MDNBR calculation was carried out for these hot annular fuel rods. The calculations showed that annular fuel rods have a sufficient margin available on MDNBR in both inner and outer surfaces relative to solid fuel. As the final result, an annular pin configuration, called annular-8, is proposed based on our fully neutronics investigations together with MDNBR calculation.