'MIDICORE' WWER-1000 core periphery power distribution benchmark proposal

The MIDICORE benchmark is a 2D calculation benchmark based on the WWER-1000 reactor core cold state geometry with taking into the account the geometry of explicit radial reflector. The main task of this benchmark is to test the pin by pin power distribution in selected fuel assemblies that are placed mainly at the border of the WWER-1000 core. This is due to an observed phenomenon at calculation of the 'first core loading' (completely composed from TVEL TVSA-T fresh fuel assemblies) at Temelin NPP (WWER-1000 core), where the maximum of fuel pin power was found in a peripheral fuel assemblies in a fuel pin at assembly edge in direction to the core centre. This phenomenon consist not only in position where this maximum occurs, but especially in relatively big difference of fuel pin power value observed when this value was determined by codes based on pin to pin diffusion difference method on one side and by codes based on nodal diffusion method with pin power reconstruction on the other side. Because value of fuel pin power is not directly measured by the core monitoring system, a decision about a proposal of benchmark of this kind has been made. In this contribution we define the MIDICORE benchmark; we present the preliminary reference Monte Carlo calculation results and also preliminary MOBY-DICK macro code calculation results. (Authors)