Power distribution gradients in WWER type cores and fuel failure root causes

Neutron flux non-uniformity and gradients of neutron current resulting in corresponding power (fission rate) distribution changes can represent root causes of the fuel failure. Such situation can be expected in vicinity of some core heterogeneities and construction materials. Since needed data cannot be obtained from nuclear power plant (NPP), results of some benchmark type experiments performed on light water, zero-power research reactor LR-0 were used for investigation of the above phenomenon. Attention was focused on determination of the spatial power distribution changes in fuel assemblies (FAs): ning fuel rods (FRs) with Gd burnable absorber in WWER-440 and WWER-1000 type cores, oring the core blanket and dummy steel assembly simulators on the periphery of the WWER-440 standard and low leakage type cores, resp., oring baffle in WWER-1000 type cores, and oring control rod (CR) in WWER-440 type cores, namely (a) power peak in axial power distribution in periphery FRs of the adjacent FAs near the area between CR fuel part and butt joint to the CR absorbing part and (b) decrease in radial power distribution in FRs near CR absorbing part. rview of relevant experimental results from reactor LR-0 and some information concerning leaking FAs on NPP Temelيn are presented. Obtained data can be used for code validation and subsequently for the fuel failure occurrence investigation.