Investigation of parameters affecting WWER-type fuel behaviour under transient conditions

The experience gained from the operation of water cooled reactor cores and studies into the problems related to their reliability made it possible to establish that the gravest cause limiting the fuel serviceability is a thermal-mechanical interaction between dioxide fuel and zirconium alloy clad. This problem has long been urgent due to the steady quest for increased burn-up, increased fuel cycle and NPP operation under load follow conditions. The studies established the main regularities of fuel failure due to a fuel-clad interaction involving a simultaneous effect of tensile stresses and aggressive fission products on a clad. In addition to the rate of a power rise and the amount of a power ramp tensile stresses are also affected by the extent of a frictional interaction between fuel pellets and cladding. The paper presents the results of the study into the fuel-cladding friction, as well as the data on the iodine induced embrittlement of a clad used to validate the fuel serviceability. (author). 2 refs, 9 figs