Research programme on critical heat fluxes in WWER fuel element bundles

The basic thermohydrodynamic problems are discussed to be experimentally resolved in justifying heat engineering reliability of active zones in WWER reactors operating under stationary conditions. The essential research trends in solving those problems are as follows: investigation of thermohydrodynamic conditions and their influence on development of critical heat transfer in cores; studies of conditions of coolant flows and mechanism of critical heat transfer in bundles along with investigations of critical heat transfer in pipes; applied studies on bundles having the geometry of WWER assemblies with a view to elucidating the effects of the following factors on the conditions that actuate critical heat transfer: coolant regime parameters; non-uniformities in heat emission over bundle cross-section and length; bundle length, number of rods, location pitch and design of spacing devices, including devices for mixing the coolant; non-heated and cooled casing wall and individual non-heated elements in assembly and casing perforation; study of temperature conditions of heat-transmitting wall in transcritical range and determination of permissible boundaries in that range, including those related to parameters of emergency decompression of the first loop; study of nonstationary effect of coolant and energy release regime parameters upon critical heat flow values. The emphasis is laid on the necessity of organizing a joint coordinating agency within the framework of the Council for Mutual Economic Assistance to initiate relevant studies