Test facility simulation of WWER fuel rods behaviour under initial stage of LB LOCA

The calculation and experimental method has been developed to calculate and to study the possibility of simulating the main parameters at the initial stage of an accident of LB LOCA-type for WWER reactor on the experimental facility. They are velocities and the way of heating of FR claddings, the levels of cladding temperatures, the rate of the external pressure drop and the creation of the natural change of pressure on the claddings at the maximum temperature. Series of experimental tests of FR simulators of WWER was carried out at the initial stage of LB LOCA. They resulted in a potential possibility of the ballooning and the depressurization of maximally heated FRs even on this stage of the accident. The results of these tests allow to study the structural changes of FR materials and to enlarge the knowledge about deformation and possible depressurization of FR claddings. To study more carefully the problems of the ballooning and a possible depressurization at the initial stage of the accident it is necessary to continue the researches and to develop scenarios of this accident for FRs with different energy release levels and to test the initial stage of LB LOCA on the experimental facility and under reactor conditions