Bench Simulation of the Stages of an Anticipated Loss-of-Coolant Accident in a VVÉR Reactor System

A computational-experimental procedure for performing a bench simulation of the first and second stages of an accident are described. Experiments studying the behavior of fuel elements and model fuel assemblies under conditions simulating the first stage of an accident showed, for the first time, that the claddings of the most highly heat-stressed fuel elements bulge out and rupture. Tests performed on model fuel assemblies with 19 and 37 fuel elements with Zr + 1%Nb and E635 alloy cladding under the conditions characteristic for the second stage of an accident showed that the fuel-element cladding becomes deformed in the course of the tests. The claddings of the fuel-element simulators rupture at the heating stage in the temperature range 820–920°C. The blockages of the flow section of the model assemblies with Zr + 1%Nb and E635 alloy claddings were 42 and 70%, respectively.