Post-test analysis by Relap5mod3.3 of VVER-440 bubble condenser tests 01 to 05 performed in BC V-213 facility

A new code assessment activity with a new set of experimental data started within the framework of the EC-EURATOM support to Russia, former Counties of Soviet Union (TACIS Program) and former satellite Countries (PHARE Program). In the present case an experiment analyzed performed at Electrogorsk s research center in Moscow dealing with the interaction between VVER-440 and the containment where a Bubble Condenser is installed. The BC is a tower where open water tanks are installed in around 1 floors. The gas-steam water mixture eventually produced by a Loss of Coolant Accident (LOCA) in other zones of the containment (here called confinement) is forced to pass in each of the tanks at the various floors. In this way the steam is condensed, and the non-gaseous fission products are absorbed by the liquid in the tanks. The confinement is designed at low pressure (i.e. at a pressure much lower than the containment pressure of Western nuclear reactors) and is vented to the environment to prevent a high pressure failure. Issues connected with BC are pressure oscillations (which could induce another confinement failure mechanism) and efficiency in steam condensation, primarily in the presence of gas (i.e. air initially present in the confinement region where LOCA occurs). The experiment showed the capabilities of the system and provided an excellent database to prove the code capabilities. The analysis of five experiments by Relap5 code is discussed in this document (experimental data and code results are compared and discussed)