The evaluation of the bubble condenser containment of VVER-440/213 plants Original Research Article

A number of pressurized water reactors of the VVER-440 type have a containment building which is connected to a bubble condenser unit reducing the design pressure of the entire containment system. The bubble condenser acts as a pressure suppression system by condensation of released steam. Some characteristic features of this system are presented. Refering to experience with the assessement of Western pressure suppression system containments of boiling water reactors (BWRs) the experimental and analytical background of the bubble condenser design has been studied. Several earlier test rigs located in the territory of the former Soviet Union and in other Eastern European countries have been studied and assessed. These test rigs served to prove the thermal efficiency of this arrangement. Characteristic properties of pressures suppression systems of Western BWRs are compared with the properties of bubble condensers and some existing test rigs. An international working group has identified a number of open questions for which neither experimental evidence nor sound analytical predictions exist. Of main interest are the response of bubble condenser structures to oscillatory condensation processes, the simultaneous interaction of a large number of gap-cap units and additionally some unresolved scale-up problems. Based on these findings a supplementary experimental research program has been proposed to answer these open questions. The suitability of existing test rigs and of a new experimental model have been assessed. The results are summarized. In view of the importance of the containment effectiveness for public safety the proposed research work deserves a high priority within a program to assist countries utilizing VVER-440 reactors in confirming an adequate level of reactor safety.