Enhancement of the Safety Function of WWER-440/V230 NPP Confinement

In the event of a loss-of-coolant, integrity and leak tightness of the confinement is a feature relevant with regard to safety as it is the confinement which acts as the final barrier preventing radioactive releases to the environment. Thus one of essential prerequisites for safety enhancement at the Bohunice V-1 NPP Units 1 and 2 is the confinement leak tightness enhancement and validation of confinement integrity at maximum design pressure. Methods and procedures to meet these objectives have been developed and implemented by VUEZ Levice and include: continuous re-sealing of the confinement, air lock upgrade, functional test of the safety flaps and signaling of their position, installation of fast-acting flaps in the vent system, integrated confinement structural integrity and leakage rate tests proving that leakage rate has been reduced by nearly two orders of magnitude. The confinement capability to preserve its integrity at 100 kPa overpressure has been proved; in preparation is the installation of redundant isolation valves in technological pipelines close to the hermetic boundary, continues the requalification of confinement components. The paper briefly describes the technical aspects of these measures and their contribution to the enhancement of confinement safety function. (author)