Review of the methods used for leak rate measurements for WWER-440/230 confinements and WWER-440/213 containments. A publication of the extrabudgetary programme on the safety of WWER and RBMK nuclear power plants

Program was initiated by IAEA in 1990 with the aim to assist the countries of Central and Eastern Europe and former Soviet Union in evaluating the safety of their first generation WWER-440/230 nuclear power plants. The main objectives were: to identify major design and operational safety issues; to establish international consensus on priorities for safety improvements; and to provide assistance in the review of the competence and and adequacy of safety improvement programs. The scope was extended in 1992 ro include RBMK, WWER-440/312 and WWER-1000 plants in operation and under construction. One of the characteristic features od confinements in WWER-440/213 reactors is their comparatively high leakage rate, ranging from several hundred per cent per day upwards, which is lower than those of WWER-440/230 but in both types of containments the task of leakage rate determination presents complex problems which do not appear in western type units. This report contains the requirements for containment leak rate testing and for integral test in the countries operating WWER reactors and comparison with the requirements in force in USA, Germany and France. It describes the leak rate testing principles and leak rate extrapolation methods, discusses in detail the differences in leakage rate definitions due to significant leakages in WWER containments and explains their consequences. The procedures for structural integrity tests of WWER-440 containments are described and recommendations given