APPLICATION OF LEAK-BEFORE-BREAK CONCEPT TO INTEGRITY AND SAFETY OF PWR PRIMARY PIPING WITH WWER-1000

The general methodology and criteria used for the leak-before-break (L BB) concept for the PWR primary circuit with WWER 1000 are described. The application of the LBB concept requires the following additional p rotections. First, the candidate system should be highly qualified pip ing, performed in accordance with the applicable regulations and guide lines, carefully screened to verify that they are not subjected to any disqualifying failure mechanism. Therefore the piping service experie nce and design bases are screened. Next, the analysis of leak-detectio n capabilities is performed. The postulated crack must be of sufficien t size that the resulting leakage will be detected by the leak-detecti on systems installed. Finally, fracture-mechanics analysis is performe d to demonstrate that the crack will not cause pipe rupture even if se ismic loads are applied before the flawed section is discovered and re paired. The calculated and experimental results obtained to date are v ery encouraging and show the applicability of the LBB concept for the PWR primary circuit with WWER 1000.