Leak-before-break qualification of primary heat transport piping of 500 MWe Tarapur atomic power plant

The advent of Leak-Before-Break (LBB) concept has now replaced the traditio nal design basis event of the Double-Ended-Guillotine-Break (DEGB) to desig n the Primary Heat Transport (PHT) system piping of the Pressurised Heavy W ater Reactor (PHWR) and Pressurised Water Reactor (PWR). This approach is b eing adopted to design the PHT system piping of 500 MWe Indian PHWR to be b uilt at Tarapur (Tarapur Atomic Power Plant 3 and 4). The LBB concept basic ally demonstrates through fracture mechanics analysis that there is negligi ble chance of any catastrophic break of PHT pipes without prior indication of leakage. There are several steps in this work of LBB qualification, name ly, evaluation of loads on the piping components, generation of tensile and fracture properties of PHT pipe base and weld material, determination of l eakage size crack (LSC) and the elastic-plastic fracture mechanics (EPFM) a nd limit load analysis of the piping components with postulated LSC to eval uate the critical load at unstable ductile tearing and the limit load, resp ectively. The paper deals with the fracture analysis of the straight pipes and elbows of three pipe lines in the PHT system of TAPP 3 and 4. Three cra ck configurations are considered in the analysis. These are throughwall cir cumferential crack at the weld location of straight pipe and extrados of th e elbow and throughwall axial crack at the elbow crown. In all the cases, n ecessary factor of safety with respect to the anticipated safe shutdown ear thquake (SSE) load and LSC are shown to be more than the minimum required v alues for LBB qualification. (C) 1999 Elsevier Science Ltd. All rights rese rved.