[en] The concept of leak-before-break (LBB) has now-a-days replaced the traditional design basis event of double ended guillotine break (DEGB) to design the primary heat transport (PHT) piping system of the future generation nuclear reactors. Consequently, the LBB approach is adopted in the design of PHT system of India's future generation 500 MWe nuclear reactors. The LBB approach aims at the application of fracture mechanics principle to demonstrate that pipes are, in general, unlikely to experience DEGB without prior indication of leakage. It shows that a through wall leakage size cracks (LSC) in the pipe is stable under the maximum credible loading condition. This is to be shown for all the piping components, namely, straight pipes, elbows and branch tees in the entire PHT system. The present report details the LBB qualification of the straight pipe portions of the 500 MWe PHT pipe layout. The qualification is done through stability analysis of the pipes with postulated LSC by J-integral-tearing modulus and limit load method. The report has been split into five sections and two appendices. Section 1 describes the general methodology of the LBB analysis. Section 2 describes the evaluation of J-integrals by analytical estimation schemes. Section 3 details the finite element analysis of the pipes with postulated cracks to evaluate J-integral, limit load and crack opening area. Section 4 shows the critical loads evaluated by J-T method. Section 5 demonstrates the LBB qualification of the pipes by showing the necessary factors of safety. Appendix A describes in brief the analytical J-estimation schemes and appendix B compares the two methods to calculate tearing modulus. (author)