High energy pipe break analysis for a Main Steam Line of a WWER NPP

• Detailed methodological approach on the High Energy Pipe Break (HEPB) analysis for NPP.
• HEPB level 3 analysis on the Main Steam Line of MO3 NPP was provided.
• Reducing the construction or modification cost on the NPP due to a less conservative approach as a level 1 or 2 analysis.
• Innovative LBB approach to treat the through-wall crack on the piping system.

The aim of this study is to show the application of the High Energy Pipe Break (HEPB) methodology to a level 3 analysis, applied to the study of the Main Steam Line (MSL) of a Mochovce (MO) NPP. The analysis highlighted the significant advantage, as compared to a standard level 1 analysis, in the minimization of extra supports and restraints. In the first part of the paper an introduction on the NUREG Standard Review Plan (STRP) and on the ANSI/ANS 58.2 used as a reference in this kind of analysis is provided. In the second part a description of the analyses (coupled mechanical and fluido-dynamic) used to analyze the HEPB is described. Finally an original approach developed at ENEL is presented for an improved evaluation of the leakage cracking by following a non standard procedure related to the LBB approach, coupled with the above-mentioned HEPB.