[en] At present there are two NPPs equipped with PWR units in Czech Republic. The Dukovany, NPP is about ten years in operation (four units 440 MW - WWBFL model 213) and Tomelin NPP is under construction (two units 1000 MW - WWER model 320). Both NPPs were built to Soviet design and according to Soviet regulations and standards but most of equipment for primary circuits was supplied by home manufacturers. The objective of the Czech LBB program is to prove the LBB status of the primary piping systems of there NPPs and the LBB concept is a part of strategy to meet western style safety standards. The reason for the Czech LBB project is a lack of some standard safety Facilities too. For both Dukovany and Tomelin NPPs a full LBB analysis should be carried out. The application of LBB to the piping system should be also a cost effective means to avoid installations of pipe whip restraints and jet shields. The Czech regulatory body issued non-mandatory requirement, open-quotes Leak Before Breakclose quotes which is in compliance with national legal documents and which is based on the US NRC Regulatory Procedures and US standards (ASMF CODE, ANSI). The requirement has been published in the document open-quotes Safety of Nuclear Facilitiesclose quotes No 1/1991 as open-quotes Requirements on the Content and Format of Safety Reports and their Supplements close-quote and consist of two parts (1) procedure for obtaining proof of evidence open-quotes Leak Before Breakclose quotes (2) leak detection systems for the pressurized reactor primary circuit. At present some changes concerning both parts of the above document will be introduced. The reasons for this modifications will be presented