Leak Before Break application for Primary Coolant Loop and Surge Line of VVER-1000/320 Plant: TACIS Project R2.09/96

Abstract Activities were carried out within the frame of TACIS-96 Program—Project R2.09/96 named “LBB Applicability Review and Basic Implementation Engineering for Primary Coolant Loop & Surge Line of VVER-1000/320 Nuclear Power Plant”. Main objective of the Project was to perform a Leak Before Break assessment for the Main Coolant Pipes and Pressurizer Surge Line of the Reactor Coolant System of a selected “reference” Unit of a VVER-1000, type V-320 Nuclear Power Plant, which was assumed the Balakovo Unit 2. This has included the following: • definition of a “reference” methodology for primary piping systems with cladding; • verification of the Leak Before Break concept applicability to primary piping, in accordance with the “reference” methodology defined; • preparation of necessary materials data and validation files; • evaluation of effectiveness and reliability of the Leak Detection systems and the In-service Inspection Programs (methodologies and qualification); • preparation of a recommendations list to improve the existing information and diagnostic systems; • transfer of know–how from Consortium to Sub-Contractor, integrating the feedback of Western experience. One of the main highlights of the Project was the definition and execution of a comprehensive Material Testing Program in order to establish the actual tensile and fracture properties of the primary piping materials: base materials, weld metals, and “heat affected zones” were tested. Compact tests and standard specimens for J – R curves determination were used; special attention was paid to the dissimilar typical joints of the Surge Line pipes, being made by carbon steel base metal with stainless steel weld. Fracture properties as J – R curves were determined both at room and operating temperatures. The “reference” methodology defined has taken into account both Western and Russian Leak Before Break approaches. The analysis has shown that criteria for Leak Before Break concept applicability to the primary piping of Balakovo VVER-1000/320 Unit 2, presented in the reference methods developed in the frame of this Project, are met.