A1.01/00 A PIP - Lot 1 Leak before break

The project is well described by the following 10 technical tasks:

Task 1. "Collection of input data for the LBB analyses; lay out, dimensions, material characteristics, loading conditions, supports characteristics and anchoring, information of main equipment as well as steam- and feed water lines".
Task 2. "Validation of experimental data on fracture mechanics properties of primary circuit material available from previous testing programs in Russia and elsewhere".
Task 3. "Evaluation of thermal ageing of primary piping material".
Task 4. "Definition of methodology for assessing thermal stratification in the SL".
Task 5. "Demonstration of LBB applicability to the MCL and SL".
Task 6. "Piping stress analyses of the MCL and SL".
Task 7. "Verification of support integrity and assessment of seismic stability (SSE) of main components".
Task 8. "Calculation of detectable and critical crack length for MCL and SL according to LBB approach"
Task 9. "Evaluation of need of plant modifications for LBB application"
Task 10. "Evaluation of ISI (In-Service Inspection) and LDS (Leak Detection System) and compatibility with LBB approach".

The objective of the project was to apply the LBB concept (according to US Standard Review Plan 3.6.3 and NUREG 1061.3) to the MCL (Main Coolant Line) and the SL (Surge Line) of Medzamor NPP Unit 2 by determining detectable "leakage crack" and "critical crack" sizes and locations for proper upgrading of the LDS (Leak Detection System).

The collection of input data for LBB was successful except for data on bi-metal weld properties (safe end weld between component; RPV and Pressurizer nozzle and piping). It was suggested that the data will not be needed since the welds are actually a part of the component itself and not the piping. Furthermore the welds are under much stricter ISI than the primary piping welds in general.

Component stability calculations showed that the main components will remain stable with the existing support design in SSE condition (Safety Shutdown Earthquake).

The main results of the project show that the LBB concept cannot be applied at Medzamor unit 2 according to Standard Review Plan 3.6.3. For the MCL the LBB approach could be applied if the LDS capability would be 1,9 l/min (standard requirement is, however 3,8 l/min). For the SL the LBB concept could be applied with the same LDS request, but only for NOC (not for SSE).

At Medzamor unit 2 the existing LDS was not designed for LBB concept. In this project the capacity of the LDS was reviewed. It was concluded that the present LDS is not fulfilling detection requests as to the LBB rules and a considerable upgrading would be needed.

The evaluation of the ISI system at the unit showed that accessibility to inspect some welds is restricted. The ISI system was not either designed for LBB concept requests. It was recommended to use automatic inspection methods in order to improve inspection reliability and follow up traceability. For the SL the ISI intervals should be increased for regions were thermal stratification could occur.