Design methodology to ensure the structural integrity of the through wall cracked sodium piping system in-service
R. Suresh Kumar , K. Velusamy , P. Puthiyavinayagam , P. Selvara 
 Head Structrual Mechanics Laboratory, Indira Gandhi Centre for Atomic Research, Kalpakkam
 Head Mechanics & Hydraulics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam
 Director, Reactor Design Group, Indira Gandhi Centre for Atomic Research, Kalpakkam
 Director, Fast Reactor Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam
Proceedings of First Structural Integrity Conference and Exhibition (SICE-2016), Bangalore July 4-6, 2016
One of the most desirable safety features of a sodium piping system to be ensured during service condition is the structural integrity during in-service condition. Leak-Before-Break (LBB) is one of the necessary criteria to be respected towards achieving the required level of structural integrity for the pressure retaining the piping system and vessels. It is necessary to ensure the inherent safety capability of providing a clear warning before breakage. The term refers to a demonstration of the system to leak before catastrophic failure. The breakage of the system pressure boundary can cause large sodium leakage. It can lead to rapid disruption and the shutdown of the plant function.
The LBB approach requires application of fracture mechanics methodology to demonstrate that the sodium piping system will ensure detectable leakage and demonstrates that the crack will be stable under the maximum credible loading conditions. The size of this crack should be large enough so that leakage is assured of detection with a margin using the installed leak detection equipment under in-service conditions. This paper discusses the design methodology adapted to Fast Breeder Reactor (FBR) piping system to ensure the structural integrity of a through wall cracked sodium piping system under service conditions. RCCMR A16 & CEGB R6 design methodology is adopted in this paper towards demonstrating the structural integrity of a typical secondary sodium piping system. Failure Assessment Diagram is used for computing the critical crack length. Using the fracture mechanics concepts the crack growth has been computed against fatigue loading. It is demonstrated that the typical 500 NB FBR pipe bend critical crack length is much greater than that the minimum crack length responsible for the detectable leak rate.