Experimental study on LBB behaviour of LMFBR pipe elbows

The concept of leak before break (LBB) has now replaced the traditional design basis of a double ended guillotine break (DEGB) to design the piping systems for new generation of nuclear reactors. The LBB aims at the application of fracture mechanics principle to demonstrate that pipes are, in general, unlikely to experience DEGB without prior indication of leakage due to through the thickness crack. Pipe elbows are the most critical components in any piping system under earthquake loading. Three cyclic load experiments have been conducted on 90° elbows of two different diameters to investigate their fatigue crack growth and leak before break behavior. A detectable leak before break was observed in all the three pipe elbows tested. Details of this experimental study and the results are presented in this paper.