Evaluation of critical crack length and fracture toughness of pressure tubes using slit burst test method

Pressure tubes (PTs) in Pressurized Heavy Water Reactors (PHWRs) operate at high temperature and pressure and undergo progressive embrittlement with increasing EFPY of operation due to synergistic effect of neutrons and hydriding. The embrittlement is manifested in reduction of fracture toughness and thereby lowers the magnitude of critical crack length (CCL) of PT. However, to satisfy Leak Before Break (LBB) criterion for assuring safe PT operation during service, CCL needs to be higher than the specified value. The slit burst test (SBT) along with fracture toughness test using CCT specimens need to be carried out to establish the CCL of the irradiated pressure tube