In this study, the cause of intergranular cracking in baffle former bolts (
BFBs) was estimated from metallurgical and chemical viewpoints based upon t
he experimental data and information published by EdF.
At first, five kinds of possibilities were estimated as the cause of interg
ranular cracking in BFBs. Five possibilities estimated were (1) mechanical
cracking caused by high strain in irradiation hardened austenitic stainless
steels, (2) O-2 SCC due to residual oxygen in the bolt stagnant region, (3
) caustic SCC due to dry and wet phenomenon, (4) low pH SCC due to oxygen c
oncentration cell, and (5) PWSCC due to radiation induced segregation.
In this study each possibility was evaluated by the calculation and some ou
t of pile tests. And also, the cause of the intergranular cracking in BFBs
was estimated by the data of the post-irradiation examinations and basic ou
t of pile tests for Type 316CW and Type 347 stainless steels in the authors
' previous study. From these evaluation, the intergranular cracking in BFBs
seems to be caused by the PWSCC, but not caused by mechanical cracking Oz
SCC, caustic SCC or low pH SCC.