Study of Delayed Hydride Cracking In CANDU and RBMK Pressure Tubes

Using Compact tension specimen （CT）, delayed hydride cracking （DHC） tests were implemented to determine cracking velocities in CANDU Zr-2.5Nb pressure tube and RBMK standard pressure tube under constant loading and different temperature and different hydrogen contents. The DHC fracture surface and hydride distribution were observed by SEM. The results of the tests show that crack growth dis-plays stairs shape, probably due to hydrogen accumulating and diffusing at crack tip. The highest DHC velocity is inherent in the CANDU pressure tubes. The DHC velocity in the RBMK pressure tubes is lower by an order and even more. This difference in the DHC velocities owes to different yield strength of CANDU Zr-2.5Nb pressure tube and RBMK standard pressure tube.