Study on the fracture toughness of heavy section steel for nuclear reactor pressure vessel

Steel plates used for nuclear reactor pressure vessels are becoming thicker as the vessels increase in size. In order to prevent brittle fracture of the vessels it is necessary to grasp the fracture toughness of heavy section steel plates used for them accurately. The authors conducted 240 mm thick CT and ESSO tests for the first time in Japan, using a 240 mm thick A 533 Gr. B Cl. 1 steel plate. As a result of these tests they could grasp the brittle fracture initiation and propagation arrest characteristics of a heavy section steel plate. They also conducted small-size tests and investigated the relation between the results of the tests and those of the full thickness large tests. The results are briefly as follows: (1) Charpy absorbed energy decreased as the location varied from surface to inside, but it presented almost uniform toughness in a thickness range of 1/4 to 3/4. (2) The critical crack size for brittle fracture initiation in case stress of 14.1 kg/mm2 was loaded at 00C was so large that leakage would occur. On the other hand, the critical crack size for propagation arrest was very smaller than that for initiation. From this fact, it can be said that the steel can be used under ordinary condition in order to prevent brittle fracture initiation but must be used in severer conditions in order to prevent propagation. (3) The data, their number is limitted, showed that the crack propagation arrest fracture toughness was uniform and independent on plate thickness when the thickness of test specimen was more than 75 mm. (auth.)