Fracture toughness of welded joint for nuclear reactor containment vessels

As the material for nuclear reactor containment vessels, SGV 49 in JIS g 3118 is mostly used, but in the technical standard of MITI, stress relief annealing is required when the thickness of welded parts exceeds 38 mm. When welding is carried out in construction sites, the annealing is difficult, therefore the thickness is limited to less than 38 mm. As the containment vessels for three-loop PWRs, the vessels of high design internal pressure and low height are desirable in view of aseismatic construction, and the use of the material of 45 mm thickness has become necessary. In order to examine the propriety of using SGV 49 plates of 45 mm thickness without stress relieving for reactor containment vessels, it was confirmed that the basic performances of the parent metal and the welded joints satisfy the technical standard and the requirements of ASME Code, Case 1714, and their fracture toughness was investigated. The chemical composition and the mechanical properties of the plates tested, the conditions of making the welded joints, the fracture toughness test of the parent metal and the welded joints and the results of Charpy impact test, weight dropping test, CT test, deep notch test, wide width tensile test of cross welded joints, limit COD, and ESSO test are described. It was proved that the welded parts of SGV 49 up to 45 mm thickness can be used without stress relieving, and the performances of the containment vessels can be sufficiently guaranteed. (Kako, I.)