Present state and subjects of defect evaluation method in light water reactor machinery and equipment

Accompanying the progress of inspection technologies, small defects became to be detected, and it is irrational to remove such small defects or to replace the parts having such small defects if such defects do not immediately cause the breakdown of the parts. Therefore, the technology for assessing detected defects becomes necessary. The standard in which the procedure of this assessment is best systematized is the ASME Boiler and Pressure Vessel Code, Section XI. The defect assessment according to the ASME Sec. XI is carried out by the procedure of the determination of the shapes and dimensions of defects, the judgement of whether the standard for permission is satisfied or not, and the countermeasures to the defects that do not satisfy the standard, such as the defect assessment by fracture mechanics analysis and repair. These procedures are described in detail. As the individual technical subjects in the assessment method, for example, the conditions of interference and combination of plural defects, the law of crack development in environment, the accuracy of stress intensity factor, the revision of Z coefficient and the method of taking safety factor are conceivable. The accuracy of the shapes and dimensions of defects, and the accuracy and easiness of use of the analytical assessment are the more important subjects. (K.I.)