Application of UT Qualification Results for VVER 440 Type RPV Structural Integrity Assessment and Improvement of ISI Programme
L. Horácek, Nuclear Research Institute, Czech Republic
ABSTRACT
Results of RPV in-service inspections are regularly used as input data for VVER 440 type RPV structural integrity assessment. Among RPV in-service inspections mechanised UT and ET examinations of VVER 440 RPV shell welds, cladding and base metal performed from RPV outer and inner surfaces, mechanised inspections of VVER 440 RPV nozzle inner radii and dissimilar safe-end welds are regarded as very important. To achieve sufficiently reliable NDT results the qualification of NDT systems consisting of qualifications of inspection procedures, applied equipment and additional personnel qualification are conducted for Dukovany NPP in the Czech Republic. The required test assemblies with intended defects for laboratory examinations, optimisation of inspection procedures and practical open trials were manufactured within the Phare project PH 4.1.2/93, completed in August 1997. The test assemblies are briefly described with emphasis on their application during Czech national NDT qualification projects and in relation to the improvement possibility of the VVER 440 RPV structural integrity assessment. The project PH 4.1.2/93 was focused what concerns VVER 440 RPV inspection areas on the design and fabrication of the test assemblies representing VVER 440 RPV safe-end weld, VVER 440 RPV nozzle inner radius. The only one missing test assembly covering VVER 440 RPV shell welds, cladding and base metal, completed within a national project in December 2000, is described with advantages received from the application of the mixture of pulse echo and TOFD techniques for defect detection and sizing. The test assembly, manufactured by original technology using only original materials with more than twenty intended defects, is suitable for the qualification of mechanised UT inspections of VVER 440 RPV shell welds, cladding and base metal performed from RPV outer and inner surfaces. Expected VVER 440 RPV in-service inspection programme changes are described in the paper in relation to the NDT qualification results and with their practical impact on the RPV structural integrity assessment. As a practical output of the integrated structural integrity and NDT qualification approach the ISI interval for mechanised UT VVER 440 RPV examinations performed from inner surface was recommended to be prolonged from four to eight years. A recommended decrease of the height of the design defect of original size of 1/4 of the RPV wall thickness is presented as the impact of the evidence provided by the NDT qualification on the procedure used within the structural integrity assessment.
Publication Source: 3nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, November 14-16, 2001, Seville Spain. Publisher: Tecnatom s.a. - [Homepage]
