Technical basis for revision of guidelines for inspection and evaluation of reactor internals of flaw characterization for uninspected region of cylindrical components

'Guidelines for Inspection and Evaluation of Reactor Internals', published by Thermal and Nuclear Power Engineering Society (TENPES) and taken over by Japan Nuclear Technology Institute (JANTI), adopted a very conservative assumption on flaw characterization for uninspected region of cylindrical components. Fully penetrated flaw should be assumed for uninspected region, when SCC is found and flaw evaluation is performed on cylindrical core internals such as core shroud. The authors suggested a modified method on flaw characterization for uninspected region based on a simple application of probabilistic approach last year. This paper describes a technical basis of modification of JANTI Guidelines, incorporating the suggested method. Confirmation for the modified method utilizing field data of an operating plant is also shown. Significance of feedback from field data on inspection and evaluation method in JANTI Guidelines is discussed. (author)