Fitness-for-service assessment of pressure tubes in CANDU nuclear generating stations

Fitness-for-Service Guidelines have recently been developed to provide acceptance criteria and evaluation methods for assessment of the integrity of the Zr-2.5 Nb pressure tubes in operating Canada deuterium uranium (CANDU) reactors. The guidelines provide a methodology for the evaluation of specific conditions in a single tube, such as manufacturing and in-service generated flaws, hydride blisters formed at points of contact between a pressure tube and its calandria tube, and generic degradation of pressure tubes properties in service. The guidelines are divided into three sections. The first section describes the requirements that must be met to qualify the tubes for continued service. The second section provides the material properties data base information needed to carry out the assessments. The third section provides the technical basis for the acceptance criteria and evaluation procedures as well as justifications and descriptions of the data bases. The guidelines were issued to CANDU reactor operators for trial use and released to the Atomic Energy Control Board of Canada for review and comment in May 1991