A review of worldwide practice and experience in the qualification of ultrasonic inspections of nuclear components over the past two decades

Inspection qualification is the term currently used to describe the process of independent assessment of a specific non-destructive test to ensure that it is capable of meeting its objectives. Such activities carried out on the Sizewell B reactor inspections were referred to as validation. In the USA, the term performance demonstration is used, though this is increasingly being reserved for the part of the assessment which uses practical trials, with qualification being used, as elsewhere, when the assessment process involves assembling evidence for the efficacy of an inspection from a wider variety of sources. Most qualification activity to date has been focused on nuclear plant because of the safety implications of nuclear plant failure and also because it is here that the cost of the qualification itself is in proportion to the cost of the plant and the consequences of failure. This paper reviews worldwide practice and experience in the qualification of ultrasonic inspections of nuclear components over the past two decades. In general, qualification has been applied to in-service inspections; however, this paper includes consideration of the application of qualification to manufacturing inspections. To date, ultrasonic inspection is the inspection method to which most qualification activity has been devoted. However, the qualification principles discussed are equally applicable to the qualification of other inspection methods. This paper includes consideration of: q Sizewell B manufacturing inspections. q ASME XI requirements, including Appendix VIII. q European developments, particularly the European Methodology for Qualification of Non-Destructive Testing developed by the European Network for Inspection Qualification (ENIQ). The ENIQ methodology has been adopted throughout Europe. The benefits of the ENIQ methodology are its flexibility and the requirement that qualification be developed taking into account the parameters of importance for a particular inspection. This means that it can provide confidence that an inspection can meet its objectives. The major disadvantage of the ENIQ approach is the requirement for scarce personnel skills in the physics and practice of inspection to develop and implement qualification requirements. Manufacturing inspections can have two purposes: (a) to ensure that any manufacturing defects that could threaten plant integrity are detected and correctly characterised so that they can be eliminated and do not enter service (fitness-for-purpose); (b) to detect defects of any size, including those smaller than could threaten plant integrity, taken as a measure of general manufacturing quality (acceptance standards for manufacturing).