Swiss Qualification Body for NDT

The current Nuclear Energy Act (KEG) entered into force in 2005 together with the Nuclear Energy Ordinance (KEV). For safety-classified mechanical plant components, the Ordinance on Vessels and Piping in Nuclear Installations (VBRK) additionally establishes requirements for in-service inspection. Accordingly, qualified procedures, qualified equipment reflecting the state of the art, and qualified personnel must be employed.

Detailed requirements for in-service NDT in Swiss nuclear power plants are set out in Guideline ENSI-B08, issued by the regulatory authority ENSI in 2022.

Guideline HSK-B07 of the regulatory authority has, since October 2008, established the requirements for the qualification of NDT systems. It thereby implements the requirements of the KEV and the VBRK for the inspections required under Guideline ENSI-B08.

Central elements are the alignment with the European ENIQ methodology and the requirement that a Swiss Qualification Body meet the criteria of an accredited Type A inspection body under ISO/IEC 17020 – with regard to independence and technical competence.

As in most European countries, the qualification of NDT systems in Switzerland follows the methodology of the "European Network for Inspection and Qualification" (ENIQ). The recommended practices deliberately allow scope for adaptation to the differing national regulations.

Requirements of the ENIQ methodology:

• Case-by-case assessment of each component: identification of the active damage mechanisms and the relevant defect types and their characteristics (position, orientation, morphology, branching, etc.).
• Fracture-mechanics determination of the maximum permissible defect size for each defect type, and derivation of a "qualification defect size" – taking into account defect growth up to the next inspection interval and a safety factor for measurement tolerances.
• The practical trials (PT) on test pieces and mock-ups (full-scale replicas) must encompass the entire measurement chain as well as relevant on-site access restrictions (e.g., space constraints).
• Test pieces and the defects contained therein must sufficiently replicate the actual condition of the component – in terms of geometry, material, manufacturing process, and surface condition, as well as signal response: artificially introduced defects must respond to the inspection method in a manner as similar as possible to real, service-induced defects.
• Personnel qualification is generally conducted as a blind trial, using a defect population unknown to the personnel.
• The scope of practical trials can be reduced through two instruments: "technical justifications" (TJ), which substantiate known physical and technical relationships, and mathematical modeling and computer simulation, which additionally support the plausibility of inspection concepts and results.

NDT systems have been qualified in Switzerland since the 1990s. Until 2008, this was carried out on a project-by-project basis under the direction of "qualification teams," with direct involvement of the regulatory authority – a phase that provided important experience for today's qualification system.

In April 2008, the Swiss NPP licensees and the SVTI agreed on the framework for the qualification system and on the establishment of the Swiss Qualification Body (QSt) as an independent organizational unit within the SVTI's Nuclear Inspectorate.

The NDT Qualification System Switzerland comprises the following organizational elements:

• Swiss nuclear power plants (qualification representatives of the NPPs)
• Swiss Qualification Body for NDT (QSt)
• Qualification Steering Committee (LAQ)
• Qualification Advisory Board (FBQ)

• As an accredited Type A inspection body under ISO/IEC 17020, the QSt is impartial and organizationally independent of plant operators and inspection companies.
• It ensures the guideline-compliant conduct of qualification projects, reviews the concepts submitted by operator representatives, and carries out all activities required for a technically competent, independent assessment of NDT systems. In Switzerland, it performs the function of a Qualification Body Type 1 as defined by ENIQ terminology.
• Upon registration of a qualification project, the QSt evaluates the documentation submitted by the NPP and the inspection company – regarding the component, the inspection task, the NDT system, the inspection procedure, and existing performance evidence – provides written comment on the qualification concept, and establishes the definitive qualification scope.
• On this basis, the QSt develops the performance evidence program to be carried out, in the form of a qualification procedure. This includes, in particular, the type and extent of practical trials, the qualification defect sizes, the acceptance criteria, and any additional documentation or technical justifications required.
• The QSt establishes the design of test pieces and defects and, after test piece manufacture, verifies their position, dimensions, and other relevant characteristics as confirmation of the manufacturer's specifications.
• The QSt oversees and evaluates the practical trials, and reviews and accepts technical documentation such as inspection procedures and technical justifications.
• For each qualification project, the QSt prepares a summary qualification report, archives all relevant documentation in the qualification dossier, and issues qualification certificates.
• To continuously improve the qualification process, the QSt evaluates operating experience gained from qualified NDT systems in Swiss nuclear power plants.
• The QSt maintains close international cooperation with foreign qualification bodies, particularly those following the ENIQ methodology, as well as with the Performance Demonstration Initiative (PDI) of the Electric Power Research Institute (EPRI) in the United States.

• Responsibility for the timely and proper conduct of the qualification lies with the plant operator as licensee. The operator initiates the qualification project by submitting a registration and a qualification concept to the QSt, proposing therein the approach to qualification it considers most appropriate.
• The registering NPP provides all information required for qualification under Swiss regulations – concerning the component, the inspection task, and the intended NDT system (inspection procedure, personnel, equipment). This includes, in particular: 
  • Definition of the inspection task (applicable guideline, special requirements, etc.)
  • Characteristics of the components (materials, geometries, manufacture, repairs, etc.)
  • Findings from the aging monitoring program
  • Damage mechanisms and defect types at the component
  • Determination of the maximum permissible defect size (e.g., by fracture mechanics)
  • Proposed qualification defect size
• For the provision of the NDT system to be qualified, the NPP generally engages an inspection company as subcontractor. As the technically competent party, this company provides all documentation on the NDT system it has developed: 
  • Inspection procedure, including descriptions and requirements for the work processes
  • Description of the equipment and required accessories
  • Technical justifications, if requested by the NPP or the QSt

• The Steering Committee sets strategic direction for the development of the qualification system, without influencing the operational activities of the Qualification Body. It reviews the QSt's work for compliance with the "Establishment and Operation" agreement governing the Qualification Body.
• It coordinates qualification projects across the Swiss plants.
• The Steering Committee comprises representatives of the Swiss operators and the SVTI.

• The Advisory Board develops proposed solutions for overarching technical and methodological questions relating to NDT qualification in Switzerland.
• It comprises technically competent representatives of the Swiss operators, the SVTI, and the regulatory authority.
• It also acts as an arbitration body for disputed technical and methodological questions relating to qualification.

Qualification concept

The basis is the inspection obligation under Guideline ENSI-B08, supplemented by any applicable regulatory requirements. The NPP operator derives the inspection objective from the postulated or specific damage mechanisms of the component and proposes the qualification defect size – taking into account a safety margin, equipment tolerances, and defect growth. Actual on-site conditions (access, environment, radiation, etc.) must be considered.

Selection of the Inspection Company
The NPP operator determines the inspection technique and engages an inspection company – preferably one with existing, applicable performance evidence.

Technical Justifications
The inspection company prepares technical justifications (TJ) for the NDT system. The need for and scope of these are defined by the NPP operator and the QSt. The TJ substantiates (and, where applicable, reduces) the extent of practical trials required.

The Test Piece TJ addresses the design of test pieces, in particular the selection of defects, and is provided by the QSt.

Existing Performance Evidence
The QSt reviews and, where possible, takes into account existing performance evidence submitted by the NPP operator, whether from other Swiss qualifications projects or from foreign bodies – in particular those within the ENIQ framework, as well as the PDI/EPRI (USA, ASME BPVC).

Qualification Scope and Plan
The operator submits a proposal; the QSt reviews the proposal and establishes the definitive scope (technical justifications, practical trials, test pieces, personnel qualification) as well as the acceptance criteria in the qualification procedure.

Practical Trial
The practical trial provides the final proof of performance of an NDT system (equipment, inspection procedure, personnel, including manipulator), covering both data acquisition and data evaluation. The NPP operator organizes the practical trial; the QSt oversees, documents, and evaluates the performance evidence of the complete NDT system. For complex systems, this is carried out in two stages:

• Separate trial of the measurement system and data evaluation on test pieces using laboratory manipulators.
• Trial of the complete equipment intended for actual field use, on mock-ups, in a subsequent "integral test."

Interviews conducted by the QSt with personnel responsible for data acquisition and data evaluation may supplement the trial, allowing the QSt to confirm that the requirements of the inspection procedure are consistently followed. In the event of erroneous results, such interviews also help identify the root cause.

The QSt prepares the qualification report and, upon successful qualification, a certificate. All relevant documentation for the qualification project is archived in the dossier. Blind test piece information is retained by the QSt. The operator receives a copy of the dossier excluding this information.

Issuance of the qualification report and certificate is the prerequisite for guideline-compliant performance of the inspection.