ENSI reviews Axpo’s project plan for the safety case of the Beznau 1 reactor pressure vessel

Kernkraftwerk_Beznau_ENSI (9)

Axpo submitted today a project plan (road map) to ENSI, the Swiss Federal Nuclear Safety Inspectorate, outlining procedures for the characterisation and evaluation of the indications in the base material of the Beznau 1 reactor pressure vessel. ENSI will review this plan in collaboration with a group of international experts.

In the project plan, the operator must outline the planned steps and methodology for characterising and evaluating the indications. ENSI will now review the plan for completeness and assess the extent to which the method chosen appears suitable for delivering reliable results on the integrity of the reactor pressure vessel. ENSI will issue a review report.

As soon as Axpo submits the documents on the characterisation and evaluation of the findings completing the safety case, ENSI will examine these as well and prepare an opinion report on the safety evaluation of the structural integrity of the Beznau 1 reactor pressure vessel.

Additional external experts

ENSI will include the opinion of a group of international experts in its assessment of Axpo’s safety case. For this reason, upon notification of the indications in the Beznau 1 RPV, ENSI rapidly decided to build up an International Review Panel. The regulator contacted recognised international experts possessing in-depth knowledge in such areas as the safety case of reactor pressure vessel integrity, materials testing, large forging fabrication and non-destructive testing methods.

These experts are consulted in a two-stage process. After reviewing the project plan, the second step is to review Axpo’s analyses and safety case with regard to such aspects as the evaluation of non-destructive measurement results, material testing as well as structural and fracture mechanics analyses taking the indications into account.

“We will incorporate the experts’ recommendations into our safety evaluation report,” says Georg Schwarz, deputy director general of ENSI and division head for nuclear power plants. “Only ENSI is responsible to take the regulatory decision regarding the possible further operation of Beznau 1.”

International Review Panel (IRP) members

  • Tim Williams, formerly of Rolls Royce plc (UK)
  • Guy Roussel, Federaal Agentschap voor Nucléaire Contrôle FANC/Bel V (Belgium)
  • Mark Kirk, US Nuclear Regulatory Commission NRC (USA)
  • Hans Vandriessche, Vinçotte (Belgium)
  • Hans-Jakob Schindler, Mat-Tec AG Winterthur (Switzerland)
  • Randy Nanstad, Oak Ridge National Laboratory ORNL (USA)
  • Isabelle Delvallée-Nunio, Institut de Radioprotection et de Sûreté Nucléaire IRSN (France)
  • Eberhard Roos, formerly of the Stuttgart University Materials Testing Institute/MPA (Germany)

Experts’ profile

  • Detailed knowledge of production and inspection requirements for heavy forgings under Swiss and/or US nuclear regulations, former and current.
  • Detailed knowledge of foundry and forging technology for reactor pressure vessel steels from the 1960s and of possible materials imperfections these may evidence.
  • Detailed knowledge of the heat treatment of reactor pressure vessel steels of the A508 series, both in the production process and for reducing neutron embrittlement.
  • Detailed knowledge of ultrasound testing of heavy plated forgings, of sizing of real defects, and of the possibilities and limitations of individual methods.
  • Ability to interpret ultrasound imaging with heavy plated forgings.
  • Detailed knowledge regarding the determination and evaluation of neutron induced embrittlement behaviour of reactor pressure vessel steels, particularly those formerly utilised and with respect to imperfections.
  • Beyond being knowledgeable about the general state of science and technology, detailed knowledge of flaw grouping rules for fracture mechanics demonstrations.
  • Fracture mechanics evaluation of materials defects in reactor pressure vessel steels under enveloping accident conditions, PTS safety case.