Axpo, operator of Switzerland's Beznau NPP, has detected "flaw indications" in the reactor pressure vessel (RPV) of unit 1 while carrying out ultrasonic measurements as a result of recommendations in connection with flaw indications found in Belgian reactors.
The Western European Nuclear Regulators' Association (Wenra) said the flaw indications "require evaluation" and Axpo had submitted a report on its findings to the Swiss Federal Nuclear Safety Inspectorate (ENSI) on 15 July. ENSI is now awaiting an assessment of these findings by Axpo. ENSI has also notified all Wenra members.
The 365MWe Beznau 1 Westinghouse pressurised water reactor began commercial operation in 1969 and is currently offline for its main annual overhaul, which included the replacement of the unit's RPV head and control rod drive. Axpo said the return to service of Beznau 1 is expected to be postponed until the end of October. Its original restart date had earlier been put back due to delays in installing the new vessel head. Georg Schwarz, deputy director of ENSI and director of the division for nuclear power plants noted: "Of course we will only issue the permission to restart Beznau-1 once we are certain that the findings do not represent any impairment of safety."
Axpo will examine and assess the ultrasonic indications in more detail, as advised by ENSI. The examination will include a detailed evaluation of the ultrasound results, in particular the size and location of the ultrasound indications. The aim will be to characterise the type and cause of the findings, Wenra said. It will also be necessary to determine whether the RPV still meets regulatory requirements. A maintenance outage at Beznau 2, also a 365MWe PWR, has been brought forward so that its RPV can also be checked. The outage will start at the beginning of August.
Following the discovery in 2012 of material defects in the RPVs at the Doel 3 and Tihange 2 reactors in Belgium, ENSI ordered that the manufacturing documents for Swiss nuclear plants should be inspected. The documents for the Beznau 1 RPV did not indicate that there were any faults in the material, Wenra said.
Switzerland has four nuclear plants with five commercial reactors at Beznau, Mühleberg, Gösgen and Leibstadt. Inspections at Mühleberg and Gösgen did not reveal any reportable ultrasound results. The Leibstadt RPV differs from Doel 3 and Tihange 2 both in manufacturer and in its manufacturing process.