22 Jul (NucNet): Operator Axpo has detected “flaw indications” in the reactor pressure vessel (RPV) of the Beznau-1 nuclear power reactor 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) has said.
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 2015. ENSI is now awaiting an assessment of these findings by Axpo. ENSI has also notified all Wenra members, Wenra said.
Beznau-1, a 365-megawatt pressurised water reactor that began commercial operation in 1969, is offline for its main annual overhaul and fuel has been removed from the reactor core, Wenra said. Operations will only resume if the safety of the RPV is confirmed.
“There is no time pressure at Beznau-1,” said Georg Schwarz, deputy director of ENSI and director of the division for nuclear power plants. “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.”
ENSI has asked Axpo to examine and assess the ultrasonic indications in more detail. The examination will include a detailed evaluation of the ultrasound results, in particular the size and location of the ultrasound indications.
In the second phase of the examination, the aim will be to characterise the type and cause of the findings, Wenra said.
It will also be necessary to determine how the RPV may have been weakened because of the findings, and whether it still meets regulatory requirements.
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.
At Doel-3 and Tihange-2, numerous material defects were detected in the base material of the forged RPVs, Wenra said.
In response to these defects, Wenra recommended that all forged RPVs in Europe should be inspected as part of routine weld seam inspections.
Switzerland has four nuclear stations – Beznau, Mühleberg, Gösgen and Leibstadt – with five commercial reactors. Inspections at Mühleberg and Gösgen did not reveal any reportable ultrasound results, Wenra said.
At the Leibstadt nuclear plant, the RPV differs from Doel-3 and Tihange-2 both in manufacturer and in its manufacturing process, and is made of rolled sheets rather than forged rings. The Belgium findings have “little significance” for the Leibstadt RPV, Wenra said.
The condition of the RPV at Beznau-2 will also be examined during its main annual overhaul in 2015, which starts at the beginning of August, Wenra said.