Swiss utility Axpo has submitted a road map to the Federal Nuclear Safety Inspectorate (ENSI) for further investigations of possible flaws in the reactor pressure vessel (RPV) of unit 1 of the Beznau plant. The unit is not now expected to restart until at least August 2016.

Ultrasonic inspections of the Beznau 1’s RPV that began in May "registered findings at some points in the base material of the block 1 RPV indicating minimal irregularities in the fabrication process". Further measurements and analyses were undertaken and submitted to ENSI to assess whether these complied with current regulations.

Axpo said it is assessing additional measurements made using testing methods developed by Belgian utility Electrabel to investigate a similar issue at Doel 3 and Tihange 2. So far these results confirm the findings of earlier measurements. The company plans to submit a new, provisional test report later this month to the Swiss Association for Technical Inspections (SVTI/ASIT) and then to ENSI.

Extensive analysis and testing over several months will be carried out by an international committee of experts nominated by ENSI. After reviewing Axpo’s project plan, the committee will assess the company’s analyses and safety case. ENSI is solely responsible for the regulatory decision as to whether Beznau 1 can resume operation. Axpo said that, based on the current results, it "remains convinced that unit 1 will go back on grid after completion of the testing phase."

Beznau nuclear plant hosts two 365MWe Westinghouse units, which are the oldest power reactors in Switzerland. Unit 1 began operating in 1969, and unit 2 in 1972. Both units provide district heating as well as power. Axpo is also conducting ultrasonic measurements on the RPV of Beznau 2, currently offline for scheduled maintenance and upgrades outage since. It noted the investigations so far have only resulted in "minute findings, which … are normal based on their number and location". A test report on the unit 2 investigations will be submitted to SVTI/ASIT shortly.

Photo: Beznau nuclear power plant