Additional vessel inspections delay Beznau 1 restart

Swiss utility Axpo has submitted a road map to the country's nuclear regulator for further investigations of flaw indications in the reactor pressure vessel of unit 1 of the Beznau plant. The company does not now expect the unit to restart until at least August 2016.

Swiss utility Axpo has submitted a road map to the country's nuclear regulator for further investigations of flaw indications in the reactor pressure vessel (RPV) of unit 1 of the Beznau plant. The company does not now expect the unit to restart until at least August 2016.

Unit 1 of the Beznau plant (Image: ENSI)

During a scheduled outage that began in May, inspections were made of the Beznau 1's RPV using state-of-the-art ultrasonic equipment. Axpo said these measurements "registered findings at some points in the base material of the block 1 RPV indicating minimal irregularities in the fabrication process". It conducted further measurements and analyses "in order to assess these in compliance with current regulations" and submitted a report to Switzerland's Federal Nuclear Safety Inspectorate (ENSI).

In July, Axpo announced that the restart of unit 1 had been postponed while the flaw indications were investigated further. At that time, the unit's restart was expected to be postponed until the end of October. However, in August ENSI called for additional investigations.

Axpo yesterday submitted a road map to ENSI for the further analysis and testing process on the unit's RPV.

Axpo said it is assessing additional measurements made with "a special testing method developed for a Belgian reactor" - a reference to work led by Belgian utility Electrabel to investigate a similar issue at Doel 3 and Tihange 2. Axpo noted that 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.

ENSI said it 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". The regulator will subsequently issue a review report.

An extensive analysis and testing phase taking several months will be carried out by an international committee of experts nominated by ENSI. After reviewing Axpo's project plan, the committee will review the company's analyses and safety case.

ENSI deputy director Georg Schwarz said, "We will incorporate the experts' recommendations into our safety evaluation report. ENSI is solely responsible for the regulatory decision as to whether Beznau 1 is allowed to resume power 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." However, it said that restart approval is not expected before the end of July 2016.

Meanwhile, Axpo said ultrasonic measurements on the RPV of Beznau 2 - which has been offline for a scheduled maintenance and upgrade outage since July - are "in an advanced stage". It noted the unvestigations so far have only resulted in "minute findings, which ... are normal based on their number and location".

Axpo said it will submit a test report on its unit 2 investigations to SVTI/ASIT "in the next few days".

It noted, "At present, nothing should stand in the way of the scheduled restart at the end of December 2015 following the completion of the unit 2 revision."

The two 365 MWe Westinghouse units at the Beznau plant are the oldest power reactors in Switzerland. Unit 1 began operating in 1969, while unit 2 entered operation in 1972. In addition to providing power, both units also produce district heating.

Researched and written
by World Nuclear News