6 Mar (NucNet): Switzerland’s Federal Nuclear Safety Inspectorate, ENSI, has given the go-ahead for the restart of the Beznau-1 nuclear unit after approving the safety case presented by owner Axpo following the discovery in 2015 of flaw indications in the reactor pressure vessel (RPV).
ENSI said in a statement that Axpo had carried out “extensive investigations and analyses” to demonstrate that the RPV is safe.
Materials testing has shown that agglomerates in the RPV do not affect its key properties and structural integrity analysis has shown that the RPV does not contain any flaws that could lead to its failure. “IRSN is satisfied that work has been done to all appropriate national and international standards,” the statement said.
Axpo said the safety case for Beznau-1, the world's oldest commercial nuclear plant still in operation, corroborates earlier assessments and investigations, and validates the existing safety margin for the safe operation of the plant for 60 years. Operator KKB will now begin the return to service process with the plant expected to be operating at full load by the end of March 2018.
In December 2015 Axpo submitted a roadmap ENSI detailing plans for further investigations of flaw indications in the RPV. During a scheduled outage that began in May 2015, inspections of the RPV registered findings at some points in the base material of the RPV indicating “minimal irregularities in the fabrication process”, Axpo said. The company carried out further measurements and analyses and submitted a report to ENSI.
In July 2015, Axpo announced that the restart of Beznau-1 had been postponed while the flaw indications were investigated further. Then in August, ENSI called for additional investigations.
Beznau-2 was not affected by the flaw indications and was returned to service after its scheduled outage in 2015.
Beznau-1, a 365-MW pressurised water reactor, began commercial operation in 1969.