Vessel checks for more Swedish reactors

Sweden's nuclear regulator has instructed the operators of two more of the country's reactors to review the conditions of the units' pressure vessels to check for defects that may have been introduced in the manufacturing process.

Sweden's nuclear regulator has instructed the operators of two more of the country's reactors to review the conditions of the units' pressure vessels to check for defects that may have been introduced in the manufacturing process.

Forsmark 3's reactor hall (Image: Vattenfall)

The Swedish Radiation Safety Authority (Strålsäkerhetsmyndigheten, or SSM) wants the operators of Oskarshamn 3 and Forsmark 3 to review and analyse documentation from the manufacture of the units' pressure vessels to see whether similar flaws to those discovered in two Belgian units are likely to be present. The operators must then decide whether the vessels need to undergo further tests. The review - and any decision on the need for further tests - must be completed by 30 June 2015.

The flaws in the pressure vessels of Belgium's Doel 3 and Tihange 3, discovered in 2012, were subsequently found to be so-called hydrogen "flakes" introduced during the manufacturing process. Belgian nuclear regulators concluded that the inclusions were of no safety significance and the plants were allowed to restart after about one year. National nuclear safety authorities immediately ordered inspections of other units whose vessels had been made by the same manufacturer, the now defunct Rotterdam Drydock Company (Rotterdamsche Droogdok Maatschappij, RDM), but no similar inclusions were found elsewhere.

Only one Swedish unit - Ringhals 2 - has a pressure vessel that was manufactured by RDM, but the vessels of Ringhals 3 and 4, Forsmark 3 and Oskarshamn 3 were manufactured using a similar forging process. No flaws have been found in the pressure vessel of Ringhals 2, which under went tests during an annual refuelling and maintenance outage beginning in September 2012. Tests are already planned at Ringhals 3 and 4, so SSM's latest instruction only covers Forsmark 3, operated by Vattenfall, and Osksarshamn 3, operated by OKG.

In 2013 the Western European Nuclear Regulators Association (WENRA) recommended that standardized reviews should be carried out at all European reactor pressure vessels, regardless of manufacturer, to verify materials quality and structural integrity.

According to Vattenfall, work has already begun on the data analysis for Forsmark 3's pressure vessel.