Belgian reactor vessels show no new inclusions

16 June 2017

No new so-called hydrogen 'flakes' have been found in the reactor vessels of Belgium's Tihange 2 and Doel 3, a comparison of inspections carried out recently with those conducted in 2014 has shown. The country's nuclear regulator said there has also been no growth of previously detected flakes.

Tihange 2 and Doel 3 were taken offline in 2012 when ultrasound testing suggested the possible presence of cracks in their reactor vessels. Further investigations indicated the defects were hydrogen flakes and had been introduced during the manufacturing process. The Federal Agency for Nuclear Control (FANC) allowed Electrabel to restart the units in May 2013, requesting further tests be conducted to evaluate the effect over time of these flakes.

In March 2014, Electrabel brought forward planned outages for the two units after additional tests on hydrogen flakes suggested these may affect the mechanical properties of their reactor vessels. These outages were originally expected to last about six weeks, but the reactors remained offline.

In mid-November 2015, FANC approved the restart of the two units after concluding it was safe to bring the reactors back into operation. It concurred with Electrabel's finding that the flakes "have no negative impact on the reactor vessel's structural integrity".

Both units were restarted in December 2015, but FANC requested Electrabel carry out further inspections of reactors vessels during their next refuelling outages and at least every three years thereafter. New inspections were performed during refuelling outages last November at Doel 3 and in April this year at Tihange 2. The units were restarted in December and May, respectively.

FANC has now said an analysis of those inspection results "allows us to conclude that no new hydrogen flakes have appeared and that there has been no change in the size of the hydrogen flakes already detected".

The regulator added, "Given the time required to analyse and interpret the results in full, FANC has agreed that Electrabel is entitled to request that the reactors be started up again after a partial analysis of the results." However, FANC has stipulated a full analysis should be completed within three months of restarting.

In the case of Doel 3, FANC said the results of the full analysis confirmed those of the provisional analysis "across the board". Electrabel must submit its full analysis results for Tihange 2 by September.

Researched and written
by World Nuclear News