Expert panel discusses Belgian reactor test results

An international expert panel recently discussed the results of the latest material tests on the reactor pressure vessels of Electrabel's Doel 3 and Tihange 2 power reactors. The panel will soon issue an opinion on the methodology the utility must use in its safety case for restarting the units.

Doel 3 and Tihange 2 were taken offline in 2012 when ultrasound testing suggested the possible presence of cracks in their reactor vessels. Further investigations indicated that the defects are so-called hydrogen 'flakes' and were introduced during the manufacturing process. The Federal Agency for Nuclear Control (FANC) allowed Electrabel to restart the units in May 2013, requesting that 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 remain offline.

FANC announced in February that additional inspections of the reactors revealed more extensive flaking within their vessels than previously identified.

An international expert panel convened by FANC and its technical subsidiary Bel V met for three days in late April to review and discuss the results of the test campaigns conducted by Electrabel over the past year.

These mechanical tests were carried out on specimens containing hydrogen flakes that had previously been irradiated in the BR2 research reactor. The tests aim to establish the implications of long-term irradiation on the mechanical properties of this material.

The expert panel is now expected to issue an opinion on the calculation method that Electrabel has to use in the safety case it will submit to FANC for restarting Doel 3 and Tihange 2.

This safety case must demonstrate that the presence of hydrogen flakes in the walls of the reactor pressure vessels does not compromise their structural integrity.

FANC said that, together with Bel V, it will "thoroughly review" the safety case in consultation with inspection services company AIB-Vinçotte, the expert review panel and an external research team. It expects this process will take several more months.

Researched and written
by World Nuclear News