Test anomalies trigger early outages at Belgian units

Belgian utility Electrabel has brought forward planned outages for units at its Tihange and Doel plants after additional tests on hydrogen flakes suggested these may affect the mechanical properties of their reactor vessels.

Belgian utility Electrabel has brought forward planned outages for units at its Tihange and Doel plants after additional tests on hydrogen flakes suggested these may affect the mechanical properties of their reactor vessels.

A reactor hall of one of Tihange's three units (Image: Electrabel)

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 by Electrabel indicated that the defects are so-called hydrogen "flakes" and were introduced during the manufacturing process. Belgium's Federal Agency for Nuclear Control (FANC) allowed Electrabel to restart the units last May, requesting that further tests be conducted to evaluate the effect over time of these flakes.

"Further research and additional testing are now needed to interpret and assess these unexpected results."

FANC

Several tests have since been carried out. However, Electrabel has reported that one set of tests to investigate the mechanical strength of irradiated specimens of similar material "did not deliver results in line with experts' expectations."

These tests involved the accelerated irradiation of hydrogen-flaked samples within a research reactor at SCK-CEN's Mol site. The results indicated that the mechanical properties of the material are more strongly influenced by this than thought. FANC noted, "Further research and additional testing are now needed to interpret and assess these unexpected results."

Electrabel has informed FANC that, as a safety precaution, it has brought forward planned maintenance outages at Doel 3 and Tihange 2, 1006 MWe and 1008 MWe pressurized water reactors respectively. Outages that had been scheduled to start on 26 April and 31 May, respectively, began today. Electrabel anticipates that these outages will last six weeks. However, the results of the follow-up tests are not expected to be known until mid-June.

Following the discovery of the flakes at the Belgian units, national nuclear safety authorities ordered inspections of other units whose vessels had been made by the same manufacturer, the now defunct Rotterdam Drydock Company (Rotterdamsche Droogdok Maatschappij, RDM). As many as 21 reactor pressure vessels made by RDM are located around the world. However, no similar inclusions were found elsewhere.

Researched and written
by World Nuclear News