The Federal Agency for Nuclear Control (Fanc) said in a statement that operator Engie Electrabel is required to regularly check that the situation has not changed since the flakes, or “hydrogen microbubbles”, were first discovered in the walls of the plant’s reactor pressure vessel in 2012.
Ultrasonic inspections showed there had been no evolution of the hydrogen flakes and no indications of new flaking, Fanc said.
Tihange-2 and Doel-3 were shut down in 2012 after the RPV flaws were discovered.
In June 2013 the units were restarted, but were shut down again in March 2014 after unexpected results from additional tests.
In November 2015, Fanc approved the restart of the two units. It said extensive inspections eventually revealed that hydrogen microbubbles were already present during the forging of RPVs. During this process, not all hydrogen was removed from the steel, leaving it to form small flattened blisters in the steel walls. “However, hydrogen microbubbles have no impact on steel structures and do not evolve over time,” Fanc said at the time.
Tihange-2, a 1,008-MW pressurised water reactor that began commercial operation in 1983, was eventually restarted on 14 December 2015.
In September, a Brussels court ruled in favour of Fanc’s 2015 decision to allow Tihange-2 to restart. Plaintiffs from Germany, the Netherlands and Luxembourg had sought to have the regulator's decision annulled.
Fanc said that a follow-up inspection carried out last month during a planned outage of Tihange-2 showed that “slight variations can be observed in the measurement results”, but the results were within expectations.
“No growth was observed in the size of hydrogen flakes already detected in the reactor vessel of Tihange-2,” Fanc said. “No new hydrogen flakes were added either.”
The 1,006-MW Doel-3 plant was restarted in summer 2019 after a scheduled outage to check for similar issues with the RPV.
The Belgian government decided in 2018 that the country’s two nuclear power stations, Tihange and Doel, would be closed in 2025. Tihange-2 is scheduled to close in February 2023.
In 2019, the seven reactors at the two stations produced almost 48% of the country’s electricity production.