Unit 3 at Belgium’s Doel nuclear plant has been cleared for early restart after a scheduled outage to check the steel walls of its reactor pressure vessel, the Federal Agency for Nuclear Control (Fanc) said on 23 July.
“Hydrogen microbubbles” in the walls of the reactor pressure vessel have not evolved and “no new indications have emerged”, Fanc said. The reactor was stopped for periodic maintenance on 7 June and was not scheduled to restart until 3 August.
Under international safety rules, Fanc had required owner/operator Engie Electrabel to regularly check that the situation “The last inspection, completed in early July 2019, showed slight variations in the measurement results, but these are due to the measurement method.” Fanc said. “This result was in line with expectations, as the same conclusions emerged from previous inspections (in 2016). No changes were observed in the size of the hydrogen microbubbles already detected in the reactor vessel of Doel 3, and no new hydrogen microbubbles appeared.
Between 2012 and 2015, the Doel 3 and Tihange 2 nuclear reactors were shut down for some time after the discovery of hydrogen microbubbles in the steel walls of the reactor vessels. In-depth inspections eventually revealed that hydrogen microbubbles were already present during the forging of the reactor vessels. However, hydrogen microbubbles had no impact on steel structures and did not change over time. Fanc, therefore, concluded in 2015 that the reactors could be restarted.
Photo: The Doel nuclear plant