Safety Evaluation of the Hydrogen Flaking Damage in the Doel 3 and Tihange 2 Reactor Pressure Vessels

In the summer of 2012, the detection of a large number of quasi-laminar flaw indications in the reactor vessel beltline ring forgings of two Belgian pressurized water reactors (Doel Unit 3 and Tihange Unit 2) posed a significant safety threat that led the licensee to shutdown both plants. Those indications were identified by the licensee as hydrogen flakes that developed during the fabrication of the forgings. As a prerequisite for a potential restart of the units, the Belgian Nuclear Safety Regulator, the Federal Agency for Nuclear Control (FANC), requested the licensee to provide, for each unit, a safety case demonstrating the acceptability of the reactor pressure vessel for continued operation. As the technical subsidiary of the FANC, Bel V performed a safety evaluation of the condition of the reactor pressure vessels. The paper documents the approach Bel V used in his safety evaluation and the criteria he defined to evaluate the acceptability of the hydrogen flaking damage in the reactor pressure vessels.