Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs Affected by Hydrogen Flakes: Methodology and Results

Abstract

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected in the reactor pressure vessels, mainly in the lower and upper core shells. The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process. As a consequence, both units remained core unloaded pending the elaboration of an extensive Safety Case demonstrating that they can be safely operated. The Structural Integrity Assessment of the RPVs, through the Flaw Acceptability Analysis, aimed at demonstrating that the identified indications do not jeopardize the integrity of the reactor vessel in all operating modes, transients and accident conditions. This demonstration, presented in this paper, has been done on the basis of a specific innovative methodology inspired by the ASME XI procedure but adapted to the nature and number of indications found in the Doel 3 and Tihange 2 RPVs.

Modular system for probabilistic fracture mechanics analysis of embrittled reactor pressure vessels in the Grizzly code

“…The reduced order representations currently used to compute fracture parameters on flaws are limited to consider only flaws aligned with the axes of the RPV. Recent experiences with the Belgian Doel 3 and Tihange 2 Nuclear Power Plants, where ultrasonic inspection revealed the presence of quasi-laminar flaws [10], has highlighted the need for a capability to simulate off-axis flaws. This is not the focus of the present paper, but Grizzly has comprehensive capabilities for evaluation of fracture integrals on flaws with arbitrary geometry.…”

Progress on Grizzly Development for Reactor Pressure Vessels and Reinforced Concrete Structures

“…• General Flaw Geometry Current codes are limited to evaluating axis-aligned flaws. The discovery of quasi-laminar flaws in Belgian reactors [5] demonstrated the need for a more general capability. Grizzly has general fracture mechanics capabilities that can be applied to arbitrary flaw geometries.…”