Doel 3 & Tihange 2 - Some Peer-reviewed Scientific Papers & Reports

Introduction

Relevance and problem statement This master thesis aims at acquiring a fundamental understanding of the so called “hydrogen cracks” or “hydrogen flakes” formed in nuclear reactor pressure vessel steel. Over the past few years, a lot of attention in Belgium and worldwide has been spent on the investigation of these flaws found in two of the Belgian nuclear reactor pressure vessels. The reactor pressure vessel is the heart of a nuclear reactor containing the nuclear fuel. It is subject to high temperatures and high pressures. For a safe operation of the reactor, the structural integrity of the reactor pressure vessel must be assured at every moment in time. Due to the number and density of these hydrogen induced flaws, some people have expressed their concerns about the safety of these nuclear units. A lot of research has already been done to assure the current integrity of both reactor pressure vessels. The conclusion of these investigations was evaluated positive, resulting in the continued operation of the reactors. As these reactors are currently planned to remain in operation for the next 6 and 7 years, it is important to investigate the possible evolution of these flaws in time. The above mentioned investigations did not focus into detail on the further development of the flaws. Therefore, the objective of this master thesis is to investigate the stability of these hydrogen induced flaws found in the reactor pressure vessels. The question whether it is possible for the cracks to grow under normal operating or accidental conditions will be handled. This problem will be treated from a theoretical point of view and by modeling. Thesis organization To cover the complete investigation on the possible evolution of the hydrogen induced flaws in two of the Belgian reactor pressure vessels, the thesis will be divided in several parts. First there is an explanation about the function and production of reactor pressure vessels. This is continued by a discussion about the discovery of flaws in the reactor pressure vessels of Doel 3 and Tihange 2 in Belgium. Furthermore, the effects of hydrogen in steel will be handled, followed by the possible sources of hydrogen during operation of the reactor and the uptake of this hydrogen by the 1