Modelling of oxide layers formed on nuclear materials (PhD)

Many structural materials protect themselves from the detrimental effects of their environment by spontaneously forming a surface film that inhibits further corrosion. This passive layer is usually an oxide or nitride and its thermodynamic and kinetic properties play a significant role in the life management and operation of both nuclear power plants and nuclear waste disposal systems.

• In the case of structural materials for generation II/III plants, stress corrosion cracking of austenitic stainless steels (e.g. IASCC), of nickel-based alloys (e.g. PWSCC) is an issue that potentially determines the lifetime of components.  Furthermore, activity build-up in coolant circuits is a major concern in terms of ALARA.

• In the case of structural materials for generation IV systems, liquid metal corrosion (LMC) and embrittlement (LME) of martensitic steels by stagnant and flowing lead or lead-bismuth eutectic (LBE) potentially jeopardize the integrity of components.

• In the case of carbon steel overpacks used for the disposal of high-level nuclear waste, the evolution of the rate of uniform corrosion allows to predict the lifetime of the waste containers.

In each of these cases the extent and quality of a protective layer - i.e. a compact oxide layer, and, potentially, a deposited outer layer - play a key role.  Hence, their quantification and qualification and the modelling thereof (the subject of this doctoral thesis) are important contributions to corrosion issues in the nuclear sector.

The common ground for all applications is a robust model for the behaviour of the oxide layer formed on materials relevant to the nuclear sector.  Therefore, the main objective of the proposed doctoral thesis is to further develop a generic film model and apply it to austenitic stainless steels, nickel-based alloys, martensitic steels and carbon steels.

The generic model is based on a point defect model.  The thesis requires development of the model beyond the “open literature” and “SCK•CEN” state-of-the-art.     

It is also important to develop suitable methodologies to determine the input parameters of the model.  Experimental input could be derived from electrochemical impedance measurements and surface analytical techniques.