Effect of Cu, P, Ni and Mn content, individually and synergistically, on the microstructure of irradiated chemically-tailored RPV steels

SCK•CEN Mentor

Stergar Erich, estergar@sckcen.be, +32 (0)14 33 31 80

Expert group

Structural Materials

SCK•CEN Co-mentor

Chaouadi Rachid , rchaouad@sckcen.be , +32 (0)14 33 31 76

Short project description

In the 2014 irradiation campaign, the RADAMO-13 irradiation program was performed where 36 different RPV steels including 23 chemically-tailored RPV steels as well as commercial RPV steels. Tensile specimens as well as microstructural bars were irradiated at 290°C to various neutron fluence levels.

For the chemically-tailored steels, the reference material is the ASTM A533B. Their chemical composition was then varied by changing only one variable (low, medium, high content) at a time and keeping all others elements similar. Of course, the aim is not to cover all possible alternatives but to investigate only relevant cases where information is missing.

It is known that Cu, Ni, P and eventually Mn play an important role in irradiation damage accumulation. In particular, under irradiation, Cu diffuses extremely rapidly to form the so-called Cu-rich precipitates (CRPs) that impede dislocation motion thereby increasing hardening and embrittlement. This phenomenon was extensively investigated in literature. P can also precipitate to form phosphorus-rich precipitates but this is less investigated. Indeed, the P-content in most materials remains very low, typically lower than 0.015%. The question that can be addressed is how these two elements, namely Cu and P, precipitate under irradiation and how they are affecting each other. Moreover, the CRPs contain a large proportion of Ni, Mn, Si and P. Therefore, in order to clarify the role of Cu in the precipitation process, irradiated steels with no Cu as well as up to 0.30%-content are available. Similarly, Ni and Mn synergy will be investigated. Ni is known to dominate the hardening/embrittlement kinetics at high fluence levels. However, it is often associated with Mn and this association is not well understood. Therefore, nine (9) irradiated steels will be available for investigation covering from nearly 0 to 1.8% Ni/Mn combinations.

All tensile test results to determine the irradiation hardening will be performed in march 2016. Only microstructural examination should be carried out using different techniques including TEM (at SCK•CEN), PAS (at SCK•CEN), SANS (with partner) and eventually ATP (with partner). The irradiation defects for the relevant neutron fluence levels cannot be observed by TEM but could provide information on the microstructure of the materials. The other three techniques are more appropriate but should be combined in order de better characterize the irradiation defects. The selection of the materials to be investigated will be based on the tensile results that will be available in March 2016.

Objective

The main objective of the present work is to support the mechanical behavior (tensile strength) with the microstructural changes after irradiation. As no single technique is available to fully characterize the microstructure of irradiated steels, a combination of various techniques will be required. These techniques include transmission electron microscopy (TEM), Positron Annihilation Spectroscopy (PAS), Small Angle Neutron Scattering (SANS) and eventually Atom Probe Tomography (APT). The two first techniques are available at SCK•CEN), the two other will be shared with partners. The radiation damage modeling tools used for RPV steels can therefore be modified to take into account the results of these investigations.

The combination of mechanical behavior (hardening) and microstructure (nature, size and number density of the nano-size defects) will help understanding the influence and interaction of these key elements (Cu/P and Mn/Ni) and in developing reliable irradiation damage tools that can be used to predict the post-irradiation behavior of RPV steels, not only those irradiated in the BR2 reactor but also those irradiated in surveillance programs.

The minimum diploma level of the candidate needs to be

Master of sciences , Master of sciences in engineering

The candidate needs to have a background in

Physics , Other
Before applying, please consult the guidelines for application for PhD.