Finite element modelling of mechanical properties of Tungsten under neutron irradiation

Zinovev Aleksandr

Promoter

Delannay Laurent, (UCL), laurent.delannay@uclouvain.be

SCK•CEN Mentor

Terentyev Dmitry
dmitry.terentyev@sckcen.be
+32 14 33 31 97

SCK•CEN Co-mentor

Malerba Lorenzo
lorenzo.malerba@sckcen.be
+32 14 33 30 90

Expert group

Structural Materials Modelling and Microstructure

PhD started

2015-10-01

Short project description

Development of qualification of materials for plasma facing and structural applications for DEMO is one the heaviest work tasks in the EUROfusion programme within HORIZONT2020 with the total budget exceeding 100ME. Tungsten and tungsten-based composites are presently considered as main candidates. An armor material needs high crack resistance under extreme thermal operation conditions as well as compatibility with plasma-wall interaction phenomena, while a structural material has to be ductile within the operation temperature range. Both material types have also to be stable with respect to high neutron irradiation doses and helium production rates.

The plasma facing materials envisaged for ITER application should receive only limited amounts of dpa during their lifetime (~0.1-0.5 dpa), while Tungsten selected as the first wall armour and Tungsten-based composites for structural applications in DEMO are expected to receive doses of 20 dpa or even higher. Under these conditions, the mechanical properties of the materials are known to degrade radically due to (i) neutron irradiation, (ii) heat transients and (iii) plasma gas uptake. Consequently, the combination of these phenomena will define structural integrity.

The physical origin of the above mentioned effects has been investigated thanks to recent developments of physically-based modelling techniques operating at different time and space scales thus capturing variety of phenomena, such as: H/He permeation and retention, evolution of radiation induced microstructure, plastic flow in the presence of radiation defects, etc. Thus a valuable information regarding the microscopic level effects is present or can be extracted on the basis of currently established expertise (to which SCK-CEN made a significant and world-wide recognized contribution). Thus, the incorporation and overall integration of the microscopic phenomena into full-scale model is the next step. While fine scale descriptions (atomistic and mesoscale methods) should be used for the understanding of fundamental mechanisms of degradation of mechanical properties, reliable full scale (i.e. comparable to experimental size) representation is needed to minimize expensive experimental load and rationalize scarce experimental results to help development and qualification of tungsten for ITER and advanced tungsten-based grades for DEMO applications.

Objective

The objective of this project is to develop FE-model capable to simulate mechanical behaviour of polycrystalline tungsten under tensile testing with the focus made on effect of test temperature and neutron irradiation damage, by drawing information from both experiments and crystal plasticity models as well as some lower scale simulation tools (such as dislocation dynamics or molecular dynamics where needed). The grain-size description will be up-scaled by using FEM, thereby to model loading of the real-size tensile sample and provide one-to-one comparison with the experiments. That way, the developed FEM will be benchmarked and tuned (if necessary) using available experimental data on mechanical properties of different non-irradiated tungsten grades, obtained earlier at SCK•CEN. Finally, the FEM model will be used to predict the mechanical integrity of commercial tungsten grades upon ITER-relevant and DEMO-relevant exploitation conditions accounting for the neutron irradiation and transient loads. The main objective is thus to envisage up to what extent the synergetic effect of heat transients and radiation-induced damage may degrade the mechanical properties of tungsten in the ITER and DEMO relevant conditions.