Joint project HRJRG – 013 supported by Russian foundation for basic research and Helmholtz Association.

Participants:

• Ulyanovsk State University (UlSU), Ulyanovsk, Russia
• JSC “State Scientific Center Research Institute of Atomic Reactors” (RIAR), Dimitrovgrad, Russia
• Karlsruhe Institute of Technology (KIT, before July of 2009 - Forschungszentrum Karlsruhe), Karlsruhe, Germany

The period of the project execution: 2008 – 2011 

The development and testing of structural materials required for the DEMO fusion reactor is one of the main objectives of the European Long Term technology R&D programme. Besides good conventional mechanical properties, the key demands for the choice of structural materials are their a) resistance to radiation-induced damage phenomena and b) attractive radiological features. Reduced Activation Ferritic Martensitic (RAFM) steels (EUROFER97, F82H-MOD, etc.) are primary candidates for application in first wall and blanket structures of the future power plant. The irradiation performance of 7-10%-Cr-WVTa RAFM steels have been extensively studied in the various low (MANITU and HFR-Ib, up to 2.4 dpa), mid (SPICE up to 15 dpa) and high (ARBOR1 30 dpa) dose irradiation campaigns. Although newly developed 7-10%-Cr-WVTa RAFM steels exhibit clearly better irradiation performance compared to the modified commercial alloys, the low temperature hardening induced by neutron irradiation accompanied by embrittlement, reduction in toughness and ductility remain as a main obstacle for their application. Within the ongoing irradiation campaign ARBOR2 several RAFM steels are irradiated up to 70 dpa at 330°C.

The study of the evolution of the microstructure under neutron irradiation by identification and assessment of radiation effects is of essential importance for the understanding of radiation damage phenomena in structural materials. There already exists a number of modelling techniques e.g. Molecular Dynamic (MD) simulation, kinetic Monte Carlo, 3D dislocation dynamics, etc. which describe primary defect (interstitials, vacancies) formation and their evolution (defect clusters, dislocation, dislocation loops, radiation-accelerated formation of brittle phases, etc.) at different time and spatial scales. Although, these modelling techniques provide vital information on the radiation damage phenomena, a direct link between the modelling and experimental results is still missing. Furthermore, many of these models are highly computing time consuming thus preventing simulation of the samples of reasonable spatial scales. The designated project aims of the development of multi-stage phenomenological modelling tools for the description of high dose irradiation performance of RAFM steels. First defects formatted by high dose neutron irradiation shall be predicted within the model. Microstructural investigations on RAFM steels will provide direct validation of the model. In the second stage model is supposed to predict mechanical performance of irradiated RAFM steels taking into account irradiation induced defects. Finally, a direct comparison of the simulation with the experimental results shall provide verification of the developed model and indicate limits of its application.

 Post Irradiation Examination (PIE) to be performed within ARBOR1 and ARBOR2 irradiation campaign will provide important input for the modelling activities. Microstructural and mechanical investigations planned within ARBOR1 and ARBOR2 will be supplemented by specific investigations in a view of model validation.

Specific goals to be reached in the project execution:

• I) Understanding of the neutron irradiation induced changes in the microstructure within proper physical models allowing description of primary defect (interstitials, vacancies) formation and their evolution (defect clusters, dislocation loops, radiation-accelerated formation of brittle phases, depletion of constituent elements, etc.). Validation of the model by direct comparison with the results of microstructural investigations.

• II) Correlation of the irradiation induced changes in the microstructure (defect clusters, dislocation loops, brittle phases, helium bubbles, etc.) to the changes in the mechanical properties. Identification of the dominant hardening/embrittlement mechanisms in the RAFM steels. Identification and quantification of helium effects.

• III) Development of the physically based phenomenological models for prediction of the irradiation induced hardening and embrittlement of the RAFM steels by taking into account microstructure evolution. Application and adaptation of the already existing physical models (e.g. Orowan model) to the RAFM steels for description of irradiation induced hardening and embrittlement.

The following work packages planned to be implemented for the achievement of the above goals

Experimental

I) Detailed microstructural characterizations of the irradiated specimens from SPICE, ARBOR1 and ARBOR2 irradiations will provide important inputs for the modelling.

II) The irradiation induced hardening and embrittlement of RAFM steels will be quantified in impact and tensile tests. The changes in the mechanical properties will be correlated to the changes in the microstructure. Dominant hardening and embrittlement mechanisms will be identified. The role of irradiation temperature in the changes of microstructure and mechanical properties will be studied.

Modelling

III) Simulation of the radiation induced damage of RAFM steels in terms of the molecular dynamics will be performed. The modelling results will be compared to the result of microstructural investigations.

IV) Analysis of defect growth kinetics under neutron irradiation will be performed. Numerical solutions of Fokker Plank equations will result defect size functions and its approximations.

V) Phenomenological model of low temperature radiation-induced hardening and embrittlement of RAFM steels will be developed by inputting the outcomes of the defect growth kinetics into appropriate physical models (e.g. Orowan model). Adaptation of these models to the specific problems of RAFM steels e.g. by incorporating helium effects will be done in addition. Empirical (mathematical) models of hardening (embrittlement) of RAFM steels will be developed simultaneously with the physical ones.

List of HRGRG – 013 meetings

1^st Meeting of HRGRG – 013 “High Dose Irradiation Damage of RAFM Steels”, Ulyanovsk, Russia, 2 – 7 April 2008

2^nd Meeting of HRJRG – 013 “High Dose Irradiation Damage of RAFM Steels”, Karlsruhe, Germany, 29 March -2 April 2009

3^rd Meeting of HRJRG – 013 “High Dose Irradiation Damage of RAFM Steels”, Ulyanovsk, Russia, 10 -13 June 2009

4^th Meeting of HRJRG – 013 “High Dose Irradiation Damage of RAFM Steels”, Karlsruhe, Germany, 12 April -17 April 2010

5^th Meeting of HRJRG – 013 “High Dose Irradiation Damage of RAFM Steels”, Ulyanovsk, Russia, 17 -19 November 2010

6^th Meeting of HRJRG – 013 “High Dose Irradiation Damage of RAFM Steels”, Ulyanovsk, Russia, 17 -19 November 2010

Main Obtained Results