SPIRIT

Title:

Migration mechanisms of helium under ion irradiation in nuclear ceramics 

Scientific frame of the study:

Neutron irradiation of advanced ceramic materials developed for applications in nuclear reactors from Generation IV will generate relatively high quantity of helium due to (n, a) reactions. The knowledge of the physico-chemical mechanisms driving the trapping/detrapping and migration of helium is of primary importance in order to model the long term behavior of these materials. Ceramics and more precisely carbides as SiC, TiC or ZrC, nitrides as TiN, or ZrN, cer-cer and cer-met composites, respectively SiC_f/SiC and Fe-Cr alloys reinforced by nano-oxide precipitates, are nowadays considered as a potentially interesting family of radiation tolerant materials due to their excellent thermomechanical properties. 

Aim of the work:

The main objectives of this PhD work can be declined in four complementary points of interest:

• to describe the thermally activated mechanisms of migration of helium ;
• to analyze the effect of irradiation damage on helium trapping and detrapping mechanisms ;
• to discriminate thermally activated and irradiation enhanced helium mobility ;
• to determine the effect of order/disorder transition or phase transformation on helium mobility. 

Scientific approach:

Specific experimental strategies will be carried out in order to achieve the above items:

• helium implantation (³He or ⁴He) followed by appropriate annealing treatment coupled with helium depth profile characterization as it has been yet applied to determine thermally activated helium migration mechanisms in model waste matrices [1] ;
• coupling helium implantation heavy ion irradiation in sequential or simultaneous modes followed by helium depth profile characterization [2] ;
• coupling a high dose ion irradiation in ballistic regime with a post-irradiation annealing or a post irradiation performed in electronic regime [3] followed by helium depth profile characterization.
• All these experiments will be conducted using ion beams from the JANNUS multi-irradiation platform [4]. Helium depth profile characterization will be performed using either nuclear reaction analysis (NRA) for helium-3 or heavy ion induced elastic recoil detection analysis (HI-ERDA) for helium-4. 

Tutors:

S. Miro and P. Trocellier, JANNUS Laboratory, CEA Saclay, France. 

References:

[1] P. Trocellier et al, Nucl. Instrum. Meth. Phys. Res. B210(2003)507.

[2] S. Miro et al., J. Nucl. Mater. 362(2007)445.

[3] A. Benyagoub et al., J. Appl. Phys. 106(2009)083516.

[4] P. Trocellier et al., Materials Research Society Symposium Proceedings of the 2010 Fall Meeting, Boston, Paper R7.1.

Contact : lucile.beck@cea.fr, patrick.trocellier@cea.fr, sandrine.miro@cea.fr.