The interaction of helium and displacement damage in inertial confinement fusion reactors
Abstract Helium is thermodynamically insoluble in metals and tends to form cavities if the conditions are appropriate for its migration. The processes of helium migration and interaction with point defects are strongly influenced by the level and the mode of displacement damage production. In this paper, we present an application of the rate theory for helium cavity formation in Inertial Confinement Fusion Reactors (ICFR's). A new computer code “EXPRESS” has been developed for the solution of the time-dependent rate equations describing the evolution of the space-averaged damage state of an ICFR first wall. An optimal algorithm was developed for the long-term solution of the rate equations (10 5 pulses) with modest computational requirements. It is shown that the timefluctuations in point defect and helium concentrations due to ICF-type pulsing lead to an overall reduction in the swelling of ICF materials.
Shock resistance capabilities of nickel crystal containing helium nanobubbles
It has been revealed in previous studies that helium bubbles have a damaging consequence on the load bearing capabilities of nickel. Shock resistance is the key characteristic of structural materials used in the construction of a nuclear reactor. Herein, atomistic simulations were performed to study the dynamic shock resistance capabilities of single crystal Ni impregnated with helium bubble. The effect of the geometrical configuration of helium bubble on a nickel crystal, which acts as a substrate in which the bubble is lodged, when subjected to shock loading, was studied. It was concluded from the atomistic simulations that the presence of helium bubble with a higher concentration of helium atom leads to a reflection of shock front energy from the shock path. The diameter of the helium bubble at the same concentration of He (the ratio of He atoms to the vacancy created by deleting Ni atoms) is less critical for the shock resistance capabilities of Ni crystal. At lower values of shock impact, the deformation is mainly controlled by dislocation emission, whereas at higher impact velocities, the phase transformation from FCC to BCC is the primary mode of deformation. The analysis presented in this article will help in elucidating the shock resistant capabilities of Ni facing challenges of transmutation.
A quantitative study of the dose and impurity dependence of the defect concentrations remaining in molybdenum after 4 MeV electron irradiation at (77°K)
Abstract Experimental measurements using resistivity techniques to follow the increase of defect concentration with electron irradiation dose were made on high purity molybdenum and molybdenum doped with nitrogen to two different levels. The marked dependence of defect concentration on impurity can be satisfactorily explained by the Walker model (1) which assumes that the interstitial defect is mobile at the irradiation temperature and that the retention of the interstitial depends on it being trapped at an impurity sink rather than annihilated at a vacancy. It appears therefore that the interstitial defect is mobile in molybdenum at 77°K. This result is in direct contrast to that of de Jong and Afman (1) who deduced from their work that the interstitial did not become mobile until Stage III, Evidence is presented to show that their results are in fact compatible with the Walker model and the implication of the present work on Stage III annealing in molybdenum is discussed.