Helium Cavities Research Articles

Experimental HDS and TEM studies of the nucleation and growth of helium cavities in molybdenum at 300K

Experimental HDS and TEM studies of the nucleation and growth of helium cavities in molybdenum at 300K

The application of TEM to the study of helium cluster nucleation and growth in molybdenum at 300 K

Abstract The addition of transmission electron microscopy (TEM) to monitor helium cluster nucleation and growth in molybdenum at ambient temperatures, has provided a useful extension to the information obtained in detailed helium desorption spectroscopy (HDS) studies. In particular, advantage has been taken of HDS helium filling techniques which allow the production of well characterized specimens containing a known number of helium atoms at a controlled low density of helium trapping centres. The problems of very dense damage structures found after conventional helium implantations have thus been avoided. This paper summarizes the filling techniques relevant to the production of TEM specimens together with the main results to date, e.g. the platelet morphology of helium cavities, their growth by loop punching, their transformation to groups of small bubbles, electron beam induced loop punching, and helium trapping at dislocations. The application of these results to the defect structures found in convent...

The interaction of helium and displacement damage in inertial confinement fusion reactors

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.

The kinetics of helium release from irradiated samples of austenitic steels OKh16N15M3B and OKh16N15M3BR

Samples of a heat-resistant austenitic steel (both boron free and with 0.005% by weight boron added) were irradiated in the active zone of Reactor WWR-M with a neutron flux of 4 × 10 13 n/cm 2 · s (E ⩾ 3 MeV) and 6 × 10 13 n/cm 2 · s (E ⩽ 0.03 eV) at fixed temperatures in the range of 600°C to 850°C. The neutron fluence was 6 to 8 × 10 19 n/cm 2 . For the study of the helium release kinetics the samples were annealed with a constant heat-up rate. The experimental equipment and procedure were described previously. Most of the helium (70 to 90%) is released at temperatures of 1420 to 1490°C. This is connected with the melting of the samples. Helium release during the annealing in the range 20 to 1300°C is observed in the form of seven peaks on the curve of gas-release rate. Attempts to interpret the helium diffusion mechanism of each stage is given by determination of the activation energies and other data. Irradiation in a helium atmosphere leads to penetration of helium into the samples, which is proportional to the external gas density. A significant intensification of the generation of helium cavities occurs at irradiation temperatures of 750 to 850°C.