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.
A rate theory of swelling induced by helium and displacement damage in fusion reactor structural materials
Abstract The combination of helium gas and displacement damage production in fusion reactor structural materials is detrimental to their integrity. A simplified rate theory is presented to explain existing fission reactor swelling data. The theory is applied also to fusion reactor conditions in both the steady-state and pulsed modes of operation. In this time-dependent rate theory both the nucleation and growth phases of cavities are treated. The smooth transition from nucleation to growth is achieved by developing an approximate equation for the time-dependent nucleation current. This current decreases sharply after the formation of the majority of cavities. Cavity growth then controls the overall swelling. It is shown that the dynamic dispersion of helium atoms into the matrix by radiation (re-solution) plays an important role at low temperature. Radiation pulsing of the tokamak-type results in a higher effective mobility for helium. This is attributed to the annealing of helium vacancy traps in between pulses. Overall lower cavity concentrations are therefore expected in this particular situation.
Electron dose-rate conversion factors for external exposure of the skin from uniformly deposited activity on the body surface.
Dose-rate conversion factors have been calculated for external exposure of the skin from electrons emitted by sources that are deposited uniformly on the body surface. The dose-rate factors are obtained from electron scaled point kernels developed by Berger (Be71; Be73; Be74). The dose-rate factors are calculated at depths of 4, 8, and 40 mg cm-2 below the body surface as recommended by Whitton (Wh73), and at a depth of 7 mg cm-2 as recommended in ICRP Publication 26 (ICRP77). The dependence of the dose-rate factors at selected depths on the energy of the emitted electrons is displayed. The dose-rate factors for selected radionuclides of potential importance in radiological assessments are tabulated.