Simulation of fast reactor void swelling in the Harwell high-voltage microscope

The production of meaningful results on the swelling of steels by high-voltage microscope (HVM) irradiations requires considerable attention to the irradiation technique, and particularly the temperature, foil thickness, beam heating, and specimen irradiation. Provided these conditions are satisfied, however, the HVM technique provides an accurate and economical method of obtaining information relevant to the reactor behaviour of materials. As an example of the information which is given by the HVM technique, the results of some irradiations on solution-treated type 316 steel are described. The rate of swelling is a function of temperature and void density (i.e. gas concentration), with a peak swelling rate at an optimum void density. Nucleation experiments show that nucleation occurs by the irradiation-enhanced diffusion of gas atoms, and that radiation resolution of gas occurs. Comparison of the accelerated test results with DFR data shows that good agreement is obtained between the HVM and DFR data over the whole temperature range studied. (author)