Radiation growth of beryllium

Full text of publication follows: Beryllium will be used as neutron multiplier in the DEMO reactor therefore investigation of neutron irradiation influence on dimension stability of the beryllium product is very actual problem. In the work radiation damage of the TE-56 beryllium grade made by hot extrusion was investigated. The beryllium specimens were irradiated in the SM high flux research reactor at the temperatures of 70 deg. C and 200 deg. C up to neutron doses of (1.3-14.2)x1022 cm-2 (E>0.1 MeV). The measurements of the geometrical dimensions and density and also microstructure investigation were carried out. Comparison of the experimental results before and after irradiation shows that increase of the geometrical dimensions and density decrease of the irradiated beryllium specimens take place. The effect of the volume increase and density decrease of some materials under neutron irradiation are well known and has the title of radiation swelling. In this case there was also discovered that the change of diameter and height of specimens cutting along and across of extrusion axis has a different value at general volume increase. This means the increase of dimensions of the irradiated specimens are anisotropic to crystallographic directions associated with crystal texture which was formed under making of the beryllium rods in hot extrusion. Microstructure investigation shows, that neutron irradiation of beryllium at 70 deg. C and 200 deg. C leads to formation of dislocation loops which are placed in basal (0001) and prismatic ((1010), (1120)) planes. Dislocation loops located in basal planes are vacancy type and loops located in prismatic planes - interstitial type. Besides after irradiation at 200 up to neutron dose of 13.1022 cm-2 (E>0.1 MeV) there are gas voids or bubbles located at the grain boundaries and inside grains. Irradiation of beryllium leads to formation of great amount of helium atoms which distorting the crystal lattice leads to swelling. Depending from irradiation temperature helium atoms are at the quasi solution state or as gas bubbles. Beryllium has the hexagonal densely packed (HDP) lattice therefore having crystallographic anisotropy can have the various swelling rate along the a- and c-axis. This is the anisotropic swelling of beryllium. So superposition of two processes - anisotropic swelling and radiation growth are in beryllium under irradiation. The description of the radiation growth effect of beryllium is unknown in literature. (authors)