Radiation changes of some physical properties of graphites with different degrees of graphitization

Abstract

On the basis of data from the work of V. I. Klimenkov and Yu. N. Aleksenko*, the authors of the present work arrived at the conclusion that the increase in volume observed during the neutron irradiation of graphite could be due to a reduction in size of the crystallites, i.e., degraphitization. To test this hypothesis, we irradiated six samples of graphite with different degrees of graphitization. Sample No. 1 was prepared from normal reactor graphite, graphitized at a temperature of about 2500"C, and sample No. 6 from stntered oil coke, which had been annealed but not graphitized. Each sample was a square-section block measuring 5 • 5 • 70 r a m . Holes 0.3 mm in diameter were drilled through the blocks in the center and at distances of 5 and 10 mm from each end. These holes were used for the insertion of thermocouples and also currentcarrying and potential leads for determining the electroresistance and the thermal conductivity of the samples. All six samples, inside a hermetically sealed aluminum container, were placed in the experimental channel of an RFT reactor. The integral neutron flux was 6.2" 10 z~ neutrons/ern s at a flux rate o f ( 1 . 5 2)" 10 ts neutrons/era z. see. During the irradiation, the temperature of the samples was kept within the limits of 350 450~ so that after irradiation, the samples retained only the quite stable structural de-