As the graphitic materials are used in the HIP, irradiation durability of some graphite was investigated, especially at high temperatures 1,400-1,700 K [12]. First of all, the shrinkage rate of graphite is the most interest. For many types of graphite (except the isotropic MPG-6 graphite based on noncalcined coke) at high irradiation tem­peratures from 1,400 to 1,700K in the interval of the neutron fluxes under study (up to 2.75-1025 m-2), the shrinkage of samples was observed in both the parallel and perpendicular directions of the cut with respect to the formation axis. A decrease in the irradiation temperature to 1,200-1,500K reduces the shrinkage rate and the anisotropy in the change of geometrical dimensions (Fig. 5.7).

At the same time, the relative change in the specific electric resistance for all graphite decreases, while the relative change in the elastic modulus increases. Such a behavior of graphite materials can be explained by considerable damage to the microscopic structure and the appearance of pores and cracks, indicating ’secondary swelling.