Energie emmagasinee par le graphite irradie. effets de la temperature d'irradiation

Abstract

Under the influence of neutron irradiation, graphite stores internal energy and various methods of measur ing this energy, developed under the auspices of the CEA, are in current use. Three methods have been developed: annealing at constant temperature, semiadiabatic annealing and differential thermal analysis. After a brief description of these methods, it is shown that the results obtained by them, from similar graphite samples, agree mutually and also with results obtained by others. The effects of irradiation temperature on the amount of energy stored in graphite were studied with reference to samples from the Gl reactors (40–150° C) and the G2 reactors (130–300° C). Measurements made by means of differential thermal analysis permit the determination of the enthalpy soldH dθ (cal/g·/dgC) as a function of the temperature θ between ambient temperature and 800° C, and the integration of the energy spectrum furnishes the total stored energy H (θ). At a given irradiation temperature, the energy liberated by the irradiated graphite increases proportionally to the irradiation dose. This linear relationship is valid only for small doses. For relatively low irradiation temperatures (30–70° C) there is a peak of energy release near 200° C. As the irradiation temperature increases, this energy peak diminishes and it disappears for an irradiation temperature of about 200° C. The amount of energy stored for a constant dose of 2 × 10 20 n/cm 2 decrease rapidly as the irradiation temperature increases from 50° C to 300° C. The results obtained with graphites irradiated in the G1 and G2 reactors are in good accord with results due to other investigators.