| Popis: |
The self-diffusion of Pu-238 in two batches of mixed uranium-plutonium mononitride (U0.8Pu0.2)N with different density, oxygen content, and XM-ratio was measured between 1500 and 1800°C. The obtained diffusion coefficients arc lower than all results for other advanced fast breeder fuels of the MX-type (M = U + Pu; X = (C + O + N)). Thus, MN is the material showing the lowest uranium and plutonium mobilities. Measurements performed at constant nitrogen partial pressure of 53 kPa (400 Torr) yielded apparent activation enthalpies, ΔH, of 451 and 497 kJ/mole (108 and 119 kcal/mole) for the two batches, respectively. The material with the higher ΔH had also the higher XM-ratio. Measurements at constant temperature and variable nitrogen partial pressure showed decreasing diffusion rates with decreasing pressure. Simultaneously, the activation enthalpies increased. This is in contrast to the behaviour of carbides indicating that bonding conditions in MN are different from those in MC. |
