An investigation of thermal release of carbon-14 from PWR Zircaloy spent fuel cladding

Abstract An investigation to study the thermally-activated release of carbon-14 from irradiated PWR Zircaloy spent fuel cladding to potential repository environments for the Yucca Mountain Site Characterization Project was performed. Experimental parameters included release temperature, atmosphere and oxide thickness. Thirteen experiments measuring carbon-14 release from irradiated Zircaloy-4 cladding samples with thin pretransition and thicker posttransition oxide films were completed. Experiments were performed in air at 373, 473, 548, and 623 K, for up to 24 h and in argon at 623 K for 8 h. The data were examined using classical diffusion models, diffusion from a semiinfinite plane and diffusion from a finite thickness plane. Diffusion coefficients were calculated at each of the four temperatures in air and for both the pre- and posttransition oxide cladding. The diffusion coefficients measured ranged from 1 × 10 −19 to 8 × 10 −14 m 2 /s with activation energies from 78–103 kJ/mol in the temperature range of 373–623 K. The data indicate that carbon-14 is released primarily from the oxide layer on these cladding samples.