Simulating the carbon distribution in zirconium alloy spent fuel cladding

Abstract

The diffusivity values of C in pure Zr and in Zr containing dissolved O (Zr(O)) were determined in a temperature range of 623–1023 K for Zr and 923–1123 K for Zr(O) from depth profiles of C obtained by glow-discharge emission spectroscopy. The C diffusivity in Zr(O) decreased as the O concentration in Zr increased and that for Zr containing 15 at % O was two orders of magnitude smaller than that for pure Zr. One-dimensional numerical calculations of Fick’s diffusion equation with a Soret effect indicated various non-uniform distributions of C in a 5-mm-thick Zr matrix under a temperature gradient of 573 to 773 K for 3 years, assuming a heat of transport of − 1.5 to + 1.5 eV. Isothermal annealing at 773 K for 10 years could result in a uniform distribution, whereas dissolution of O in the interstitials of the Zr matrix would hinder C transport through the interstitials.Graphical As concentration of O increased in HIP Zr by 15 at%, the diffusivity of C decreased more than two orders of magnitude.For the positive {{Q}^{*}}_{c}, concentration of C slightly segregated at the surface of the cooler side but had maximum peaks at a middle to a higher temperature zone, and depleted at the surface of the hotter side.For the negative {{Q}^{*}}_{c}, concentration of C depleted at the surface of the cooler side and at the middle to the higher temperature zone, and highly segregated at the surface of the hotter side.