The measurement of silver diffusivity in zirconium carbide to study the release behavior of 110mAg in the ZrC TRISO-coated nuclear fuel particle

Abstract

The tri-structural isotropic (TRISO) coated particle fuel has been developed and used for high temperature gas-cooled reactors (HTGRs). It provides a unique robustness of the first barrier for the fission products. The TRISO fuel particle has typically consisted of a UO 2 or UCO kernel, surrounded by successive layers of porous carbon, dense inner pyrocarbon, silicon carbide, and dense outer pyrocarbon. During operation, however, the SiC layer has been known to release radioactive silver 110m Ag which makes maintenance more difficult and thus costly.Zirconium carbide has been considered as a promising alternative to the SiC fission product barrier. ZrC exhibits high temperature stability and possibly possesses superior Pd resistance, while the retention properties especially for silver have not been adequately studied.To help elucidate the diffusive behavior of silver in the ZrC coating of the TRISO-coated particle, a new diffusion experimental technique, called the encapsulating source method, has been developed by constructing a constant source diffusion couple between ZrC and Ag gas originated from Zr-Ag solid solution. SEM, WDS, EBSD Scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy (WDS), electron backscatter diffraction (EBSD) and optical methods were used to analyze the diffusion couple annealed at 1500 C. The resultant diffusion coefficient of Ag in single-crystalline ZrC 0.84 at 1500 C was experimentally determined to be about 2.8 (± 1.2) × 10 -17 m 2 /s.

The Evaluation of the High Temperature Gas Cooled Reactor Safety to Fulfill the Requirement of the Next Generation Nuclear

“…Due to neutron irradiation, Liang et al [24] found that (1) the buffer layer will experience cracks when the burn-up larger than 40,000 MWd/t; (2) PyC layer will undergo shrinkage to finally develop tensile stress, which can generate compression stress to the SiC layer; and (3) SiC layer will experience thermal decomposition at temperatures above 1600 0 C. Yang and Allen [25] conclude that SiC and PyC coating layers play an important role to provide a barrier to the release of gaseous fission product from the kernel. The integrity of the TRISO layers to retain gases and metallic fission products is still intact for temperatures of approximately 1600 0 C.…”

Fabrikasi Kernel TRISO-UN dan Karakternya, Sebuah Kajian

“…Data konduktifitas UN yang ditampilkan oleh Yang juga mirip dengan hasil yang diperoleh oleh Baranov. , 2016;Malkki, 2015).…”

“…Akibatnya, integritas mekanik lapisan SiC akan berkurang, terutama setelah suhu mencapai 1700 o C karena akan terjadi transformasi dari b-SiC menjadi a-SiC serta mengakibatkan dekomposisi termal. Oleh karena itu penelitian mengganti SiC dengan ZrC saat ini sedang dilakukan dengan intensif (Yang, 2016;Porter dkk., 2013;Kim dkk., 2014). Senyawa ZrC berfungsi untuk penangkap oksigen yang akan membatasi pembentukan CO dan memperlambat migrasi kernel.…”

Silver diffusivity measurement in ZrC with SIMS to study the release behavior of 110mAg for nuclear fuel applications

“…The release of radioactive silver ( 110m Ag) in particular has been of considerable concern because it can contaminate various surfaces in the primary circuit of a direct-cycle HTGR and make maintenance difficult and thus costly [20,21]. However, there are few studies that address Ag retention in the ZrC TRISO-coated particle [22][23][24].…”

“…For high temperature Ag diffusion experiments in ZrC, it has been difficult to find an effective experimental technique. To overcome such experimental difficulty in the present material system and make it possible to fabricate more reliable diffusion experimental samples, Yang et al [24] has recently developed a new experimental technique, referred to as the encapsulating source method. They fabricated a sample applying this method, diffusion annealed it, and determined the Ag diffusivity in ZrC at 1500 C with wavelength-dispersive X-ray spectroscopy (WDS).…”