Chan Bock Lee

Formation of intermetallic compound at interface between rare earth elements and ferritic-martensitic steel by fuel cladding chemical interaction

Abstract The intermetallic compounds formation at interface between rare earth elements and clad material were investigated to demonstrate the effects of rare earth elements on fuel-cladding chemical interaction (FCCI) behavior. Mischmetal (70Ce-30La) and Nd were prepared as rare earth elements. Diffusion couple testing was performed on the rare earth elements and cladding (9Cr2W steel) near the operation temperature of (sodium-cooled fast reactor) SFR fuel. The performance of a diffusion barrier consisting of Zr and V metallic foil against the rare earth elements was also evaluated. Our results showed that Ce and Nd in the rare earth elements and Fe in the clad material interdiffused and reacted to form intermetallic species according to the parabolic rate law, describing the migration of the rare earth element. The diffusion of Fe limited the reaction progress such that the entire process was governed by the cubic rate law. Rare earth materials could be used as a surrogate for high burnup metallic fuels, and the performance of the barrier material was demonstrated to be effective.

Interaction between multi-component lanthanide alloy and ferritic-martensitic steel

Studies were carried out to evaluate the effect of lanthanide elements which are generated during the fission process on the interaction between metal fuel and cladding material. Quartenary lanthanide alloy as Nd-Ce-Pr-La and Sm-contained quintenary alloy were manufactured by vacuum arc remelting and a diffusion couple test with HT9 (12Cr1MoWV) alloy was carried out at 660 and 700 °C for up to 231 h followed by microstructural analysis. The results showed that interdiffusion between lanthanide element (Nd, Ce) and Fe took place as the diffusion couple test proceeds to form intermetallic compounds as an RE2(Fe,Cr)17 (RE=Nd, Ce, Pr, La) type. As the number of alloying elements increased, the reaction layer thickness increased, but a deviation of the theoretical non-linear relationship as well as an increase in the rate exponent occurred. Instantaneous diffusion of Fe into a lanthanide side and its associated Fe depletion beneath the interface acted as the major driving force in forming the reaction layer. The addition of Ce enhanced the Nd diffusion and increased the layer growth when compared to pure Nd alone.

Effect of Vapor Deposition on the Interdiffusion Behavior between the Metallic Fuel and Clad Material

This study aimed to evaluate the performance of diffusion barriers in order to prevent fuel-cladding chemical interaction (FCCI) between the metallic fuels and the cladding materials, a potential hazard for nuclear fuel in sodium-cooled fast reactors. In order to prevent FCCI, Zr or V metal is deposited on the ferriticmartensitic stainless steel surface by physical vapor deposition with a thickness up to 5μm. The diffusion couple tests using uranium alloy (U-10Zr) and a rare earth metal such as Ce-La alloy and Nd were performed at temperatures between 660~800°C. Microstructural analysis using SEM was carried out over the coupled specimen. The results show that significant interdiffusion and an associated eutectic reaction ocurred in the specimen without a diffusion barrier. However, with the exception of the local dissolution of the Zr layer in the Ce-La alloy, the specimens deposited with Zr and V exhibited superior eutectic resistance to the uranium alloy and rare earth metal. (Received January 17, 2011)

Interaction Behavior between Lanthanide Element and Ferritic-Martensitic Steel

A study has been carried out to evaluate the interaction behavior between a lanthanide element and clad material in order to analyze the effect of the lanthanide element on the fuel cladding chemical interaction (FCCI). A diffusion couple test between Misch metal (70Ce-30La) and ferritic-martensitic steel (Gr.92) was performed at 660 degrees C, followed by a microstructural analysis of the coupled sample. The results showed that Ce in the Misch metal, rather than La, reacted with the ferritic-martensitic steel (FMS) to form an interaction layer that penetrated the clad thickness. Fe diffused outside the clad interface to form an Fe(2)Ce compound, leaving a depletion of Fe caused by excess diffusion as well as by the formation of Cr-rich precipitation inside the interaction layer. The rate of growth followed the cubic rate law, which indicated that Fe depletion was caused by the diffusion of Fe and that the associated Cr-rich phase formation controlled the whole diffusion process.