High Temperature Corrosion Behavior of 15-15Ti Cladding Tube Material in Contact with Liquid Lead, Outside, and Cs2MoO4, Inside

Abstract

Lead-Cooled Fast Reactors are one of the emerging new technologies connected to the Generation IV reactor designs. Even though the reactor features are extensive and beneficial, some technical and regulatory difficulties remain that hinder the deployment. One of them is the corrosion behavior of fuel claddings in high burn-up and elevated temperatures, as fuel claddings are a part of accident barriers. In this study, 15-15Ti austenitic steel was the investigated cladding material.As this cladding would be used in a tube form, corrosion attack from both sides, inside and outside is studied in contact to their respective environments. From the outside of the tube, the proposed coolant liquid lead is the corrosive substance. At the inside of the tube, the major corrosive species in our test setup is, for simplicity reasons, Cs2MoO4. However, this choice has been made from some considerations regarding the fuel evolution upon burn-up.In a high burn-up situation, the generated fission products would start to accumulate to the gap between the fuel pellet and the cladding tube. These accumulated products are the so-called “Joint-Oxide Gain” (JOG) phases, and they are the corrosive substances in question when discussing the corrosion attack from the inside of a cladding tube. Cs2MoO4 has been identified as one of the main components of JOG phases and thus will be focused on in this study.A new capsule was designed to investigate the dual-atmosphere corrosion of cladding tubes. Unexposed capsule parts (a) and the basic schematic of the assembled capsule (b) can be seen in the Figure below. The cladding tube material itself is used as the container for JOG as it is filled with Cs2MoO4 and sealed on both ends. This assembly is then placed inside a bigger capsule, which is filled with lead powder to submerge the cladding tube assembly. All assemblies were done in Ar-filled glovebox. The capsules were then exposed to 600-1000 oC for 52 to 168 hours, which was followed by cutting and epoxy embedding to investigate the cross-sections. Figure 1