July/August_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 0 6 2 iTSSe TSS iTSSe TSS FeCrAl alloys have been also widely investigated as both alternative fuel cladding materials and coating materials for Zr-alloy cladding by virtue of formation of a protective alumina layer under high temperature accident conditions. However, the use of FeCrAl coating on Zr-alloy at elevated temperatures is limited by the low eutectic temperature in the Fe-Zr system (928°C). Therefore, research focus shifted toward develop- ment of diffusion barrier coatings (e.g., Mo layer) between FeCrAl coating and Zr-alloy substrate. FeCrAl-Mo dual layer coated Zr-alloy cladding tube was developed with fine ad- justment of cold spray process [4] . The Mo interlayer prevented diffusion-induced eutecticmelting in the substrate while outer FeCrAl coatingmitigated oxidation of the underlying substrate. NEAR-NET SHAPE MANUFACTURING FOR ADVANCED NUCLEAR REACTOR COMPONENTS CST also has been investigated for near-net shape manu- facturing of oxide dispersion strengthened (ODS) steels being considered for fuel cladding and structural components in ad- vanced nuclear reactor applications. ODS steels consist of uni- form dispersion of nanometer sized oxide clusters (typically of Y-Ti-O) in a fine-grained ferritic steel matrix which provides superior high temperature creep strength and irradiation dam- age resistance. Manufacturing ODS fuel cladding tubes by CST has been demonstrated as an alternative to the conventional cost-prohibitive method, which involves powder consolida- tion, multiple hot/warmextrusion, and annealing steps [5] . Here cold spray of ODS steel powder is performed on a tubularman- drel, which is subsequently disposed using processes such as dissolution after deposition leaving behind a free-standing ODSsteelclass.Detaileddevelopmentofcoldsprayprocesspa- rameters and post-deposition surface treatments for this con- cept has been performed at UW-Madison, and an example of free standingODS cladding tube fromthese studies is shown in Fig. 2. The tube shown in Fig. 2 has a wall thickness of 1.2 mm (typically higher than claddingwall thickness) and image anal- ysis revealed a porosity level of 0.03%. Post-deposition heat treatments are also being investigated. The ferritic steel phase in the feedstockpowderwaspreserved in theas-manufactured ODS steel material. Advanced high-resolution characterization confirmed the presence of dispersed oxide nanoparticles such as Ti-Y-O and TiO 2 in the ferritic steel matrix. COATINGS FOR USED NUCLEAR FUEL STORAGE CONTAINMENTS CST is being evaluated as a mitigation method for chlo- ride-induced stress corrosion cracking (CISCC) that may po- tentially occur in the fusion welded regions of steel canisters in dry cask storage system (DCSS) [6] . Susceptibility of CISCC in stainless-steel canisters is an important consideration for ex- tended storage of used nuclear fuel (UNF) in interim storage systems. Studies at UW-Madison and other institutions have demonstrated dense and continuous stainless steel coatings on sensitized 304L stainless steel plates with a population of prototypical CISCCs [6,7] . The coating successfully sealed the crack openings, thereby acting as a physical barrier hindering further growth of CISCC as shown in Fig. 3a. In addition, CST has been investigated for cost-effective deposition of Cu liners Fig. 2 — (a) Photograph of an oxide dispersion strengthened (ODS) steel tube manufactured by cold spray process. (b) SEM cross- sectional image of the ODS steel tube (performed by the authors’ group) [4] . Fig. 3 — Cross-sectional SEM image of (a) cold spray 304L coating on 304L stainless steel substrate with prototypical chloride-induced stress corrosion cracking (CISCC) (work performed by the authors’ group) [6] . (b) Photograph of a small scale (1/10th) Cu coated steel container produced by cold spray process. The red arrows indicate the CISCCs in the stainless steel [8] . FEATURE 12