NAC International Inc. (NAC) is providing transportable storage canisters (TSCs) to Central Plateau Cleanup Company CPCCo) for long term dry storage of capsulized radioactive waste at the Hanford Site in Richland, WA. The TSC consists of 316/316L stainless-steel components welded to form a cylindrical canister that acts as a confinement boundary for the payload. The heat affected zones of the welded areas are most susceptible to Chloride Induced Stress Corrosion Cracking (CISCC), that may limit the life of the TSC. To mitigate CISCC during the anticipated 300-year storage period, an overcoating is applied to the heat affected zones of all external TSC fabrication welds, referred to as Cold Spray. This paper will discuss the purpose, development, and application of Cold Spray to the CPCCo TSCs. Cold Spray is a process whereby metal powder particles are deposited upon a substrate by means of ballistic impingement via a high-velocity stream of gas, resulting in a uniform deposition with minimal porosity and high bond strength. Temperatures are below the melting thresholds of many engineering materials enabling a large variety of application uses. NAC developed a process for Cold Spray application onto the 316/316L stainless-steel TSCs to serve as a CISCC protective/mitigative coating for its canister products. Testing during development arrived at nickel as the deposited coating material and nitrogen as the gas vehicle, along with a set of various application parameters. The qualified process was implemented onto the CPCCo TSCs. Prior to application, the equipment and process are validated via coupons that are sprayed and then tested to meet requirements for adhesion strength (ASTM C633) and porosity (ASTM E2109). After successful coupon testing, Cold Spray is performed on the external TSC fabrication welds, to include heat affected zones. Acceptance testing of the resulting deposition is performed via visual inspection.

Diffusion bonded compact heat exchangers have exceptionally high heat transfer efficiency and might significantly improve the performance and reduce the cost of supercritical carbon-dioxide Brayton cycle power plants using high temperature heat sources, like high temperature nuclear reactors and concentrating solar power plants. While these heat exchangers have an excellent service history for lower temperature applications, considerable uncertainty remains on the performance of diffusion bonded material operating in the creep regime. This paper describes a microstructural modeling framework to explore the plausible mechanisms that may explain the reduced creep ductility and strength of diffusion bonded material, compared to wrought material. The crystal plasticity finite element method (CPFEM) is used to study factors affecting bond strength in polycrystals mimicking diffusion bonded microstructures. Additionally, the phase field method is also employed to simulate the grain growth and recrystallization at the bond line to model the bonding process and CPFEM is used to predict the resulting material performance to connect processing parameters to the expected creep life and ductility of the material, and to study potential means to improve the structural reliability of the material and the resulting components by optimizing the material processing parameters.

CWT (combined water treatment) was introduced in Japan in 1990 and over 50 power generation boilers are now in operation. However, the effect of oxygenated treatment on the steam oxidation of the ferritic-martensitic steels and austenitic stainless steels that are used for superheaters and reheaters is currently far from clear. In this study, laboratory tests were used to examine the effect of the oxygen level of the feed water on the scale growth and the scale exfoliation propensity of T91 ferritic-martensitic steel and 300-series austenitic stainless steels, as represented by TP316H and TP347H (coarse- and fine-grained, respectively). The oxygen level of the feed water had little effect on the steam oxidation rates of all the steels tested. Hematite (Fe 2 O 3 ) formed in the outer layer of the oxide scales on both the ferritic and austenitic steels and is considered to have been encouraged in the simulated CWT atmosphere. The adhesion strength of the oxide scale formed on T91 in the simulated CWT atmosphere, that is, scale in which hematite was present, was lower than that of the oxide scale formed in the simulated AVT (all volatile treatment) atmosphere. The oxidation rate of fine-grained TP347H was confirmed to be slower than that of coarse-grained TP316H. Hematite significantly influenced the scale exfoliation of the austenitic steels and the critical oxide thickness for exfoliation decreased with increasing proportion of hematite in the outer scale.