Highly Efficient Diffusion Bonded Inconel 617 Heat Exchanger for Nuclear Energy Applications

A novel design and diffusion bonding technology is proposed for manufacturing heat exchangers and reactors for nuclear energy applications that require high-performance materials to withstand harsh nuclear reactor conditions. The proposed material is Alloy 617, which at 800°C has approximately triple the strength of stainless steel Alloy 316. Alloy 617 is also known commercially as Nickel Alloy 617, and is sold under the brand name Inconel® 617. Alloy 617 is a nickel-chromium-cobalt alloy known primarily for its exceptional metallurgical stability. Alloy 617 diffusion bonded heat exchangers will allow operating temperatures up to 800°C at the high pressure of supercritical carbon dioxide. Importantly, supercritical carbon dioxide-based power systems do not require access to a water reservoir and avoid the discharge of heated water into the local environment. This alleviates one of the major environmental concerns of most commercial nuclear power plants. While Alloy 617 is an approved material for nuclear applications, Alloy 617 diffusion bonded heat exchangers have not been demonstrated in nuclear power facilities. This material has very high chemical resistance, which is good for corrosion resistance. Diffusion bonded heat exchangers feature photochemically etched channels. However, the very high chemical resistance of Alloy 617 makes photochemical etching challenging. In addition, milled Alloy 617 sheets have a strong surface oxide layer that resists diffusion bonding. The project team has developed a successful Alloy 617 etching process, and has also developed techniques to remove the surface oxide layer prior to diffusion bonding. The initial bonded test block has reached tensile strength over 90% of the base material at room temperature. Further optimization of these techniques is required to demonstrate the diffusion bonding process for making heat exchangers. In Phase I of this project, a new patent-pending design will be used to demonstrate the manufacturability of diffusion bonded Alloy 617 heat exchangers for nuclear applications. The new architecture offers substantially greater efficiency due to having more primary heat transfer area compared to traditional diffusion bonded heat exchangers. The Phase I work will optimize the Alloy 617 surface treatment technique with 4”x4”x3” test blocks, optimize the photochemical etching conditions, fabricate an Alloy 617 heat exchanger with the new architecture, and provide a computer simulation of the novel heat exchanger in nuclear applications. In Phase II, a prototype heat exchanger will be fabricated for third party performance testing at an experimental nuclear power facility. The project team specializes in designing, engineering and manufacturing compact heat exchangers with its unique diffusion bonding technology. The new patent-pending heat exchanger architecture is derived from extensive experience and knowledge established over 10 years. In Phase III, the technology developed in this project will be commercialized by the project team and its extensive network of business collaborators.