Ultra-Compact Heat Exchangers for SMR

Statement of the problem or situation that is being addressed. In the past, the cost and complexity of high temperature heat exchangers for nuclear reactors have been inversely proportional due to the difficulties inherent in manufacturing finely-detailed welded or brazed structures. To address this problem, additive manufacturing is being used to produce a heat exchanger with extremely large surface area per volume and therefore high heat transfer rates. However, to date, only six metallic alloys have been approved as structural materials in high temperature nuclear reactor applications and no additively manufactured materials have been approved. General statement of how this problem is being addressed. This problem will be addressed by generating metal powder from approved materials and developing printing parameters for additive fabrication of mechanical and thermal test components. These will be used for qualification campaign demonstrating fabrication of one of these materials by additive manufacturing and comparing results to wrought alloy. What was done in Phase I? Analytical heat exchanger performance models were created and designs were generated for additively manufactured microchannel heat exchanger designs relevant to several reactor types. The Phase I effort focused on the gas reactor steam generator design since it accounts for a significant portion of the overall reactor size and offers the best opportunity for overall size, cost and weight savings compared to the existing technology. A lab-scale steam generator sample was fabricated and tested to validate both the pressure integrity of the design and the heat transfer predictions in the analytical model. What is planned for the Phase II project? Qualification will be pursued for the additive manufacturing of materials that, in wrought forms, are already approved for high temperature and pressure nuclear applications. This will include developing printing and post processing techniques followed by metallurgical and mechanical evaluation. The intention is to demonstrate base material equivalency between additive fabrication and the existing code qualified materials though mechanical testing and metallurgical evaluation of printed components. Commercial Applications and Other Benefits. The heat exchanger design is not a one-size-fits-all scheme, but instead the general design architecture is readily tailored to purpose. This versatility is due to the parametric design, which allows capacity rate matching between streams, geometric flexibility, and different flow mediums (for example steam, liquid metal, CO2, or molten salt and water). This unique design optimization combined with responsive manufacturing means that the heat exchanger technology could be a replacement for many of the different types of heat exchangers to reduce cost and volume allocations. Additive manufacturing of high temperature qualified materials