The mission of the U.S. Department of Energy (DOE), Office of Nuclear Energy is to advance nuclear power in order to meet the nation’s energy, environmental, and energy security needs. Advanced high temperature reactor systems will require compact heat exchangers (CHX) for the next generation of nuclear reactor plant designs. A necessary step for achieving this objective is to ensure that the ASME Boiler and Pressure Vessel Code, Section III, Division 5 has rules for the construction of CHXs for nuclear service.
Given their high thermal efficiency and compactness, expanding the use of Alloy 800H diffusion bonded Printed Circuit Heat Exchangers (PCHEs) beyond their current application in Section VIII, Division 1 to the high temperature nuclear applications is of interest. The research being completed under the Department of Energy project is focused on preparing a draft Code Case for consideration by the ASME Code Committees for high temperature nuclear components which must meet the requirements of Section III, Division 5, Subsection HB (Class A), Subpart B.
Acceptance of a Code Case by the ASME Code Committees to use PCHEs in nuclear service requires a broad understanding of PCHE failure mechanisms. At the highest level, the ASME Code requirements prevent failures of structures and pressure boundaries. Historically, the approach is a process of understanding the known failure modes, such as overload failures, plastic collapse, progressive distortion (ratcheting) and fatigue, and then establishing rules for construction to preclude those failure modes in components. For Division 5 applications, attention to differential thermal expansion, creep life, and creep-fatigue must also be considered. Failure from these loadings is manifest within PCHEs both within the internal micro-channel geometry, and at substantially larger solid header and nozzle attachments. To address the adequacy of the PCHE, a Failure Mode Effects Analysis (FMEA) has been performed for standard etched channel PCHEs. This FMEA is linked to the proposed rules in the code case for compact heat exchangers in Section III, Division 5 Class A applications. The PCHE FMEA covers all design failures addressed by Section III.