Remote-Handling Residual Stress Measurements for Non-irradiated and Irradiated Monolithic U-10Mo Nuclear Reactor Fuel Plates

The US High Performance Research Reactor (USHPRR) Project is working to develop and qualify a new low enriched monolithic fuel for use in High Performance Research Reactors. The fuel consists of Uranium Molybdenum (U-10Mo) alloy foils with a Zr diffusion barrier interlayer, clad in 6061 Al alloy by hot isostatic pressing. During fabrication or irradiation residual stresses can be induced due to the different mechanical thermal properties and constrained interfaces. The residual stress state may have a significant influence on the fuel plate’s ability to resist delamination during reactor operation, a key requirement for fuel qualification. To best understand the crucial stress state during reactor cooldown, it is desired to measure the fuel after use in the reactor, when it is unfortunately the most radioactive. Therefore, the testing constraints require fully remote operation, so existing residual stress measurement techniques are not suitable. The remote manipulation requirements led to the design of a slitting system with eddy current sensors to measure deflection and a fine, high-speed cutting tool to introduce the slit. The data is used to calculate a residual stress profile using a Tikhonov regularization inverse technique allowing for stress discontinuities across interfaces. Measurements have been taken on unirradiated fueled mini plates using the remote slitting system and analysis is in progress. Companion talks will present on irradiated fuel measurements and will compare the results to models that try to capture the complicated material behavior under operating conditions.