U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Measuring Residual Stresses in Monolithic Fuel Foils using Neutron Diffraction Bjørn Clausen 1, Donald W. Brown 1, Maria Okuniewski 2 1 Los Alamos National Laboratory, Los Alamos, New Mexico 2 Idaho National Laboratory, Idaho Falls, Idaho Funded by US DOE OBES

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Motivation Replace HEU with LEU in research reactors Uranium 10wt% molybdenum foil clad with aluminum Zr diffusion layer is roll-bonded to the foil during hot rolling Foil (with Zr diffusion layer) is then cold rolled, and finally HIP’ed into the Al cladding CTE mismatch results in residual stresses which can cause distortions during processing and use – Mini-plates (~factor of 6 smaller than the full-size fuel) – 1.5 mm total thickness – 0.25mm thick U10Mo foil Red quadrant represent area measured with SXRD and green stars represent locations for ND

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Blistering of Fuel Plates Occurs Following Irradiation Blister test – Heating of irradiated fuel plates to temperatures above standard operating conditions generates blisters Blister Formation Hypotheses – Blisters form due to localized accumulations of fission gases when localized bond strength between laminate layers is too low or crack propagation resistance is too low Overall Issue: – Prevent blocking of 1 mm wide cooling channels between fuel plates by formation of blisters – Prevent release of fuel to cooling water in case of ruptured blisters Interface failure influenced by residual stresses – Investigate residual stress state in foils at every step during manufacturing steps

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Fuel Foils Probed Following Different Processing Steps Parameters of the individual steps can be varied HIP’ing step is the same for all samples List of samples measured on SMARTS: Sample IDHot RollPHR AnnealCold RollPCR Anneal %NA %923 K, 45 min.NA %923 K, 45 min.20%NA %923 K, 45 min.50%NA %923 K, 45 min.50%923 K, 60 min %923 K, 45 min.50%1023 K, 60 min %923 K, 45 min.50%1123 K, 60 min

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Neutron Diffraction used to Determine Residual Stress in all Phases Increased divergence of incident beam and acceptance of detectors results in better grain statistics in Al and Zr compared to SXRD Determined texture and dislocation density (qualitatively) as well Several samples were studied with different processing conditions before and after cladding – Able to determine road map for developing processing steps and resulting microstructure and residual stress state in the fuel foils Translator

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Residual Stress Set By Processing Residual stress at center of foil at various processing steps Bare Foil

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Residual Stress Set By Processing Final stress controlled by cladding Clad FoilBare Foil

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Residual Stress Set By Processing Final stress controlled by cladding CladdingClad FoilBare Foil

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA a.) Hot Rolledb.) PHR Annealedc.) 20% CRe.) 923K Annealf.) 1023K Annealg.) 1123KAnneal N d.) 50% CR Recovery Recrystallization Anneal conditions are similar Difference in outcome due to input microstructure Results Provide View Into Microstructural Evolution During Processing

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Atypical Approach Pseudo-strains due to changes in scattering geometry – Cannot use radial collimators due to thin foils – Misalignment of large sample with respect to translation axes Pseudo-strains due to chemistry changes – Heat treatment of fuel foils causes precipitation of a-U particles in the U10Mo foils, changing the chemistry, and thus lattice parameter

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Partly filled gauge volume

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Partly filled gauge volume

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Partly filled gauge volume

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Partly filled gauge volume

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Partly filled gauge volume

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Shift in Center-of-Gravity due to misalignment

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Shift in Center-of-Gravity due to misalignment

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Shift in Center-of-Gravity due to misalignment

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo-Strain due to Changes in Scattering Geometry Shift in Center-of-Gravity due to misalignment

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA On-Board Calibrant Corrects for Sample Misalignment Annealed copper foil attached to both sides of the fuel plate – Sample translated in the Normal direction to validate approach – Copper lattice parameter forced to be constant Copper

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Significant Pseudo Strains due to Offset Measured pseudo strains using first point as reference – The slopes are within error bar of each other Copper

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo Strains can be Predicted Predicted pseudo strains for TOF instrument Copper X.-L. Wang, Y. D. Wang and J. W. Richardson, J. Appl. Cryst., 2002

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Pseudo Strains can be Predicted Predicted pseudo strains for TOF instrument – SMARTS: L 0 = 31 m, L 1 = 1.5 m, 2  = 90 degrees: C x = 364 X.-L. Wang, Y. D. Wang and J. W. Richardson, J. Appl. Cryst., 2002

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Measured and Predicted Pseudo Strain are in Good Agreement X.-L. Wang, Y. D. Wang and J. W. Richardson, J. Appl. Cryst., 2002 Copper Predicted pseudo strains for TOF instrument – SMARTS: L 0 = 31 m, L 1 = 1.5 m, 2  = 90 degrees: C x = 364

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA On-Board Calibrant Corrects for Sample Misalignment Annealed copper foil attached to both sides of the fuel plate – Sample translated in the Normal direction to validate approach – Copper lattice parameter forced to be constant Copper

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA On-Board Calibrant Corrects for Sample Misalignment Annealed copper foil attached to both sides of the fuel plate – Sample translated in the Normal direction to validate approach – Copper lattice parameter forced to be constant – Same correction applied to U-10Mo and Zr lattice parameter values Copper U-10Mo Zr

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Measurement Locations on Mini-Plate Copper foil was applied to a large portion of the Mini-Plates – Copper was present at all measurement locations

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA The Mo content changes during HIP’ing as  -U precipitates form – This means that we cannot use a common stress-free lattice parameter, a 0, for all samples The stress state is determined using the these assumptions: – Isotropic elastic behavior, i.e. Hooke’s laws applies with E and fully describing the properties – The average of all normal stresses measured more than 20 mm away from the edge of the foil is set to zero These are reasonable assumptions for the U10Mo and the Al as they are fairly isotropic, but not for Zr as it is relatively anisotropic and has a strong texture Atypical Reference Determination due to Low Chemistry Stability

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Directional Variation of Lattice Parameter is Indicative of Residual Stress The lattice parameters are very similar for Longitudinal and Transverse directions, whereas the normal direction is significantly lower – This is consistent with an in-plane tensile residual stress in the u-10Mo due to the difference in CTE between U-10Mo and Zr Bare Foil

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Directional Variation of Lattice Parameter is Indicative of Residual Stress Process: 650C Post Cold Roll Anneal prior to cladding – The cladding process flips the relative difference in lattice parameter of the in-plane and out-of-plane lattice parameters Bare FoilClad FoilCladding

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Cladding Residual Stresses Close to Yield Stress Process: 650C Post Cold Roll Anneal prior to cladding – Cladding generates compressive in-plane stresses in the foil due to CTE difference – The cladding show matching tensile in-plane stresses – Close to yield stress (about 50 MPa) Clad FoilCladding

U N C L A S S I F I E D Operated by the Los Alamos National Security, LLC for the DOE/NNSA Conclusions Using on-board calibration in the form of annealed copper foils allowed us to measure the residual stresses in several fuel foils after various processing steps A single stress-free lattice parameter reference could not be used for U10Mo due to chemistry changes during processing – Assumption of zero normal stress at the center of the thin foils was successfully applied Residual stress state in aluminum cladding is tensile and close to or at the yield stress; about 50 MPa Matching in-plane compressive state in the U10Mo foil; up to MPa The measurement matrix for the various processing steps provide the ability to design the processing route to control the microstructure and meet specific performance demands