ORNL/TM-2015/161 PIE on Safety-Tested Loose Particles from AGR-1 Compact 4-4-2 John D. Hunn Tyler J. Gerczak Robert N. Morris Charles A. Baldwin Fred C. Montgomery April 2016 Approved for public release. Distribution is unlimited. DOCUMENT AVAILABILITY Reports produced after January 1, 1996, are generally available free via US Department of Energy (DOE) SciTech Connect. 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Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. ORNL/TM-2015/161 Fusion and Materials for Nuclear Systems Division PIE ON SAFETY-TESTED LOOSE PARTICLES FROM AGR-1 COMPACT 4-4-2 John D. Hunn Tyler J. Gerczak Robert N. Morris Charles A. Baldwin Fred C. Montgomery Date Published: April 2016 Work sponsored by US DEPARTMENT OF ENERGY Office of Nuclear Energy - Advanced Reactor Technologies under the Advanced Gas Reactor Fuel Development and Qualification Program Prepared by OAK RIDGE NATIONAL LABORATORY Oak Ridge, TN 37831-6283 managed by UT-BATTELLE, LLC for the US DEPARTMENT OF ENERGY under contract DE-AC05-00OR22725 ORNL/TM-2015/161-R0 CONTENTS List of Figures ............................................................................................................................................... iv List of Tables .............................................................................................................................................. vii Acronyms ................................................................................................................................................... viii Acknowledgments ......................................................................................................................................... ix 1. Introduction ............................................................................................................................................ 1 2. Examination Procedure .......................................................................................................................... 2 3. Furnace testing results ........................................................................................................................... 4 4. IMGA results ......................................................................................................................................... 9 5. Microstructural Analysis ..................................................................................................................... 20 5.1 Particles with Failed TRISO—X-ray Tomography and Optical Microscopy ................. 20 5.2 Particles with Failed TRISO—SEM with EDS ............................................................... 29 5.3 Particles that Retained Cesium—Optical Microscopy and SEM with EDS .................... 39 6. Conclusion ........................................................................................................................................... 47 7. References ............................................................................................................................................ 50 iii ORNL/TM-2015/161-R0 LIST OF FIGURES 1. CCCTF fuel holder assembly for the loose-particle test: a) fifteen-particle tray, b) five-tray assembly, and c) tray assembly in standard CCCTF graphite holder. ................................................... 2 2. Cumulative release of cesium and krypton from Compact 4-4-2 loose particles at 1800°C. Note that the magnitude of the cesium release may be off due to uncertainty in the deposition cup collection efficiency, as discussed at the end of this section. ................................................................ 4 3. Average rate of cesium release during each deposition cup collection interval. ....................................... 5 4. Cumulative release of silver, europium, and strontium from Compact 4-4-2 loose particles at 1800°C. Note that the magnitude of the plotted release may be off due to uncertainty in the deposition cup collection efficiency, as discussed at the end of this section. ....................................... 6 5. Time-dependent cumulative release of silver from 1800°C safety test of Compact 4-4-1. ....................... 7 6. Schematic of the CCCTF furnace [Baldwin et al., 2012]. ......................................................................... 8 7. Ratio of 137Cs in 4001 particles deconsolidated from as-irradiated Compact 4-4-2 versus the calculated inventory, adjusted for variation in fissionable material and burnup with the measured 144Ce activity [Hunn et al. 2013a, 23]. ................................................................................... 9 8. Ratio of 110mAg in 90 as-irradiated Compact 4-4-2 particles versus calculated inventory, adjusted for variation in fissionable material and burnup with the measured 137Cs activity [Hunn et al. 2013a, 25]. ....................................................................................................................... 10 9. Ratio of 154Eu in 90 as-irradiated Compact 4-4-2 particles versus calculated inventory, adjusted for variation in fissionable material and burnup with the measured 137Cs activity [Hunn et al. 2013a, 24]. ........................................................................................................................................... 10 10. Radioisotope retention fraction of 75 particles after 1800°C safety testing. ......................................... 14 11. Particle 442-A009: (a and b) oblique orthogonal x-ray tomographs showing SiC crack aligned with buffer/IPyC crack, with adjacent U-dispersion in IPyC; (c) optical micrograph of a polished section showing U dispersion in the IPyC; (d) another area in the same polished section where typical local SiC degradation at the tip of an IPyC crack was observed that was not associated with the TRISO failure. ......................................................................................... 21 12. Particle 442-A064: (a and b) oblique orthogonal x-ray tomographs showing SiC crack at top and bottom of image and noticeable loss of kernel material; (c) 3D visualization using threshold filter to display SiC surface (OPyC layer is semitransparent) to show extended SiC crack that almost circumnavigated this particle, (d–f) optical micrographs of polished section showing SiC crack and degradation at IPyC/SiC interface. ................................................................ 22 13. Particle 442-A053: (a and b) oblique orthogonal x-ray tomographs showing through-layer SiC degradation aligned along an IPyC crack and significant uranium dispersion throughout the buffer and IPyC, (c) sectioned 3D visualization using a threshold filter to emphasize SiC and higher-density material (pyrocarbon not visible) and showing an extended SiC crack with degradation, (d and e) optical micrographs of polished section showing metallic clusters in SiC and degradation extending out into SiC along the crack. ............................................................. 23 14. Particle 442-A053: Set of images obtained further from midplane compared to Figure 13; (a) x-ray tomograph showing same plane as (b), (b–e) optical micrograph of polished section showing SiC degradation along crack and missing pockets of IPyC associated with radial dispersions of uranium visible in (a), (f) SiC degradation in another plane that was parallel and close to (c) showing a crack through the degraded region. ........................................................... 24 15. Particle 442-A072: (a and b) oblique orthogonal x-ray tomographs showing SiC crack (lower left) and kernel protrusion with significant local dispersion in IPyC with related SiC degradation that did not penetrate the layer, (c–e) optical micrographs of polished section showing kernel reaction with buffer and degradation in the IPyC and SiC where kernel material had protruded to the IPyC. ..................................................................................................... 25 iv ORNL/TM-2015/161-R0 16. Particle 442-A050: (a and b) oblique orthogonal x-ray tomographs showing SiC degradation through layer at tip of IPyC crack associated with edge of buffer delamination, (c) 3D semitransparent visualization showing kernel protrusion and extended SiC degradation along a crack in the SiC, (d and e) optical micrographs of polished section showing SiC degradation at tip of IPyC crack. ......................................................................................................... 26 17. BEC micrograph from Particle 442-A009 showing the localized SiC degradation at the tip of an IPyC crack also shown in Figure 11d. ............................................................................................ 30 18. BEC micrographs of Particle 442-A009 showing two magnifications of the region near the through-layer crack with a large, concentrated dispersion of high-Z features in the IPyC and SiC. ...................................................................................................................................................... 30 19. BEC micrographs of Particle 442-A009 for comparison to Figure 18 showing two magnifications of a region away from the through-layer crack with more typical dispersion of high-Z features. ............................................................................................................................... 31 20. BEC micrographs of Particle 442-A064 showing the distribution of uranium features in the SiC layer in (a) a region with an IPyC crack near the IPyC/SiC interface, and (b) an area away from any cracks in the TRISO layers. ........................................................................................ 31 21. SiC fracture area in Particle 442-A064 showing SEI micrograph and corresponding EDS maps of x-ray intensity indicating concentration profiles of uranium, silicon, and carbon. ............... 32 22. SEI micrograph and corresponding EDS x-ray intensity map of the uranium concentration showing the dispersion of uranium in the buffer of Particle 442-A053. ............................................. 33 23. Particle 442-A053 SEM micrographs showing (a) the SiC layer next to a uranium dispersion lobe with significant SiC attack and (b) the SiC layer with no adjacent uranium dispersion lobe in the IPyC layer. ......................................................................................................................... 33 24. SEM analysis of Particle 442-A053 showing (a) close-up SEI micrograph of degraded region surrounding a SiC crack filled with a dense material, and (b) close-up BEC micrograph confirming high-Z features flanking the degraded region and low-Z material nearest the crack. .................................................................................................................................................... 34 25. SEM/EDS analysis of Particle 442-A053 showing an overview SEI micrograph of the region surrounding a through-layer crack in the SiC and corresponding EDS x-ray intensity maps indicating relative concentrations of uranium, silicon, and carbon. .................................................... 34 26. SEI micrograph of Particle 442-A072 showing an area where the kernel protrusion contacted the IPyC layer; the marked zones (1 and 2) indicate regions investigated by the EDS x-ray mapping presented in Figure 27 and Figure 28. .................................................................................. 35 27. Particle 442-A072 EDS analysis showing SEI micrograph of Figure 26 Zone 1 and corresponding EDS x-ray intensity maps indicating relative concentrations of the most prominent elements. ............................................................................................................................. 36 28. Particle 442-A072 EDS analysis showing SEI micrograph of Figure 26 Zone 2 and corresponding EDS x-ray intensity maps indicating relative concentrations of the most prominent elements. ............................................................................................................................. 37 29. Particle 442-A072 BEC micrographs showing (a) the SiC layer next to a uranium dispersion lobe with significant SiC attack and (b) the SiC layer with no adjacent uranium dispersion lobe in the IPyC layer. ......................................................................................................................... 37 30. SEM analysis of a SiC decomposition area in Particle 442-A050 showing SEI micrograph and corresponding EDS x-ray intensity maps indicating relative concentrations of uranium, silicon, and carbon. The linear features observed in the SEI micrograph are due to delamination of the ~8-nm-thick carbon coating applied to reduce charging of the sample during analysis. .................................................................................................................................... 38 31. Particle 442-A050 BEC micrographs showing SiC layer not adjacent to a crack in the IPyC layer. .................................................................................................................................................... 39 32. Optical micrographs of particles that retained cesium: (a) Particle 442-A074 with high silver retention, and (b) Particle 442-A016 with low silver retention. .......................................................... 40 v ORNL/TM-2015/161-R0 33. Particle 442-A063 SEM analysis showing (a and c) SEI versus (b and d) BEC micrographs at two magnifications; some typically-observed features are identified. ................................................ 41 34. Optical micrograph of Particle 442-A063 showing SiC degradation at OPyC/SiC interface. .............. 41 35. Comparison of BEC micrographs of TRISO layers from particles in Table 7 highlighting the interaction of fission products with the SiC as a function of silver retention. ..................................... 42 36. SEI micrograph of Particle 442-A055 showing regions of SiC degradation. ........................................ 42 37. SEM/EDS analysis of IPyC and SiC layers in Particle 442-A074 showing SEI micrograph and corresponding EDS x-ray intensity maps of relative silicon, ruthenium, rhodium, palladium, and uranium concentrations. ................................................................................................................ 43 38. SEM/EDS analysis of IPyC and SiC layers in Particle 442-A046 showing SEI micrograph and corresponding EDS x-ray intensity maps of relative silicon, ruthenium, rhodium, palladium, and uranium concentrations. ................................................................................................................ 44 39. SEM/EDS analysis of IPyC and SiC layers in Particle 442-A063 showing SEI micrograph and corresponding EDS x-ray intensity maps of relative silicon, ruthenium, rhodium, palladium, and uranium concentrations. ................................................................................................................ 44 40. SEM/EDS analysis of IPyC and SiC layers in Particle 442-A016 showing SEI micrograph and corresponding EDS x-ray intensity maps of relative silicon, ruthenium, rhodium, palladium, and uranium concentrations. ................................................................................................................ 45 41. SEM/EDS analysis of IPyC and SiC layers in Particle 442-A055 showing SEI micrograph and corresponding EDS x-ray intensity maps of relative silicon, ruthenium, rhodium, palladium, and uranium concentrations. ................................................................................................................ 45 42. SEM/EDS analysis of IPyC and SiC layers in Particle 442-A059 showing SEI micrograph and corresponding EDS x-ray intensity maps of relative silicon, ruthenium, rhodium, palladium, and uranium concentrations. ................................................................................................................ 46 vi ORNL/TM-2015/161-R0 LIST OF TABLES 1. Distribution of radioactive isotopes detected in the CCCTF furnace internals after the Compact 4-4-2 loose-particle furnace test ............................................................................................. 5 2. Analysis of measurement bias after recalibration for activity of several gamma-emitting isotopes in as-irradiated Compact 4-4-2 particles ............................................................................... 11 3. Activity in Bq/particle of gamma-emitting isotopes in particles before safety test ................................. 12 4. Activity in Bq/particle of gamma-emitting isotopes in particles after safety test .................................... 15 5. Fraction of gamma-emitting isotopes retained in particles after safety test ............................................ 17 6. Activity in Bq/particle of gamma-emitting isotopes in graphite trays (Figure 1) .................................... 19 7. Description of the six particles investigated by optical microscopy and SEM analysis that retained cesium (as well as ruthenium, antimony, and cerium), but exhibited varied retention of silver or europium. ........................................................................................................... 39 vii ORNL/TM-2015/161-R0 ACRONYMS 3D Three-dimensional AGR Advanced Gas Reactor Fuel Development and Qualification Program AGR-1 First AGR Program irradiation experiment ART Advanced Reactor Technologies ATR Advanced Test Reactor (at INL) BEC Backscattered-electron composition BWXT BWX Technologies CCCTF Core Conduction Cooldown Test Facility (at ORNL) DOE-NE Department of Energy Office of Nuclear Energy EDS Energy-dispersive spectroscopy FACS Fuel Accident Condition Simulator (at INL) FB-CVD Fluidized-bed chemical vapor deposition (coating furnace) FIMA Fissions per initial metal atom GMT Greenwich Mean Time HFEF Hot Fuel Examination Facility (at INL) HTGR High Temperature Gas-cooled Reactor IFEL Irradiated Fuels Examination Laboratory (ORNL Building 3525) IMGA Irradiated Microsphere Gamma Analyzer (at ORNL) INL Idaho National Laboratory IPyC Inner pyrolytic carbon (layer) M/C Measured versus calculated ratio OPyC Outer pyrolytic carbon (layer) ORNL Oak Ridge National Laboratory PIE Post-irradiation examination SD Standard deviation SEI Secondary-electron imaging SEM Scanning electron microscope SiC Silicon carbide (layer) TAVA Time-averaged and volume-averaged (compact irradiation temperature) TRISO Tristructural isotropic (coated particles) Z Atomic number viii
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