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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Experimental and Modeling Review of the Plutonium-Zirconium (Pu-Zr) System: Lost in Translation and Over Time?

This article presents a review of the phase equilibria of the Pu-Zr system and discusses the contradictory reports on the experimental phase diagram and misinterpretations that have led to confusion over time. In addition, a review of the few Pu-Zr CALPHAD (CALculation of PHAse Diagrams) assessments is presented with emphasis on the heat of formation of the bcc phase, highlighting a disagreement between CALPHAD and ab initio calculations. Based on the information gathered in this study, a critical re-assessment of the Pu-Zr system involving the ζ (Pu 28 Zr), θ (Pu 4 Zr), kinetically hindered κ (PuZr 2 ), and once observed ι phases is called for.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Pre-Transient Characterization of Historic EBR-II Pins for Transient Testing

Current interest in sodium-cooled fast reactor (SFR) designs, such as TerraPower’s Natrium Reactor, has highlighted the need for advanced reactor fuel technology development. Modern U-Zr and U- Pu-Zr pin designs are primary candidates to fuel SFRs and boast high fuel utilization capacity, increased fuel-cladding compatibility, and improved safety through inherent feedback mechanisms. Despite over 60 years of metallic fuel irradiation, uncertainties exist in the performance of the fuel system, particularly under transient overpower (TOP) and loss of flow (LOF) scenarios. Throughout historical testing within the Experimental Breeder Reactor II (EBR-II) and the Fast Flux Test Facility (FFTF), fuel behavior has demonstrated benign response to transient reactor conditions; however, accurate predictions of failure thresholds to inform operational limitations rely heavily on fuel composition, burnup, and irradiation history. In expanding TOP and LOF testing, the Transient Heat sink Overpower Response (THOR) Capsule will be used to test modern fuel technologies in a static sodium environment in the Transient Reactor Test (TREAT) Facility. The THOR capsule is highly instrumented and will provide time-dependent thermal behavior of SFR fuel pins subjected to accident conditions within TREAT. The THOR-Metallic (THOR- M) campaign aims to validate and expand historical TOP and LOF testing on high burnup U-Zr and U-Pu- Zr fuel alloys previously irradiated in EBR-II by running the rods to failure. This contribution focuses primarily on the pre-transient engineering-scale destructive and non- destructive characterization that has been conducted on both the test and sibling pins used for the TOP and LOF tests. All pins underwent visual examination, neutron radiography, element contact profilometry, and precise gamma scan. The sibling pins used for each test were further analyzed using gas assay, sampling, and recharge analysis (GASR), and optical microscopy. The results from each technique confirmed that the fuel pins were intact and devoid of any atypical developments when compared to historical data. Additionally, the analyzed measurements establish a baseline for comparison to post-transient analysis. Key fuel behaviors quanitifed include axial elongation of the fuel column, diametral strain of the pin, patterns in fluff structure geometry, changes in axial isotope distribution, evolution of constituent redistribution, porosity, and fission gas release. The pre-transient measurements and changes attributed to transient behavior from post-transient measurement will be compared to historical data to capture the behavioral dependence on composition, burnup, and irradiation history. Results from this work advance the initiatives of the THOR-M campaign, which aid in informing fuel performance models and establishing safety criteria for SFR operational limits. The novel combination of test environment, in-situ instrumentation, and comprehensive suite of characterization methods provides greater understanding of transient fuel behavior. Overall, information on the time and condition of pin failure for high burnup U-Pu-Zr will greatly expand the limited existing TOP and LOF test data.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Pre-Transient Characterization of Historic EBR-II Pins for Transient Testing

Current interest in sodium-cooled fast reactor (SFR) designs, such as TerraPower’s Natrium Reactor, has highlighted the need for advanced reactor fuel technology development. Modern U-Zr and U- Pu-Zr pin designs are primary candidates to fuel SFRs and boast high fuel utilization capacity, increased fuel-cladding compatibility, and improved safety through inherent feedback mechanisms. Despite over 60 years of metallic fuel irradiation, uncertainties exist in the performance of the fuel system, particularly under transient overpower (TOP) and loss of flow (LOF) scenarios. Throughout historical testing within the Experimental Breeder Reactor II (EBR-II) and the Fast Flux Test Facility (FFTF), fuel behavior has demonstrated benign response to transient reactor conditions; however, accurate predictions of failure thresholds to inform operational limitations rely heavily on fuel composition, burnup, and irradiation history. In expanding TOP and LOF testing, the Transient Heat sink Overpower Response (THOR) Capsule will be used to test modern fuel technologies in a static sodium environment in the Transient Reactor Test (TREAT) Facility. The THOR capsule is highly instrumented and will provide time-dependent thermal behavior of SFR fuel pins subjected to accident conditions within TREAT. The THOR-Metallic (THOR- M) campaign aims to validate and expand historical TOP and LOF testing on high burnup U-Zr and U-Pu- Zr fuel alloys previously irradiated in EBR-II by running the rods to failure. This contribution focuses primarily on the pre-transient engineering-scale destructive and non- destructive characterization that has been conducted on both the test and sibling pins used for the TOP and LOF tests. All pins underwent visual examination, neutron radiography, element contact profilometry, and precise gamma scan. The sibling pins used for each test were further analyzed using gas assay, sampling, and recharge analysis (GASR), and optical microscopy. The results from each technique confirmed that the fuel pins were intact and devoid of any atypical developments when compared to historical data. Additionally, the analyzed measurements establish a baseline for comparison to post-transient analysis. Key fuel behaviors quanitifed include axial elongation of the fuel column, diametral strain of the pin, patterns in fluff structure geometry, changes in axial isotope distribution, evolution of constituent redistribution, porosity, and fission gas release. The pre-transient measurements and changes attributed to transient behavior from post-transient measurement will be compared to historical data to capture the behavioral dependence on composition, burnup, and irradiation history. Results from this work advance the initiatives of the THOR-M campaign, which aid in informing fuel performance models and establishing safety criteria for SFR operational limits. The novel combination of test environment, in-situ instrumentation, and comprehensive suite of characterization methods provides greater understanding of transient fuel behavior. Overall, information on the time and condition of pin failure for high burnup U-Pu-Zr will greatly expand the limited existing TOP and LOF test data.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on Pu3Zr by Materials Project

Pu3Zr is alpha La-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Pu sites. In the first Pu site, Pu is bonded to eight Pu and four equivalent Zr atoms to form PuPu8Zr4 cuboctahedra that share corners with twelve equivalent PuPu8Zr4 cuboctahedra, edges with eight equivalent ZrPu12 cuboctahedra, edges with sixteen PuPu8Zr4 cuboctahedra, faces with four equivalent ZrPu12 cuboctahedra, and faces with fourteen PuPu8Zr4 cuboctahedra. There are four shorter (3.22 Å) and four longer (3.25 Å) Pu–Pu bond lengths. All Pu–Zr bond lengths are 3.22 Å. In the second Pu site, Pu is bonded to eight equivalent Pu and four equivalent Zr atoms to form PuPu8Zr4 cuboctahedra that share corners with four equivalent PuPu8Zr4 cuboctahedra, corners with eight equivalent ZrPu12 cuboctahedra, edges with twenty-four PuPu8Zr4 cuboctahedra, faces with six equivalent ZrPu12 cuboctahedra, and faces with twelve PuPu8Zr4 cuboctahedra. All Pu–Zr bond lengths are 3.25 Å. Zr is bonded to twelve Pu atoms to form ZrPu12 cuboctahedra that share corners with four equivalent ZrPu12 cuboctahedra, corners with eight equivalent PuPu8Zr4 cuboctahedra, edges with eight equivalent ZrPu12 cuboctahedra, edges with sixteen equivalent PuPu8Zr4 cuboctahedra, faces with four equivalent ZrPu12 cuboctahedra, and faces with fourteen PuPu8Zr4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pu3Zr by Materials Project

Pu3Zr is alpha Samarium-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pu is bonded to eight equivalent Pu and four equivalent Zr atoms to form PuPu8Zr4 cuboctahedra that share corners with four equivalent ZrPu12 cuboctahedra, corners with fourteen equivalent PuPu8Zr4 cuboctahedra, edges with six equivalent ZrPu12 cuboctahedra, edges with twelve equivalent PuPu8Zr4 cuboctahedra, faces with four equivalent ZrPu12 cuboctahedra, and faces with sixteen equivalent PuPu8Zr4 cuboctahedra. There are two shorter (3.22 Å) and six longer (3.31 Å) Pu–Pu bond lengths. There are two shorter (3.27 Å) and two longer (3.28 Å) Pu–Zr bond lengths. Zr is bonded to twelve equivalent Pu atoms to form ZrPu12 cuboctahedra that share corners with six equivalent ZrPu12 cuboctahedra, corners with twelve equivalent PuPu8Zr4 cuboctahedra, edges with eighteen equivalent PuPu8Zr4 cuboctahedra, faces with eight equivalent ZrPu12 cuboctahedra, and faces with twelve equivalent PuPu8Zr4 cuboctahedra.

36 MATERIALS SCIENCE↗