Engineered Zircaloy Cladding Modifications for Improved Accident Tolerance of LWR Fuel

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1 Engineered Zircaloy Cladding Modifications for Improved Accident Tolerance of LWR Fuel Brent J. Heuser Nuclear, Plasma, & Radiological Engineering University of Illinois at Urbana-Champaign US DOE NEUP ATF-IRP UIUC Prime

2 Objectives and Background Response to large amounts of H generation due to high temperature oxidation of Zr-base cladding A major concern both Post-Three Mile Island and Post-Fukushima Several US and International Programs Issues: Extensive experience with Zr-based cladding Irradiation performance, processing experience, Qualification issues, Very difficult to move to a new cladding material Approach: Examine Zr-based cladding with improved high temperature oxidation resistance

3 Participants

4 UIUC AFT-IRP Philosophical Approach U.S. LWR assets are safe, well-maintained, and well-operated. Zr-based cladding performs well in LWRs under normal operational conditions. Extensive performance data base with respect to normal and transient conditions. Regulatory approval/industry acceptance for modified Zr-based cladding path of least resistance. Modifications of Zr-based cladding can lead to ATF without significant impact on performance under normal operational conditions.

5 Two Solution Pathways to Mitigate Accelerated Oxidation and H 2 (g) Production Oxide-resistant coating Self-healing Deposition Co-extrusion χ phase composition modification Reduced oxide growth Increase time to breakaway oxide growth Reduced heat input; reduced H 2 generation Increase in coping time

6 Self-healing pathway Zircaloy ATI Wah Chang (intermediate stock supplier) χ phases χ phases with additives: Si, Al, Mo, Cr Additives segregate to free surface; incorporated into oxide; lower growth kinetics; longer onset to accelerated oxide growth. χ precipitates dissolve ~900 C T Stable χ precipitates at LWR operating T

7 TMA1 Reactor systems modeling PARCS RELAP MCNP TRACE Deliverable T(t, r) q(t, r) FALCON BISON TMA2 Cladding performance Exp. Database Predictive capability Predictive capability Work Scope Flow Diagram Holistic Approach Oxide weight gain vs. time, m(t) IASCC BWR/PWR k[m(t), phase behavior (χ, Zr-H, zirconia)] Materials performance modeling Predictive capability BISON DICTRA VASP Cladding sample fabrication

8 Participation Interconnections Predictive Capability DFT/ThermoCalc/DICTRA UIUC/INL BISON/INL Benchmarking INL/UIUC Refined Materials Selection [stage 2, 3, ] Material Selection [stage 1] TMA1 dpa UM/UIUC/UoM Specimen Fabrication ATI/UIUC Experimental Phase Database m(t)/uiuc/uom SCC/UF/UM IASCC/UM k/uiuc UIUC/Univ. Illinois UF/Univ. Florida UM/Univ. Michigan UoM/Univ. Manchester INL/Idaho National Laboratory ATI/ATI Wah Chang

9 Experimental Capabilities Sample Fabrication Sputter deposition: U. Illinois Cladding fabrication: ATI Wah Chang

10 Experimental Capabilities In-service corrosion Autoclave capability: U. Michigan, U. Florida, U. Manchester Ion accelerator capability: U. Illinois, U. Michigan, U. Manchester

11 Experimental Capabilities Off-normal oxidation TGA: U. Illinois, U. Manchester

12 Experimental Capabilities Microanalytical Characterization Microanalytical: U. Illinois (FS-MRL), U. Michigan, U. Florida, U. Manchester AES, TOF-SIMS, XPS, FIB, X-ray based techniques, TEM, SEM, AFM, ANL: IVEM, APS

13 U.S. DOE NEUP/U.K. RCEP Investment

14 Zr-Sn phase diagram

15 Zr-H and Zr-H-O Phase Diagrams β-bcc δ-fcc 700 C ε-fct α-hcp Relevant region for in-service and UFS

16 Zr-H phase behavior at low H concentration

17 Conclusions Multidisciplinary Approach to Accident Tolerant Fuel Cladding materials, neutronics, irradiation performance, processing, corrosion, Response to large amounts of H generation due to high temperature oxidation of Zr-base cladding A major concern both Post-Three Mile Island and Post-Fukushima International Collaborations