1. Fuel Behavior in Long-term Management of Spent Light-Water Reactor Fuel International Conference on Management of Spent Fuel from Nuclear Power Reactors May 31 – June 4, 2010 Albert Machiels Senior Technical Executive

2. 2 © 2010 Electric Power Research Institute, Inc. All rights reserved. Topics Managed Storage Structural Materials Ageing Dry Storage & Transportability of Spent Fuel Thermal Creep Hydriding Re-orientation Delayed Hydrogen Cracking Summary/Discussion

3. 3 © 2010 Electric Power Research Institute, Inc. All rights reserved. Issues for Consideration (from IAEA) (12) Can we confidently model current fuel and material behaviour for long-term storage? What are the technological criteria for ensuring that long-term storage be sustainable? (26) How sustainable is storage for the long term? (28) Is there a possibility for an international consensus on the future strategy for fuel management?

4. 4 © 2010 Electric Power Research Institute, Inc. All rights reserved.

5. 5 LWR Power Block

6. 6 © 2010 Electric Power Research Institute, Inc. All rights reserved. LWR Power Block Managed Storage

7. 7 © 2010 Electric Power Research Institute, Inc. All rights reserved. LWR Power Block Managed Storage Geologic Repository

8. 8 © 2010 Electric Power Research Institute, Inc. All rights reserved. LWR Power Block Managed Storage Geologic Repository FR Power Block

9. 9 © 2010 Electric Power Research Institute, Inc. All rights reserved. LWR Power Block Managed Storage Geologic Repository FR Power Block

10. 10 © 2010 Electric Power Research Institute, Inc. All rights reserved. Managed Storage (continued) Interim nature: functional requirements such as retrievability Protection of public health and environment –Safety (shielding, subcriticality, confinement/containment) Potentially long storage period: century scale Systems: passive or low-complexity active  Emphasis on materials degradation phenomena –Security Material accountability (theft) Protection against malicious acts –Public acceptance Public dislike for radioactivity, and especially wastes

11. 11 © 2010 Electric Power Research Institute, Inc. All rights reserved. Structural Material Ageing Ageing Management –Evolved in the context of “License Renewal Application” for operating nuclear power plants beyond their original licenses US Code of Federal Regulations, Title 10, Part 54 –Provides well-tested approach for successful interactions between licensees and regulators Integrated plant assessment Time-limited aging analyses (TLAA)

12. 12 © 2010 Electric Power Research Institute, Inc. All rights reserved. Dry Storage & Transportability of Spent Fuel

13. 13 © 2010 Electric Power Research Institute, Inc. All rights reserved. Dry Storage & Transportability of Spent Fuel Over 1250 Casks Loaded in the US

14. 14 © 2010 Electric Power Research Institute, Inc. All rights reserved. Dry Storage & Transportability of Spent Fuel Scenario: Spent UOx Fuel in Dry Storage for 50-150 years followed by transportation Material issues: –Normal Conditions Maintaining high level of cladding integrity No substantial alteration of normal assembly geometry –Accident Conditions Maintaining subcriticality Emphasis on fuel rod cladding

15. 15 © 2010 Electric Power Research Institute, Inc. All rights reserved. Material Degradation Issues Mechanisms –Air Oxidation –[Cladding Stress Corrosion Cracking] –Thermal Creep and Creep Rupture –Hydride Re-orientation [and Migration] and Impact on Cladding Mechanical Properties –[Delayed Hydrogen Cracking (DHC)]

16. 16 © 2010 Electric Power Research Institute, Inc. All rights reserved. Material Degradation Issues Mechanisms –Air Oxidation –[Cladding Stress Corrosion Cracking] –Thermal Creep and Creep Rupture –Hydride Re-orientation [and Migration] and Impact on Cladding Mechanical Properties –[Delayed Hydrogen Cracking (DHC)] Driving Forces – (Peak) Temperature – Cladding stresses

17. 17 © 2010 Electric Power Research Institute, Inc. All rights reserved. Thermal Creep Prevention of creep rupture: limit diametric creep strain to < 1%

18. 18 © 2010 Electric Power Research Institute, Inc. All rights reserved. Thermal Creep However, any strain value is acceptable as long as local cladding stress remains below yield strength –Fuel rods are closed systems: Creep deformations tend to be self-limiting –Limiting peak temperatures are likely to be relatively high, even taking annealing effects into account

19. 19 © 2010 Electric Power Research Institute, Inc. All rights reserved. Initial Hydride Morphology

20. 20 © 2010 Electric Power Research Institute, Inc. All rights reserved. Hydride Morphology (after heating to ~400°C and cooling under “low” stresses)

21. 21 © 2010 Electric Power Research Institute, Inc. All rights reserved. Hydride Morphology (after heating to ~400°C and cooling under “moderate” stresses)

22. 22 © 2010 Electric Power Research Institute, Inc. All rights reserved. Hydride Morphology (after heating to ~400°C and cooling under “high” stresses)

23. 23 © 2010 Electric Power Research Institute, Inc. All rights reserved. Impact on Cladding Mechanical Properties Impact of Re-orientation on Room Temperature Mechanical Properties

24. 24 © 2010 Electric Power Research Institute, Inc. All rights reserved. Hydride Re-orientation – Impact on Cladding Mechanical Properties Mechanical Properties vs. Testing Temperature

25. 25 © 2010 Electric Power Research Institute, Inc. All rights reserved. Delayed Hydrogen Cracking Recent controversy about rate controlling process for DHC propagation (cfr. Journal of Nuclear Materials) – Y.S. Kim et al.: “Precipitation First Model” –Hydride precipitates at a crack upon the imposition of a tensile stress –Concentration gradient results in diffusion of hydrogen to the crack tip – M. P. Puls et al.: “Diffusion First Model” –Stress gradient results in diffusion of hydrogen to the crack tip –Crack grows if hydrogen concentration > solubility limit for hydride precipitation

26. 26 © 2010 Electric Power Research Institute, Inc. All rights reserved. When Does It Matter? Normal Conditions –Maintaining high level of cladding integrity –No substantial alteration of normal assembly geometry Time (yrs) Hoop Stress (MPa) 200 MPa Without Creep 150 MPa Without Creep 100 MPa Without Creep 200 MPa With Creep 150 MPa With Creep 100 MPa With Creep

27. 27 © 2010 Electric Power Research Institute, Inc. All rights reserved. When Does It Matter … Not? Accident Conditions –Maintaining subcriticality Transportation applications

28. 28 © 2010 Electric Power Research Institute, Inc. All rights reserved. When Does It Matter … Not? Accident Conditions –Maintaining subcriticality Transportation applications Risk Information Criticality Safety Information Impact of misloading Impact of fuel reconfiguration

29. 29 © 2010 Electric Power Research Institute, Inc. All rights reserved. Summary Managed Storage Thermal Creep and Hydride Re-orientation in the context of dry storage and transportability –IAEA Coordinated Research Program (CRP) on Spent Fuel Performance Assessment and Research (SPAR) TECDOC-1343 (SPAR-I) TECDOC-wxyz (SPAR-II): to be published –EPRI 1015048 “Spent Fuel Transportation Applications – Assessment of Cladding Performance: A Synthesis Report” (2007)

30. 30 © 2010 Electric Power Research Institute, Inc. All rights reserved. Discussion Can we confidently model current fuel and material behavior for long-term storage? –Qualified yes! –Modeling of entire system is important –Confirmatory surveillance/demonstration program What are the technological criteria for ensuring that long- term (dry) storage be sustainable? –Ageing management for structural materials –Transportability and transportation safety