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Evaluation of creep during dry storage in low and high burnup fuels

Evaluation of creep during dry storage in low and high burnup fuels. F. Feria, L.E. Herranz. CONTENTS. Motivation and objective Extension of FRAPCON-3.3 creep law Creep assessment Final remarks. 1. MOTIVATION AND OBJECTIVE. Safety objectives:. Radiation dose Subcriticality

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Evaluation of creep during dry storage in low and high burnup fuels

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  1. Evaluation of creep during dry storage in low and high burnup fuels F. Feria, L.E. Herranz CONTENTS • Motivation and objective • Extension of FRAPCON-3.3 creep law • Creep assessment • Final remarks

  2. 1. MOTIVATION AND OBJECTIVE Safety objectives: • Radiation dose • Subcriticality • Confinement • Retrievability Cladding integrity Degrading mechanisms SCC Creep DHC Evaluation in low and high burnup

  3. 2. EXTENSION OF FRAPCON-3.3 CREEP LAW In-FRAPCON modelling Creep law:

  4. 2. EXTENSION OF FRAPCON-3.3 CREEP LAW Creep law validity range Restricted to in-reactor conditions Extension of the creep law is needed to apply the code to dry storage conditions

  5. 2. EXTENSION OF FRAPCON-3.3 CREEP LAW Zircaloy-4 database (EDF) Generic correlation

  6. 2. EXTENSION OF FRAPCON-3.3 CREEP LAW CIEMAT creep law

  7. 2. EXTENSION OF FRAPCON-3.3 CREEP LAW CIEMAT creep law

  8. 2. EXTENSION OF FRAPCON-3.3 CREEP LAW Implementation Together with a suitable logic that allows choosing between the “in-reactor” equation and the dry storage equation, according to the prevailing conditions at the calculation time The extension splits in two hoop stress ranges: • sq ≥ 121 MPa → Creep law parameters derived from irradiated claddings data • sq≤ 121 MPa → Creep law parameters derived from non-irradiated claddings data No experimental data is available with irradiated material under low hoop stress

  9. 3. CREEP ASSESMENT Postulated scenarios a) Zircaloy-4 45 GWd/tU b) Zircaloy-4 63 GWd/tU Phases 1º) In-reactor irradiation 2º) Pool storage (1 year) 3º) Dry out (1 day) 4º) Dry storage (2 years)

  10. 3. CREEP ASSESMENT Results a) Zircaloy-4 45 GWd/tU b) Zircaloy-4 63 GWd/tU • Once dry storage starts hoop stress causes a creep-out situation

  11. 3. CREEP ASSESMENT Results • The creep main impact would take place during the first months • In no case creep reaches 1 % strain limit • Nearly 4 times higher hoop strain as burn-up is increased by 40 %

  12. 4. FINAL REMARKS • High burn-up effect seems substantial and causes major differences in the nuclear fuel response in terms of creep • The results would have a conservative nature because the irradiation hardening effect is not considered at low stresses • Further work: • Extend CIEMAT creep law to irradiated fuel rods submitted to low stresses • Extend the study up to 100 yearsto estimate the final creep asymptotic value

  13. ACKNOWLEDGMENTS The authors are indebted to ENRESA for their financial support and the technical discussions held and to the FRAPCON-3 developers for their technical support during this work

  14. THANK YOU FOR YOUR ATTENTION

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