Nuclear Safety Research Unit Vienna (Austria), IAEA meeting Evaluation of creep during dry storage in low and high burnup fuels F. Feria, L.E. Herranz CONTENTS 1.Motivation and objective 2.Extension of FRAPCON-3.3 creep law 3.Creep assessment 4.Final remarks

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting 1. MOTIVATION AND OBJECTIVE Safety objectives: -Radiation dose -Subcriticality -Confinement -Retrievability Degrading mechanisms SCC Creep DHC Cladding integrity Evaluation in low and high burnup

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting In-FRAPCON modelling 2. EXTENSION OF FRAPCON-3.3 CREEP LAW Creep law:

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting 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

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting Zircaloy-4 database (EDF) 2. EXTENSION OF FRAPCON-3.3 CREEP LAW Generic correlation

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting CIEMAT creep law 2. EXTENSION OF FRAPCON-3.3 CREEP LAW

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting CIEMAT creep law 2. EXTENSION OF FRAPCON-3.3 CREEP LAW

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting Implementation   ≥ 121 MPa → Creep law parameters derived from irradiated claddings data   ≤ 121 MPa → Creep law parameters derived from non-irradiated claddings data 2. EXTENSION OF FRAPCON-3.3 CREEP LAW 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: No experimental data is available with irradiated material under low hoop stress

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting 3. CREEP ASSESMENT a) Zircaloy-4 45 GWd/tU 1º) In-reactor irradiation 2º) Pool storage (1 year) 3º) Dry out (1 day) 4º) Dry storage (2 years) Phases b) Zircaloy-4 63 GWd/tU Postulated scenarios

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting 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

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting The creep main impact would take place during the first months 3. CREEP ASSESMENT Results In no case creep reaches 1 % strain limit Nearly 4 times higher hoop strain as burn-up is increased by 40 %

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting 4. FINAL REMARKS High burn-up effect seems substantial and causes major differences in the nuclear fuel response in terms of creep Further work: Extend CIEMAT creep law to irradiated fuel rods submitted to low stresses Extend the study up to 100 years to estimate the final creep asymptotic value The results would have a conservative nature because the irradiation hardening effect is not considered at low stresses

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting 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

Nuclear Safety Research Unit Vienna (Austria), IAEA meeting THANK YOU FOR YOUR ATTENTION