1. Oxygen Potential in High Burnup LWR Fuel using Themochimica in MOOSE/BISON Theodore M. Besmann

2. 2 Outline Introduction to thermodynamics and chemistry of fission products Introduction to T HERMOCHIMICA New thermodynamic model for nuclear fuel Model of fission product inventory with burnup Implementation validation of thermodynamics model for oxygen potential in nuclear fuel Coupling of oxygen potential with existing burnup models Next steps

3. 3 Motivation The evolving chemical composition of LWR fuel during irradiation and the corresponding thermochemical properties strongly influence the fuel’s behavior in normal operating conditions and during transients. The chemical state influences physical properties and response of the fuel including thermal conductivity, heat capacity, swelling, creep, fission product volatility, etc.

4. 4 Motivation Thermochemical equilibrium calculations are only one of the tools for estimation of the nuclear fuel’s chemical state and behavior. During irradiation, the FP are continuously generated and change due to transmutation and decay, the oxygen chemical potential changes with the burnup and production of fission products, and temperature and chemical potential gradients affect the formation of various phases and species transport and spatial distribution. A thermochemistry equilibrium solver needs to be a part of a larger multi-physics simulation system in order to achieve its full potential.

5. 5 Thermochemical Model of LWR Nuclear Fuel

6. 6 Thermochemical Modeling of Burnup

7. 7 SCALE Simulation for High Burnup LWR Fuel The irradiation history of UO 2 fuel used in the current simulation.

8. 8 Burnup Simulation using SCALE SCALE model geometry where r is the outer radius of the annular section in mm.

9. 9 Evolution of Fission Products with Burnup

10. 10 Title The predicted average chemical element inventory compared to experimental measurements of Walker et al. 2005.

11. 11 Title The predicted oxygen potential compared to experimental measurements of Walker et al. 2005. The measurements for the location r/r o =0.1 were not reproducible in experiments and had large errors. The correlation with experiments is fairly good  Experiments had an estimated error of 10%

12. 12 Title The predicted oxygen potential distribution along the radius of the pellet compared to experimental measurements of Walker et al. 2005.

13. 13 Integration with Existing Burnup Models in BISON (a) Temperature [K], and (b) oxygen potential [J/mol] for time 18800 s (5.2 hr) (a)(b)

14. 14 Title (a) Oxygen potential [J/mol] and (b) oxygen to metal ratio at 1.32828e+07 s (154 days) (a)(b)