# Fully-coupled engineering and mesoscale simulations of thermal conductivity in UO2 fuel using an implicit multiscale approach

## Abstract

Reactor fuel performance is sensitive to microstructure changes during irradiation (such as fission gas and pore formation). This study proposes an approach to capture microstructural changes in the fuel by a two-way coupling of a mesoscale phase field irradiation model to an engineering scale, finite element calculation. This work solves the multiphysics equation system at the engineering-scale in a parallel, fully-coupled, fully-implicit manner using a preconditioned Jacobian-free Newton Krylov method (JFNK). A sampling of the temperature at the Gauss points of the coarse scale is passed to a parallel sequence of mesoscale calculations within the JFNK function evaluation phase of the calculation. The mesoscale thermal conductivity is calculated in parallel, and the result is passed back to the engineering-scale calculation. As this algorithm is fully contained within the JFNK function evaluation, the mesoscale calculation is nonlinearly consistent with the engineering-scale calculation. Further, the action of the Jacobian is also consistent, so the composite algorithm provides the strong nonlinear convergence properties of Newton's method. The coupled model using INL's \bison\ code demonstrates quadratic nonlinear convergence and good parallel scalability. Initial results predict the formation of large pores in the hotter center of the pellet, but few pores on the outer circumference.more »

- Authors:

- Publication Date:

- Research Org.:
- Idaho National Laboratory (INL)

- Sponsoring Org.:
- DOE - NE

- OSTI Identifier:
- 989275

- Report Number(s):
- INL/JOU-09-16784

Journal ID: ISSN 1742-6588; ISSN 1742-6596; TRN: US1007060

- DOE Contract Number:
- DE-AC07-05ID14517

- Resource Type:
- Journal Article

- Journal Name:
- Journal of Physics: Conference Series

- Additional Journal Information:
- Journal Volume: 180; Journal Issue: 1; Journal ID: ISSN 1742-6588

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; ALGORITHMS; CONVERGENCE; EVALUATION; FISSION; IRRADIATION; MICROSTRUCTURE; NUCLEAR FUELS; PERFORMANCE; SAMPLING; THERMAL CONDUCTIVITY; phase field models; reactor fuel simulation; scale bridging

### Citation Formats

```
Tonks, Michael, Gaston, Derek, Permann, Cody, Millett, Paul, Hansen, Glen, and Newman, Chris.
```*Fully-coupled engineering and mesoscale simulations of thermal conductivity in UO2 fuel using an implicit multiscale approach*. United States: N. p., 2009.
Web. doi:10.1088/1742-6596/180/1/012078.

```
Tonks, Michael, Gaston, Derek, Permann, Cody, Millett, Paul, Hansen, Glen, & Newman, Chris.
```*Fully-coupled engineering and mesoscale simulations of thermal conductivity in UO2 fuel using an implicit multiscale approach*. United States. doi:10.1088/1742-6596/180/1/012078.

```
Tonks, Michael, Gaston, Derek, Permann, Cody, Millett, Paul, Hansen, Glen, and Newman, Chris. Sat .
"Fully-coupled engineering and mesoscale simulations of thermal conductivity in UO2 fuel using an implicit multiscale approach". United States. doi:10.1088/1742-6596/180/1/012078.
```

```
@article{osti_989275,
```

title = {Fully-coupled engineering and mesoscale simulations of thermal conductivity in UO2 fuel using an implicit multiscale approach},

author = {Tonks, Michael and Gaston, Derek and Permann, Cody and Millett, Paul and Hansen, Glen and Newman, Chris},

abstractNote = {Reactor fuel performance is sensitive to microstructure changes during irradiation (such as fission gas and pore formation). This study proposes an approach to capture microstructural changes in the fuel by a two-way coupling of a mesoscale phase field irradiation model to an engineering scale, finite element calculation. This work solves the multiphysics equation system at the engineering-scale in a parallel, fully-coupled, fully-implicit manner using a preconditioned Jacobian-free Newton Krylov method (JFNK). A sampling of the temperature at the Gauss points of the coarse scale is passed to a parallel sequence of mesoscale calculations within the JFNK function evaluation phase of the calculation. The mesoscale thermal conductivity is calculated in parallel, and the result is passed back to the engineering-scale calculation. As this algorithm is fully contained within the JFNK function evaluation, the mesoscale calculation is nonlinearly consistent with the engineering-scale calculation. Further, the action of the Jacobian is also consistent, so the composite algorithm provides the strong nonlinear convergence properties of Newton's method. The coupled model using INL's \bison\ code demonstrates quadratic nonlinear convergence and good parallel scalability. Initial results predict the formation of large pores in the hotter center of the pellet, but few pores on the outer circumference. Thus, the thermal conductivity is is reduced in the center of the pellet, leading to a higher internal temperature than that in an unirradiated pellet.},

doi = {10.1088/1742-6596/180/1/012078},

journal = {Journal of Physics: Conference Series},

issn = {1742-6588},

number = 1,

volume = 180,

place = {United States},

year = {2009},

month = {8}

}