AREVA Idealized Case

Rod Design Specifications

The rod simulated for this particular case was based on an idealized commercial reactor fuel rod. Details of the rod geometry and specifications are summarized in Table 1.

Operating Conditions and Irradiation History

The operating conditions for this simulation were based on power cycles in a commercial French PWR. The operating conditions used are shown in Table 2.

Figure 1: Section of BISON mesh with temperature contour.

Geometry and Mesh

The fuel rod geometry specified in Table 1 was used as a basis for the mesh used in this simulation. The fuel pellets were meshed as a single smeared fuel column. The mesh consists of 1375 axial elements and 12 radial elements in the fuel, and 1375 axial elements and 4 radial elements in the clad, see Figure 1. This simulation was meshed as a 2D-RZ axisymmetric geometry with quadratic elements.

Material and Behavioral Models

The following material and behavioral models were used for the UO fuel:

• UO2Thermal - NFIR: For temperature and burnup dependent thermal properties.

• ComputeFiniteStrainElasticStress and UO2ElasticityTensor: elastic mechanical behavior

• UO2VolumetricSwellingEigenstrain: volumetric expansion due to solid and gaseous swelling

• UO2RelocationEigenstrain: relocation strains, relocation activation threshold power set to 5 kW/m

• ComputeThermalExpansionEigenstrain:thermal expansion with a constant instanteous thermal expansion coefficient

• UO2Sifgrs: fission gas release model used with the gaseous swelling model UO2VolumetricSwellingEigenstrain

For the clad material, a constant thermal conductivity of 16 W/m-K was used and both thermal and irradiation creep were considered using the Limback model (Limbäck and Andersson, 1996). The following material and thermal behavior models were used for the cladding:

• HeatConductionMaterial: Thermophysical material properties

• ZryCreepLimbackHoppeUpdate and ZryElasticityTensor: mechanical creep and elastic deformation behavior for Zircaloy-2

• ZryIrradiationGrowthEigenstrain: ESCORE model for volumetric swelling due to irradiation exposure

• ZryThermalExpansionMATPROEigenstrain: thermal expansion of Zircaloy with the MATPRO model

Boundary and Operating Conditions

The power history used for this simulation is shown in Figure 2, with axial peaking factors shown in Figure 3. The average fast neutron flux was input as a function as well and is shown in Figure 4 with axial peaking factors shown in Figure 5. The clad temperature was calculated using the coolant channel model.

Figure 2: BISON input power history for the AREVA Idealized Case.

Figure 3: BISON input power axial peaking factors for the AREVA Idealized Case.

Figure 4: BISON input average fast neutron flux for the AREVA Idealized Case.

Figure 5: BISON input fast neutron flux axial peaking factors for the AREVA Idealized Case.

Fission Gas Release

The expected fission gas release values are shown in Table 3 (IAEA, 2008-2012).

BISON predicts the total fission gas release reasonably well during the early and mid-burnup regimes, however FGR is under predicted at high burnup. BISON also compares well with other well known fuel performance codes, see Figure 6.

Figure 6: BISON predicted fission gas release in comparison to measured data and multiple fuel performance codes (code data digitized from FUMEX-III report (IAEA, 2008-2012)).