IFA 519 Rod DH and Rod DK

Rod Design Specifications

Summary of the rod specifications for rods DH and DK are shown in Table 1.

Operating Conditions and Irradiation History

The HBWR operating conditions are tabulated in Table 2. The total reactor power history for rods DH and DK in the IFA-519.9 experiment is shown in Figure 1 and Figure 2. The measured reactor coolant temperature was used as the boundary temperature on the clad outer surface.

Figure 1: Full irradiation power history for rod DH in the IFA-519.9 experiment.

Figure 2: Full irradiation power history for rod DK in the IFA-519.9 experiment.

Geometry and Mesh

The assumed geometry and mesh for the two rods are shown in Figure 3. The fuel pellet stack for each rod was modeled as a smeared column. A 2-dimensional axisymmetric quadratic mesh was used for each rod. The fuel columns were meshed with 48 axial and 11 radial element and the clad were meshed with 48 axial and 4 radial elements.

Figure 3: (a)2-D axisymmetric quadratic mesh for IFA-519 Rod DH simulation. (b)2-D axisymmetric quadratic mesh for IFA-519 Rod DH simulation. Note the figures above are scaled radially by a factor of 10.

Material and Behavioral Models

The following material and behavioral models were used for the 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 instantaneous 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 (primary and secondary) and irradiation creep were considered using the Limback creep 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-0

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

• ZryThermalExpansionMATPROEigenstrain: thermal expansion of Zircaloy with the MATPRO model

Details and references for all of these models listed above can be found on the linked BISON documentation pages.

Fission Gas Release

Table 3 summarizes the end of life (EOL) total fission gas release comparisons to the puncture results obtained durning post irradiation examination (PIE). It has been shown that the prediction of total FGR within a factor of 2 is considered acceptable (Pastore et al., 2015). Since the BISON FGR prediction is within this range, it is concluded that the FGR predictions are acceptable. As there is no fuel centerline temperature data available for comparisons, it is unknown if the underprediction of FGR is caused by a difference in the predicted and actual fuel temperature.