JOYO B14 fuel pin PTM003

Rod Design Specifications

The fuel specifications from (Maeda et al., 2011) and (Ikusawa et al., 2017) for the PTM003 fuel pin are summarized in Table 1.

Operating Conditions and Irradiation History

The irradiation power history is shown in Figure 1. The axial power profile and the cladding temperature profile are shown in Figure 2 and Figure 3 respectively.

Figure 1: Power history for the B14 experiment (Maeda et al., 2011). The experiment consists in 48 hours of preconditioning at 102 MWt with a final transient of 10 minutes at 125 MWt.

Figure 2: Axial power profile for the pin PTM003 over the position from the core mid plane (DFCC). Picture by courtesy of Takayuki Ozawa (JAEA) during a presentation at INL.

Figure 3: Axial cladding temperature profiles over the position from the core mid plane for the pins of the B14 experiment at 125 MWt. Picture by courtesy of Takayuki Ozawa (JAEA) during a presentation at INL.

Geometry and Mesh

The fuel rod PTM003 was modeled as a smeared fuel pellet stack for the 2D RZ simulations. The geometric parameters specified in Table 1 were used to create the meshes for these simulations. The smeared fuel was meshed as a single smeared fuel column with 20 radial elements and 100 axial elements. For the 1D simulations meshes of 200 elements were used. Figure 4 shows a section of the mesh in 2D RZ with a temperature contour plot. This contour plot was made near the end of the run. Actual numbers are irrelevant in this case as this plot is only meant to show the discretization.

Figure 4: A section of the PTM003 fuel rod mesh with a temperature contour plot.

Material and Behavioral Models

The following material and behavioral models for MOX fuel were used:

FissionRateMOX: model that takes into account of the pore migration for the fission rate calculations

MOXPoreContinuity: pore migration, or restructuring, is modeled by applying the concept of pore conservation (Novascone et al., 2018).

MOXPoreDiffusion: pore migration, or restructuring, is modeled by applying the concept of pore conservation (Novascone et al., 2018).

MOXPoreVelocity: calculates pore speed according to (Sens, 1972) and (Novascone et al., 2018)

MAMOXThermal: model for temperature and porosity dependent thermal properties

ComputeFiniteStrainElasticStress: elastic mechanical behavior

MAMOXElasticityTensor: constant values from JAEA are used for the two elastic constants Young's modulus ( Pa) and Poisson ratio ()

MAMOXThermalExpansionEigenstrain: isotropic thermal expansion's eigenstrain from (Kato et al., 2011) and (Kato et al., 2016)

The following material and thermal behavior models were used for the cladding:

SS316Thermal: Thermophysical material properties

SS316ElasticityTensor: temperature-dependent Young's modulus and constant Poisson ratio ()

SS316ThermalExpansionEigenstrain: eigenstrain due to thermal expansion for Stainless Steel 316 using a function that describes the mean thermal expansion as a function of temperature

SS316CreepUpdate: steady state creep as sum of thermal and irradiation creep, following (Altenbach and Gorash, 2013) and (Garner and Porter, 1988)

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

Central void

The calculated central void size , (Novascone et al., 2018),for the fuel rod PTM003 is compared to the measured data in Figure 5, Figure 6 and Figure 7. There is also a comparison between 1D and a 2D simulations. The Multi-app was used in the 2D simulation order to have a better numerical solution in a point of view of convergences respect to a fully-coupled system. We assumed a value of 75% of porosity as threshold to consider a void and we delimited the end of the equiaxed region where the porosity equals the as-fabricated value.

Figure 5: Comparison between the two simulations taken into account and the data for the sample 1 (+33 cm from the core mid plane). The Experimental dotted black line refers to the radius of the central void (Maeda et al., 2011).

Figure 6: Comparison between the two simulations taken into account and the data for the sample 2 (+97 cm from the core mid plane). The Experimental dotted black line refers to the radius of the central void (Maeda et al., 2011).

Figure 7: Comparison between the 2D simulation and the experimental data about the central void size for the fuel pin PTM003 in a range of (Maeda et al., 2011).

Discussion

The use of a Multi-App system with a fine mesh and many positions for the interpolation is recommended for the simulation of the central void.