gFHR Steady state simulation results

Contact: Dr. Mustafa Jaradat, [email protected]

Sponsor: Dr. Steve Bajorek (NRC)

Model summarized, documented, and uploaded by Dr. Mustafa Jaradat and Dr. Samuel Walker

Here we report the steady state results of this coupled multiphysics simulation.

The power multiphysics coupling methodology is shown in Figure 1.

Figure 1: Multiphysics coupling for the asymptotic core calculation from (Ortensi et al., 2023).

The power distribution peaks radially at the center of the RZ model as expected shown in Figure 2 and peaks axially at the bottom of the core shown in Figure 3. Overall the Griffin power profile appears to be consistent with the Kairos Power Advanced Core Simulator (KPACS). Currently, the Griffin solutions overpredict the axial and radial peaking away from the side and top reflector regions. We expect the Griffin solutions to further improve as new cross-section preparation capability becomes available.

Figure 2: Griffin radial power shape of the equilibrium core gFHR from (Ortensi et al., 2023).

Figure 3: Griffin axial power shape of the equilibrium core gFHR from (Ortensi et al., 2023).

The coefficients of reactivity for the gFHR equilibrium core are shown in Table 1. Note that the current Griffin tabulation does not separate the coolant temperature and density, thus both components of the reactivity feedback are included in the Griffin result. Both the fuel and void coefficient of reactivity are consistent with the KPACS results, but the two coefficients that rely on graphite thermal scattering (moderator and reflector) do not. This could be attributed to differences in the S(α,β) thermal scattering treatment between the data sets, but further work is warranted to resolve this discrepancy.

Global results from the coupled steady-state calculation are included in Table 2. Here again the burnup limit is adjusted to produce a 1% / reactivity bias, which slightly increases the discharge burnup for the coupled model. The coupled model includes nine burnup groups, each with distinctive fuel and moderator temperatures in each core mesh zone. The maximum fuel and moderator temperatures are approximately 5% higher than the core average with the current model where only the fuel includes temperature-dependent thermophysical properties. We expect this to increase in the future when we incorporate the temperature and fluence dependence of the various materials.

The solid and fluid temperature fields are shown in Figure 4, and fluid density and pressure in Figure 5. The peak temperatures are observed at the top of the active core region with a 300 K gradient across the height of the core. Temperature peaks in the solid materials appear near the reflector zones consistent with power peaks. The lower temperature in the reactor vessel and barrel reveal the enhanced heat transfer to and from the inlet coolant flow in the downcomer region. The current model of the fluidic diode exhibits a pressure gradient of 40 kPa with a temperature gradient of 80 K.

Figure 4: Steady-state core thermal solution from (Ortensi et al., 2023).

Figure 5: Steady-state core fluid density and pressure from (Ortensi et al., 2023).

The velocity field in Figure 6 shows an average velocity of 1 m/s in the downcomer region, except for the regions with sharp turns in which velocity increases due to the sudden changes in the flow direction. The flow area then expands when entering the core, thus reducing the velocity to 0.3 m/s. In the steady-state configuration for this model, no flow is allowed to pass through the fluidic diode, and it all exits at the core outlet.

Figure 6: Steady-state fluid velocity m/s from (Ortensi et al., 2023).

module load use.moose moose-apps bluecrab

mpiexec -n 48 blue_crab-opt -i gFHR_griffin_cr_ss.i

conda deactivate
conda activate bluecrab

mpiexec -n 48 blue_crab-opt -i gFHR_griffin_cr_ss.i

mpiexec -n 48 ~/projects/bluecrab/blue_crab-opt -i gFHR_griffin_cr_ss.i