atw - International Journal for Nuclear Power | 2.2024

70
Research and Innovation
2.2 Modeling TRISO particles in OpenMC
Since, the Triso particles are randomly packed in the
SiC matrix of the FCM fuel pallet. OpenMC can generate
TRISO particles and distribute them randomly in the
SiC matrix. The OpenMC. model. pack_spheres model
has been used to distribute the Triso particles randomly
within the fuel pallet. To model individual particles,
a specific universe has been created, to model
the individual particles, which not only reduces the
simulation time but also improves the performance of
performance by reducing the number of cells.
3. Results and Discussion
In this study, FCM fuel based on UN and UCO TRISO
particles fuel has been replaced for the SMART reactor
without the design alteration of the SMART reactor and
core. Therefore, the SMART reactor core has been
modeled in OpenMC according to the design reported
by the KAERI in [23] . The core burns up of the SMART
reactor core have been evaluated without the control
rods and Integral Fuel Burnable Absorber (IFBA) insertion.
However, a boron concentration of 140 ppm has
been considered according to the design as described
in [23] . The burnup of UN and UCO-based FCM fuel has
been simulated for identical operational and design
constraints. In this study, the average axial thermal flux
for FCM fuels of UN and UCO triso base particles has
been simulated and compared with the reference design
fuel (UO₂). The packing fractions of UN and UCO
are 0.48 and 0.6 respectively. The comparison of the
axial fluxes is shown in Figure 4. FCM fuel of UN and
UCO has elevated thermal flux compared to the UO₂.
The thermal flux is distributed over the dimension
of the core 192.78 cm × 192.78 cm of mesh size of
4.8195 × 10 -1 . The candidate flux has elevated flux even
with the presence of SiC and in the FCM fuel matrix.
This is because of the higher enrichment and density
of FCM fuel.
One of the prime parameters to ensure the safety of the
reactor operation is the reactor power density. Figure 5
depicts the comparison of normalized axial power. The
normalized radial power distribution has been found
to be almost identical at BOL, MOL, and EOL of fuel
lengths. However, the elevated power has been seen at
corner zone 2 (Figure 6) due to the higher enrichment
of zone 2 assemblies. Whereas the flux at the central
zone is less as compared to zone 2 because of the low
enrichment of zone 1 (2.82 %wt of uranium). The FCM
fuel loading follows the same configuration with
15.5 %wt of uranium in zone 2 assemblies and 9.5 %wt
of uranium in zone 1 assemblies, which results in lower
burnup at the central assemblies. However, the outer
Fig. 4.
Comparison of the thermal flux of the original fuel (UO 2 ) of the SMART reactor with the replaced FCM fuels (UCO and UN)
Fig. 5.
Axial normalized power distribution of SMART core at the BOL, MOL, and EOL of UO 2 and FCM fuels of UCO and UN kernels
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