PCI CODE is a semi-empirical computer program developed by B&W that simulates the thermo-mechanical behaviors of light water reactor fuel rods based on models for pellet crack, fuel relocation, pellet hourglassing, SCC (stress corrosion cracking), temperature distribution, fuel creep, and cladding creep.
Thermo-mechanical behaviors of annular and solid pellet fuel with the same base power history were compared under the assumptions that the annular pellet fuel has about 10 volume% central hole, higher enrichment (4.5 vs 2.8 wt%), higher hydrogen to uranium ratio (5.7 vs 4.4) and lower density (90 vs 95% TD) than the solid pellet fuel.
In simulating the thermo-mechanical behaviors of the annular pellet fuel with use of PCI CODE, hourglassing and thermal model were modified while the rest of models for the solid pellet fuel were used without any modification. This simulation showed that the maximum temperature of the annular pellet fuel was lower than that of the solid pellet fuel, namely, 230 to $460^\circ{C}$ at a linear heat rate of 300 to 500 W/cm. The contact between the fuel pellet and the cladding occurred in the solid pellet fuel at about 7500 hours after start up of operation, while it occured in the annular pellet fuel at about 10000 hours.
At the base load of 200 to 220 W/cm the cladding of both the solid and annular pellet fuels exhibited compressive hoop stress of approximately from -75 MPa to -50 MPa, which signifies no pellet-cladding interaction.
The ramping failure of the solid pellet fuel was predicted to occur at a peak linear heat rate of 360 W/cm whereas the failure of annular pellet fuel was predicted at 430 W/cm, at the ramp rate of 10 Kw/m/min and at burnup of 35000 MWd/Mtu.
These results from PCI simulation showed that the annular pellet fuel can withstand pellet-cladding interaction better than the solid pellet fuel with the same power history.
