Viability of uranium nitride (UN) as annular fuel for AP-1000

In this work, we examined the possibility of using uranium nitride annular fuel instead of the commonly used uranium oxide solid fuel in the core of an AP-1000 reactor. The fuel we used in the reactor core was internally and externally cooled, which we simulated using MCNPX 2.7.0 code. We also calculated the following thermal hydraulic parameters: the pressure drop in the core, the surface heat flux, the fuel and the coolant temperatures and the departure from nucleate boiling ratio, using RELAP5 code. We used UN instead of UO2 because of the higher theoretical density of the UN. We found that the burnup of the solid fuel was about the same as the annular design because of the same enrichment. However, the nuclear annular fuel showed many advantages, such as the ability to increase the thermal power of the nuclear plant. Also, the MDNBR of the annular fuel rods had enough margin of safety in both the inner and the outer surfaces relative to the cylindrical solid fuel. This margin made it possible to operate the reactor at a 125% power-uprate. Finally, we proposed a 12 × 12 assembly based on our neutronics and thermal hydraulic calculations. [Display omitted] •The core of the AP-1000 reactor was simulated based on the use of internally and externally cooled UN annular fuel rods.•We compared the performances of the annular fuel with the traditional UO2 solid fuel.•The power output could be increased up to 125% nominal power while ensuring safety requirements.•The annular fuel showed a sufficient margin available on DNB and fuel temperature.•The annular fuel exhibits much lower peak fuel temperature than a typical solid fuel rod at 125% power.