Thermal-hydraulic performance evaluation of annular fuel based on modified FROBA-ANNULAR

In this study, based on the modification of the pellet cladding mechanical interaction, gap closure process, and the cladding water corrosion model, Fuel Rod Behavior Analysis-ANNULAR (FROBA-ANNULAR) was uprated. The modified code was verified with FRAPCON-ANNULAR and ABAQUS. The verification calculation was under low power density when both two gaps were open. The calculation results showed good agreement. The modified code was then utilized to evaluate the annular fuel behavior, compared with the original code FROBA-ANNULAR. In this study, the annular fuel exhibits a much lower peak fuel temperature(about 900K). The different results for heat flux fraction(0.55 for the original code, 0.66 for the modified code) indicated that the gap closure process strongly affected the movement of the adiabatic pellet line. The internal pressure results (7.5 MPa for the original code, 6 MPa for the modified code) were also affected by the different assumptions. The results also showed that Zr's oxidation thickness and hydrogen concentration were related to both time and temperature. The higher the temperature was, the larger the oxidation rate was when the transition thickness was reached.