Fig. 1. Schematic diagram of annular fuel rod structure ( r₁=4.316 5 mm, r₂=4.888 0 mm, r₃=4.950 0 mm, r₄=7.050 0 mm, r₅=7.112 0 mm, r₆=7.683 5 mm, S=16.51 mm)

Fig. 2. Heat transfer partition diagram of heated channel

Fig. 3. Flow chart of THCAFS code

Fig. 4. Comparison of annular fuel thermal hydraulic code (a) Heat transfer coefficient of inner channel, (b) Heat transfer coefficient of outer channel, (c) DNBR of inner channel, (d) DNBR of outer channel

Fig. 5. Verification of the temperature field of fuel cell at the hot spot

Fig. 6. Flow chart for solving effective temperature of annular fuel cell

Fig. 7. Refined modeling of annular fuel cell

Fig. 8. Radial node division of annular fuel

Fig. 9. Radial power distribution under different burnups

Fig. 10. Changes of nuclide density under different burnups

Fig. 11. Fitting of polynomial coefficients a( x), b( x) and c( x)

Fig. 12. Ratio of fitting function value to simulation value under different burnup

Fig. 13. Temperature field of fuel cell at the hot spot (40 MWd·kgHM^-1)

Fig. 14. Calculation of effective temperature for fuel cell at the hot spot (40 MWd·kgHM^-1)