A Source-expansion-based method for transient Pin-Power reconstruction

Highlights: • A source-expansion method was proposed for transient pin-power reconstruction. • The transient fixed-source term was expanded by the second-order Legendre polynomial. • The corner-discontinuity factor was employed to improve the accuracy. In this paper, the transient pin-power reconstruction based on source-expansion method has been proposed. The transient calculation is sufficient to simulate the reactor-physics process in second-time scale, such as the load-dump process and dynamic rod worth measurement. During the transient process, the pin-power distribution is essential for the determination of the power-peak factors, including F_q and F_ΔH. However, with the widely-applied transverse-integrated nodal methods for transient simulation, the detailed pin-averaged results can't be provided directly. To address this problem, the transient pin-power reconstruction was proposed. It was derived from the transient fixed-source problem assuming the total-source and the transient fixed-source terms could be respectively expanded by the fourth-order Legendre polynomials and the biquadratic Legendre polynomials constructed from the nine-node problem. Moreover, to improve the accuracy of pin-averaged results, the corner-point condition and corner-discontinuity factors were employed in the reconstruction process. This proposed transient pin-power reconstruction method has been implemented in our self-developed code named SPARK and verified with several benchmarks. Results of the verification indicated that this proposed method for transient pin-power reconstruction can provide a satisfactory accuracy in transient process.