A high-fidelity core simulator is developed by applying the two advanced nodal methods Source Expansion Nodal Method (SENM) and Triangle-based Polynomial Expansion Nodal (TPEN) to the time-dependent Simplified P3 (SP3) equations temporarily discretized with the Backward Differentiation Formula (BDF) method. And the BDF temporal discretized P1 Course Mesh Finite Difference (CMFD) system is realized and coupled to the SP3 nodal modules to accelerate the solution convergence. In this advanced core simulator, the second moment flux shape drastically changing at the interface of nodes where different materials are loaded is determined precisely with the SENM hyperbolic functions for the rectangular core problems. Also, fidelity hexagonal core analyses are achieved by expanding two-dimensional SP3 intra-nodal solutions in each hexagon to the third order TPEN shapes. The time derivatives of the SP3 higher order odd angular moments is numerically considered with the BDF application which expresses time derivatives in terms of the solution history data and time step sizes. The time derivatives of the odd moments are then treated as a newly defined source named Moment Derivative Source (MDS) in SP3 nodal systems. In order to make the formulation of the time-dependent SP3 equations be the steady-state equations, the Transient Specific Source (TSS) and the second order analytic precursor integration schemes are used as normally implemented in conventional core transient simulators. The outstanding performance of the advanced core simulator is certified by evaluating the BDF method, the second order analytic precursor integration, the time derivatives of the odd angular moments, and the SP3 SENM and TPEN in various benchmark core transient simulations. And it is confirmed that the advanced SP3 nodal application leads to considerable improvement in core transient analyses. Thus it is demonstrated that the advanced core simulator developed in this work can be used effectively in high-fidelity core simulations.
