Development Of OTSG Thermal-Hydraulic Parallel Simulation Program Based On JFNK Method

Once-through steam generator is hub of the primary and secondary loops in nuclear power plants.The safety and economy of a nuclear power plant are closely related to the stability and safety of steam generator operation.Due to the complex two-phase flow and heat transfer phenomena occurred in the secondary side,operating characteristics and control methods of a once-through steam generator are different from those of traditional steam generators.Therefore,reasonable research methods must be used to study its characteristics.Numerical simulation technology has the advantages of low cost and high efficiency,which is a favorable means to study the thermal hydraulic characteristics of a once-through steam generator.Therefore,in order to accurately simulate the transient characteristics of a once-through steam generator,it is necessary to establish an accurate simulation model and develop a corresponding solution code.Based on the principle of mass,momentum and energy conservation,a five-equation drift flow model of the casing once-through steam generator is established by using the control volume modeling method,and the first-order semi-implicit Euler scheme and the first-order upwind scheme are used to discretize the drift flow model.At the same time,the heat transfer model and flow friction model suitable for narrow annular flow channels are adopted in the code.The Jacobian-Free Newton-Krylov(JFNK)method is used to solve the five-equation drift flow model.The effects of forcing factors,perturbations and algebraic preprocessing techniques on the convergence rate of the JFNK method are systematically studied.The structure of the casing once-through steam generator and the hot modules of the serial code are analyzed.The thermal-hydraulics parallel simulation code of Casing Once-Through Steam Generator(THCOTSG)is developed by using MPI + OpenMP parallel technology and FORTRAN.The CPU is 3900 X.The performance of the parallel code was tested on a single-node computer with a memory of 16.0GB.During the test,CPU frequency was locked at 4.4GHz.Compared with the serial code,the computational efficiency of THCOTSG was significantly improved,and the speedup reached to 12.74.THCOTSG is used to simulate the steady-state and dynamic conditions of a casing oncethrough steam generator whose rated power is 3.0 MW.The steady-state simulation results are compared with the experimental results.Among the five steady-state conditions,the maximum error is 1.126 %.Comparing the transient simulation results with the calculation results of RELAP5,the transient change trend of each parameter is consistent.Under the five transient conditions,the maximum error of the steam generator is 1.125 %,which verifies the accuracy of THCOTSG.THCOTSG provides a tool for study of the thermal-hydraulic characteristics of once-through steam generators,and has certain engineering practical significance.