采用目前工业上成熟的非线性迭代计算策略,基于两群粗网有限差分方法和多群UNM 节块方法,开发了针对压水堆工况的三维瞬态扩散计算程序。UNM 方法采用解析基函数作为基函数,通过方程变换解决了解析节块法在临界节块计算不稳定的问题,提高了计算精度。热工计算采用单通道模型和燃料棒一维导热模型,相比目前堆芯在用的经验关系式方法,该模型可以更加准确地计算燃料棒温度分布。采用基于横向积分方程的三节块方法,可以有效减轻控制棒尖齿效应对瞬态计算的影响。为测试程序性能,采用NEACRP等基准算例对程序进行了校验。数值结果表明,开发的程序计算结果正确,适用于压水堆堆芯瞬态过程的模拟。

Transient calculation is one of the key parts in reactor safety analysis and system simulation. With the fast development of computer technology, now 3D spatial dependent kinetics calculation is feasible and has already been used in the system simulator. This paper reports a new transient nodal code based on the widely used non-linear iteration scheme. The new code applies the two-group CMFD and multi-group unified nodal method (UNM). The UNM nodal method applies equations of analytical nodal method (ANM) but eliminates the instability of ANM by mathematical transformation. It is highly accurate and also has good efficiency. In the thermal-hydraulic module, the 1D heat conduction equation is solved instead of the currently well used formulation form to give better accuracy. The three-nodes method based on the transverse leakage equation is applied to reduce the impact of control rod cusping on transient calculations. To test the performance of the new code, the Nuclear Energy Agency Committee on Reactor Physics(NEACRP) benchmark is calculated. Numerical results show that its accuracy is similar to that of other high performance nodal codes.