Nodal code development for pressurized water reactor transient analysis based on non-linear iteration method

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.