Operational Characteristics Of Passive Residual Heat Removal System Under Ocean Condition

Passive residual heat removal systems were widely used in nuclear power plants because of its inherent safety. But for the sailing ships, the movements induced by ocean conditions will affect the operational characteristics of nuclear reactors and passive safety systems. Therefore,it is very important to study the operational characteristics of passive residual heat removal systems under ocean conditions. In this article, some simulation works have been done.This paper introduced mathematical expressions described ship motion conditions, and the concept of mass force and additional inertia force under ocean conditions by introducing momentum equation in the non-inertial system. Based on fluid mechanical analysis under ocean conditions,a common computing model applicable to any non-inertial coordinate system origin position and any ship movements was established.For the case that passive residual heat exchanger is arranged in the main loop or the second loop of nuclear power plants, a numerical model of the passive residual heat removal system was built through analyzing the basic thermal-hydraulic model under ocean conditions. Based on appropriate numerical algorithm and MATLAB platform, a thermal hydraulic analysis program for passive safety system under ship motion conditions was developed. Through analyzing the calculation results of the operation characteristics of the primary/secondary passive residual heat removal system under ship motion condition, the adaptability of the two arrangement forms under motion condition was evaluated. The calculation results show that:For the primary passive residual heat removal system, rolling and pitching change the effective height between the loop heating and cooling sources and generate accessional inertial forces, which can reduce the average loop flow rate and cause the periodical fluctuation of the fluid temperature and flow rate. Due to large accessional inertial forces of fierce rolling condition, the passive residual heat removal system cannot operate normally which may seriously affect the core residual heat removal.Ship yawing and linear acceleration which can only generate accessional inertial forces have limited effects on the operation of passive safety system. For the heaving motion, the oscillation of loop flow rate will accumulate in the reactor core causing the fluctuation of flow rate increasing.For the secondary passive residual heat removal system, ship inclination changes the effective height between the loop heating and cooling sources and then causes the change of loop nature circulation flow rate. For the pitching motion, the passive residual heat removal system can operate normally which indicates the effects of motion condition is limited. But this effects will increase with the increasing of motion amplitude or reducing of motion period. For the rolling, yawing and surging motions, because of the effective height between the loop heating and cooling sources keeps constant and the accessible inertial acceleration generated by motions is relatively small, the motion effects on the system operation is limited. In the calculation condition herein, compared to the primary residual heat removal system,the adaptability under motions of secondary passive residual heat removal system is much better. Therefore, in the practical ship nuclear power plant design, we suggest to evaluate the local ocean environment and the ship motions limitation to choose the secondary passive residual heat removal system.