Modeling And Simulation Of The Passive Residual Heat Removal System For Nuclear-Powered Ship

The passive safety system becomes an important develpoment direction of the nuclear power system, because it dosent rely on the external power and consists of less equipments, which lowers the failure rate of equipments and makes the nuclear power system safer. As an important nuclear safety system, the passive residual heat removal system (PRHR system) is responsible for removing residual heat of the reactor after the normal shutdown or accidental shutdown, which means its performance directly determines the safety of the reactor. Currently, the passive residual heat removal system has been applied to the land nuclear power plant, while no evidence shows that it has been applied to the nuclear-powered ship, and the research on the dynamic characteristics of the passive residual heat removal system applied to the nuclear-powered ship is not much. In the paper, dynamic mathematical models of the PRHR system are established, a thorough research is done on dynamic mechanism of the PRHR system in numerical simulation approach.The paper proposes a modeling method with modularization, generalization, partition lumped and three-loop coupling. And the system is divided into multi-control-volumes according to its internal mechanism. Rational dynamic mathematical models, which sucessfully reflect the flow and heat transfer feature of two-phase flow as well as the coupling method of the three natural circulations, are established to describe this system. The models include:the thermal-hydraulic model, equipment models such as the point-reactor kinetic model, the main pump model, the steam generator model and the heat exchanger model, auxiliary calculation models such as the state equation model, the heat transfer model, the flow resistance model and the physical property model.To solve the dynamic mathematical models, a rational numerical approach is selected, which not only meets the requirement of the model precision but also takes the real-time performance into consideration. Based on this, a transient analysis code is developed with C# to simulate the PRHR system, thus the dynamic numerical simulation enviroment of the PRHR system is built. The code is divided into modules according to its calculating function and the equipment it describes. By calling the modules, the dynamic simulation of the whole system is realized.To verify the accuracy of the code developed in this paper, its result is compared to that of the RELAP5 code and several published papers in both static and dynamic ways. The dynamic characteristics of the PRHR system are investigated with the code under the blackout accident. The dynamic responses of the main parameters as well as the dynamic coupling relationships between the parameters are revealed. The result shows that the PRHR system is able to guarantee the safety of the core by removing the residual heat in time, and at the same time make sure the temperature and pressure of the primary and secondary loops stay within the safety range. Moreover, the dynamic characteristics of the PRHR system are studied when the ship is in motions such as heaving and inclining.Based on the IMAGE software, which is a graphical simulation supporting environment for the simulation of thermal-dynamic systems, the dynamic characteristics of the active residual heat removal system (RRA system) after the normal shutdown are studied, and the responses of the temperature of the primary loop and the power of the heat exchanger caused by the step disturbance of the flow regulating valve are analyzed. Meanwhile, the dynamic characteristics of the PRHR system are studied with the PRHR code in the same operating condition, so that the difference in dynamic characteristics between the PRHR and RRA systems can be analyzed. Based on the analysis, the advantages and disadvantages of the two systems are summarized.The above studies are of value for the design and operation of the PRHR system applied to the nuclear-powered ship, and provide environment for training operators.