兆瓦级空间气冷堆系统启停堆瞬态分析

本文针对兆瓦级高温气冷堆布雷顿循环系统，采用Fortran语言开发系统分析程序TASS，包括堆芯、透平-发电机-压气机、回热器、冷却器和热管式辐射散热器等模型。通过设计值与程序计算值对比对TASS进行验证，并利用TASS对系统启动、停堆瞬态工况进行数值模拟。结果显示，通过分两阶段、阶梯式引入正反应性和提高涡轮机械的转轴速度，堆芯流量和功率匹配良好，系统可在3.5 h内完成启动过程，达到反应堆功率3 406 kW、流量14.2 kg/s的稳态运行。系统停堆过程中，反应堆可依靠自身的非能动余热排出能力，确保芯块和包壳温度与熔点间存在较大安全裕量，实现安全停堆。

Transient Characteristics Analysis of Start-up and Shutdown of Megawatt Gas-cooled Space Reactor System

Among numerous space nuclear power sources, the high temperature gas-cooled reactor with closed Brayton cycle has the advantages of both high power and high energy conversion efficiency. An open-grid megawatt gas-cooled space nuclear reactor (OMEGA) was investigated in this paper. It mainly consists of three parts: a heat source provided by the reactor core, an energy conversion system converting heat into electricity, a heat rejection system as heat sink. Generally there are four structural layouts of gas-cooled space reactor (GCSR), including porous prism core mainly used for nuclear thermal propulsion, pin-block type reactor, pellet bed reactor and open-grid type reactor. Not alike the other three, there is no solid matrix in open-grid type reactor. Consequently, it is hard for the core removing fission and decay power through heat conduction under the transient condition of core coolant flow reduction or even totally loss. Due to the absence of relevant research, passive decay heat removal capability during shutdown transient condition was investigated in this paper. Especially radiation heat transfer among fuel rod claddings was calculated. Furthermore, a system transient analysis code of start-up and shutdown (TASS) was developed by staggered grid technique and solved by GEAR algorithm, including core, turbine-generator-compressor, regenerator, condenser, heat pipe radiator and other modules. TASS was verified by comparing the design value with the program calculation value, and the transient conditions of system start-up and shutdown were simulated by TASS. The results show that the core flow and power match well by inserting positive reactivity in two stages and elevating the rotating speed of turbomachinery in a ladder-type. The start-up process of the system can be accomplished in 3.5 h, and the steady-state operation of reactor power 3 406 kW and flow rate 14.2 kg/s can be achieved. At the beginning of start-up, an additional power supply of 5 kW is required for the turbomachinery. During scheduled shutdown, average temperature of fuel element experiences a trend of decline, rise and fall. During emergency shutdown, pellet temperature continues to drop and cladding temperature is slightly lower than pellet temperature. No matter it’s a scheduled shutdown or emergency shutdown, due to the existence of radiation heat transfer among fuel rod claddings, maximum temperature of cladding and pellet is lower than the safety limits of their materials, which reflects the passive safety of core design. And as a result of the Biot number of fuel element is lower than 0.1, cladding temperature is close to the pellet temperature, which requires special attention.