The widely construction and operation of commercial nuclear power plants,plays an important role in settling the problems of electricity supplying and environmental pollution.However,it hardly meets some potential applications,such as isolated islands,small bases and space propulsion.Therefore,small sized,portable nuclear reactor systems,covering a large scale of fission power,are in great need in future.Considering the merits of high-level outlet temperature and outstanding nuclear safety embedded in pebble bed reactor,a nuclear reactor with thermal power of 5 MW was designed,which was coupled with closed Brayton cycles.Meanwhile,the essential system parameters,general physical and thermohydraulics features were provided in the paper.It is indicated that the energy conversion efficiency is nearly 35.2% with the system specific mass of 6.14 kg/kWe.The excess reactivities in the beginning of lifetime and end of lifetime are 4.88 $ and 2.28 $,respectively,which are able to achieve the duration of 10 years.Under the normal operation,the helium temperatures in the inlet and outlet of reactor are 868.7 K and 1 295.8 K,respectively.At the same time,the maximum temperature in fuel pellet comes to 1 576 K,which is below the limiting value of 1 600 K.%商用核电站的大规模建造和并网,缓解了我国电力供应和环境污染等问题,但很难满足孤立岛屿、小型基地、航天推进等潜在的应用环境.因此,须发展不同功率范围的小型化、可移动式核反应堆系统,以适应未来电力市场和动力装置对核能的需求.考虑到球床堆具有出口温度高、安全性好等特点,设计了一个基于闭式布雷顿循环、热功率为5 MW的核反应堆系统,给出了总体设计参数和反应堆部分的物理、热工特性.结果表明,该系统的能量转换效率约为35.2%,可达到6.14 kg/kWe的比重量.反应堆寿期初和寿期末的剩余反应性分别为4.88 $和2.28 $,满足10 a设计寿命的燃耗要求.反应堆进、出口温度分别为868.7 K和1 295.8 K,额定功率下燃料最高温度为1 576 K,低于设计温度限值1 600 K.
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