中国散裂中子源靶—反射体—慢化器系统的模拟和优化研究

【作者】 殷雯；

【导师】 梁九卿；

【作者基本信息】 山西大学 ， 理论物理， 2004， 博士

【摘要】 本论文结合当前中国散裂中子源(China Spallation Neutron Source，CSNS)工程概念设计的迫切需要，选择国际上广泛使用的基于蒙特—卡罗方法，用于模拟粒子输运过程的程序MCNP4A和NMTC／JAM作为研究工具，首次对CSNS靶站进行了全面的模拟与优化，内容包括靶、反射体与慢化器系统的中子通量分布以及热量沉积，同时计算了靶的温度场与应力场分布。本论文的研究结果为中子散裂源工程建设提供了必要的研究数据，为选择靶的设计方案提供了基本依据。 首先利用高能粒子输运程序NMTC／JAM计算了入射质子能量、靶的材料、形状、尺寸以及靶与慢化器耦合对中子通量的影响。研究结果表明，当入射质子能量高于1.6GeV时，随着入射质子能量的增加，用于产生π介子的能量也增加，中子有效通量反而降低；从中子产量、费用、机械性能和耐蚀性能几方面综合考虑，钨适合用作散裂源中靶的材料；在截面积相同时，矩形扁靶可比方形靶给出更高的中子通量；对相同形状的靶，中子通量随着靶截面积减小先增加然后减小；当高能粒子进入慢化器后，会在慢化器中发生散裂反应与(n，2n)核反应，因此，反射体可以大大提高中子通量；在慢化器长度等于分离靶的分开距离时，分离靶的总中子通量比整体靶可提高20.1％，但同时也会大大增加制造成本。 接下来根据已优化的靶的参数，利用低能粒子输运程序MCNP4A进一步计算高能中子(快中子)进入慢化器后，在慢化器中的输运过程。得到经水慢化器慢化后，中子通量在慢化器厚度与高度方向上的分布；比较了水与液态氢的慢化能力以及中子在水、液态氢、液态甲烷这三种慢化器慢化后的能谱；在CSNS的靶站设计中，引出慢中子的导管不完全位于慢化器中子引出面的法线方向上，因此进一步计算了中子通量角分布。 最后计算了靶、反射体以及不同慢化器(水、液态氢、液态甲烷)中的热量沉积，并以此为依据，利用工程软件IDEAS进一步计算了各种冷却条件下，靶中温度场与应力场分布。由于CSNS是千瓦级的散裂中子源，所以温度与热应力都不会对靶的寿命、机械性能产生太大影响。更多还原

【Abstract】 According to the demand of the concept design of China Spallation Neutron Source (CSNS), the target station, i.e. the target, the reflector and the moderator have been simulated and optimized using Monte Carlo simulation software, NMTC/JAM and MCNP4A, firstly. The neutron flux escaping from the target and the moderator and the heat deposition in the target, the reflector and the moderator are calculated. These results provided essential data as a basis of the spallation neutron source design.It is clear that the most important work is to optimize the source parameters and provide basic data necessary for engineering design. At first, the effect of the target on the neutron flux is discussed to determine the optimal proton energy, target material, shape and dimension by using the high-energy particle transport code NMTC/JAM. When theincident proton energy EP increases, the effective neutron flux decreases. It is becausethat the proton energy consumed for the pion production increases with EP. Tungstenhas relative high neutron yield due to high atomic number density and after considering other properties such as strength, corrosion resistance, mechanical resistance and cost, tungsten is the most acceptable material of the solid target. A rectangular target with its aspect ratio 2.5:1 gives the higher neutron flux than square target with the same area. For the same shape, the neutron flux increases then turn to decrease with decreasing the area of the target. The reflector can increase the neutron flux obviously and the main processes of the neutron yield in reflector are spallation reaction induced by energetic hadrons and (n, 2n) reaction. When the moderator height is equal to the distance between the upper part and the lower part of the split target, the total neutron flux of the split target will be higher by 20.1 % than that of the integral one.Secondly, the high-energy neutron escaping from the target will enter into the moderator and be slowed down. This process has been simulated by low-energy particle transport code MCNP4A. The distribution of the slow neutron flux along the moderator height and depth has been calculated. The capability of moderating between water andhydrogen has been compared. In CSNS neutrons are extracted from a moderator not only to the normal direction and also with definite angles. The neutron flux extracted to different angles has been calculated.Finally, The heat depositions in the target, the reflector and the moderator have been calculated. Based on these results, the temperature and stress distribution hi tungsten target under different cooling condition have been calculated too. The results show that the heat deposition hi the target for setting up lOOKW-level spallation neutron source is not a serious obstacle.更多还原