Spallation Neutron Source Target - Reflector - Slow System Of Simulation And Optimization Studies,

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.