Fission Rate Distribution Research For ADS Sub-critical Assembly "Venus-1"

As is known to us all, the accelerator-driven system (ADS) has been thought as the most powerful tool to deal with the long life and high-radioactive nuclear waste, the IAEA has decided to add it into the list of advanced nuclear energy systems, and considered it as the new kind of energy system for transmuting nuclear waste and generating power. The ADS consists of high-current, high-energy accelerator, high-atomic number target and the subcritical reactor. In this process, a beam of high-energy protons is directed at a high-atomic number target and after spallation a lot of neutrons are produced by the incident proton beam. The spallation neutrons can maintain the chain reactions in the subcritical reactor as the role of external neutron sources, and by causing stable rate of nuclear reactions, the ADS can output a stable power. So it can transmute the long life and high-radioactive waste, especially the minor Actinides, and supplies energy for other systems at the same time. No matter we utilize the ADS for transmuting radioactive waste or generating power, we should know the distribution of both the neutron flux and the power in the system, and they can be represented by the fission rate in the reactor. If we don't take burn-up into account, when the effective multiplication factor don't change, the factors which can affect the distribution of the fission rate are only the density, the energy and the locations of the spallation neutrons. So it is an important topic for researching the relationship between the external neutron sources and the distribution of the fission rate, the results would be very useful for improving the systematic performance and efficiency about the ADS.In this article we obtain the distributions of fission rate by adopting the MCNP codes in the ADS——the Venusl# assembly which is the first ADS in China, consists fast-thermal-coupling structure. We have done comprehensive analysis about the distribution by considering different density, energy and locations of the external neutron sources and summarized some rules. And by taking them into account we have optimized experiment plans and the distribution of the detectors, then by utilizing the solid-state nuclear track detectors(SSNTD), we measured the fission rate in the thermal zone of the Venus#1 when it was driven by a external neutron source-252Cf source. With the settled neutron source, we obtained the distribution of the fission rate, and validated the feasibility of the SSNTD's application in the ADS. Our work can be the foundation of the further research of this topic.