Studies On The Typical Kinetic Process Of Fast And Thermal Lead Reactor The Venus-Ⅱ

The accelerator drive subcritical system(ADS)is driven by the high-energy protons accelerator,which can be used to generate the external neutrons by bombarding the spallation target to drive the subcritical reactor system operating stable.The inherent safety characteristics of subcritical core and the characteristics of energy amplification at the shallow level subcritical make the ADS system have a great potential in nuclear waste transmutation and energy production using certain special fuel.Extensive research has been carried out on the ADS system at home and abroad,among which the research of Europe and China has entered the stage of engineering research.Compared the ADS subcritical system with the critical reactor system,there are a lot of differences in neutronics features,one of them is neutron kinetic behavior.Due to the external neutron source term and the characteristics of the sub-critical core,the kinetic behavior of ADS system has great difference.These kinetic differences are the start point for the scheme design of startup,operation,control,and system shutdown,they are also the basic reason of the transient response characteristics,and furthermore,kinetic behaviors are the fundamental of experiments for key parameters such as the effective multiplication factors.During many researches in the ADS neutron kinetics,Europe,the United States,Japan and other countries have developed many space-time kinetic codes for simulation study,in addition,many experimental studies were carried out in the zero power devices such as the MUSE,YALINA,VENUS-F and KUCA.Recent years,a few time-space kinetic codes were developed and a zero power reactor named Venus-II was constructed in China.They gives a good opportunity for the reaches of ADS kinetic behaviors.This dissertation is carried out to realize the four following listed objects: 1.Establish the space-time kinetic simulation method based on deterministic transport method;2.Obtain the neutron space-time kinetic characteristics of the external source driven subcritical core;3.Study the kinetic behavior during experiments for the key reactor parameters;4.Assess the reliability of the time-space kinetic simulation method.Based on the Lead Reactor of Venus-II,which is constructed by the cooperation of Chinese Academy of Science(CAS)and the China Institute of Atomic Energy(CIAE),kinetic studies were carried out by simulations and experiments.Three-dimensional space-time kinetic simulations were carried out using the DASIY codes,which is developed by Xi’an JiaoTong University.By analyzing the neutron spectrum features in different zone of the lead reactor,the few group constants and kinetic parameters were made by the Monte-Carlo method using a fine core model.A complex deterministic reactor model was established considering the core characters and the simulation requires.Form the steady-state analysis,we obtained many key parameters such as the effective multiplication factor,control rods value,the neutron flux distribution and the neuron energy group distribution.These data are in good agreement with the experimental or simulated results,which means the deterministic simulation model is reliable and accurate.Then,the typical kinetic behavior of the lead reactor in the critical state and subcritical state was simulated.From those behaviors,assessments were also done from the kinetic principle for many reactivity measurement methods.Through the simulation studies,we mastered the kinetic characteristics for the control rods lifted and drop processes from a critical state,spatiotemporal kinetic characteristics of the jumping source process,Beam-Trip process,and reactivity insertion processes by control rods in different external source driven sub-critical levels were also obtained.In addition to the above characteristics,The following important conclusions have been acquired:(1).The space-time difference during kinetic response has no significant influence for the reactivity determination using the periodic method.But it can lead obvious difference for the reactivity value measured by rod drop method.For example,during the drop of 2# safety rods,the data obtained by the counter 2 is nearly 13% larger,and data at position 1 is nearly 37% larger.(2).If the kinetic behavior of the source jerk can be accurately measured,it is expected to obtain an experimental results that is about 600 pcm large than the actual reactivity in deep subcritical level that the Keff is nearly 0.85,which is the acceptable from the view of engineering.(3).In the reactivity by Beam-Trip experiments,the prompt neutron decay constant method is affected by the space-time dynamic effect and is difficult to confirm the right fitting function,the ratio method is simple and can be used to get more precise results.At the same time,a time selection method and the time-space differences were given,the later of the ratio method and the time and space effect is given for the ratio method,the latter can be used for the correction of the results.(4)Through the space-time dynamic response behavior of reactivity insertion process,the correction factor for modified source multiplication(MSM)method used in the reactivity measurement is presented.In addition,the applicability of the MSM method for the reactivity monitoring is evaluated.The results showed that when the core effective multiplication factor is less than 0.97,delayed neutron effects smaller,reactivity monitoring could be realized by the MSM method.A preliminary experimental study was carried out on the lead reactor of Venus-II for kinetic behavior during the source jump process and the reactivity insertion in shallow sub-critical state.Compared with the experimental results and the simulation results,the following important conclusions are obtained:(1).The result of the jump source experiment is in good agreement with the simulation results,which shows the reliability of the deterministic method to simulate the dynamic process caused by the source effect;(2)The response behavior during the reactivity insert experiment was consistent with the simulation results,indicating the deterministic program can get the qualitative response behavior.However,limited by the method of determinism,there are certain differences in the specific range and the spatial characteristics.It is suggested that more experimental studies should be carried out in deeper sub-critical level further accuracy and reliability assessment,and the neutron source should be put in the central part of the core.In this paper,a reliable determinism simulation model for the lead reactor is established,and the modeling method can be used as reference for the follow-up work.Through simulation and experiment study,detailed time-space behavior was mastered,assessment of the reactivity measurement method were also done.Those results can provide important references data to the further experiments carried out in lead reactor,but also to the design work of ADS system.The reliability of the deterministic procedure and method is preliminarily evaluated,which can support the nuclear design of Ci ADS.