Application Of Stochastic Neutron Dynamics

Stochastic neutron kinetic is concerned with the stochastic processes of neutron transport in multiplying assembly. The interaction of the neutron with the medium and the emission of source neutron are random processes, which result in the randomness of neutron transport. The stochastic effect can be ignored in conventional neutron transport, however, it is significant in the presence of weak source. In subcritical system, neutron parameters can be obtained by fluctuations of the weak neutron field. The correlative studies are widely applied to reactivity measurement and nuclear material detection. In supercritical system, the stochastic evolution of the weak neutron induce the neutron pulse burst randomly. The stochastic process is essential to reactor start-up, ignition of nuclear weapon and evaluation and analysis of critical accident. It determines the initial condition of the power burst.Study on stochastic neutron dynamics began in 1950s. It was mainly in the basis of initiation experiments performed on the pulse reactors and neutron noise measurements. In the past half century, however, there lacks available method and tool to implement quantitative analysis of some problems such as probability distribution of burst waiting time of neutron initiation in pulse reactor. Not until 2011, some important progress was made in generalized semi-Markov process (GSMP) simulation method, which was applied to stochastic neutron kinetic process simulation. It reveals inherent law of neutron initiation experiments which are conducted in pulse reactor.Based on the study of the GSMP simulation method, this paper systematically expounds the theoretical and mathematical basis of this method, and gives a detailed algorithm design principle and implementation strategy. By using this method, measured results of pulse experiments on Godiva and Caliban are analyzed. The correctness and feasibility of the GSMP simulation method are verified.Neutron kinetics is an important subject in the design of nuclear power and nuclear reactor safety. At the beginning of the study on nuclear fission system, the research interest was mainly about the point reactor kinetics based on lumped parameters, and it was focus on how to obtain the dynamic parameters and the development of effective numerical algorithm. In this thesis, the GSMP simulation is introduced to the point reactor kinetics equations (PKEs) solution, and the implementation strategy of the numerical method is studied in detail. The impact of the reactivity on neutron generation time is also investigated.In nuclear industry, criticality safety is very important. Nuclear fuel processing and spent fuel reprocessing is the key link of criticality accidents. These accidents always occur with weak source, and the early stochastic process of neutron field is significant. Criticality safety evaluation methods are widely studied, though, none of them can analyze the stochastic effect quantitatively. In this thesis, the GSMP method is used to simulate the stochastic neutron field and solve the PKEs. The method and numerical code for criticality safety evaluation involving weak source is developed.In order to eliminate the dependence on the lumped kinetic parameters of fission assembly, it is necessary to develop a three-dimensional time-dependent transport code on the basis of the GSMP simulation method. Therefore, this thesis carried out study on relevant theory, architecture design and optimization of algorithm, design of data structure and program frame, and development and evaluation of the code named TiBES. This code is used to simulate the weak neutron transient. In additional, it is used to explore the feasibility of this method to solve the space-time dependent kinetics equation.