CHANGE OF THE NEUTRON SPECTRUM IN FAST NONSTATIONARY PROCESSES

摘要

The study of fast nonstationary processes in a nuclear reactor is necessary for safety analysis. It is difficult to calculate to a high degree of accuracy the nonstationary processes associated with reactivity build-up because this requires obtaining a comprehensive solution to the problem of the flow of the entire dynamic process.rnThe following algorithm for solving dynamical problems has been developed in computational practice. First, stationary programs are used to calculate the elementary fragments of a reactor (cells, fuel assemblies, and others) and a library of small-group constants (absorption and fission cross sections, and so forth) in the form of tables of the dependence of these quantities on the parameters (fuel temperature, water density, and so forth) is created. When the dynamic process is calculated directly, depending on the reactor state existing at a concrete moment in time the required constants are chosen from the library, ordinarily by interpolating from previously computed tables, and the neutron transport problem is solved. As a result, a new distribution of the energy-release field is obtained, a new temperature distribution is computed, and the next step in time is calculated.