Mid-Weighed Kinetic Parameters for Use in the Two-Group Diffusion Model of Reactor Dynamics with Fuel Based on a Mixture of Fission Isotopes
ARTICLE PDF

Keywords

reactor dynamics, kinetics parameters, delayed neutrons, fraction of delayed neutrons, mixture of fissile isotopes

How to Cite

Khalimonchuk, V. (2019). Mid-Weighed Kinetic Parameters for Use in the Two-Group Diffusion Model of Reactor Dynamics with Fuel Based on a Mixture of Fission Isotopes. Nuclear and Radiation Safety, (1(81), 58-61. https://doi.org/10.32918/nrs.2019.1(81).10

Abstract

In the model of reactor kinetics based on the description of neutron transport in the two-group diffusion approximation, the number of equations describing the change in the concentration of delayed neutron precursors depends not only on the number of groups of delayed neutrons, but also on the number of fissile isotopes present in nuclear fuel. Since each isotope is characterized by six groups of delayed neutrons, the total number of differential equations describing concentrations of delayed neutron precursors is equal to the product of the number of fissile isotopes (M) and the number of groups of delayed neutrons for each isotope (i = 6). This is true provided that the decay constant of the concentrations of delayed neutron precursors that were formed from the division by fast or thermal neutrons can be taken in the same way. In fact, there is a difference, though small, in these values for the two energy groups. Therefore, the number of the corresponding equations is twice as high. In this paper, a mathematical expression is obtained for the weighted average decay constant of delayed neutron predecessors from fission by fast and thermal neutrons in a multiplying medium with several fissile isotopes. This, together with the conventional procedure of weighing the fraction of delayed neutrons from fission by fast or thermal neutrons in a similar multiplying medium, allows the two-group diffusion model of the reactor kinetics to be limited to only six equations for the concentrations of delayed neutron precursors and thus the kinetic model of the reactor to be simplified.

https://doi.org/10.32918/nrs.2019.1(81).10
ARTICLE PDF

References

1. Hetrick, D. L. (1975), Dynamics of Nuclear Reactors [Dinamika yadernykh reaktorov]. Мoskow: Atomizdat. 400p.

2. Keepin, G. R. (1967). Physics of Nuclear Kinetics. Мoskow: Atomizdat.

3. Khalimonchuk, V. A. (2008). Dynamics of a Nuclear Reactor with Distributed Parameters in Studies of Transient and Emergency Operation of VVER and RBMK. Nuclear Safety Series [Dinamika yadernogo reaktora s raspredelennymi parametrami v issledovaniiakh perekhodnykh i avariinykh rezhymov ekspluatatsii VVER i RBMK. Seriia Bezopasnost atomnykh stantsii], Osnova, Kiev, 226 p.

4. HELIOS Methods. Studsvik® Scandpower, Version 1.10, April 2008. 192 p.