Assessment of critical condition for IBR reactor with subcritical block in the equilibrium mode

3/22/2017 2017 - #01 Modelling processes at nuclear facilities

Brezhnev A.I. Gulevich A.V. Kukharchuk O.F. Fokina O.G.

https://doi.org/10.26583/npe.2017.1.08

A system consisting of a fast batch pulsed reactor of the IBR-type and subcritical block (thermal in terms of neutronics) is examined. The reactor is equipped with a reactivity modulator, which provides for a short time of the «transition» of the system from deeply subcritical state to supercritical state on prompt neutrons and back. During the intervals between pulses the system is in the deeply subcritical state.

This type of reactor system can function in the equilibrium (static) mode in the case when the critical condition for the kinetic parameters describing its operation is fulfilled. Description of neutron kinetics is made in two-point approximation. It is assumed here that the change in reactivity occurs periodically according to parabolic law. Numerical simulation of the critical condition is extremely difficult and time-consuming, while analytical representation is almost impossible due to the necessity to solve ordinary differential equations with variable coefficients.

Methodology is suggested in the present paper allowing approximating the parameters of the coupled system consisting of the batch pulsed reactor and subcritical block operating in the equilibrium mode. Analytical relations in a quadrature form for the calculation of «critical» condition of such a system in «frequent» pulses approximation, when one can neglect the collapse of the delayed neutron precursors during the interval between pulses, are obtained.

Calculations of the critical condition are illustrated using the example of a laser system consisting of a batch pulsed reactor IBR-2 and subcritical block multiplying neutrons, in which fission energy is converted into laser emission energy.

Estimates of critical system parameters were obtained using analytical expressions, as well as by direct numerical calculations using STIK code modeling the kinetics of neutrons in the system under examination in the two-point approximation.

Good agreement between the results of direct calculations and estimations obtained using analytical expressions was demonstrated.

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laser system fast butch pulsed reactor subcritical block equilibrium mode critical condition analytical ratios numerical simulation STIK program

Link for citing the article: Brezhnev A.I., Gulevich A.V., Kukharchuk O.F., Fokina O.G. Assessment of critical condition for IBR reactor with subcritical block in the equilibrium mode. Izvestiya vuzov. Yadernaya Energetika. 2017, no. 1, pp. 83-93; DOI: https://doi.org/10.26583/npe.2017.1.08 (in Russian).