Determination of the relative power density distribution in a heterogeneous reactor from the results of measurements of

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rmination of the Relative Power Density Distribution in a Heterogeneous Reactor from the Results of Measurements of the Reactivity Effects and the Neutron Importance Function A. A. Bobrov, E. S. Glushkov, A. A. Zimin, A. V. Kapitonova, G. V. Kompaniets, V. I. Nosov*, R. P. Petrushenko, and O. N. Smirnov Russian Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia Received March 18, 2011

Abstract—A method for experimental determination of the relative power density distribution in a heteroge neous reactor based on measurements of fuel reactivity effects and importance of neutrons from a californium source is proposed. The method was perfected on two critical assembly configurations at the NARCISS facil ity of the Kurchatov Institute, which simulated a smallsize heterogeneous nuclear reactor. The neutron importance measurements were performed on subcritical and critical assemblies. It is shown that, along with traditionally used activation methods, the developed method can be applied to experimental studies of special features of the power density distribution in critical assemblies and reactors. Keywords: smallsize heterogeneous nuclear reactor, power density, power density measurement method, fuel reactivity effects, importance of neutrons from a californium source, critical assembly, experiment. DOI: 10.1134/S1063778812130017

INTRODUCTION One of the most important neutronic characteris tics of smallsize heterogeneous nuclear reactors is the spatial power release distribution in the reactor core, which is determined by computations and studied experimentally on critical assemblies in which physi cal features of reactors under development are simu lated [1]. Measurements of the power release are usually per formed by activation methods using uraniumcon taining foils or solidstate track detectors [2]. In addi tion, experimental methods for determining the neu tronic characteristics based on measurements of reactivity in nuclear reactors are being developed [3]. In the present work, a method for determining the power release distribution in a heterogeneous reactor based on measuring the fuel reactivity effects and importance of neutrons from a californium source is proposed. The method was perfected in experiments on a critical assembly of the NARCISS facility of the Kurchatov Institute. The relative power distribution in two critical assembly configurations is obtained. In order to simulate the special features of the power release distribution in fuel elements surround ing safety rod channels of reactors, in experiments with one of the reactor core configurations, a channel without fissile material was used.

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1. METHOD FOR DETERMINING THE POWER RELEASE IN A HETEROGENEOUS REACTOR BASED ON MEASUREMENTS OF FUEL REACTIVITY EFFECTS AND IMPORTANCE OF NEUTRONS FROM A CALIFORNIUM SOURCE The program of experiments on the NARCISS critical facility presumes measurements of power release in fuel cores of fuel elements of these reactors. The power release in