Abstract
The measurements of physical parameters of the TRIGA reactor and Nuclear power plant Krško (NEK) reactor cores have been in the past performed on hand of the neutron flux signal obtained from uncompensated ionization cells and by employment of the a digital meter of reactivity (DMR). At the TRIGA reactor only one ionization cell is currently used for flux measurements. During the insertion of one control rod the neutron flux distribution is significantly altered affecting the flux measurements of inserting different control rods. The problem is presently solved by assigning a correction factor to each control rod what introduces an additional uncertainty. In the present paper the implementation of four fission cells for reactivity measurements is presented. In this way determining the correct gamma background and its subtraction, performed by DMR algorithms, becomes less important as previously by using ionization chambers. The larger number of detectors also reduces the flux redistribution effects on the signal during individual control rod movements.
Highlights
THE control rod worth in research reactors and power plants can be determined by different methods [1 - 7]
The analysis is performed by transferring the data of the neutron flux from nuclear instrumentation to a digital reactivity meter (DMR) consisting of a high-quality electrometer and a computer using special software for analysis of the signal
The effect can be compensated by the usage of a neutron flux depression factor, what has been done in the past
Summary
THE control rod worth in research reactors and power plants can be determined by different methods [1 - 7]. In the present work the rod-insertion method, by employing measurement of the neutron flux with fission cells, is studied. This method is convenient because it is very quick and simple to perform. During the rod-insertion measurement the flux is, redistributed and a flux depression forms at the position of the inserted control rod Due to this redistribution the signal at the detector is not necessarily proportional to the average flux in the core. The effect can be compensated by the usage of a neutron flux depression factor, what has been done in the past Another possibility is to use multiple detectors, symmetrically positioned around the core. The possibility to what extent the axial dependence of the flux depression factor can be omitted is performed, and comparison between the method of using a single detector and the average of four detectors is performed in the scope of this work
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