Measurement of the Void Reactivity Coefficient Under Reactor Xenon Poisoning and Graphite Temperature Reduction

12/10/2025 2025 - #04 Global safety, reliability and diagnostics of nuclear power installations

Prokhorov I.A. Moiseev I.F. Druzhinin V.E. Lysov D.A. Ivanov S.O.

https://doi.org/10.26583/npe.2025.4.07

The steam void reactivity coefficient is one of the most important measured neutronic characteristics of RBMK-1000 reactors. It characterizes the safety of the reactor unit and largely determines decisions regarding the formation of core loading patterns. In view of this, high requirements are imposed on the accuracy of monitoring the value of the steam void reactivity coefficient. Measurements of the steam void reactivity coefficient are carried out by an indirect method. This method is based on measurements of reactivity and technological parameters obtained during a series of special experiments conducted on the RBMK-1000 reactor. These experiments include tests with perturbation of the feedwater flow rate as well as a separate test for determining the reactivity worth of a segment of the automatic regulator rod. The measurements of the steam void reactivity coefficient are performed while the reactor is operating at a steady-state power level in the range from 40% to 98% of nominal power. The article evaluates the influence of non-stationary xenon-135 poisoning effects and changes in graphite temperature on the estimates of the steam void reactivity coefficient that are calculated from the measurement results. Based on this evaluation, recommendations are provided for the selection of the hold time interval after power reduction and before the start of steam void reactivity coefficient measurements at nuclear power plants equipped with RBMK-1000 reactors. In addition, a method for processing the measurements performed under the above-described conditions is proposed. This method is intended to improve the reliability of the resulting estimates by accounting for the identified transient effects during data analysis.

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RBMK-1000 reactivity steam coefficient of reactivity reactor poisoning

Link for citing the article: Prokhorov I.A., Moiseev I.F., Druzhinin V.E., Lysov D.A., Ivanov S.O. Measurement of the Void Reactivity Coefficient Under Reactor Xenon Poisoning and Graphite Temperature Reduction. Izvestiya vuzov. Yadernaya Energetika. 2025, no. 4, pp. 96-109; DOI: https://doi.org/10.26583/npe.2025.4.07 (in Russian).