Ядерна фізика та енергетика Nuclear Physics and Atomic Energy   ISSN: 1818-331X (Print), 2074-0565 (Online)   Publisher: Institute for Nuclear Research of the National Academy of Sciences of Ukraine   Languages: Ukrainian, English   Periodicity: 4 times per year   Open access peer reviewed journal

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V. I. Borysenko^*, V. V. Goranchuk

Institute for Safety Problems of Nuclear Power Plants, National Academy of Sciences of Ukraine, Kyiv, Ukraine

^*Corresponding author. E-mail address: vborysenko@ispnpp.kiev.ua

Abstract: The article presents the results of the numerical simulation of the signal formation process of the background wires of self-powered neutron detectors (SPND) under the action of gamma radiation in the VVER-1000 core using MCNP code. The validation of the MCNP model was carried out on the results of experimental determination of the current of the background wires of the SPND, obtained at three different power units with VVER-1000 during the fuel campaign. The article also proposes a new gamma-ray method for determining the thermal power of the VVER-1000 reactor (TPR) based on the signals from the background wires of the SPND. TPR is an important safety parameter of VVER-1000, therefore, increasing the accuracy of determining TPR with the introduction of an additional gamma method for its determination is an urgent task, given the plans to increase the TPR of VVER-1000. The results of the experimental determination of the VVER-1000 TPR by the traditional neutron method based on the SPND signals are presented, and problematic issues regarding the error in determining the TPR by the neutron method are pointed out. The article presents the results of modeling to study the influence of the main factors affecting the change in the proportionality coefficient K_gm between the actual TPR and the TPR determined by the gamma method. To improve the accuracy of determining the TPR by the gamma method, a correction model for K_gm is proposed, which takes into account the effect of nuclear fuel burnup on the change in the signal of the background wires of the SPND. Taking into account that the signal of the background wires of the SPND is inertialess with respect to the change in the neutron power of the reactor, the introduction of the method for determining the TPR by the gamma method is promising for the implementation of an additional alternative channel for generating an emergency protection signal in terms of both power and the period of the reactor.

Keywords: reactor thermal power, weighted average thermal power, self-powered neutron detector, SPND background wire, MCNP model of SPND, Compton effect, photoelectric effect, pair formation, emergency protection formation.

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