VVER-1000 Power Monitoring Based on Neutron Detector Signals

V. I. Borysenko¹, D. V. Budik², V. V. Goranchuk¹

¹Institute for Safety Problems of NPP, NAS of Ukraine,
12, Lysogirska st., Kyiv, 03028, Ukraine
²Severodonetsk Research and Production Association “Impulse”,
2, Peremohy av., Severodonetsk, 09405, Ukraine

DOI: doi.org/10.31717/2311-8253.19.2.1

Abstract

The value of the thermal power of the reactor (TPR) is used in the VVER-1000 control systems in most algorithms for generating control signals, interlocks and protections, and the technical and economic indicators of the power unit are determined by TPR. Plans to increase VVER-1000 TPR to 101.5 % of the nominal, and in the future to 104–107 % of the nominal, require additional research and justification on the accuracy of the determination of TPR. Ways to improve the accuracy of determining TPR based on the signals of VVER-1000 neutron flux monitoring systems were discussed in the article. The main factors affecting the errors in the determination of TPR by the parameters of the neutron flux in the systems are considered: neutron flux monitoring system (NFMS); in-core monitoring system (ICMS). To increase the accuracy of TPR determination in NFMS, a model of automatic correction of the ionization chamber signal is proposed depending on changes in temperature and boric acid concentration in the coolant, the position of the control rods, fuel burnup, etc. The implementation of a model for correcting the signals of NFMS ionization chambers will allow for a wide range of transient operating modes of VVER-1000, including during power maneuvering, to provide regulatory requirements for the error in determining the neutron power of a reactor. Possible additional methods for the determination of TPR, which can be used to determine the weighted average thermal power of the reactor, are proposed. For example, the analysis of changes in the signals of the background conductors of self-powered neutron detectors (SPND), over several VVER-1000 fuel campaigns, shows the fundamental possibility of using the signal of background conductors to determine TPR, along with the signals of the SPND itself. The results of the analysis of the change in the error in determining the weighted average thermal power of the reactor in the case of applying an additional method for determining TPR based on the signals of the background conductors of the SPND are presented.

Keywords: reactor thermal power, neutron flux parameters, self-powered neutron detectors, background conductors, correction model, weight coefficients.

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