Constant monitoring of the state of the core ensures safe operation of a nuclear reactor. This article examines the reconstruction of the energy release in the core of a nuclear reactor on the basis of the indications of height sensors. Situations where some sensors fail are not rare. Any reduction in the number of sensor indications increases the error. However, the missing measurement information can be reconstructed by mathematical methods, and replacement of the failed sensors can be avoided. The simplest algorithm for reconstruction missing indications consists in approximating the height distribution by harmonic functions. However, the coeffi cients of these functions are found to be correlated. It is suggested that a set of natural functions determined by means of statistical estimates obtained from archival data be constructed. The procedure proposed makes it possible to reconstruct the fi eld even with a signifi cant loss of measurement information.Safe and effi cient operation of a nuclear reactor is secured by constantly monitoring the state of the core, including the energy release, by means of sensors used for in-reactor monitoring. In VVER, direct-charge sensors (DCS) are united into neutron-measurement channels with seven sensors uniformly arranged along the height in each channel [1]. Radial and height sensors comprised of four extended sensitive sections for monitoring the energy release (SMER) are installed in RBMK [2]. Situations where some in-reactor sensors fail are not rare in the practice of operating nuclear reactors. If a sensor fails, then the use of its indications is prohibited. For example, if more than one section of a RBMK sensor fails, then the detector is considered to be 'prohibited'. A neutron measurement channel in VVER is prohibited upon failure of more than two sensors.A reduction in the number of in-reactor monitoring sensor indications on the basis of which the energy release in the reactor core is reconstructed results in a larger determination error and requires modifi cation of the standard reconstruction algorithm. We note that in VVER the sensors can be replaced only between runs while in RBMK they can be replaced 'on the fl y' without stopping the reactor, but this complicates the work because not just the sensor but the entire fuel assembly must be replaced so that actually unplanned refueling is performed.The missing measurement information can be restored by mathematical methods and premature replacement of the failed detectors can thereby be avoided, which is also expedient economically. For this, it is proposed that the missing sensor indications be calculated by fi tting the known points using functions determined on the basis of archival data. We shall clarify this for the following example.

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The paper proposes an elementary mathematical model of the distribution of coolant flows through water communications in the group distributing header (GDH) of a power unit with an RBMK reactor. This model used to determine the flow rate in the channel with a “forbidden” flow meter. An equation is given based on the mass balance of the coolant in the allocated volume. The results of the solution are used to construct an algorithm for determining the flow rate of the coolant in the channel. The results of the application of the technique on the measurement data from the power unit are presented. It is shown that the relative discrepancy with the measured value of the flow rate at a constant position of the flow control valve is on the order of several percent.

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