Automatic constants optimization and self-certification of the algorithms of the special software in the SKALA-mikro system of RBMK-1000 reactors during reactor operation

Abstract

The problems of increasing the accuracy of energy release distribution and storage monitoring up to the limits of safe operation of RBMK-1000 reactors are examined. Accuracy can be increased by automatically optimizing some constants used in the special software of the SKALA-mikro system and by periodic self-certification of the algorithm used to determine the computational error in the energy-release distribution. It is shown that tests performed by periodically scanning the core with a calibrated detector and by successively switching off the detectors give close results.It is well known [1] that increasing the monitoring accuracy of the energy release distribution increases the margin factors up to the limits of safe operation of a RBMK-1000 core with respect to a crisis of heat transfer and the linear power density of the fuel elements, decreases the true and measured coefficient of radial nonuniformity of the energy release, and in individual cases is a necessary condition for the reactor to be put into the nominal power regime after prolonged shutdown, for example, after major repairs [2]. In addition, it creates additional possibilities for optimizing the energy release distribution. Monitoring accuracy is increased primarily by individual calibration of in-reactor detectors and by determining more accurately the constants used in special software. Ordinarily, calibration is performed by periodically scanning the core with Dt-6 hafnium calibration detectors [1] and (or) by calibrating control samples for each in-reactor detector on the IRT-2000 reactor (Moscow Engineering Physics Institute), which was recently put into operation.An important function of the SKALA-mikro system is to estimate the monitoring error for the energy-release distribution of each fuel assembly, directly influencing the margin factor up to the limit of safe operation. Periodic metrological certification of the evaluation algorithm is performed using scan results and Fisher's test. In addition, automatic optimization of some constants, used in the software, and self-certification of the error in reconstructing the distribution of the energy release by mathematical analysis of the data on the real state of the core, likewise increasing the accuracy of monitoring, have been adopted in RBMK-1000.The present article compares the results of constants optimization which are obtained by scanning and processing information on the running values of the RBMK-1000 core parameters.In the first case, the ratio of the power W i p of the ith fuel assembly calculated with the "Prizma-M" computer program of the SKALA-mikro system to the power W i sc obtained by scanning a fuel assembly with a Dt-6 hafnium detector is