Improvement of the algorithm for the calculation of the average weighted thermal power of the VVER-1000 core and the estimation of its error

Abstract

Measurements of the thermal power of the reactor core (RC) at nuclear power plants (NPP) with a water-cooled power reactor with an electrical capacity of 1000 MW (VVER-1000) can be characterized as indirect, unequal and independent. An analysis of the five existing methods for estimating the thermal power of RC is presented. The existing problem of estimating of the error of the average weighted thermal power (AWTP) of RC is shown. Estimation of the AWTP value is the best estimate for the resulting series (out of five values) of the thermal power of the RC. In this case, the estimates of the weight coefficient of each measurement are associated with an estimate of the error of this measurement. If we have the higher accuracy of the method to we have the higher weight of this assessment. The analysis of the thermal power rating of the RC which is implemented in the system of in-core monitoring system (SVRK) of VVER-1000 is presented. It is shown that for practical use for estimating the thermal power of the RC at a NPP with a VVER-1000, taking into account all classes and types of error is possible with a correct assessment of two components - random and systematic error. In this case, the account of both components of errors (random and systematic) is mandatory. Developed a technique that takes into account the following main aspects: for each direct measurement (pressure, temperature, etc.), both the magnitude and its error are estimated; for each (out of five) methods of measuring the thermal power of RC, based on the functional dependences and the error of direct measurements, an estimate of the error of indirect measurement of this thermal power is carried out; assessment of the weighting coefficients of each measurement method is carried out by the magnitude of the error of indirect measurement of the thermal power of RC; the estimation of the absolute error of the weighted average power value is carried out according to the method for assessing the accuracy for indirect measurements. As a result, the SVRK algorithm which existing at NPPs was supplemented with calculated dependencies for estimating the error of the AWTP of RC and calculations of the error of all components necessary for the calculation of the AWTP. The ways of modification of the algorithm existing in the SVRK and specification of the constant database of the SVRK are presented to improve the accuracy of the estimation of the AWTP of RC.