Reliability of the RBMK-1000 coolant flow measurement system
An analysis of statistical data of diagnostic measurements of two parameters determining the operability of the RBMK-1000 reactor’s SHADR-8A flowmeters – the minimum value of the amplitude negative half-wave of the flow measuring unit input signal and the mean-square deviation over the flowmeter ball rotation period – made it possible to develop a mathematical model of the flow sensor parametric reliability. The mathematical model of the flowmeter reliability is a random process, which is a superposition of two delayed recovery processes. Studying the flow sensor operation reliability model provides an exponential estimate of the probability that the parameters determining the sensor performance will not exceed the specified levels. Using the Bernoulli scheme and the probability-estimating relationship for the sensor performance parameters, it is possible to calculate the probability of failure-free operation of both a single reactor quadrant and the reactor coolant flow measurement system. In addition, it becomes possible to estimate the intensity of the quadrant failures. Important for practice is the ability to predict the number of failed sensors, depending on the time the system is running. The index of the system reliability can be the average number of failed sensors, the ratio for which is given in the paper. All the research results were obtained without any additional assumptions about the laws of random distributions.
The obtained results can easily be generalized to the case when the dimension of the vector of the defining parameters is greater than two. The use of the results of this study is illustrated by calculated quantitative values of the parametric reliability indices of the flow sensors and the reactor coolant flow measurement system.
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