Distributed system for acquisition and analysis of NPP systems noise data

Since years '90 the noise analysis for nuclear stations is more frequently used because: - the data can be acquired by making use of the NPP instrumentation; - acquisition may be performed in a steady-state regime, at rated capacity; - reactor dynamical regime data are obtainable although steady-state regime data are used. The signal noise analysis is based on the dynamical information about the reactor operation obtained from instrumentation signal fluctuations as determined in steady-system regime. The small fluctuations are due to the stochastic effects inherent to physical processes such as heat transfer, boiling, turbulences in coolant flow, moderator collective motions, fission process, structural vibrations and pressure oscillations. Specifically, for CANDU type reactors, the results may be applied for: - surveillance of the functioning characteristics of detectors and transducers; - signaling or predicting misfunctioning of detectors and transducers, what implies establishment of optimal time rate for macro-sampling; - signaling or prediction of misfunctioning of reactor core components, what implies setting up methods and procedures for detecting vibrations inside the fuel channels, based mainly on the signals from the ROPT adjacent detectors and on the flow rate transducers. The system of signal acquisition is a distributed, fixed-data acquisition system provided with a limited number of inputs, based on a number of modules of local analog signal processing and conversion to digital representation. The signal, local processing implies noise removal out of signal through continuous current component elimination, an amplification of the signal, low-pass filtering for alias frequency removal, 16 bit analog-to-digital conversion and digital value serial way transmission. The local processing is based on the characteristics of the acquired signal (noise), namely: - the frequency band, 0.01 Hz - 200 Hz; - the signal amplitude level, 16 - 32 MeV superimposed over a continuous background of 3 - 7 V. The distributed data acquisition and analysis system of the noise is based on simultaneous acquisition of the analog signal, its local processing and transmission on a serial way of the digital value towards a PC. The local processing of the signal implies removal of the continuous current component, signal amplification and limitation of the upper band to 200 Hz. The module is provided also with a microcontroller (μC) which performs the analog-to-digital signal conversion, and subsequent transmission of the digital value towards the central computer on a serial way. To obtain a simultaneous signal acquisition of all the modules, μC needs a synchronizing signal from the (PC) central computer. Linked to the central computer each local processing module will communicate serially by means of the 'PC Interface' module. The serial communication speed is determined by the acquired signal peak frequency, the analog-digital converter resolution, the used communication medium (optical fiber, twisted pair cable) and maximal number of acquired signals. The distributed acquisition and analysis system of the noise produced in NPP systems can be used as a tool of surveillance, diagnosis and prediction of the NPP processes and instrumentation, with no interference with NPP operation and no decrease of the system availability. In addition, by working in steady-state regimes some dynamical parameters can be determined without intervention of particular events such as fast shutdowns or power variations