Structural Material Anomaly Detection System Using Water Chemistry Data, (III)

A method to determine the electric conductivity of water continuously and directly at elevated temperature up to 300°C was developed which can be applied as a sensor for corrosion behavior foreknowledge and diagnosis systems using water chemistry data of BWR primary coolant. Complex impedance was measured between a couple of parallel platinum electrodes installed with a constant distance and dipped in the water. By analyzing frequency dependence of the impedance, the resistivity of the water between the platinum electrodes was estimated separately from the impedance caused by surface reactions on the platinum electrodes, which was the source of error in the measurement of electrical conductivity at elevated temperature.

Increase of necessary frequency to obtain the surface impedance at elevated temperature was evaded by the extrapolation of the frequence dependence of the impedance with calculations by using the data up to 100 kHz in which electric conductivity shows negligibly small dependence on the frequency of applied voltage.

The measured conductivity of pure water up to 300°C showed a good agreement with the calculation based on the dissociation data of water, which shows the applicability for the in-line monitor of electrical conductivity at elevated temperature.     

Structural Material Anomaly Detection System Using Water Chemistry Data, (VII)

Abstract

A method to detect small changes in water quality and diagnose their causes by analyzing on-line conductivity and pH data was proposed. Laboratory tests showed that effective noise reduction of measured on-line data could be got by using a median filter to detect small changes of conductivity; a relative change of 0.001 μS/cm was distinguishable. By simulating the changes of pH and conductivity in the reactor water against a small concentration change of sodium ion or sulfate ion in the feedwater, it was found that an adequate elapsed time for the diagnosis was 4 h from the start of the concentration change. A conductivity difference of 0.001 μS/cm in the reactor water made it theoretically possible to distinguish between a sodium ion concentration change of 4.6 ppt and a sulfate ion concentration change of 9.6 ppt in the feedwater.     

Structural Material Anomaly Detection System Using Water Chemistry Data

The concept of an advanced water chemistry diagnosis system for detection of anomalies and preventive maintenance of system components is proposed and put into a concrete form. Using the analogy to a medical inspection system, analyses of water chemistry change will make it possible to detect symptoms of anomalies in system components.

Then, correlations between water chemistry change and anomaly occurrence in the components of the BWR primary cooling system are analyzed theoretically. These fragmentary correlations are organized and reduced to an algorithm for the on-line diagnosis system using on-line monitoring data, pH and conductivity. By using actual plant data, the on-line diagnosis model system is verified to be applicable for early and automatic finding of the anomaly cause and for timely supply of much diagnostic information to plant operators.     

Structural Material Anomaly Detection System Using Water Chemistry Data, (II)

A calculation model was developed to predict the dose rate, caused by ⁵⁸CO which is formed by the activation of ⁵⁸Ni, around the recirculation pipes m boiling water reactors (BWRs). The model is characterized by considering direct deposition of Ni ion on the nuclear fuel cladding surface and the geometrical contact probability for the ferrite formation reaction between deposited Ni(Co) and Fe₂O₃ on fuel cladding surface.

This model showed the important role of the amount of Fe crud on the surface to reduce ⁵⁸CO ion concentration in the reactor water. And the necessary Fe concentration in the feedwater for reducing the dose rate in the primary system was estimated as a function of the operating time. This model also enables the quantitative predictions of the effect of prefilming treatment of the feedwater heater tubes or another methods to reduce dose rate in an Fe crud suppressed BWR.     

Development of Water Chemistry Diagnostic System for BWRs Using Fuzzy Reasoning

A diagnostic system for BWR water chemistry has been developed incorporating high-speed fuzzy reasoning, holding in view preventive maintenance as principal objective.

The system combines two expert systems—one for detecting an anomaly in the plant operating condition and quickly inferring its cause in a preliminary analysis, and the other performing a detailed diagnosis of the detected anomaly.

The system for anomaly detection and quick preliminary diagnosis infers the occurrence of various anomalies and their causes from the fuzzy relation existing between the fuzzy causes and symptoms, applying a high-speed method for solving the inverse problem of fuzzy correspondence. The system can be run on a small size computer, and is thus conveniently adapted to practical application at machine side.

The system for detailed diagnosis incorporates the expertise of water chemistry engineers, and outputs pertinent information and data to guide operators.

Trial application of the system using data from actual plant operation conclusively demonstrated its effectiveness as a practical preventive maintenance system for actual plants.