A method and a system for performing real-time, continuous, measurements of the boron concentration in the water entering a nuclear reactor coolant system. The invention utilizes knowledge of the impact that boron contained in liquid water has on the attenuation of acoustic or ultrasonic waves. This information, coupled with radiation damage resistant and high temperature operability capable transmitter and receiver equipment, provides the means to place the measurement system sensors and signal processing electronics on the reactor coolant system charging flow piping or the hot leg or cold leg of the reactor coolant loop. This will allow the reactor operator to directly monitor both the reactor coolant system boron concentration value and detect changes in the reactor coolant system boron concentration relative to a reference value as they occur.