Measurement of pH in Simulated Water-Cooled Nuclear Reactor Heat Transport Circuits

Abstract The use of palladium-hydride electrodes (Pd black on Pd, Pt, and Au) for the measurement of pH in high-temperature aqueous systems (298 K to 548 K) is described. The electrodes were calibrated against boric acid/lithium hydroxide buffer solutions, whose pHT versus temperature profiles have been calculated using known dissociation constants for the components. Linear potential versus pH correlations are observed for all temperatures studied. However, the gradients of the correlations deviate from the predicted Nernstian values. Furthermore, thermodynamic analyses of the systems demonstrate that above 373 K the observed potential deviated significantly from the equilibrium values calculated on the supposition that the potential-determining reaction is H++e−⇄H(Pd,α+β). Possible reasons for the observed deviation from ideal behavior are identified.