Behaviour of dissolved inorganic salts in the cooling water of a nuclear power plant open recirculation system and formation of water discharge

The main problem in the operation of nuclear power plants is the scale formation of mineral impurities in an open recirculating system. However, water discharge from an open recirculating system into water bodies can lead to changes in the chemical equilibrium of wastewater components and requires constant monitoring. The purpose of this study was to analyse the behaviour of dissolved inorganic salts in water in an open recirculating system during water treatment using the example of the Rivne Nuclear Power Plant. Moreover, the analysis impact of their discharge with return water in the Styr River. The dissolved inorganic salt concentration has a significant impact on the efficiency of the system and the environment of an open recirculating system power plant. Altogether, each dissolved inorganic salt component was analysed separately using standard measurement methods, using statistical methods of data processing, and correlation analysis. In addition, the annual discharge of the dissolved inorganic salts components was calculated and the amount of discharge was assessed for compliance with the maximum discharge limit. Thus, the influence of the formation of the dissolved inorganic salts and changes in their concentration value during the discharge of returned water into a natural water body was analysed.

Methods
Measurements were performed for the nuclear power plant ORS process and return water and water of the Styr River in the RNPP discharge area using standard methods. Water pH was measured by potentiometric method with a multi-meter І-160. Ca2+, Mg2+, and TH were measured by ethylenediaminetetraacetic acid complexometric titration. Flame photometry has been used for measuring the concentration of Na+, K+, and silver nitrate titrate has been used for measuring the concentration of Cl-. Method of barium sulfate turbidity has been used for measuring the concentration of SO42-. TDS was measured using the gravimeter method. TA, and ΣHCO3-, CO32- – were measured by titration method. The ORS RNPP is designed for operation at COC ranging from 1.5 to 7.0. The DIS discharge (D, t) for each component was calculated using the formula D = C · F / 1000000 (where: C – is the concentration components of DIS in the return cooling water, mg/dm3; F – is the amount of return cooling water, m3). The statistical processing of the research results involved determining the range of data series (min-max), arithmetic mean (M), standard deviation (±SD), Pearson coefficient (r), significance of the connection (p) of the appropriate sample, and factor analysis of the data was carried out using standard methods of mathematical statistics with the software package Minitab software (Version 21.4.1, Minitab, LLC).