Abstract: The construction of the port approaching industrial zone has led to changes in the local tidal field of the water intake and outlet of nuclear power plant,which brings effect to the dilution and diffusion of liquid effluent.Taking Lianjiang Port in the Beibu Gulf of China as an example,by using two-dimensional numerical simulation calculation,the concentration distribution of ¹³¹I and ⁶⁰Co nearby the water intake and outfall during mid-tidal in summer was analyzed,with and without consideration of construction of the zone after the two units of the nuclear power plant went into operation.The results showed that before the construction of the zone,¹³¹I and ⁶⁰Co mainly followed the tidal movement,and the average enveloping area of the concentration of ¹³¹I and ⁶⁰Co diluted by 10 times is 0.9×10^-3 km² and 1.2×10^-3 km² respectively.The high concentration area is mainly distributed in the Anpu Bay where the outfall is.After the construction of the zone,the tidal current field only changed in the vicinity of the industrial zone.The eastward side of the zone was significantly larger than the west side and a recirculation zone was formed on the east side.The flow in the vicinity of the zone is weaker due to the jet flow.The flow close to the industrial zone is affected most,and the flow rate and direction are significantly changed.The average envelope area of the concentration of ¹³¹I and ⁶⁰Co diluted 10 times was 1.0×10^-3 km² and 3.0×10^-3 km² respectively.The average envelope area of the concentration of 1 000 times diluted was 109.21 km² and 265.41 km² respectively.The high concentration zone of ¹³¹I and ⁶⁰Co increased by 11.1% and 150% respectively after the construction,while the low concentration zone decreased by 12.5% and 3.2% respectively,indicating that the industrial zone is not conducive to the dilution and diffusion of liquid effluent.The results will provide reference for optimizing the intake and drainage schemes,avoiding floodplain discharge and local concentration accumulation and providing technical support in reducing the environmental impact of liquid effluent discharge.

Key words: Lianjiang Port, liquid effluent, dilution and diffusion, numerical simulation