3　Seawater Source，and Intake and Discharge

3.0.1　In the design of seawater desalination system，the water quality characteristics and variation of seawater in the water intake and discharge area and the environmental requirements in the surrounding sea shall be learnt.

3.0.2　The following data shall be obtained before design:

1　Tide data，including the highest tidal level，lowest tidal level of local sea area and occurring time in recent 5 years，and the seawater salinity，suspended solid，chemical oxygen demand（COD）and oil content at highest，lowest and intertidal levels of each month in the most recent year；

2　Water temperature data，including the seawater temperature monitoring data of each month during the most recent year at the water intake；

3　Full analysis data of seawater quality，including at least full analysis data of water quality in each quarter during the most recent year，including sediment concentration and particle size distribution.The format of the seawater quality analysis report shall comply with the provisions in Table A of this code.

3.0.3　The design water quality of seawater desalination water source shall be determined comprehensively on the basis of water quality data and expected water quality variation trend in the water intake area.

3.0.4　The design water temperature of seawater desalination water source shall be determined on the basis of the incoming water temperature of the desalination system and desalination process requirements，and be checked against minimum and maximum water temperatures.

3.0.5　The water source of seawater desalination system shall be determined on the basis of factors such as requirements of desalination process，water supply mode of unit cooling water system and the water temperature conditions in cold and hot seasons，with comprehensive consideration of the water intake plans for the near and far phases projects，and according to the following principles:

1　For distillation desalination process，when the cooling water system of the power plant is directly supplied from seawater，raw seawater can be used for both raw water and cooling water.When the pretreatment system requires increasing the water temperature，the water discharged from the power plant cooling water system can be used.When the cooling water system of the power plant is supplied from circulating seawater，raw seawater should be used as raw water；

2　For SWRO desalination process，when the cooling water system of the power plant is directly supplied from seawater，raw seawater or discharged water should be used depending upon seawater temperature.When the cooling water system of the power plant is supplied from circulating seawater，raw seawater should be used as its water source.Provisions shall be made to increase water temperature if the water temperature is below that required by desalination process.

3.0.6　The water intake way of the seawater desalination system shall comply with the following provisions:

1　When raw seawater is taken directly，the effect of sediment，ice，wind and waves，marine life，red tide and other marine hydrological conditions shall be taken into full consideration.Surface water intake should be adopted，including water intake on shore，via tidal channel and pipe culvert.When geological conditions permit，the water intake by drilling well on shore can be adopted after techno-economic analysis；

2　When water is supplied from the plant's once-through water supply system，a pipe can be tapped on the water supply pipe；when it is supplied from the plant's discharge water，the water intake point should be located in front of siphonic well weir for water supply by gravity flow or by pressurizing without damaging the siphon；

3　When it is supplied from the circulation seawater supply system of the power plant，a pipe can be directly led from the circulating water pipe.

3.0.7　The water intake facilities of the seawater desalination system shall be determined according to the desalination process requirements and the water supply mode for the units，and be determined on the basis of fully utilizing the design margin of the power plant cooling water system，and shall comply with the following provisions:

1　The water intake facilities should be designed on a unified basis and set up in combination with the water intake facilities of the cooling water or makeup water system of the power plant.The water intake facilities can be set up independently if the water intake capacity does not match the water supply mode and the design of power plant cooling water system；

2　In a power plant with once-through supply of seawater，the separately arranged seawater desalination water intake pump should be located in the water intake pump house，and a standby pump shall be provided.The water suction device of seawater desalination water intake shall be located inside the pump flow channel，or a separate channel shall be arranged；

3　In a power plant with circulating seawater supply system，the desalinating water pump shall be of the same type as the plant makeup water pump，provided with a standby pump.Common channel water cleaning facilities should be used.

3.0.8　When the seawater desalination system reaches the planned capacity，there shall be no less than two seawater conveying pipes for desalination.When one of them is put out of service，the remaining pipes shall be able to convey 75% of the maximum water flow.

3.0.9　The discharge way of concentrated seawater for the seawater desalination system shall be determined according to the specific conditions of the project，and reclaimed use shall be considered when conditions permit.The environmental protection requirements of the discharge sea area shall be met when concentrated seawater is directly discharged into the sea area.

3.0.10　The design of the water intake and discharge system for seawater desalination shall comply with the relevant provisions in the current industrial standard DL/T 5339 Code for Hydraulic Design for Fossil Fuel Power Plants and design requirements of nuclear power plants.