Abstract: The basic technical criteria of operation ability for the boron recycle system is the quantity of discharged reactor coolant for treatment, which is the basis of the capacity design of important equipments such as head storage tanks, intermediate storage tanks, etc. Through theoretical analysis and calculation, the paper gives out the discharge amount of recycled reactor coolant needed for pressurized water reactor power plant design basis. The discharge amount provides the critical design inputs and basis of analysis for engineering design of boron recycle system.