Abstract: This paper discussed the design rules of the boric acid tank volume of reactor boron and water makeup system（REA） in PWR nuclear plant and the limit requirements of the tank volume in the operation technical specification. Based on the comparison and analysis of the arguments of Daya Bay nuclear plant 18 months refueling modification and Ling’ao nuclear plant 1/4 refueling modification, the paper pre-assessed and calculated the lack of the REA boric acid tank volume as the fuel enrichment upgraded to 4.95% in the future, and proposed the suggestion of increasing the volume or boric acid concentration of the REA system in new nuclear plant design in order to meet the operation technical specification requirements.