Abstract: On the premise of safety,economy is one of the important objectives of nuclear power plants.For VVER-1000,there are several cases of operation modes when the plant is off the grid,such as the critical operation after refueling,the hot shutdown and critical operation,and the critical operation after test.For the purpose to reduce the time of the operations,the consumption of materials,and the amount of waste water produced,the optimization researches are carried out on these cases.The qualitative and quantitative analysis is carried out,on the configurations of the control rod and boric acid,which are the important factors to influence the shutdown and critical operations.The general steps and the basic principles of the optimizations are described.Three cases are optimized.