Abstract: This paper mainly discusses the first application of constant injection test method to measure the inner leakage rate of MCR in domestic nuclear power plant. Through research for calculation principle of inner leakage rate, injection rate and the balance judgment criterion, the suitable tracer gas, suitable injection point and injection rate are selected for the first test domestically. Some key influential factors are also investegated in order to solve the problems of design and construction. This test method has good reproducibility and can be applied in other domestic nuclear power plants.

Key words: MCR, inner leakage rate, constant injection test method