Abstract: Collective dose is an important indicator of radiation safety for nuclear power plants. There are many factors affecting the collective dose, but the most fundamental one is the radiation source term of nuclear power reactor units. However, the control of source term is not so simple, and the source term is related to many factors such as reactor unit type, loop number, operation cycle, reactor unit operation time, primary circuit equipment material, chemical control process, purification unit capacity, fuel state and so on. Due to the lack of experience and appropriate attention, many factors that could improve source term control in the design, construction, installation and commissioning stage were ignored for most reactor units. In order to make good use of the key stage of operation preparation, related work has been carried out in six aspects: including purification capacity improvement, special washing, cleaning and decontamination, special test tracking, shielding improvement and comprehensive improvement, in order to minimize the source term level. A lot of valuable data and experience for the source term control has been accumulated through this work.

Key words: Operation preparation, Source term control, Collective dose