Study on the influence factors of exit burnup reduction in Qinshan CANDU reactor

In the recent years, the exit burnup of Qinshan CANDU reactor two units has reduced significantly, which directly affects the fuel economy and increases the refueling load. In this paper, theoretical analysis is made on the influence to exit burnup of various factors such as excess reactivity, moderator and coolant heavy water purity, pressure tube creep, refueling design, etc. Then exit burnup is calculated based on the annual average data of these parameters using physical codes, and the influence is analyzed of individual factor and the whole. Finally the feasible method of increasing exit burnup is put forward. (author)