Abstract: Considering the abnormal spike of source count for RPN system present on several units of various nuclear projects of China General Nuclear Power Group, even causing the trip of the unit, it is considered as the very serious issue for the power increasing of the unit. In order to avoid this phenomenon, a professional site team is built to do the investigation and propose the modification. Taking units 2 and 3 of project B as examples in this paper, good experiences are implemented in the erection. Long time operation from commissioning, start-up and commercial operation verified that no abnormal spike count is observed.