Abstract: During the operation of a nuclear power plant, it is necessary to measure the neutron flux distribution in the reactor core. As components related to neutron flux measurement enter fuel assemblies, where fission reactions occur and the components themselves become activated, there exists an extremely high and complex risk of unplanned radiation exposure to personnel. From 1997 to 2024, several serious unplanned radiation exposure incidents related to neutron flux measurement have occurred in the industry. Taking the M310 reactor type as the reference, this paper conducts a detailed risk analysis based on the operational process of neutron flux measurement. By combining the failure causes of unplanned radiation exposure incidents in the industry, and on the basis of optimizing general control and prevention measures for nuclear power plants, this paper further applies the principle of defense-in-depth and proposes an innovative method of “using physical barriers and interlocks to compensate for potential human errors”. This method has been applied for the first time in the M310 reactor type. The risk analysis and control measures described in this paper can serve as a reference for domestic reactor types evolved from the M310, such as CPR1000, CNP600, and CNP1000, to prevent the recurrence of similar incidents and protect personnel safety.

Key words: nuclear power plant, neutron flux measurement, flux detector, thimble, risk of unplanned radiation exposure, control and prevention measures, recommendations