In small integrated reactors, the control rod drive mechanism (CRDM) is located within a high-intensity radiation field. The sealing coil of the CRDM may experience performance degradation due to intense irradiation, making accurate dose rate assessment essential for predicting maintenance cycles.

This study aims to evaluate the irradiation dose rate at the CRDM sealing coil in a small reactor during normal operation, identifying the main contributors to the dose rate.

Radiation source terms, including core fission neutrons and photons, fission and activated corrosion products in the primary coolant, and activation product N-16, were calculated. Computational models were developed using the Monte Carlo methods for photon transport and the point-kernel integration for dose rate evaluation. Conservative assumptions were applied to coolant density and source distribution.

The total dose rate at the CRDM sealing coil was found to be 4.1 Gy·h⁻¹. N-16, produced via neutron activation in the coolant, was the dominant contributor, accounting for nearly the entire dose. Contributions from fission products, activated corrosion products, and core fission photons were negligible (less than 1%).

The irradiation dose rate at the CRDM sealing coil is primarily due to N-16 decay gamma rays, with the majority originating from coolant within a 1.5-meter thick region centered around the dose point. These results provide a basis for predicting coil lifespan and planning replacement intervals.