Radiation Protection Calculation and Optimization for Shielding Design Around the Refueling Pipelines of HTR-PM

The high-temperature gas-cooled reactor pebble-module (HTR-PM), which is under constructed in Shidao, Shandong Province of China, adopts the spherical graphite coated components as fuel elements. During the operation of the reactor, the spherical fuel elements will be reloaded into the core periodically through the refueling pipelines, which will cause radioactive irradiation to personnel and facilities in several corridors and rooms. The three-dimensional geometry model was built according to the real structure and the radiation shielding design was verified and optimized by the QAD-CGA program. In the calculation, the average gamma intensities of the spherical fuel elements of 15 different cycle times were adopted as the source term. From the results, it can be concluded that: 1) For the 20-meter corridor, the dose rate will be less than 1E−6mSv/h at 30cm outside the concrete wall of 0.6m thickness by single fuel elements; 2) For the 0-meter corridor, an extra 32.0 cm steel shield should be added to satisfy the personnel dose rate limit of 0.03mSv/h; 3) For semiconductor electrical equipment closed to the pipelines, the required steel shield thickness is 12.0 cm under the accumulative dose limit of 50Gy; 4) For non-radiation resistant cables, the required steel shield thickness is 4.5 cm under the accumulative dose limit of 1000Gy.