Evaluation of the effectiveness of the hot water layer (HWL) in reducing the pool top radiation level for a typical open pool research reactor

The open pool-type research reactor (OPAL) is designed to enable operators to perform tasks in reactor hall while operation. The main source of radiation in reactor pool is reduced and managed through the hot water layer (HWL) system. This paper presents the effect of HWL in reducing the radiation level on the pool surface considering the major source of radioactivity which comes from the buildup of the fission products. OPAL core was modeled using MCNP6.1 code to calculate the concentration and activity of the fission products for certain operation interval at full power. Also, the dose rate profile inside the reactor pool and the pool top was calculated for both normal and abnormal operation. The dose rate results of normal operation with HWL on the pool top have shown it is safe, but with HWL failure, the dose rate on the pool top exceeded the permissible dose limits.