Modeling the activity and scaling factor of 129I in the primary coolant and CVCS resin of operating PWR

To estimate the activity of 129I at the primary coolant and chemical and volume control system (CVCS) resin in Korean pressurized water reactor (PWR) plants, a theoretical methodology was developed on the basis of an existing model of primary coolant activity and new model of CVCS resin activity. In order to reflect the difference between 129I and 137Cs, the different power-related diffusivities in the defective fuel were derived, and the variable removal efficiency of the CVCS resin for 137Cs was applied as a function of the coolant activity ratio of 131I/137Cs. The current computational method was validated by using the measured coolant activities of 137Cs, and the results show better agreement than a previously suggested parameter correlation method between 129I and 137Cs. There was also reasonable agreement in a comparison of the results of the test resin columns of the coolant from the PWR plants of other countries. It was shown that the ratio of the effective removal efficiency of 129I and 137Cs in the CVCS resin linearly influences the activity ratio of 129I/137Cs in the coolant, but on the other hand, its influence on the activity ratio in the CVCS resin is relatively less sensitive compared with that in the coolant.