Implementation of the indirect assessment method for 129I and 135Cs accumulation in the RBMK-1500 reactor coolant purification system

The transport of long-lived radionuclides 129I and 135Cs in technologic chains of the Ignalina NPP and their accumulation in by-pass purification system filtering materials was investigated by spectrometric measurements and mathematical modelling. The database of regular gamma spectrometric measurements performed at the NPP was analysed. Results of gamma spectrometric measurement of specific activities of 131I and other short-lived isotopes of iodine as well as of 134Cs and 137Cs isotopes have been analysed and parameters specific to the reactor operation have been estimated. Accumulated activities of 129I and 135Cs in spent filtering materials of the reactor by-pass purification system as well as specific activities are evaluated. Specific activities are compared with preliminary acceptance criteria for a near surface repository which is at the stage of design at the Ignalina NPP. Moreover, scaling factors for these radionuclides for the by-pass purification system radioactive waste are assessed.