Investigation of the water to air conversion factor dependency to the spent fuel cooling time, irradiation history and burnup for gamma dose rate determination of TRR spent fuels

‎Routine gamma dosimetry of spent fuels in nuclear power stations is mandatory to manage their storage in dry or wet spent fuel storages‎. ‎Mostly the spent fuel gamma dose rate measurements out of the spent fuel pool is impossible because of the high exposures of the operators‎. ‎Therefore‎, ‎determination of a conversion factor as precise as possible is important that could be applied to convert the measured gamma dose rate inside the water shield to the air values‎. ‎Simulation methods are powerfully applied to investigate the conversion factor variation trends due to different burnup‎, ‎cooling time and irradiation history of the spent fuels‎. ‎The present work uses MCNPX Monte Carlo-based code to determine the trend‎. ‎The obtained results of this computational study showed that the conversion factor would not have any dependency to the cooling times‎, ‎burnup values and irradiation history if the detector is placed at special positions in air or water environments‎. ‎Comparison of the simulation and experimental data showed an acceptable conformity‎, ‎so that the experimental verified the simulation data trend