Study on Behaviour of Hydrogen Generation due to Radiolysis during the Transport of Damaged Fuel from Fukushima Daiichi Nuclear Power Station

In the transport of intact spent fuel discharged from an ordinarily operated nuclear power station, the amount of hydrogen generated by radiolysis was reported well within the safe range. The water in the spent fuel pools of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to as \"1FSFP\") contains seawater constituents, because the 1FSFP were cooled by seawater during the accident. Hence, in the transport of damaged spent fuel from the 1FSFP, the hydrogen generation affected by such pool water conditions and leachate from the damaged fuel may exceed the permissible range. To evaluate the radiolysis behaviour properly, S/NRA/R conducted experiments with the objectives;Measurement of equilibrium concentration of hydrogen generated by radiolysis of water withseawater and iodine ions or other ionic constituent,Measurement of G values for hydrogen generation under the above water conditions, andVerification of evaluation model for radiolysis behaviour based on the above results.The following parameters were selected for the experiments in consideration of transport conditions including 1FSFP water:Test water: pure water with artificial seawater (hereinafter referred as \"simulated water\"), pure water with bromine ions and pure water with iodine ionsTest water temperature: room temperature and 150 ºCExposure dose rate: up to 103 Gy/hExposure period: up to 100 hThe results indicate that the effect on the hydrogen generation by iodine among the test materials was the largest. Moreover, when the iodine ions of a particular concentration coexist under presence of seawater, iodine ions were found to have a dominant effect on the hydrogen generation. The experimental results will be used as a technical basis for future safety evaluation of the transport of damaged fuel from 1FSFP.