After the Fukushima accident, the disposal of radioactive liquid waste has received great attention. The analysis of nuclide activity and composition in the containment liquid waste after severe accident is the premise for the liquid waste treatment. According to the source and reduction mechanism of the radionuclides in containment liquid waste after severe accident, the calculation model for radionuclide activity was established. Taking the passive PWR as an example, the activity and composition of radionuclides in the containment liquid waste after severe accident was studied.After the severe accident, the nuclides released from the reactor core into the containment, and the activities of each group nuclides in the containment liquid waste gradually increased. After the core stopped releasing nuclides to the containment, with the exception of the lanthanum group nuclides, the activities of the other group nuclides decreased with time. The lanthanum group nuclides had a different trend over time from other group nuclides. After the core stopped releasing nuclides to the containment, the total activity of the lanthanum group nuclides continued to increase and then decreased. The total iodine radioactivity decreased the fastest, and the total cesium radioactivity decreased the slowest.In the early stage of the severe accident, iodine was the main nuclide in the liquid waste, which activity accounted for more than 80% of the total activity, followed by the cesium group nuclides. The proportion of cesium activity in the total activity decreased first and then increased, while that of other groups increased first and then decreased. One year after the accident, the cesium activity accounted for about 94% of the total activity, and the barium, strontium and lanthanum group nuclides activity accounted for about 5% of the total activity.For iodine, the activity of 131I decreased the slowest, which was the focus of radioactive liquid waste, however it can be removed after a long period of attenuation. One year after the accident, the activity of 131I decreased to about 103Bq. For the other groups of nuclides, 134Cs, 137Cs, 89Sr, 90Sr, 127Tem, 106Ru, 144Ce, 241Pu and 90Y decayed very slowly. One year after the accident, the radioactivity of these nuclides remained at the level of 1013~1016Bq, which could not be removed only by the nuclide decay for a long time. Therefore, these nuclides were the important components of the radioactive liquid waste.

Study on Main Radionuclides of Liquid Waste in Containment Under Severe Accident

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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