Estimation of temporal variation of tritium inventory discharged from the port of Fukushima Dai-ichi Nuclear Power Plant:analysis of the temporal variation and comparison with released tritium inventories from Japan and world major nuclear facilities

Abstract

ABSTRACT We estimate monthly discharge inventory of tritium from the port of Fukushima Dai-ichi Nuclear Power Plant (1 F) from April 2011 to March 2020, using the Voronoi tessellation based on monitoring inside 1 F port and other techniques utilizing radioactive ratio of tritium to 137Cs in stagnant contaminant water and in discharge amounts. From the estimated results, we find that it dropped immediately after closing the seaside impermeable wall in October 2015 and simultaneously coincided with the sum of input inventories published by TEPCO. By comparing with published data on tritium release inventories in nuclear facilities, we find that the annual discharge inventory from 1 F port in the year 2011 is comparable to the maximum of operating pressurized water reactors in the order. At the national level, the total domestic release inventory significantly decreased after the accident owing to the operational shutdown of most plants. Furthermore, the total Japanese discharge inventory including 1 F are found to be minor compared with those of nuclear reprocessing plants and heavy-water reactors on a worldwide level. From the above results, we suggest that various scenarios can be openly discussed regarding the management of tritium stored inside 1 F with the help of the present estimated data.