Discussions on Tritiated Water Treatment for Fukushima Daiichi Nuclear Power Station

A series of discussions on tritiated water of the Fukushima Daiichi Nuclear Power Station (FD-NPS) was carried out. A large amount of contaminated water has been generated in FD-NPS. Radioisotopes in the contaminated water have been removed except tritium, and thus, tritiated water has been left and stored. As of March 2019, 1 126 500 m3 of tritiated water has been stored in tanks. The average tritium concentration in the tritiated water is 1000 Bq/cm3.Various options for handling the tritiated water, such as discharge into the sea, geosphere injection, underground burial, and vapor or hydrogen release with and without pretreatment, were discussed on the basis that there is no scientific impact on people. Through the discussions, 11 options for handling tritiated water were summarized. At the same time, some experimental tests of tritium separation (with small-scale and/or full-scale component test stands) were also carried out. As a result, it was concluded that the tested separation technologies could not yet be applied to the case of FD-NPS. No selection from the 11 options has yet been recommended, and further discussions for the tritiated water have continued with public hearings

Qualification tests for detritiation to validate scrubber column technology for use at ITER DS with a pilot-scale scrubber column

The atmosphere detritiation system (DS) function is to remove tritium from the atmosphere to mitigate the impact on the environment in the case of accidental tritium release. The DS uses the technique of catalytic oxidation of tritium and collection of tritiated water vapor. The DS of ITER uses scrubber column technology for collection of tritiated water vapor, not water adsorption method conventionally used for DS, considering a failure occurrence probability of switching valves during long term operation. This technology is based on isotopic exchange between water vapor and liquid water to be arranged in a packed type column. This technology has never been applied to the DS of existing tritium facilities. Hence, qualification tests have been performed for detritiation to validate scrubber column technology for use at ITER with a pilot-scale scrubber column of 1/5 size of an ITER scale. The test column was filled with packing material and internal components of the same type as is used at ITER. In this qualification test, key objectives of the scrubber column design are to 1) collect tritium to meet DS design requirements, 2) achieve high reliability/availability and 3) avoid production of excessive tritiated water to be processed by WDS. The qualification test shows that detritiation factor (DF) is strongly influenced by a liquid flow rate with increasing the liquid flow rate resulting in higher DF. DF of scrubber column highly depends on lambda value which is defined as a flow rate of gas/liquid. A scrubber column of 2.88 m height with sufficient wettability of packing and efficient water dispersion by water distributor achieved high DF in the condition that lambda is one. Test results indicate that scrubber column technology achieves both high availability for detritiation and reduction of tritiated water production.12th International Conference on Tritium Science and Technology (Tritium 2019