Basic study on tritium monitor using plastic scintillator for treated water discharge at Fukushima Daiichi Nuclear Power plant

In response to the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, the treated water from which the primary radioactive substances were removed contained tritium, and the Japanese government discussed how to treat this water. As the storage capacity of the treated water reached its limit, the Japanese government decided on a method to discharge the treated water into the sea in 2023. Herein, a basic study was conducted to develop a tritiated monitor to directly measure tritium in wastewater for preparing the release of tritiated water from the FDNPS. Two plastic scintillators with different shapes (sheet and pellet types) were compared as detectors. The pellet-type detector was found to be more sensitive to tritiated water than the sheet-type, with an efficiency of 2.95 × 10−5 cps Bq−1 L in the test configuration. In the future, optimizing the design for background reduction should achieve a minimum detectable radioactivity of 1,500 Bq L−1, the emission standard set by nuclear power plant operators. Through this study, we could obtain basic data for developing such a practical tritiated monitor.