Development of a practical tritiated water monitor to supervise the discharge of treated water from Fukushima Daiichi Nuclear Power Plant

As part of the Fukushima Daiichi Nuclear Power Plant (FDNPP) decommissioning, the release of stored treated water began in 2023. We developed a practical tritium monitor to continuously supervise the tritiated water concentration at FDNPP. The monitor contains a flow cell detector comprising plastic scintillator pellets and incorporating simultaneous measurements by three detectors, a veto detector, and lead shielding to reduce the influence of environmental γ rays. The system reached a detection limit of 593 Bq L−1 in 60 min, which is lower than the discharge standard for tritiated water of 1500 Bq L−1.