Measurement of nitrogen leakage by Raman lidar for observation inside the Fukushima No.1 reactor building

Ishii, Moe*; Somekawa, Toshihiro*; Kurahashi, Shinri*; Matsuda, Shohei  ; Kuze, Hiroaki*; Shiina, Tatsuo*

Over a decade after the severe accident at the Fukushima Daiichi nuclear power plant in 2011, there are still concerns about partial damage to the primary containment vessel, which could result in aerosol and gas leaks. Here, to remotely monitor gas leakage, we have developed a compact Raman lidar with a 355 nm 50 kHz DPSS laser. This lidar has two Raman channels for detections of nitrogen and oxygen. We measured these gases in a 1.5 m plastic tube along the laser path at a distance of 10 m from the lidar, with and without artificial injection of nitrogen gas at a flow rate of 10 NL/min. The results indicate that the system is capable of distinguishing the ambient concentration around 80% and the concentration of nearly 100% in the flow. The reduction in oxygen concentration was also detected.