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

In the Fukushima Daiichi nuclear power plant accident, hydrogen gas was generated by the reaction of nuclear fuel with water, which caused an explosion and radioactive leakage. To prevent a recurrence, the reactor containment vessel is maintained under nitrogen gas. Lidar technology provides remote sensing with high spatial resolution. In this study, we aimed to investigate aerosol flow and nitrogen leakage using the developed compact Raman Lidar with a 355 nm 50 kHz DPSS laser. To demonstrate the system concept, we measured nitrogen gas artificially released at a flow rate of 10 NL/min at a distance of 10 m from the Lidar. The Lidar data were acquired with integration time of 20 s. Comparison of the data with and without nitrogen gas flow revealed that the system is capable of distinguishing the ambient concentration around 80% and the concentration of nearly 100% in the flow contained along the laser path inside a 1.5 m plastic tube. The reduction in oxygen concentration was also detected with another Raman channel.