A large quantity of radioactive materials - including Cesium-137 and tritium - has been detected at the Wolsong nuclear power plant in Gyeongju, North Gyeongsang Province. 

The Nuclear Safety and Security Commission on Friday announced the tentative findings of its inspection of the reactor site. The probe began in March amid growing health concerns; highly concentrated tritium was detected at the site in 2019. 

According to the commission, up to zero-point-37 becquerels per gram of cesium-137 were detected in a soil sample near the spent fuel storage pool of the Wolsong-1 reactor. 

Among the 37 water samples from the site, five had up to 756-thousand becquerels per liter of tritium. 

The agency presumed that a water barrier for the spent fuel storage pool of the Wolsong-1 reactor was likely constructed differently from the design in 1997 and failed to perform its function since then. 

Whether radioactive materials were leaked outside the site requires a further probe, it said.