The Nuclear Regulation Authority denied Monday that the March 2011 earthquake damaged piping for key safety equipment at the Fukushima Daiichi nuclear power plant before tsunami waves hit the complex.
The NRA presented the view after conducting an on-site inspection of the No. 1 reactor building, where the isolation condenser equipment is located, to study what caused a water leak there immediately after the magnitude 9.0 quake rattled the plant.
An influential nuclear accident investigation panel indicated in its report released last year that the leak may have occurred because piping for the isolation condenser was damaged by the quake, but the NRA said that water inside the No. 1 spent fuel pool likely poured out because of the shaking.
According to the NRA, members who conducted the field survey in late May did not find any damage to the piping that could have resulted in the water leak.
A worker who witnessed the leak said water rather than steam was released, in another sign that damage to the piping was unlikely.
The NRA believes that a container, which allows water to flow in when the coolant inside the spent fuel pool spills out, may have leaked water.
The NRA plans to conduct another on-site investigation in June or July to look into the cause of a hydrogen explosion at the No. 4 reactor building.
At the time the earthquake and tsunami struck on March 11, 2011, the No. 4 reactor was offline for maintenance work and its fuel was stored in the spent fuel pool.
While hydrogen explosions occurred at the Nos. 1 and 3 reactor buildings due to the reaction of zirconium in the melted fuel rods with steam from the coolant water, no major damage to the fuel assemblies has been confirmed inside the No. 4 spent fuel pool, according to the NRA.