The Nuclear Regulation Authority denied Monday that the Great East Japan Earthquake damaged piping related to critical cooling equipment in the building housing reactor 1 at the Fukushima No. 1 power plant before the tsunami hit.
The NRA made the assertion after inspecting the building to study why a water leak developed near the No. 1 reactor’s two isolation condensers after the magnitude 9.0 quake struck on March 11, 2011.
An influential nuclear investigation panel said in a report last year that the leak might have been caused by quake-related damage to the piping for the condensers, but the NRA said the water likely splashed out of the reactor’s spent fuel pool during the violent quake. The leaked water was radioactive.
The purpose of isolation condensers is to change steam into water and route it back to the reactors to cool them. The condensers stopped functioning right after the quake.
According to the NRA, the members who conducted the field survey in late May did not find any damaged piping that could have lead to the water leak.
A worker who witnessed the leak said that water, not steam, was released, which means it was unlikely that the condensers’ pipes were damaged because they are only supposed to be filled with steam.
Instead, the NRA believes that a container designed to collect excess water from the spent fuel pool may have leaked.
In the meantime, the NRA plans to conduct another investigation either this month or next month into the cause of the hydrogen explosion that took place in the No. 4 reactor building. The reactor had been defueled for maintenance when the earthquake and tsunami struck and its fuel had been stored in the spent fuel pool perched above it.
Massive hydrogen explosions blew the tops off of reactor buildings 1 and 3 as the zirconium cladding on their uncooled fuel rods melted and reacted with steam from the coolant water to produce the gas.
But no major damage to the fuel assemblies stored in the spent fuel pool of reactor 4 has been confirmed, according to the NRA. That pool also contained fresh fuel rods.