The rupture of a corroded pipe in an earthquake and the subsequent increase in waste gas led to last month's shutdown of a reactor at a nuclear power plant here, plant operator Tokyo Electric Power Co. confirmed Wednesday.
A small pipe at the No. 6 reactor of the Fukushima No. 1 plant ruptured during a magnitude 6.1 quake July 21, Tepco officials said, adding that air flowing in from the broken pipe rapidly increased radioactive gas emissions from the reactor.
The pipe had previously been damaged by repeated heat and strain.
No radioactivity leaked outside the plant after Tepco manually shut down the reactor following the quake, which jolted extensive areas of eastern Japan.
The ruptured pipe, measuring 34 mm in outside diameter and attached to a safety valve, suffered metal fatigue as steam repeatedly passed through it, according to the Ministry of International Trade and Industry.
The officials also examined pipe joints at five other reactors in the plant and detected deterioration but no cracks.
Tepco officials said they plan to remove the corroded pipe from the No. 6 reactor and a similar pipe at the No. 2 reactor.
It is rare for a reactor pipe to rupture during a quake, according to Tepco.