Metal fatigue was apparently responsible for last month's nuclear plant accident in Japan's Fukui Prefecture. According to a recent announcement by the plant operator, a massive amount of radioactive coolant water had leaked from a cracked reactor pipe.

The ministry of international trade and industry has submitted its report to the Nuclear Safety Commission (nsc) . The plant operator added that further investigations are necessary to specify the cause of the metal fatigue. However, some experts believe it was a result of repeated temperature changes of the primary coolant that runs through the pipe.

An investigating team found out that there were 11 cracks and scratches on the 8.9-cm-wide stainless steel pipe, including a 15.1-cm-long crack that breached the pipe allowing 50 tonnes of primary cooling water to leak. The crack may have originated from at least three points inside the pipe, officials said. The other major damage included three cracks that are 10 cm, 7.2 cm and 2.6 cm long respectively along the axis of the pipe. There are five more cracks running around the pipe and two scratches, one on either side of the breached crack, according to the report. None of these damages have been observed in the last regular inspection in 1991, the officials said, and no other pipe of the same specification in the heat regenerator has shown any damage.