高浜４号機 蒸気発生器伝熱管損傷事象における プラント長期停止の影響について
概要
The cause of the steam generator tubing failure that was identified during the 23rd plant outage at Takahama Unit 4 was presumed to be caused by wear of the tubing due to repeated contact with exfoliated dense scale, which was formed on the tubing surface. It is suspected that the scale exfoliated because the scale could not follow the heat expansion and shrinking of the tubing applied during plant startup and shutdown operations, and then partial cracking occurred, resulting in exfoliation of partial scale. After the accident at the Fukushima Daiichi Nuclear Power Plant, Takahama Unit 4 had been out of service for approximately 6 years, so we investigated the effect of this long-term outage on the scale exfoliating behavior. The investigation result has shown that under the long-term steam generator storage conditions with hydrazine water, some of the constituent particles of the scale may have become coarse and easily exfoliated.
