Tokyo Electric Power Company (Tepco) is installing four tie rods at the top of the core shroud of the Fukushima Daini 3 BWR, to address surface stress corrosion cracking (SCC) found in early July.
Officials at the Ministry of Economy, Trade and Industry (METI), Japan’s regulator, said that a deep circumferential crack had been confirmed in the lower part of the shroud, but that metallurgical investigations indicated that the crack was not growing. The SCC was found in the weld that joins the bottom of the shroud with the core support piece, a shop weld.
The crack prompted alarm at Tepco, METI and Japanese vendor firms because it was the first incidence of SCC in Japan found in 316L, a low-carbon steel that utilities had assured METI was immune from SCC.
