Serious damage has occurred in fuel cores at two other reactors of Japan's Fukushima nuclear complex, Tokyo Electric Power Co. (TEPCO) said Sunday.
The damage further complicates the task of bringing the reactors to a safe shutdown while avoiding the release of high levels of radioactivity, the Wall Street Journal reports.
A similar meltdown of the core took place at the No. 1 reactor 16 hours after the plant was struck by a magnitude-9 earthquake and tsunami on Mar. 11, TEPCO acknowledged Thursday.
Japanese engineers have abandoned their latest attempt to stabilize the No. 1 reactor due to flooding in the basement, the BBC reports.
TEPCO had planned to cool the reactor by filling the containment chamber with water, but has since said that melting fuel rods had created a hole in the chamber, allowing 3,000 tons of highly radioactive water to leak into the basement.
According to the WSJ, the revelations are likely to force an overhaul of the six-to-nine-month blueprint for bringing the reactors to a safe shutdown stage and end the release of radioactive materials.
However, a government spokesman said the latest setback would not affect the deadline of next January to achieve a cold shut-down at the plant. "We want to preserve the timetable, but at the same time we're going to have to change our approach," Goshi Hosono said, the BBC reports.
TEPCO says it will come up with a new plan to stabilize the reactor by Tuesday.