An official of Tokyo Electric Power Co. said Sunday other officials at the utility believe "there will be a major delay to work" to stabilize the situation at the Fukushima Daiichi plant because of core meltdowns at the plant's No.1, 2 and 3 reactors, Kyodo News reported.
The official said the meltdowns may have breached the fuel's pressure vessels, the report said.
The latest development likely will change the road map Tepco announced April 17 to bring the troubled reactors to what is called "cold shutdown" stabilization in six to nine months.
It may also force changes in any government effort to allow the return to homes of those evacuated from near the plant after it was struck by the March 11 earthquake and tsunami that set off one of the world's worst nuclear crises.
On Sunday, the utility also reported the pump used to inject seawater into the No. 5 reactor and fuel pool had stopped for about 15 hours Saturday night due to motor problems before backup pumps could take over. The No. 5 reactor along with No. 6 reactor had been shut down for routine checkups when the March 11 struck and hence have remained stable thus far.
Kyodo reported if the situation at the No. 5 reactor had not been taken care of, the water holding its nuclear fuel could have evaporated, exposing the fuel.
A typhoon was headed toward Japan Monday, but it was not yet known if the Fukushima plant would be in its path, the BBC reported.