The people of Japan just can't seem to catch a break.

Authorities in Japan raised the prospect Friday of a likely breach in the all-important containment vessel of the No. 3 reactor at the stricken Fukushima Daiichi nuclear power plant, a potentially ominous development in the race to prevent a large-scale release of radiation.

Contaminated water likely seeped through the containment vessel protecting from the reactor's core, said Hidehiko Nishiyama of the Japan nuclear and industrial safety agency.

Three men working inside the No. 3 reactor stepped into water this week that had 10,000 times the amount of radiation typical for that locale, Nishiyama said. That water likely indicates "some sort of leakage" from the reactor core, signaling a possible break of the containment vessel that houses the core.

The containment vessel is designed to prevent radioactive material from escaping into the atmosphere, even if other parts of the reactor are damaged. A rupture in the containment vessel could pose problems for workers who are trying to prevent that, depending on its severity.

The three workers who were exposed to radiation by stepping in the contaminated water had the highest levels of radiation recorded so far, said Tokyo Electric Power Co., which owns the plant.