TOKYO — Cool water powered by diesel generators or firetruck pumps continued to circulate around nuclear fuel rods in reactors at the tsunami-stricken Fukushima Dai-ichi nuclear power plant Tuesday, limiting the potential for further releases of toxic particles. But workers were still struggling to contain the spread of radioactive contamination.

Crews piled sandbags and concrete blocks around the mouths of flooded tunnels to keep contaminated water from spilling out into the sea, while slowly pumping radioactive water out of dark turbine rooms.

At the same time, scientists – under orders from nuclear regulators – painstakingly increased their documentation of the damage that explosions from the malfunctioning reactors and probable leaks from one or more reactor cores have begun to inflict on the country’s food and water supply and its environment.

“Monitor,” “measure,” “follow” and “study” have become the mantras of government officials who have only the earliest glimpses of how the disaster will evolve.

NUCLEAR PLANT OPERATOR CRITICIZED

At a meeting of the Japanese parliament, Prime Minister Naoto Kan criticized plant operator Tokyo Electric Power Co. for failing to adequately protect the facility from disaster. The plant was flooded by a wave that easily swept over its 20-foot-high protective wall.

“It’s undeniable,” Kan said in language unusually harsh by Japanese standards, that Tokyo Electric’s “assumptions about tsunamis were greatly mistaken.”

When asked about whether contaminated water on the site is continuing to spread, Hidehiko Nishiyama, director general for the Nuclear and Industrial Safety Agency, said at a news conference that he had no data to show that it was.

But Tokyo Electric should “strengthen surveillance and monitoring,” Nishiyama said. The same goes for tracking the extent of plutonium already found in five soil samples taken on the plant, or the path of radioactive iodine that’s been traced in the ocean.

More than 11,000 bodies have been recovered since the March 11 earthquake and tsunami, but officials say the final death toll is expected to exceed 18,000. Hundreds of thousands of people remain homeless, their homes and livelihoods destroyed. Damage could amount to $310 billion, the most expensive natural disaster on record.

The plant has been leaking radiation that has made its way into vegetables, raw milk and tap water as far away as Tokyo. The highly contaminated water was first discovered outside the reactor in giant turbine rooms last week; three men suffered radiation burns while working in one of the rooms. And Monday, the utility reported that underground tunnels outside the building were filled with water.

WORKERS SHORT OF FOOD, WATER

Radiation doses in both buildings near the second reactor measured in excess of 1,000 millisieverts per hour, potent enough to cause serious illness after several hours of exposure. The limit on workers there is 250 millisieverts of radiation per year, which they would reach in 15 minutes at the most radioactive sites in the facility.

Nuclear regulators and Tokyo Electric officials say they still do not know the precise source of the leak. They believe it is a broken pipe or a crack in a condensation chamber near the base of the reactor building, and that seepage has come into contact with partially melted nuclear fuel rods in the reactor’s core.

Government officials said Tuesday that they would work to improve conditions for the hundreds of workers who are risking their lives to bring the plant under control. An inspector for the nation’s nuclear regulator on Monday offered the public a rare picture of harsh and chaotic work conditions: The workers eat only two meals a day because of sporadic shipments of food, and sleep in one large room or hallways at a headquarters near the plant. They have limited fresh water and no outside phone lines.