As workers at the tsunami-stricken Fukashima Daiichi nuclear plant Tuesday endured soaring radiation levels to limit the spread of radioactive contamination, the president of the utility that runs the plant checked into the hospital for hypertension and dizziness, the company said.

Masataka Shimizu, the president of Tokyo Electric Power Company, has been largely silent since the March 11 earthquake and tsunami sent the plant careering toward nuclear disaster. Utility officials had previously said the president suffered from a brief “small illness.” Shimizu, 66, has not spoken in public since March 13.

Chairman Tsunehisa Katsumata will take charge of the troubled utility while the president recovers.

At a press conference Wednesday afternoon, Katsumata apologized “deeply” to the public for the destruction of the plant and the “release of radioactive substances” and expressed his condolence to victims of the earthquake.

Cool water powered by diesel generators or firetruck pumps continued to circulate around nuclear fuel rods in reactors at the plant on Tuesday, limiting the potential for further releases of toxic particles.

Crews piled sandbags and concrete blocks around the mouths of flooded tunnels to keep contaminated water from spilling out into the sea and slowly pumped stagnant 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 supplies 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.

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 Tepco’s “assumptions about tsunamis were greatly mistaken.”

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

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

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 on Monday, the utility reported that underground tunnels outside the building were filled with 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 Tepco officials say they still do not know the precise source of the leak. They think 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.

In Washington, U.S. officials expressed concern about the limited information shared by the Japanese. Citing “many gaps in our knowledge,” Peter Lyons, acting assistant secretary at the Department of Energy, told the Senate Environment and Public Works Committee, “It appears all three reactor cores are damaged,” but to unknown extent.

Bill Borchardt, executive director for operations at the Nuclear Regulatory Commission, said that units 2 and 3 had suffered “some primary containment damage.”

To help survey the facility, the Energy Department is sending a robot and several radiation-shielded cameras, a spokeswoman said Tuesday. The tank-treaded robot, called Talon, is being dispatched from the Idaho National Laboratory and will scout the most radioactive areas of the plant with cameras and radiation sensors.

Kim Kearfott, a professor of nuclear engineering and radiological sciences at the University of Michigan, said the level of complexity at the Fukushima plant is akin to “three Three-Mile Island” cleanups because there are multiple reactors in critical condition and very radioactive materials in multiple places around the plant.

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 they sleep in one large room or hallways at a headquarters near the plant. They have limited fresh water and no outside phone lines.

Banri Kaieda, deputy head of a government nuclear disaster task force, acknowledged that the lodging arrangements were “not in a situation in which minimum sleep and food could be ensured,” according to Kyodo News.

As scientists began to fill spreadsheets with new data points, they have tracked contamination to farms, stirring consumer fears and financial anxieties among farmers.

The government last week banned the shipment of 11 vegetables from three prefectures and recommended that people in Japan not eat them. The blow to agricultural life is seen as contributing to the death of a 64-year-old farmer in Sukagawa City, who reportedly hanged himself last Thursday.

The farmer’s two adult children told the Asahi Shimbun newspaper that their father had grown distraught over the future of his cabbage farm after the government banned the shipment of leafy vegetables in Fukushima prefecture that were found to have elevated levels of radiation.

“I think he felt like he lost everything he built, devoting his life,” the man’s 35-year-old son said, according to the newspaper.

Staff writer Brian Vastag and special correspondents Kyoko Tanaka and Tetsuya Kato contributed to this report.