A pair of robots that entered Japan's tsunami-ravaged nuclear reactor on the weekend emerged with bad news on Monday for a country with more than its share: Radiation levels remain so high repair crews cannot enter them.

Nevertheless, officials remained hopeful they can stick to their freshly minted "roadmap" for cleaning up the radiation leak and stabilizing the Fukushima Daiichi plant by year's end so they can begin returning tens of thousands of evacuees to their homes.

"Even I had expected high radioactivity in those areas. I'm sure [plant operator Tokyo Electric Power Co.] and other experts have factored in those figures when they compiled the roadmap," Chief Cabinet Secretary Yukio Edano said.

Officials said Monday that radiation had spiked in a water tank in Unit 2 and contaminated water was discovered in other areas of the plant. They also described in detail for the first time the damage to fuel in three troubled reactors, saying pellets had melted.

That damage, sometimes referred to as a partial meltdown, had already been widely assumed, but the confirmation, along with the continued release of radiation from other areas, serves to underscore how difficult and how long the cleanup process will be.

Two American-made Packbots that entered a pair of buildings at the tsunami-flooded Fukushima Daiichi nuclear power plant on Sunday found a harsh environment too radioactive for workers to enter. (Tokyo Electric Power Co./AP)In fact, government officials themselves have acknowledged that there are still many setbacks that could crop up to slow down their timeline.

Angry at the slow response to the nuclear crisis and to the catastrophic earthquake and tsunami that caused it, lawmakers tore into Prime Minister Naoto Kan.

"You should be bowing your head in apology. You clearly have no leadership at all," opposition Liberal Democratic Party lawmaker Masashi Waki shouted during a Monday grilling of Kan and his cabinet in parliament.

"I am sincerely apologizing for what has happened," Kan said, adding that the government was TEPCO's president, Masataka Shimizu, appeared ill at ease as lawmakers heckled and taunted him. "I again deeply apologize for causing so much trouble for residents near the complex, people in Fukushima and the public," Shimizu said.

Workers have not been able to enter the reactor buildings at the stricken plant since the first days after the cooling systems were wrecked by the March 11 earthquake and tsunami that left more than 27,000 people dead or missing. Hydrogen explosions in both buildings in the first few days destroyed their roofs and scattered radioactive debris.

On Sunday, a plant worker opened an outer door to one of the buildings and two Packbots, which resemble drafting lamps on tank-like treads, entered. After the worker closed the door, one robot opened an inner door and both rolled inside to take readings for temperature, pressure and radioactivity. They later entered a second building.

Tokyo Electric Power Co. president Masataka Shimizu bows as he makes an appearance at the upper house of parliament in Tokyo on Monday. (Yuriko Nakao/Reuters)On Monday, the robots reported radioactivity readings of up to 49 millisieverts per hour inside Unit 1 and up to 57 inside Unit 3. Radiation levels in both reactors are such that if workers were in the units for four or five hours they would reach their maximum allowable radiation exposure from a lifetime of work in a power plant.

Indeed, the damage could actually be worse, since the robots were unable to get past debris to do a more accurate survey of the interior.

Polls released Monday by a trio of newspapers indicated the Japanese people are unhappy with the government's handling of the situation. About two-thirds of respondents expressed dissatisfaction.

However, a majority of respondents to the poll indicated they would support tax increases to cover the costs of rebuilding areas affected by the tsunami.

With files from The Associated Press