Japanese officials managed to restore electricity to three damaged reactors at Fukushima Daiichi by March 28 but were battling to keep the unit’s radioactive water from leaking into the sea.

Tokyo Electric Power Corp. (TEPCO) reported that water in concrete tunnels beneath Unit 2 was emitting radiation levels of 1,000 millisieverts per hour, or about 100,000 times the reactor’s normal level.

The Japanese government also reported that it had detected the presence of plutonium in the soil around the reactors, a possible indication that a partial meltdown could have occurred at one of the three units.

“The crisis at the Fukushima Daiichi plant has still not been overcome, and it will take some time to stabilize the reactors,” said Yukiya Amano, the director general of the International Atomic Energy Agency (IAEA). “The Fukushima crisis has confronted the agency and the international community with a major challenge.”

Despite injecting water into the reactors to cool the fuel, TEPCO said water levels have not risen, which could indicate the reactor cores may not be completely sealed off—possibly because of a breach or puncture. The radioactive water could be leaking, according to the utility.

Amano said that, once the situation has been stabilized, the IAEA would like to send an international expert mission to assess the accident. He also called for a “high-level” conference on nuclear safety to take place at IAEA headquarters in Vienna before the summer.

On March 28, the IAEA gave a detailed rundown of the condition of each unit. The agency said the core and fuel integrity at units 1, 2 and 3 were damaged, and damage was suspected to containment in units 2 and 3. Further, there is severe damage to the first, third and fourth buildings. Unit 4 was not operating at the time of the March 11 earthquake and tsunami, but the spent-fuel pool lost water and an explosion occurred.

IAEA said about half the fuel is uncovered inside the first three reactors, but the fuel is stable. Pressure inside the vessel is increasing slightly in unit 1 but is stable in units 2 and 3. Crews were injecting fresh water into all three units’ reactor pressure vessels, though, in unit 2, it was necessary to use a diesel generator to pump the water into the vessel. Firefighters were pumping seawater into the spent-fuel pools through their cooling lines.

The IAEA said temperatures were decreasing slightly, but that unit 1 still had a temperature of 575� F.

David Lochbaum, director of the Union of Concerned Scientists’ nuclear safety project, was scheduled to appear before the Senate Energy and Natural Resources Committee on March 29. Lochbaum said he will propose to the panel that U.S. plants limit the contents of spent-fuel storage pools to fuel that has been removed from the reactor in the past five or six years; everything older than that should go in dry-cask storage, he said.