Key lawmakers and regulators this week will dig into unfolding details surrounding the nuclear emergency Japan declared in the wake of a massive 8.9 magnitude earthquake and tsunami and how U.S. officials are safeguarding the domestic nuclear fleet.

Rep. Fred Upton (R-Mich.), chairman of the House Energy and Commerce Committee and a proponent of nuclear power, said he will use a Wednesday hearing to question the head of the Nuclear Regulatory Commission about the Fukushima Daiichi nuclear power plant, as well as domestic operations.

"We will use that opportunity to explore what is known in the early aftermath of the damage to Japanese nuclear facilities, as well as to reiterate our unwavering commitment to the safety of U.S. nuclear sites," Upton said in reference to the hearing at which NRC Chairman Gregory Jaczko will testify.

Energy Secretary Steven Chu is slated to join Jaczko at the joint hearing of the Subcommittee on Energy and Power and the Subcommittee on Environment and the Economy. The hearing was scheduled to review the Obama administration's fiscal 2012 budget request for the Department of Energy and NRC, but attention has turned to the unfolding events in Japan.

Chu also is scheduled to testify tomorrow before the House Energy and Water Development Appropriations Subcommittee, where lawmakers also are likely to press him for details about the situation in Japan before turning to budget questions (see related story).

NRC said this weekend it sent two officials to Japan with expertise in boiling water nuclear reactors as part of a U.S. International Agency for International Development team. Yesterday NRC said no radiation at harmful levels would reach the United States from the damaged Japanese plants.

Containment efforts

Japanese officials are scrambling to prevent a meltdown at different nuclear reactors in the areas of the country hardest hit by the earthquake and tsunami and have begun evacuating residents in the vicinity of certain plants.

Over the weekend, an explosion rocked the Unit 1 reactor at the Fukushima Daiichi plant on the eastern coast of Japan, and the International Atomic Energy Agency (IAEA) said four workers were injured. The blast happened outside the primary containment vessel of the reactor, not inside, and plant operator Tokyo Electric Power Company (TEPCO) confirmed that the integrity of the primary containment vessel remains intact, IAEA said Saturday, citing Japanese officials.

The Fukushima Daiichi plant is a boiling water reactor, and coolant or water is needed to carry heat away from the reactor's core even after the plant has been shut down because the fuel continues to emit heat.

After receiving approval from Japan's nuclear safety agency, TEPCO began injecting sea water mixed with boron into the primary containment vessel, IAEA said. Japan's nuclear safety agency has confirmed the presence of caesium-137 and iodine-131 in the vicinity of Fukushima Daiichi Unit 1 and an initial increase in levels of radioactivity around the plant, IAEA said.

TEPCO yesterday said readings showed radiation doses measured at the site were increasing again after a previous reading that showed levels to be subsiding. The company said it was struggling to cool water in the spent nuclear fuel pool.

TEPCO is trying to reduce the pressure within the reactor containment vessels in the Unit 2 reactor and has begun venting that structure. TEPCO is conducting similar venting at the Unit 3 reactor at the Fukushima Daiichi plant through a controlled release of vapor. After a high-pressure injection system at Unit 3 failed, IAEA said officials began injecting water first and then sea water, and authorities have warned the "accumulation of hydrogen is possible."

Problems for TEPCO have surfaced elsewhere. The company is trying to reduce pressure in the containment vessel of its Fukushima Daini nuclear plant's Units 1, 2 and 3 and is venting the reactor containment vessels there, which could include "partial discharge of air containing radioactive materials," TEPCO said.

And the company reported the lowest state of emergency at its Onagawa nuclear plant in northern Japan, where three reactor units are "under control" although radioactivity readings are exceeding allowed levels in the area surrounding the plant, IAEA said. Authorities there are investigating the source of radiation, the agency said, and Reuters reported yesterday the company was attributing the high readings to radiation leakage at another plant in the neighboring prefecture.

Schedule: The hearing is Wednesday, March 16, at 9:30 a.m. in 2123 Rayburn House Office Building.

Witnesses: Energy Secretary Steven Chu, Nuclear Regulatory Commission Chairman Gregory Jaczko and additional witnesses TBA.