How are Japan’s nuclear and financial crises affecting America?

Last week's earthquake and tsunami look to have taken tens of thousands of lives in Japan. They've also brought the country to the brink of a nuclear catastrophe, after explosions at nuclear reactors released radiation into the atmosphere and forced the evacuation of surrounding areas.

But as the island nation struggles to deal with the fallout, there have been fears about the unfolding disaster's potential impact here in the United States as well--on everything from public health to energy policy to the economy. Here's a rundown on some of the major worries -- and how concerned you should be:

Could radiation escaping from Japan's nuclear reactors drift across the Pacific and affect Americans in Hawaii, or even on the U.S. mainland?

That's highly unlikely. Gregory Jaczko, the head of the U.S. Nuclear Regulatory Commission, said yesterday there's "a very low probability that there's any possibility of harmful radiation levels in the United States or in Hawaii or any other U.S. territories." And Hawaii's health department said air samples show radiation at normal levels. Still, Hawaiians are understandably nervous: Health-food stores in the state are said to have run out of potassium iodide, a compound that can help fight off radiation poisoning.

Nuclear power is one of the few viable large-scale energy sources that doesn't contribute to global warming. Does the crisis in Japan mean we're going to ditch that too?

Probably not. Germany has said it plans to shut down seven aging nuclear reactors in response to the events in Japan. But in the United States, the reaction has been more measured. Energy Secretary Steven Chu told Congress today that the United States should learn from Japan's experience, but that the administration remains committed to nuclear power as one of several energy sources. Chu also affirmed that the federal government has "rigorous safety regulations in place" for the nuclear industry. The administration wants $36 billion to help finance new U.S. reactors over the next decade.

But don't we have some nuclear plants that sit near geological fault-lines in California? Why couldn't a similar earthquake/tsunami/nuclear-meltdown scenario happen here?

Both the San Onofre and Diablo Canyon nuclear sites in southern California are relatively close to fault-lines. But experts say that unlike the quake-devastated region of Japan, southern California has no "subduction zone," where one plate slides under another. That means that even if an earthquake did occur, there's essentially no risk of it generating a tsunami of the size that hit Japan. Still, not everyone is comforted. "The world is filled with lots of risk, and placing big bottles filled with massive amounts of radioactivity near earthquake faults doesn't make much sense," Dan Hirsch, who runs a nuclear policy organization, told the LA Times.

What about the stock market?

The Japanese government -- already facing a huge debt burden--said yesterday it would pump more than $180 billion into the country's financial system, which was dealt a massive blow by the disaster. With investors gripped by panic, Japan's stock market has plunged nearly 16 percent in two days--the largest two-day drop since the 1987 crash. That's had a ripple effect on Wall Street, where stocks also have fallen sharply this week. Japan accounts for 10 percent of U.S. exports, so there's concern that American companies could be hit hard if Japanese consumers stop spending. But experts say we likely won't know the full extent of the financial and economic damage--either in Japan or here--for weeks.

Japan has shut down some factories. How will that affect the global supply chain?

Japan accounts for one-fifth of the world's semi-conductor production, so technology companies--including those that produce smartphones, tablets, and computers--have been hard hit by the disaster. Amid transportation problems and power blackouts across northern Japan, Texas Instruments said it had suspended two Japanese plants, and that they wouldn't return to full production until July. And Toyota said it plans to halt production at all 12 of its Japanese plants, and Honda said it would do the same at least until next week. Ford and G.M. said they had seen no disruptions to their supply chains yet. Still, Dave Andra, an economist with the Original Equipment Suppliers Association, told Reuters that the disaster could have the largest impact on the global auto industry since World War II.

Evacuees are screened for radiation exposure at a testing center Tuesday, March 15, 2011, in Koriyama city, Fukushima prefecture, Japan. (AP Photo/Wally Santana)