While the death toll continues to mount in Japan after the massive earthquake and tsunami on Friday, authorities are growing more concerned over a nuclear meltdown. There have been explosions in two of three nuclear reactors, spilling radioactive materials into the air.

The threat of a meltdown appears to be getting closer. In response, Japanese officials are evacuating over 200,000 people that live within a 12 mile radius of the Fukushima Daiichi Power Plant. The exposure to radioactivity is unknown so far but the potential for problems is mounting.

A second reactor building exploded early Monday following a similar explosion in Reactor 1 on Saturday. Now, there is word that the third reactor at the Fukushima Daiichi site is beginning to overheat. Workers are pumping sea water into all three reactors trying to cool them down. The normal cooling process was knocked off line by the huge earthquake and tsunami that rocked the country on Friday. The only good news so far is that the two explosions have only destroyed the buildings surrounding the reactors and not the reactor casings. Still, the possibility for a full nuclear meltdown is growing.

"The worst case scenario is that the fuel rods fuse together, the temperatures get so hot that they melt together into a radioactive molten mass that bursts through the containment mechanisms and it is exposed to the outside so there's spewed radioactivity into the ground into the air into the water some of that radioactivity could carry in the atmosphere to the west coast of united states," said nuclear security expert Joe Cirincione.

About one-fifth of U.S. energy comes from nuclear power. In all, we have 104 working reactors including two plants right here in Central Pennsylvania, Three Miles Island and Peach Bottom. The Nuclear Regulatory Commission says people shouldn't worry about the safety of U.S. plants. They say each plant was built to prepare for the most severe natural disasters estimated for both the site and the surrounding area.

Still, our area has a bit more reason for concern. From Central Pennsylvania to New Jersey, there are seven nuclear power plants, the most in the country. Out of those seven, four use similar nuclear reactors to Fukushima.

Nuclear disasters are graded on a 1 to 7 scale, with 7 being the worst. Chernobyl was the worst, rated a 7. The Three Mile Island disaster in 1979 was a 5. Fukushima now stands at a 4, but things could get worse.