Though the chance is extremely remote, Pennsylvania nuclear reactors, including those near Lancaster and Beaver Creek, could be vulnerable to radiation leaks if their power were knocked out for days, an Associated Press investigation has found.

The risk exists for all U.S. nuclear reactors if there are no other means to keep the reactors cool, but some are more susceptible than others, according to the AP investigation, conducted in the wake of radiation leaks at Japan's Fukushima Daiichi nuclear plant.

One simulation presented by the Nuclear Regulatory Commission in 2009 showed that it would take less than a day for radiation to escape from the Peach Bottom Atomic Power Station outside Lancaster if there were a blackout and the reactor couldn't be kept cool. That atomic power station has reactors of the same older make and model as those releasing radiation in Japan.

While regulators say they have confidence that measures adopted in the U.S. will prevent or significantly delay a core from melting and threatening a radioactive release, the events in Japan, which was stricken by an earthquake and tsunami, raise questions about U.S. power plants.

"We didn't address a tsunami and an earthquake, but clearly we have known for some time that one of the weak links that makes accidents a little more likely is losing power," said Alan Kolaczkowski, a retired nuclear engineer who worked on a risk analysis of Peach Bottom.