Is a nuclear reactor meltdown taking place in Japan?  No one seems to know for sure, but given what the country has already endured since Friday’s devastating 8.9-magnitude earthquake, a nuclear meltdown is the last thing anyone wants at this point.

According to an official with Japan’s Nuclear and Industrial Safety Agency, a meltdown may very well be happening at this hour at one of Fukushima Daiichi’s nuclear power reactors.

“There is a possibility, we see the possibility of a meltdown,” says Toshihiro Bannai, director of the agency’s international affairs office. “At this point, we have still not confirmed that there is an actual meltdown, but there is a possibility.”

Let’s back up for just a moment. What exactly is a nuclear meltdown?

A nuclear meltdown refers to a major severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency nor by the U.S. Nuclear Regulatory Commission.

A meltdown occurs when a severe failure of a nuclear power plant system prevents proper cooling of the reactor core, to the extent that the nuclear fuel assemblies overheat and melt. A meltdown is a major hazard due to the fact that radioactive materials could be released into the environment.

A core meltdown will also pretty much make the nuclear reactor unstable until it is repaired.

Bannai says that engineers really haven’t been able to get close enough to figure out what’s going on. Still, he bases his findings on the fact that radioactive isotopes were measured in the air on Saturday.

“What we have seen is only the slight indication from a monitoring post of cesium and iodine,” he said. Since that time, officials at the power plant have been injecting sea water and boron into the plant to try and cool its core.

“We have some confidence, to some extent, to make the situation to be stable status,” he said. “We actually have very good confidence that we will resolve this.”

Hopefully, that will do the trick. We certainly don’t need another Chernobyl disaster.  We’ll find out soon enough.