The concerns continue to mount after Japan's devastating earthquake and subsequent tsunami, which may further heighten recent anxiety in the financial markets. An explosion near the No. 1 reactor at the Fukushima Dai-Ichi nuclear power station has industry experts talking about the possibility of a meltdown. According to Bloomberg:

"If the fuel rods are melting and this continues, a reactor meltdown is possible," Kakizaki said. A meltdown refers to a heat buildup in the core of such intensity it melts the floor of the reactor containment housing. "If they cannot get the nuclear reactor back under control during the day, this may end up being the biggest problem of all," said Ken Courtis, former vice chairman of Goldman Sachs Group Inc. in Asia. "A meltdown, which would cause massive immediate damage, would also set the nuclear industry back decades. This would have vast implications for the global energy equation and perforce the world economy."

Japanese Chief Cabinet Secretary Yukio Edano said at a press conference that the blast didn't damage the reactor container, only the structure outside it, and that there was no major radiation leakage with the explosion. The nuclear reactors are about 150 miles north of Tokyo. New reports in Japan have indicated the radioactivity at the site was rising to 20 times normal levels.

"If the water level remains at this level, the reactor core might be damaged, but we are now pouring water into the reactor to prevent it from happening," Dow Jones Newswires quoted a Tepco spokesman as saying.

According to Wikipedia, a nuclear 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 considered very serious because of the potential that radioactive materials could be released into the environment. A core meltdown will also render the reactor unusable until and unless it is repaired.

• Within the former Soviet Union several nuclear meltdowns of differing severity have occurred. In the most serious example, the Chernobyl disaster, design flaws and operator negligence led to a power excursion that subsequently caused a meltdown.

• A core damage accident is caused by the loss of sufficient cooling for the nuclear fuel within the reactor core. The reason may be one of several factors, including a loss of pressure control accident, a loss of coolant accident (LOCA), an uncontrolled power excursion, or in some types, a fire within the reactor core.

Hopefully over the coming days, the people of Japan can get some good news in the form of the odds being reduced relative to the possibility of a meltdown. From an investment perspective, it may contribute to an already fragile state of the markets. As we head into Monday's open, we will continue to monitor the situation as well as the relative performance of defensive assets.