Q+A: What's the real threat of N.Korea's nuclear program?

By Jon Herskovitz

SEOUL (Reuters) - There is increased activity at North Korea's known nuclear test site, a South Korean news report said on Thursday, suggesting Pyongyang is gearing up for a new test as it has threatened in response to tightened U.N. sanctions.

Following are some questions and answers about the secretive state's nuclear arms program:

WHAT IS NORTH KOREA'S NUCLEAR WEAPONS CAPABILITY?

North Korea is thought to have produced enough plutonium for about six to eight weapons and has already produced one rudimentary nuclear device. It likely cannot miniaturize a nuclear weapon to mount on a missile and would need a significant amount of testing to master the technology, weapons experts say. And its Soviet-era bombers would not be able to evade the advanced air forces of the United States, Japan and South Korea to deliver a bomb, which means it may be many years before North Korea can actually threaten the world with a nuclear weapon.

HOW LONG WOULD IT TAKE THE NORTH TO CONDUCT A NUCLEAR TEST?

Impoverished North Korea, whose only nuclear test in October 2006 led to U.N. sanctions, could be ready to test another nuclear device in a matter of weeks, experts said. Politically, North Korea wants to play out its test preparations, many of which can be seen by U.S. spy satellites, as long as possible to increase its leverage in negotiations. Some experts believe a second test would not come for several months, if at all.

Experts said the North's only nuclear test was only a partial success because the strength of the blast was relatively low, indicating problems with the weapons design or the fissile material at its core.

WOULD THERE BE MORE THAN ONE?

North Korea probably would only conduct one because it does not want to deplete its meager plutonium stockpile.

Future testing would depend on its ability to restore its aging Yongbyon nuclear plant, which was being disabled under a six country disarmament-for-aid deal. The plant can produce about one bomb's worth of fissile material a year.

The United States and others have charged North Korea with having a secret program to enrich uranium, giving it another avenue to produce nuclear weapons, but experts doubt that the North has seriously developed the program.

HOW BIG IS THE SECURITY THREAT?

The North's nuclear arms program is not a major security threat at present because it has not yet shown it can build an effective bomb, nor does it have an effective delivery system.

The biggest security threats posed by the North come from its hundreds of mid-range missiles that can hit all of South Korea and most of Japan as well as its artillery batteries posted close to its border with the South. Jane's Defense estimated the North could rain 500,000 shells an hour into the Seoul area, which is home to about half of South Korea's 49 million people.

A North Korean first strike with artillery and rockets, which may also carry biological weapons or material to spread radiation poisoning, would cause major damage to economic powers South Korea and Japan, which in turn would deal a heavy blow to the global economy. It would also be a suicidal move, because the U.S.-led counter-strike would quickly destroy the country.