With Pyongyang having threatened to conduct a “new type” of nuclear test, attention is being drawn to what method it might employ for a fourth test and how far its military nuclear technology has come.

Analysts argue that the communist state may carry out a more powerful nuclear experiment as it seeks to show off its “nuclear deterrence” capability and up the ante in future negotiations with the international community.

For the fourth test, the North is most likely to carry out an experiment using highly enriched uranium, which would differentiate it from past tests.

The North conducted plutonium-based tests in 2006 and 2009. What fissile material was used for last year’s test remains unknown as the South and the U.S. failed to obtain and analyze post-test radioactive materials.

“The most likely scenario is that Pyongyang uses highly enriched uranium and publicly announces it to the outside world, so as to corroborate its claim that it has succeeded in having a variety of nuclear detonation methods,” said Kim Tae-woo, nuclear politics expert at Seoul’s Dongguk University.

“Then, it may also warn that it could mass-produce those various types of nuclear arms as it has claimed.”

Another likely scenario is that Pyongyang will test a “boosted fission weapon,” which experts have called a “1.5-generation” nuclear bomb. The development of this weapon is known to be a preliminary step toward the production of a hydrogen bomb, regaarded as a “second generation” nuclear weapon.

Some observers also raise the possibility of the North conducting a test of a hydrogen bomb, while many say the North has not reached a high enough level of technology for this.

“The North could also shock the world by claiming that it will test a boosted fission weapon. Although the chances are low, the North could also declare that it had conducted a test of a hydrogen bomb,” said Kim.

The provocative state could also conduct a simultaneous test of various nuclear arms. It could also fire off Rodong missiles or longer-range missiles to demonstrate its technological advancement in miniaturizing nuclear warheads, which would pose a security challenge to the U.S. and its allies in Asia.

Should the North push ahead with the fourth test, it is expected to test a bomb with much greater explosive power than the previous ones.

In the North’s first nuclear test in 2006, the explosive power was about 1 kiloton, which is equivalent to 1,000 tons of TNT. Due to its weak explosion, experts evaluated the test as a failure.

But the second one, recorded at between 2 kilotons and 6 kilotons, was regarded as a “half success.” In the last test, the North used a nuclear device with an estimated yield of 10 kilotons.

As for the North’s stockpiles of weapons-grade plutonium, it is believed to have accumulated some 40 kg of plutonium after it reprocessed spent fuel rods at least three times, in 2003, 2005 and 2009, according to Seoul officials. To produce one nuclear bomb, around 6 kg of plutonium is required.

After the third nuclear test last year, Pyongyang restarted its main nuclear complex in Yongbyon and is thought to have produced more plutonium.

Regarding the North’s uranium enrichment program, Pyongyang has claimed to have some 2,000 operational centrifuges capable of producing some 40 kg of HEU each year. To produce one HEU bomb, more than 15 kg of HEU is required.

By Song Sang-ho (sshluck@heraldcorp.com)