"Recent commercial satellite imagery shows that, over the past year, Pyongyang has begun to refurbish a major mill located near Pyongsan - a county in the southern part of the country - that turns uranium ore into yellowcake. The renovation suggests that North Korea is preparing to expand the production of uranium from a nearby mine," said Jeffrey Lewis in an analysis posted on August 12 on 38 North, the website of the US-Korea Institute at Johns Hopkins University.

The arms control expert at the Monterey Institute of International Studies added that this suggests that the North Korean regime - which has staged three successful nuclear tests in 2006, 2009 and 2013 - "intends to mine and mill a significant amount of uranium that could serve as fuel for expanding its nuclear weapons stockpile."

The analysis comes days after experts at IHS Jane's said satellite images suggested Pyongyang was operating a second hall of uranium enrichment centrifuges at its Yongbyon nuclear complex.

And in April, Joel Wit, the founder of 38 North, told DW that the East Asian country was on the verge of rapidly increasing its nuclear weapons stockpile to 20, 50 or 100 bombs within five years, from an estimated 10-16 weapons at that time, adding to regional concerns.

In a DW interview, Jeffrey Lewis, talks about how much uranium the regime could extract from the mill and what the latest findings mean for North Korea's nuclear ambitions.

DW: To which extent is North Korea expanding its capacity to mine and mill uranium ore?

Jeffrey Lewis: North Korea is completely modernizing its main mill for turning uranium ore into yellowcake. This represents a significant investment, so I would expect to see North Korea produce yellowcake at the site for many years.

Where exactly is Pyongyang getting the uranium from and how is it being mined?

The mine is adjacent to the mill and connected by a conveyor belt. The deposit was surveyed in the 1960s, but the mine probably did not start operating until the 1980s. The mine was apparently dormant for many years, although it seems to have operated for a short period sometime in the mid-2000s.

How much uranium could it obtain?

I have not seen reliable estimates of the size of each deposit, but North Korea is reported to have at least 4 million tons of uranium resources at two mines. (Some sources cite a higher figure of 26 million tons, but this uranium may not be economical to recover.)

The Pyongsan mine is thought to be the larger of the two. Previous reports have indicated the plant might have the capacity to produce about 300 tons of uranium per year.

What can Pyongyang do with this uranium ore?

North Korea can turn the uranium into fuel for its nuclear reactors, either using natural uranium or enriching it to about 5 percent U235. North Korea could also enrich it further, to weapons-grade or about 90 percent U235, to expand its nuclear arsenal.

Does this explain how North Korea is getting the material necessary to fuel its nuclear reactor program or weapons?

Yes. The Pyongsan mine is thought to be North Korea's major source of uranium. If we know how much uranium North Korea is mining and milling, we can estimate North Korea's demand for uranium.

When combined with other information, such as the number and type of reactors and the size of enrichment plants, it may be possible to determine if there are other sources of demand - such as secret enrichment plants - that we do not know about.

What does North Korea's expansion of its uranium mine operations indicate about the country's nuclear ambitions?

This is a significant investment, which means that North Korea plans to process a significant amount of uranium. This suggests to me that North Korea plans to build more nuclear reactors and more nuclear weapons. The heavy investment suggests that North Korea is not planning on trading its nuclear weapons away, despite hopes for a diplomatic breakthrough after the Iran agreement.

Jeffrey Lewis is arms control expert at the Monterey Institute of International Studies.