Additional Reprocessing of Plutonium at Yongbyon?

A study of the thermal patterns at the Yongbyon Nuclear Scientific Research Centre conducted and published by researchers at 38North suggests that North Korea has engaged in two plutonium reprocessing campaigns not previously, publicly, known which naturally boosts external estimates of the available plutonium stock that North Korea has for its nuclear weapons programme. The report also indicates possible activity at the Experimental Light Water Reactor, and reports little to no activity at the possible tritium separation plant.

The term “additional” needs to be parsed carefully. The time period that the reports spans is from September 2016 to June 2017.

According to the report the Radiochemical Laboratory, where North Korea separates plutonium-239 from the spent fuel rods from its 5MWe plutonium production reactor

Concentrated heat patterns were observed with stronger temperature differences from the surrounding area between September to October of last year. The thermal patterns then returned to lower levels until March 2017, when a distinct increase in thermal activity is observed that has continued through last month. These intermittent surges in thermal activity suggest North Korea has conducted batch rather than continuous processing of spent fuel rods from the 5 MWe Reactor

The report indicates little increased thermal signature at the 5MWe reactor itself, for the time period concerned, other than for December 2016 and January 2017.

Media reports, correctly, state that this implies that North Korea has more plutonium for nuclear weapons than previously thought, however, this possible increase is not a result of resumed operations at the 5MWe reactor rather it involves the reprocessing of spent fuel rods previously irradiated, that is, most likely, before 2016. So, to restate, “additional” plutonium means additional to what we knew rather than additional production activity associated with a resumption of operations at the 5MWe reactor.

On the Experimental Light Water Reactor the report notes that increased thermal signatures coincides with the increased thermal signature at the adjacent 5MWe reactor, and likely is a by product of the 5MWe reactor thermal signature, *however*

We cannot completely, however, eliminate the possibility that this elevated thermal pattern was the result of short-term activity at the ELWR itself—for example, heating the structure to prevent pipes from freezing, allowing ongoing internal construction work, or pre-startup testing. It is important to note that no other significant patterns of thermal activity were observed over the ELWR throughout the study period

Pre start up activity would be the most concerning. The ELWR is estimated to be a 25-30MWe light water reactor designed to generate electricity, and to serve as a stepping stone for more powerful electricity generating reactors of the type pledged by the “international community” as part of the collapsed Agreed Framework. Though a light water reactor, which are designed to produce electricity, hence they have reactor grade plutonium as a fission product when nominally employed at high burnup, nonetheless at low burnup such a reactor can be employed as a plutonium production reactor.

At 25MWe the ELWR could produce about 19 to 20 kilogrammes per annum of weapons grade plutonium, significantly more than the 5MWe reactor. The IAEA defines 8kg of plutonium-239 as a significant quantity for weapons purposes, but that is surely an overestimate. After 5 nuclear weapons tests, we may assume North Korea can use less plutonium, especially given that North Korea could manufacture composite plutonium-uranium fissile pits and is credited with the ability of boosting fissile yields through thermonuclear reactions.

The startup of the ELWR has been much delayed, but once operational, as shown above, it would be able to significantly add to North Korea’s nuclear weapons capability. Furthermore, it would also greatly increase Pyongyang’s capacity to produce tritium, critical for boosting the fissile yield of nuclear weapons, which has a half-life of 12.3 years so needs to be continually replenished. By also adding power to the electricity grid, important for energy starved North Korea, start up of the ELWR means outside powers have less leverage to influence North Korean nuclear policy, a neglected but potentially serious implication of the reactor.

Finally, regarding the possible tritium separation and production facility

The thermal patterns at the probable Isotope/Tritium Production Facility have remained consistently low throughout the period under study, suggesting that the facility is not operational, or is operating at a very low level

This lends further support to the thesis that tritium production and separation has hitherto occurred at the 8MWt IRT-2000 research rector, which has a small isotope production laboratory adjacent to it. It has been suggested that separation of highly enriched uranium at the Yongbyon uranium enrichment plant has enabled the start up of the IRT-2000 reactor. Historically, research reactors have been fuelled by highly enriched uranium provided by the nuclear weapon states, part of the cold war era nonproliferation grand bargain, however North Korea’s supply, from Moscow, is understood to have been irradiated.

To reemphasise, North Korea has likely reprocessed fuel rods from its 5MWe plutonium production reactor previously irradiated and the probable reprocessing campaign did not arise from the resumption of plutonium production at the reactor.