Since North Korea, or the Democratic People's Republic of Korea (DPRK) left the Non-Proliferation Treaty (NPT) in 2003, the DPRK nuclear fuel cycle has continued operation as well as further development, without transparency to international inspectors. A recent addition to the DPRK fuel cycle is the Experimental Light Water Reactor (ELWR), a 100 MWth light water reactor in Yongbyon, which, as appears to be in operation since October 2023.

Considering the non-NPT-signatory status of DPRK, it is of concern that the ELWR may be used to produce plutonium for nuclear warheads, in addition to or instead of its use for electricity production. In this work we explore the possibility to model the fissile material production in the ELWR, by modelling the core with Serpent2, and integrating information from available remote monitoring, such as satellite imagery of cooling water outlets from the facility.

Little openly available and verified information exists on the details of the ELWR, such as nuclear fuel design and core geometry. Therefore, a base case based on available statements is used to create a core model similar to conventional international LWRs. Multiple scenarios for core load options are based on either assumptions on 1) uniform enrichment optimised for low burnup and production of weapons-grade plutonium, 2) heterogeneous core with drivers of enrichment fuel and targets of natural uranium for plutonium production or 3) uniform enrichment for high burnup and electricity production. Plutonium production made possible using the ELWR is estimated per MWd, as well as per year of operation. Special consideration is given to cycle length constraints from requirement of weapons-grade quality of the produced plutonium, and implications on availability and stoppage frequency, which might be monitored remotely, unless online refuelling is a possibility.

Possible implications on the DPRK Pu stockpile are discussed, as well as attempts to identify unknown parameters of importance (i.e. attempting to make unknown unknowns into known unknowns).