Verifying North Korea’s Plutonium Production with Nuclear Archaeology

North Korea produced weapon-grade plutonium in its graphite-moderated 5-MWe reactor. Estimating the total production of fissile materials provides an important baseline for denuclearization efforts. Nuclear archaeology can improve such production estimates by measuring isotope ratios in the graphite moderator of the reactor. The accumulation of certain trace isotopes in the graphite enables to accurately estimate life-time reactor fluence which can then be related to plutonium production. This article uses the open-source reactor physics software ONIX to simulate the operation of the 5-MWe reactor. It discusses consolidated estimates of plutonium production from 1986 to 2020 based on publicly available operation history data. An updated mathematical framework to relate isotope ratio uncertainties to fluence uncertainties and its implementation in a special ONIX module for nuclear archaeology are also presented. The module is used to identify which isotope ratios should be measured in the 5-MWe reactor to minimize uncertainties on plutonium estimation.