Democratic People’s Republic of Korea (DPRK) has produced weapon-grade plutonium in a graphite-moderated experimental reactor at the Yongbyon nuclear facilities. The amount of plutonium produced can be estimated using the Graphite Isotope Ratio Method (GIRM), even without considering specific operational histories. However, the result depends to some degree on the operational cycle length. Moreover, an optimal cycle length can maximize the number of nuclear weapons made from the plutonium produced. For conservatism, it should be assumed that the target reactor was operated with an optimal cycle length. This study investigated the optimal cycle length using which the Calder Hall MAGNOX reactor can achieve the maximum annual production of nuclear weapons. The results show that lower enrichment fuel produced a greater number of critical plutonium spheres with a shorter optimal cycle length. Specifically, depleted uranium (0.69wt%) produced 5.561 critical plutonium spheres annually with optimal cycle lengths of 251 effective full power days. This research is crucial for understanding DPRK’s potential for nuclear weapon production and highlights the importance of reactor operational strategy in maximizing the production of weapons-grade plutonium in MAGNOX reactors.

1. Introduction
2. Optimal Cycle Length for MaximumNumber of Nuclear Weapons
    2.1 Calder Hall MAGNOX Reactor
    2.2 Depletion Calculation of the MAGNOX Reactor
    2.3 Effect of Cycle Length on the Annual Productionof Plutonium
    2.4 Effect of Cycle Length on the CriticalMass of Plutonium
    2.5 Effect of Cycle Length on the Number ofNuclear Weapons
3. Conclusions
Conflict of Interest
Acknowledgements
REFERENCES

• Seongjin Jeong(Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Republic of Korea)
• Jinseok Han(Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Republic of Korea)
• Hyun Chul Lee(Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Republic of Korea) Corresponding author