![Sample our Politics & International Relations journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/5947/TOC-Subject-Sample-2021-Politics-International-Relations.jpg"})
Abstract
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.
Acknowledgments
We are grateful for the continuous support by Alexander Glaser throughout the development of ONIX, and the help from Siegfried Hecker with regards to the details on the North Korean program. Calculations were carried out using Sherlock, the Stanford University Cluster. Julien de Troullioud de Lanversin received generous funding from the Stanton Foundation as well as the John D. and Catherine T. MacArthur Foundation.
Disclosure statement
The authors have no conflicts of interest to declare.
Notes
1 It is assumed that the first (October 2006), second (May 2009), and fourth (January 2016) nuclear test used plutonium only. The sixth test (September 2017), assumed to be a two-staged thermonuclear device, also used plutonium. These assumptions result from personal communication with Dr. Siegfried Hecker.
2 Director General of the International Atomic Energy Agency, Application of Safeguards in the Democrative People’s Republic of Korea, GC(64)/18 (Vienna: International Atomic Energy Agency, 2019), https://www.iaea.org/sites/default/files/gc/gc64-18.pdf.
3 Steve Fetter, “Nuclear Archaeology: Verifying Declarations of Fissile-material Production,” Science & Global Security 3 (1993): 237–259, https://doi.org/10.1080/08929889308426386.
4 Julien de Troullioud de Lanversin, Moritz Kütt, and Alexander Glaser, “ONIX: An Open-Source Depletion Code,” Annals of Nuclear Energy 151 (2021), https://doi.org/10.1016/j.anucene.2020.107903.
5 International Atomic Energy Agency, “Fact Sheet on DPRK Nuclear Safeguards,” 1 June 2002, https://www.iaea.org/newscenter/mediaadvisories/fact-sheet-dprk-nuclear-safeguards.
6 David Albright and Kevin O’Neill, eds., Solving the North Korean Nuclear Puzzle (Washington, DC: Institute for Science and International Security, 2000), 113–114.
7 Albright and O’Neill, Solving the North Korean Nuclear Puzzle, 115–117.
8 Choe Sang-Hun, “North Korea Destroys Tower at Nuclear Site,” The New York Times, 28 June 2008.
9 Siegfried S. Hecker, Robert L. Carlin, and Elliot L. Serbin, “A Technical and Political History of North Korea’s Nuclear Program Over the Past 26 Years,” Center for International Security and Cooperation, Stanford University, 2018, https://fsi-live.s3.us-west-1.amazonaws.com/s3fs-public/narrativescombinedfinv2.pdf.
10 Siegfried S. Hecker, Robert L. Carlin, and Elliot L. Serbin, “A Comprehensive History of North Korea’s Nuclear Program: 2018 Update,” Center for International Security and Cooperation, Stanford University, 2019, https://fsi-live.s3.us-west-1.amazonaws.com/s3fspublic/2018colorchartnarrative_2.11.19_fin.pdf.
11 Elliot L. Serbin, “North Korea’s Yongbyon Nuclear Facilities,” 16th PIIC Beijing Seminar on International Security, Arms Control Association, Shenzhen, China, 16th October, 2019; Julia Masterson, “UN Experts See North Korean Nuclear Gains,” Arms Control Today, September 2020 https://www.armscontrol.org/act/2020-09/news/un-experts-see-north-korean-nuclear-gains. For 2021, there are indications that North Korea might again resume operation (Olli Heinonen, Jack Liu, and Samantha J. Pitz, “Nuclear Complex: 5 MWe reactor might still be operating,” 38 North, 8 October 2021, https://www.38north.org/2021/10/north-koreas-yongbyon-nuclear-complex-5-mwe-reactor-may-still-be-operating/).
12 Albright and O'Neill, Solving the North Korean Nuclear Puzzle. While the book provides burnup levels, no information is given on the time of operation in days.
13 Albright and O’Neill. Solving the North Korean Nuclear Puzzle
14 Paul K. Romano et al., “OpenMC: A State-of-the-Art Monte Carlo Code for Research and Development,” Annals of Nuclear Energy 82 (2015): 90–97, https://doi.org/10.1016/j.anucene. 2014.07.048.
15 Albright and O’Neill, Solving the North Korean Nuclear Puzzle.
16 The burnup macro-steps used for the simulations are the following: 0, 8.7, 50, 100, 200, 300, 400, 500, 600, and 700 MWd/t.
17 Data can be accessed on the following GitHub repository, https://github.com/jlanversin/5MWe or at the following DOI address https://doi.org/10.5281/zenodo.5111592.
18 These assumptions result from personal communication with Dr. Siegfried Hecker.
19 Siegfried S. Hecker, Robert L. Carlin, and Elliot L. Serbin, A Comprehensive History of North Korea’s Nuclear Program: 2018 Update (2019), https://fsi-live.s3.us-west-1.amazonaws.com/s3fspublic/2018colorchartnarrative_2.11.19_fin.pdf.
20 Fetter, “Nuclear Archaeology.”
21 In reality, natural isotope ratios are not fixed and depend on geochemical and geophysical processes. These variations in the ratio, however, are negligible compared to other forms of uncertainties. In this work, natural ratios are considered fixed.
22 Travis Gitau and Mathew Swinney, “Implementing Nuclear Archaeology in Safeguards-by-Design,” Proceedings of the 57th Annual Meeting of the Institute of Nuclear Materials Management, 24–28 July 2016, Atlanta, Georgia, USA, 1524–1532.
23 Thomas W. Wood et al., “Feasibility of Isotopic Measurements: Graphite Isotopic Ratio Method,” Pacific Northwest National Laboratory, PNNL-13488, https://www.osti.gov/biblio/967937-3WERpE/.
24 Alex Gasner and Alexander Glaser, “Nuclear Archaeology for Heavy-Water-Moderated Plutonium Production Reactors,” Science & Global Security 19 (2011): 223–233, https://doi.org/10.1080/08929882.2011.616124.
25 Gasner and Glaser.
26 Bruce D. Reid et al., “Trawfynydd Plutonium Estimate,” Pacific Northwest National Laboratory, PNNL-13528, 2009, https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-13528.pdf.
27 Jungmin Kang, “Using the Graphite Isotope Ratio Method to Verify the DPRK’s Plutonium-Production Declaration,” Science & Global Security 19 (2011): 121–129, https://doi.org/10.1080/08929882.2011.586309.
28 Julien de Troullioud de Lanversin, Malte Göttsche, and Alexander Glaser, “Nuclear Archaeology to Distinguish Plutonium and Tritium Production Modes in Heavy-Water Reactors,” Science & Global Security 26 (2019): 70–90, https://doi.org/10.1080/08929882.2018.1518693.
29 Sébastien Philippe and Alexander Glaser, “Nuclear Archaeology for Gaseous Diffusion Enrichment Plants,” Science & Global Security 22 (2014): 27–49, https://doi.org/10.1080/08929882.2014.871881.
30 Antonio Figueroa and Malte Goettsche, “Nuclear archaeology: Reconstructing Reactor Histories From Reprocessing Waste,” ESARDA Bulletin 59 (2019): 39–46.
31 Moritz Kütt, Julien de Troullioud de Lanversin, and Malte Göttsche, “Understanding Uncertainties in Nuclear Archaeology,” Proceedings of the 59th Annual Meeting of the Institute of Nuclear Materials Management, 22–26 July 2018, Baltimore, Maryland, USA, 1872–1881.
32 Benjamin Jung, “Reconstructing Plutonium Production with the Isotope Ratio Method: Uncertainty Assessments” (Master’s Thesis, RWTH Aachen University, 2020); Patrick G. Heasler et al., “Estimation Procedures and Error Analysis for Inferring the Total Plutonium (Pu) Produced by a Graphite-moderated Reactor,” Reliability Engineering and System Safety 91 (2006): 1406–1413, https://doi.org/10.1016/j.ress.2005.11.036.
33 From the point of view of reactor physics, the isotope ratio R is the dependent variable which depends on the independent variable Φ. This approach is adopted when defining the sensitivity factor to make it more intuitive (how sensitive a given ratio is to fluence change). However, it is important to note that the current analysis considers the fluence Φ as the dependent variable and R as the independent variable.
34 For this demonstration, the relative errors are considered small enough so that they can be related to logarithm functions, i.e., This remains valid in practice as common relative errors on ratio and fluence are smaller than a few percent.
35 Harry Bateman, “Solution of a System of Differential Equations Occurring in the Theory of Radio-Active Transformations,” Mathematical Proceedings of the Philosophical Society Cambridge 15 (1910): 423–427.
36 Julien de Troullioud de Lanversin, “ONIX: An Open-Source Burnup Code for Nuclear Archaeology” (Ph.D. Thesis, Princeton University, 2019);
37 Wood et al., “Feasibility of Isotopic Measurements: Graphite Isotopic Ratio Method.”
38 North Korea is known to have manufactured graphite for an additional, larger reactor (50 MWe). In 1997, the IAEA inspected half of the amount required for that reactor, which would be more than sufficient to replace the graphite in the 5-MWe reactor (Director General of the International Atomic Energy Agency, Implementation of the Agreement Between the Agency and the Democratic People’s Republic of Korea for the Application of Safeguards in Connection with the Treaty on the Nonproliferation of Nuclear Weapons, GC(41)/17 (International Atomic Energy Agency, 1997), https://www.iaea.org/sites/default/files/gc/gc41-17_en.pdf). Hence, it can not be excluded that the irradiated graphite in the 5-MWe reactor at some point in the lifetime of the reactor was replaced with fresh graphite. However, if the DPRK had changed the graphite in the past, it would likely be discovered in future inspections, e.g., because of ratio-derived fluences much lower than what would be expected.
39 Reid et al., “Trawfynydd Plutonium Estimate.”
40 David C. Gerlach et al., “Final Report on Isotope Ratio Techniques for Light Water Reactors,” Pacific Northwest National Laboratory, PNNL-18573 986731, July 1, 2009, http://www.osti.gov/servlets/purl/986731-T7ppN9/.
41 Y. Shi, C. Broome, and R. Collins, “Determination of Radiogenic Silicon and Its Isotopes in Neutron Irradiated Aluminum Alloys by ICP-MS,” Journal of Analytical Atomic Spectrometry 31 (2016): 1174–1178, https://doi.org/10.1039/C6JA00081A.
42 Reid et al., “Trawfynydd Plutonium Estimate.”
43 Alexander Glaser and Stefan Bürger, “Verification of a Fissile Material Cutoff Treaty: The Case of Enrichment Facilities and the Role of Ultra-Trace Level Isotope Ratio Analysis,” Journal of Radioanalytical and Nuclear Chemistry 280 (April 2009): 85–90, https://doi.org/10.1007/s10967-008-7423-0.
44 Suresh Kumar Aggarwal and Chen-Feng You, “A Review on the Determination of Isotope Ratios of Boron with Mass Spectrometry,” Mass Spectrometry Reviews 36 (July 1, 2017): 499–519, https://doi.org/10.1002/mas.21490.
45 Jung, “Reconstructing Plutonium Production with the Isotope Ratio Method: Uncertainty Assessments.”