Assessments of radiation emission from molten salt reactor spent fuel:
Implications for future nuclear safeguards verification

Vaibhav Mishra - Department of Physics and Astronomy, Uppsala University
Erik Branger - Dept. of Physics and Astronomy, Uppsala University, Sweden
Sophie Grape - Dept. of Physics and Astronomy, Uppsala University, Sweden
Markus Preston - Department of Physics and Astronomy, Uppsala University
Zsolt Elter - Department of Physics and Astronomy, Uppsala University & Seaborg Technologies
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Safeguards verification using non-destructive assay (NDA) techniques is an important pillar of the safeguards regime to ensuring that nuclear technology is not used for non-peaceful purposes. The methods and approaches for safeguards verification for conventional spent nuclear fuel (SNF) originating from the global fleet of water-cooled reactors are well-established. However, for reactors such as molten salt reactors (MSR), accountancy verification method of irradiated fuel salts is not quite well-established. This is primarily since the irradiated salt is in “bulk form” whereas more conventional LWR SNF encountered by the safeguards inspectors is in “item form”. Moreover, much about the nature of such SNF still remains unknown due to the lack of operational MSRs and equipment adequate to further study, develop and test NDA verification methods. As MSRs could play a complementary role with the existing fleet of reactors in the near future, verification methods concerning the nature of emissions from irradiated fuel salts is timely. Therefore, in this current study we aim to quantify and study the nature of gamma and neutron emissions as well as decay heat production in irradiated fuel salt from the Compact Molten Salt Reactor (CMSR) developed by Seaborg Technologies in Denmark. Simulations were carried out using the Monte-Carlo particle transport code Serpent as well as the code SOURCES 4C to compute nuclide inventories and the associated emission rates of gamma and neutron (from spontaneous fissions, or SF and from (α, n) reactions) emissions and decay heat calculations. These results will shed more light on the implications for nuclear safeguards verification for irradiated fuel salts and also highlight some of the challenges and opportunities associated with detecting and characterizing the emissions using NDA methods in the future for SNF of such unique nature.