https://doi.org/10.1140/epjs/s11734-026-02249-3
Regular Article
Operation history consideration for evaluating radionuclide inventories in a CANDU-type reactor in Korea
1
Department of NPP Engineering, KEPCO International Nuclear Graduate School, 45014, Ulsan, Republic of Korea
2
TBM Technology Team, Korea Institute of Fusion Energy, 34133, Daejeon, Republic of Korea
a
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Received:
21
September
2025
Accepted:
3
March
2026
Published online:
8
May
2026
Abstract
Accurate estimation of activation inventories is essential in reactor decommissioning. In particular, CANDU-type reactors require dedicated methodologies because of their unique design and operation features. Wolsong Unit 1, the first CANDU reactor in Korea, was operated for about 36 years and permanently shut down in 2019. This study investigates the influence of operation history on the evaluation of radionuclide inventories in major in-core structures. Conventional assessments generally assume uniform full-power operation using an average load factor. In contrast, this work considers annual variations in reactor power during the actual operation history. Neutron flux and energy spectrum distributions were calculated using MCNP6.2 with a full-core geometry model. Elemental compositions of the pressure tube and calandria tube were defined, including alloying and impurity elements relevant for activation. FISPACT was applied to compute inventory changes of key radionuclides such as 60Co, 63Ni, 59Ni, 90Sr, 14C, 94Nb, and 3H. Results show that long-lived radionuclides such as 59Ni and 94Nb exhibit negligible differences between the two approaches. In contrast, short-lived radionuclides with relatively high production cross-sections, including 60Co and 3H, show significant discrepancies. During extended shutdown periods, conventional assessments overestimate 60Co buildup, whereas operation-history-based results reveal steep reductions due to decay. Tritium also demonstrates unique behavior, combining rapid buildup from the 6Li(n,α)3H reaction with sharp decreases during outages. This study demonstrates that accurate consideration of operation history is essential for reliable assessment of short-lived activation products. The proposed approach improves prediction fidelity, providing a more realistic basis for waste classification, worker protection, and decommissioning cost estimation.
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© The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature 2026
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
