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Accidental Criticality Estimation for Advanced CANDU Type Fuel Bundles containing Th-based Fuel Compositions |
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PP: 59-66 |
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doi:10.18576/jrna/020204
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Author(s) |
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Cristina Alice Margeanu,
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Abstract |
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| The paper aims to present the criticality (effective multiplication coefficient, k-eff) estimation for advanced CANDU type fuel bundles containing Thorium and LEU (low enriched uranium) oxides mixture, in some accidental scenarios. For this purpose, advanced CANDU fuel bundles with 37 and 43 fuel elements have been considered, both for fresh and spent Th-based fuel compositions. The scenarios take into account fuel bundles accidental immersion in light or heavy water, for several ″dangerous″ geometrical configurations (2, 3, 5 or 6 fuel bundles stacked close together at distances that could lead to critical conditions, but maintaining their structural integrity). For spent fuel analysis, Th-based fuels irradiation in CANDU reactor conditions was simulated, by means of ORIGEN-S burn-up code, to reach 20 MWd/kg HE (heavy element) fuel burn-up, using specific powers for each considered fuel bundle. A number of 27 combinations of (Th, LEU) mixed oxides fuel have been investigated by considering different values for: fuel pellet density (8.5 g/cc, 9.0 g/cc and 9.5 g/cc), enrichment in U235 (9 wt%, 10 wt% and 11 wt%) and U/Th mass content ratio (20%, 25% and 30%). The criticality estimation has been performed using the Monte Carlo KENO-VI code, considering that the fuel bundle elements contain the same fuel composition. The study results are comparatively presented for different fuel compositions in each fuel bundle case, and also for the same fuel composition considering different fuel bundle projects. Considered accidental scenarios led to subcritical k-eff values (less than 1), for both fresh and irradiated fuel compositions, assuming realistic neutrons leakage treatment. Estimated k-eff values are greater for fuel bundle with 43 fuel elements comparatively with the other fuel bundle project, but as U/Th content ratio increased the situation changed k-eff becoming greater for the fuel bundle with 37 elements. |
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