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Abstract
A subset of pressurized water reactor (PWR) studies from Exercise II-2 of the Uncertainty Analysis in Modeling for Light Water Reactors (UAM-LWR) benchmark study has been performed to quantify the importance of both nuclear data uncertainties and manufacturing uncertainties in an assembly depletion calculation and a mini-core rod movement transient. The depletion study of the 15 × 15 PWR assembly using the SAMPLER and TRITON modules of the SCALE code system revealed a maximum uncertainty in keff of 0.49% for fresh fuel, decreasing to 0.38% at the midpoint of the fuel cycle and rising back to 0.48% at the end of the fuel cycle. Uncertainties and correlations of various homogenized cross sections and other group constant data, such as keff, have been determined, and the effect of randomly applied manufacturing uncertainties was found to be largely negligible relative to nuclear data uncertainties for bulk lattice parameters. However, for local parameters, such as the pin power factors, assembly discontinuity factors, and diffusion coefficients, the effects from manufacturing uncertainties were appreciable and sometimes dominant.
Nuclear data uncertainties were found to be the dominant contributors to uncertainty in the isotopic composition of the overall assembly, with the exception of very early in the fuel cycle, where manufacturing uncertainties such as perturbations to the fuel density and pin radius made nonnegligible contributions to total uncertainty. The contribution of manufacturing uncertainties to isotopic uncertainties was nonnegligible at a pin-by-pin level, but still smaller than the contributions from nuclear data uncertainty. Studies of the PWR mini-core rod movement transient using homogenized data from the SCALE models in the PARCS diffusion code showed little difference between the tested modeling approaches and demonstrated that nuclear data uncertainties dominated the manufacturing uncertainties in the global figures of merit considered, such as the equilibrium core boron concentration, the maximum core power factor, and the maximum reactivity insertion. For local effects, such as maximum pin power during the transient, the randomly applied manufacturing uncertainties were dominant. It was found in general that for global system properties, nuclear data uncertainties made significantly larger contributions to total uncertainty, whereas for local parameters the impact of manufacturing uncertainties was at least nonnegligible, and for some parameters, dominant.
Acknowledgments
This work was funded by the Natural Sciences and Engineering Research Council of Canada and the University Network of Excellence in Nuclear Engineering.
Disclosure Statement
No potential conflict of interest was reported by the authors.
Nomenclature
| ADF1 | = | = fast group ADF |
| ADF2 | = | = thermal group ADF |
| D1 | = | = fast group diffusion coefficient |
| D2 | = | = thermal group diffusion coefficient |
| keff | = | = neutron multiplication factor |
Greek
| ∑A1 | = | = fast group absorption cross section |
| ∑A2 | = | = thermal group absorption cross section |
| ν∑f1 | = | = fast group fission cross section multiplied by average number of neutrons per fission |
| ν∑f2 | = | = fast group fission cross section multiplied by average number of neutrons per fission |
| ∑S 1->2 | = | = fast to thermal energy group scatter cross section (i.e., downscatter) |
Acronyms
| ADF | = | = assembly discontinuity factor |
| BOC | = | = beginning of cycle |
| EOC | = | = end of cycle |
| HFP | = | = hot full power |
| HZP | = | = hot zero power |
| LWR | = | = light water reactor |
| MWd/kg | = | = megawatt-days per kilogram of uranium |
| PWR | = | = pressurized water reactor |
| ppm | = | = parts per million |
| RSD | = | = relative standard deviation |
| UAM-LWR | = | = Uncertainty Analysis in Modelling for Light Water Reactors benchmark study |
Notes
a While the work performed in this paper includes some uncertainty in kinetics parameters, which results from differences in nuclear data between trials, the inclusion of uncertainties in the delayed neutron group fractions and precursor decay constants was not available in the official SCALE release at the time of this work.