Speaker
Description
Reactivity measurements in research reactors serve a dual purpose. First, they are essential to ensure safe reactor operation and to evaluate safety margins. Second, they are used to study the reactor responses to applied perturbations and to characterize sample materials. Any of these measurements depends on the description of the reactor transient behavior. Under a number of simplifying assumptions, the point kinetic equations reduce the full transient neutron transport to a time dependent relationship between neutron flux amplitude and reactivity. This simplification is made possible through the use of effective kinetic parameters, such as the prompt neutron lifetime (Λ_eff) and the effective delayed neutron fraction (β_eff), which represent the system averaged prompt and delayed neutron behavior. These parameters can be calculated in Monte Carlo simulations using the Iterated Fission Probability (IFP) method and they are sensitive not only to delayed neutron data but also to the nuclear data used in the transport simulation.
VENUS F is a fast, zero power research reactor where, among others, a wide range of reactivity measurements are performed. Effective kinetic parameters β_eff and Λ_eff from Serpent2 calculations are commonly employed in the experimental data analysis. The objective of this work is to quantify the impact of nuclear data uncertainties on the calculated kinetic parameters and how they propagate to the actual results of VENUS F reactivity experiments.
The analysis is performed through stochastic sampling of the nuclear data relevant for the effective kinetic parameters, by generating random nuclear data samples to perform uncertainty quantification of the kinetic parameters. The impact of those uncertainties is evaluated for selected reactivity measurements performed at the VENUS-F facility. Measurements carried out using the oscillation technique rely on the kinetic parameters to reconstruct sample reactivity worth. Therefore, their contribution to the overall experimental uncertainty budget must be quantified. In this study, data from a previous experimental campaign measuring the reactivity worth of a B4C sample are analyzed. Finally, reactivity results including kinetic parameter uncertainties are compared across different nuclear data libraries. Previous studies have shown that kinetic parameters from different libraries can lead to noticeable differences in the measured reactivity. This work investigates whether those discrepancies persist once nuclear data uncertainties are explicitly accounted for.
| Session | Uncertainties and Covariance Matrices (methodology and reactor calculation impacts) |
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