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TransAT TSAis a system-code model developed at ASCOMP’s Nuclear Energy Division, performing Time Series Analysis (TSA) of BWR reactor-types to determine the reactor stability index (Decay Ratio, DR). TransAT-TSA could be also implemented in other industries, in which operational data has been saved in a time series way.

TransAT TSA analyzes the reactor power oscillations using parametric and non-parametric perturbation approaches. The parametric approach (whether Auto Regressive or Auto Regressive Moving-Average) involves determination of the model parameters and model order. The model order may be evaluated by the Akaike Information Criterion (AIC) or other more restrictive criteria that penalize the high model order. Finally an optimized model order is sought among the poles of the transfer function.

Physics and Workflow

The outcomes of the time-series analysis are the decay ratio and the resonance frequency related to the specific operation point; see Figure below. These are obtained from the poles of the system transfer function. The resonance frequency could be alternatively evaluated from the power spectral density diagram, during the non-parametric analysis.


TransAT-TSA requires the following input data:

  • Power time series (LPRMs, and APRMs)

TransAT-TSA provides the following information:

  • Decay ratio
  • Resonance frequency
  • Power spectral density

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