Uncertainty assessment on the prediction of the CABRI power transients

O. Clamens (1) , P. Blaise (1) , Jp. Hudelot (1) , J. Lecerf (1) , B. Biard

1 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)

CABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute (IRSN) and operated by CEA at the Cadarache research center. It is designed to study fuel behavior under RIA (Reactivity Initiated Accident) conditions. Reactivity is injected by depressurization of a neutron absorber (3He) situated in the so called transient rods inside the reactor core. A multiphysics code, called SPARTE (Simulation, Prediction and Analysis for RIA Transients and Excursions), was developed and designed to predict the CABRI power transients. This paper presents a method for uncertainty assessment on the the CABRI power transients prediction with the SPARTE code. It is based on the BEPU (Best Estimates Plus Uncertainties) approach.The SPARTE code includes surrogate models based on Best Estimates simulations and experimental analysis. The surrogate models were developed through the ROOT based URANIE uncertainty platform. Specific models were developed for 3He depressurization, 3He reactivity function of the pressure, Doppler coefficient variation, prompt neutron generation time, axial profile of neutron flux determination and rod dropping reactivity insertion. Those models are now included in the SPARTE code and are being experimentaly validated. Coupled with the platform URANIE, SPARTE is optimized for uncertainty analysis thanks to an adapted dataset and a short simulation time (below 1 min).The uncertainty propagation method consists, first, in building a design of experiments (DOE) based on the Sobol sequence with normal distributions of the parameters around their nominal values. Following the DOE, hundreds of SPARTE simulations are launched. This method allows us to evaluate the uncertainties linked to the prediction of a specific CABRI power transient. From every simulation, we extract the characteristics of the power transients (maximum power, peak time, energy, FWHM). Then the statistics are calculated in order to get mean values and standard deviations for each output. The paper gives an overview of driving parameters as a function of the type of CABRI transient.

Mots clés: CABRI; URANIE; Power transients; Point Kinetics; Uncertainty

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

O. Clamens, P. Blaise, Jp. Hudelot, J. Lecerf, B. Biard. Uncertainty assessment on the prediction of the CABRI power transients. PHYSOR 2018 - Reactor Physics paving the way towards more efficient systems, Apr 2018, Cancun, Mexico. ⟨hal-02416244⟩