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Improvement of the thermal and epithermal neutron scattering data for the interpretation of integral experiments

Juan Scotta 1
1 LEPH - Laboratoire d'Etudes de PHysique
SPRC - Service de Physique des Réacteurs et du Cycle : DEN/DER
Abstract : In the present report it was studied the neutron thermal scattering of light water for reactors application. The thermal scattering law model of hydrogen bounded to the water molecule of the JEFF-3.1.1 nuclear data library is based on experimental measures performed in the sixties. The scattering physics of this latter was compared with a model based on molecular dynamics calculations developed at the Atomic Center in Bariloche (Argentina), namely the CAB model. In the frame of this work, experimental measurements of the double differential cross sections were done at room temperature. The new microscopic data were used to analyze the performance of the CAB model and JEFF-3.1.1. The CAB model exhibits an improvement over JEFF-3.1.1. The impact of these models was evaluated on application on reactor calculations at cold conditions. The selected benchmark was the MISTRAL program (UOX and MOX configurations), carried out in the zero power reactor EOLE of CEA Cadarache (France). The contribution of the neutron thermal scattering of hydrogen in water was quantified in terms of the difference in the calculated reactivity and the calculation error on the isothermal reactivity temperature coefficient (RTC). For the UOX lattice, the calculated reactivity with the CAB model at 20 °C is +90 pcm larger than JEFF-3.1.1, while for the MOX lattice is +170 pcm because of the high sensitivity of the thermal scattering to this type of fuels. In the temperature range from 10 °C to 80 °C, the calculation error on the RTC is -0.27 ± 0.3 pcm/°C and +0.05 ± 0.3 pcm/°C obtained with JEFF-3.1.1 and the CAB model respectively (UOX lattice). For the MOX lattice, is -0.98 ± 0.3 pcm/°C and -0.72 ± 0.3 pcm/°C obtained with the JEFF-3.1.1 library and with the CAB model respectively. The results illustrate the improvement of the CAB model in the calculation of this safety parameter. Finally, the uncertainties on the thermal scattering data were quantified creating covariance matrices between the parameters of the CAB model and the JEFF-3.1.1 library. The uncertainties were propagated to produce covariance matrices for the thermal scattering function and for the scattering cross section of hydrogen bounded to the light water. The uncertainty on the calculated reactivity of the MISTRAL benchmark (UOX fuel) is ±125 pcm for JEFF-3.1.1 and ±71 pcm for the CAB model (20 °C).
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Submitted on : Wednesday, July 11, 2018 - 4:06:47 PM
Last modification on : Tuesday, April 28, 2020 - 11:28:09 AM
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Juan Scotta. Improvement of the thermal and epithermal neutron scattering data for the interpretation of integral experiments. Nuclear Experiment [nucl-ex]. Université d'Aix-Marseille (AMU), 2017. English. ⟨tel-01835720⟩

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