Pile noise experiment in MINERVE reactor to estimate kinetic parameters using various data processing methods

Abstract

MINERVE is a two-zone pool type zero power reactor operated by CEA (Cadarache, France). Kinetic parameters of the core (prompt neutron decay constant, delayed neutron fraction, generation time) have been recently measured using various pile noise experimental techniques, namely Feynman-, Rossi-and Cohn-. Results are discussed and compared to each other's.The measurement campaign has been conducted in the framework of a tri-partite collaboration between CEA, SCK•CEN and PSI. Results presented in this paper were obtained thanks to a time-stamping acquisition system developed by CEA. PSI performed simultaneous measurements which are presented in a companion paper.Signals come from two high efficiency fission chambers located in the graphite reflector next to the core driver zone. Experiments were conducted at critical state with a reactor power of 0.2 W. The core integral fission rate is obtained from a calibrated miniature fission chamber located at the center of the core. Other results obtained in two sub-critical configurations will be presented elsewhere.Best estimate delayed neutron fraction comes from the Cohnmethod: 747 ± 15 pcm (1 ). In this case, the prompt decay constant is 79 ± 0.5 s -1 and the generation time is 94.5 ± 0.7 μs. Other methods give consistent results within the confidence intervals.Experimental results are compared to calculated values obtained from a full 3D core modeling with the CEA-developed Monte Carlo code TRIPOLI4.9 associated with its continuous energy JEFF3.1.1-based library. A very good agreement is observed for the calculated delayed neutron fraction (748.7 ± 0.4 pcm at 1 ), that is a difference of -0.3% with the experiment. On the contrary, a 10% discrepancy is observed for the calculated generation time (104.4 ± 0.1 μs at 1 ).

Sensitivity of power spectral density techniques to numerical parameters in analyzing neutron noise experiments

“…A set of neutron noise measurements have been performed on the MINERVE zero power reactor at Cadarache research center in France during September 2014. This experimental campaign was conducted in the framework of a tri-partite collaboration between CEA, PSI and SCK-CEN (Geslot et al, 2015;Perret, 2015;Gilad et al, 2016). Measurements were then also processed and analyzed in the framework of a collaboration between CEA, Ben-Gurion University of the Negev (BGU), and the Israeli Atomic Energy Commission (IAEC).…”

“…Several well-known and widely used neutron noise techniques were implemented for analyzing the experimental measurements, e.g., Cohn-α, Feynman-Y, and Rossi-α methods. These methods were used to obtain the reactor core integral kinetic parameters, i.e., the effective delayed neutron fraction β eff and the prompt neutron generation time Λ (Geslot et al, 2015;Gilad et al, 2016). More specifically, the Cohn-α method is considered as the standard data processing procedure in the case of a current acquisition system that works at high fission rates by digitizing the current signal issued by fission chambers (Diniz and dos Santos, 2002;dos Santos et al, 2006;Geslot et al, 2015).…”

“…These methods were used to obtain the reactor core integral kinetic parameters, i.e., the effective delayed neutron fraction β eff and the prompt neutron generation time Λ (Geslot et al, 2015;Gilad et al, 2016). More specifically, the Cohn-α method is considered as the standard data processing procedure in the case of a current acquisition system that works at high fission rates by digitizing the current signal issued by fission chambers (Diniz and dos Santos, 2002;dos Santos et al, 2006;Geslot et al, 2015). Such a system has recently been developed and qualified by CEA and is able to process signals on line without any data loss (de Izarra et al, 2015).…”

“…The statistical uncertainties associated with the Cohn-α method are usually thoroughly analyzed and are propagated to the final results, i.e., the integral kinetic parameters, using well established methodologies and considerations. For example, Geslot et al (2015) recommend using the values obtained by the Cross-Correlation Power Spectral Density (CPSD) estimator following data processing considerations and final uncertainties associated with the results. This estimator has proved to be very robust and produced minimum uncertainties.…”

Nuclear instrumentation and measurement: a review based on the ANIMMA conferences

“…A study of the measurement of very small worth reactivity samples comparing open and closed loop oscillator techniques [34] shows the equivalency of the two techniques with regard to uncertainties in reactivity values. Neutron noise measurements at the MINERVE reactor were performed jointly by CEA and PSI [35,36]. Various data processing methods were used to estimate the kinetic parameters (delayed neutron fraction, critical decay constant and generation time) and to compare them mutually and also with calculation results.…”