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Innovative local pile oscillator technique in the Minerve reactor: comparison between open loop and closed loop

Abstract : Pile oscillator techniques are powerful methods to measure small reactivity worth of isotopes of interest for nuclear data improvement. The principle is to create, in a well-known neutron flux, a weak and localized perturbation, the characteristics of which (level, spectrum) can be connected to physical parameters of the source (i.e. cross sections). Techniques are called open loop if the reactor power is free to drift. On the contrary, it is called closed loop if a power control system is activated. Such pile oscillator experiments have long been held in the Minerve reactor, operated by CEA at Cadarache. A closed loop reactivity oscillator method is implemented which is based on measuring the global reactivity perturbation associated to samples motion in the core center. The technique has recently been extended by introducing CEA-made miniature fission chambers close to the irradiation channel in order to measure local perturbations of the neutron flux. New detectors and associated acquisition systems were developed by CEA for that purpose. A measurement campaign, called MAESTRO-SL, took place in 2015 in Minerve. Its objective was to assess the feasibility of the method and investigate the possibility to disentangle global and local perturbation. Main experimental results are presented and discussed in this paper, which focus on comparing data processing methods of open vs closed loop setups.First, it is demonstrated that the open loop is equivalent to the closed loop setup. Uncertainty management and methods reproducibility are discussed. Second, results show that measuring local flux depression around the oscillated sample provides indeed valuable information regarding neutron cross sections. The technique is found to be very sensitivity to the capture cross section at the expense of scattering, making it very useful to measure small capture effects of highly scattering samples.
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https://hal-cea.archives-ouvertes.fr/cea-02437090
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Submitted on : Monday, January 13, 2020 - 3:19:34 PM
Last modification on : Thursday, April 30, 2020 - 8:58:05 AM

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  • HAL Id : cea-02437090, version 1

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B. Geslot, A. Gruel, S. Breaud, P. Leconte, P. Blaise. Innovative local pile oscillator technique in the Minerve reactor: comparison between open loop and closed loop. INTERNATIONAL CONFERENCE on ADVANCEMENTS in NUCLEAR INSTRUMENTATION MEASUREMENT METHODS and their APPLICATIONS, Jun 2017, Liege, Belgium. ⟨cea-02437090⟩

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