scholarly journals Power calibration methodology at the CROCUS reactor

2020 ◽  
Vol 225 ◽  
pp. 04022 ◽  
Author(s):  
Vincent Lamirand ◽  
Axel Laureau ◽  
Oskari Pakari ◽  
Pravel Frajtag ◽  
Andreas Pautz

In the present article, we detail the method used to experimentally determine the power of the CROCUS zero-power reactor, and to subsequently calibrate its ex-core monitor fission chambers. Knowledge of the reactor power is a mandatory quantity for a safe operation. Furthermore, most experimental research programs rely on absolute fission rates in design and interpretation – for instance, tally normalization of reaction rate studies in dosimetry, or normalization of power spectral density in neutron noise measurements. The minimization of associated uncertainties is only achieved by an accurate power determination method. The main experiment consists in the irradiation, and therefore, the activation of several axially distributed Au-197 foils in the central axis of the core, which activities are measured with a High-Purity Germanium (HPGe) gamma spectrometer. The effective cross sections are determined by MCNP and Serpent Monte Carlo simulations. We quantify the reaction rate of each gold foil, and derive the corresponding fission rate in the reactor. The variance weighted average over the distributed foils then provides a calibration factor for the count rates measured in the fission chambers during the irradiation. We detail the calibration process with minimization of respective uncertainties arising from each sub-step, from power control after reactivity insertion, to the calibration of the HPGe gamma spectrometer. Biases arising from different nuclear data choices are also discussed.

2018 ◽  
Vol 170 ◽  
pp. 04009
Author(s):  
Benoit Geslot ◽  
Adrien Gruel ◽  
Stéphane Bréaud ◽  
Pierre Leconte ◽  
Patrick Blaise

Pile oscillator techniques are powerful methods to measure small reactivity worth of isotopes of interest for nuclear data improvement. This kind of experiments has long been implemented in the Mineve experimental reactor, operated by CEA Cadarache. A hybrid technique, mixing reactivity worth estimation and measurement of small changes around test samples is presented here. It was made possible after the development of high sensitivity miniature fission chambers introduced next to the irradiation channel. A test campaign, called MAESTRO-SL, took place in 2015. Its objective was to assess the feasibility of the hybrid method and investigate the possibility to separate mixed neutron effects, such as fission/capture or scattering/capture. Experimental results are presented and discussed in this paper, which focus on comparing two measurements setups, one using a power control system (closed loop) and another one where the power is free to drift (open loop). First, it is demonstrated that open loop is equivalent to closed loop. Uncertainty management and methods reproducibility are discussed. Second, results show that measuring the flux depression around oscillated samples provides valuable information regarding partial neutron cross sections. The technique is found to be very sensitive to the capture cross section at the expense of scattering, making it very useful to measure small capture effects of highly scattering samples.


2018 ◽  
Vol 170 ◽  
pp. 04023 ◽  
Author(s):  
Žiga Štancar ◽  
Tanja Kaiba ◽  
Luka Snoj ◽  
Loïc Barbot ◽  
Christophe Destouches ◽  
...  

A series of fission rate profile measurements with miniature fission chambers, developed by the Commisariat á l’énergie atomique et auxénergies alternatives, were performed at the Jožef Stefan Institute’s TRIGA research reactor. Two types of fission chambers with different fissionable coating (235U and 238U) were used to perform axial fission rate profile measurements at various radial positions and several control rod configurations. The experimental campaign was supported by an extensive set of computations, based on a validated Monte Carlo computational model of the TRIGA reactor. The computing effort included neutron transport calculations to support the planning and design of the experiments as well as calculations to aid the evaluation of experimental and computational uncertainties and major biases. The evaluation of uncertainties was performed by employing various types of sensitivity analyses such as experimental parameter perturbation and core reaction rate gradient calculations. It has been found that the experimental uncertainty of the measurements is sufficiently low, i.e. the total relative fission rate uncertainty being approximately 5 %, in order for the experiments to serve as benchmark experiments for validation of fission rate profiles. The effect of the neutron flux redistribution due to the control rod movement was studied by performing measurements and calculations of fission rates and fission chamber responses in different axial and radial positions at different control rod configurations. It was confirmed that the control rod movement affects the position of the maximum in the axial fission rate distribution, as well as the height of the local maxima. The optimal detector position, in which the redistributions would have minimum effect on its signal, was determined.


Author(s):  
S.B. Dubovichenko ◽  
◽  
N.A. Burkova ◽  
R.R. Shamitova ◽  
◽  
...  

Within the framework of a modified potential cluster model with forbidden states, radiation n12C capture at energies from 10-5 keV to 5 MeV is considered, taking into account a wide resonance at Ex = 8.2 MeV. It is shown that on the basis of potentials that are consistent with the energies of the bound states, it is possible to correctly transfer the available experimental data. Based on the obtained total cross sections, the n12C capture reaction rate was calculated. The results for reaction rate are approximated by simple expressions, which simplifies their use in applied research.


2010 ◽  
Vol 2 ◽  
pp. 12001 ◽  
Author(s):  
J.N. Wilson ◽  
S. Siem ◽  
S.J. Rose ◽  
A. Georgen ◽  
F. Gunsing ◽  
...  

2018 ◽  
Vol 4 ◽  
pp. 27 ◽  
Author(s):  
Roberto Capote ◽  
Andrej Trkov

Key reactions have been selected to compare JEFF-3.3 (CIELO 2) and IAEA CIELO (CIELO 1) evaluated nuclear data files for neutron induced reactions on 235U and 238U targets. IAEA CIELO evaluation uses reaction models to construct the evaluation prior, but strongly relied on differential data including all reaction cross sections fitted within the IAEA Neutron Standards project. The JEFF-3.3 evaluation relied on a mix of differential and integral data with strong contribution from nuclear reaction modelling. Differences in evaluations are discussed; a better reproduction of differential data for the IAEA CIELO evaluation is shown for key reaction channels.


2020 ◽  
Vol 142 ◽  
pp. 107383
Author(s):  
Chenghui Wan ◽  
Jialong Xu ◽  
Liangzhi Cao ◽  
Hongchun Wu

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