-
[show abstract]
[hide abstract]
ABSTRACT: For the on-line monitoring of high fast neutron fluxes in the presence of a strong thermal neutron component, SCK·CEN and CEA are jointly developing a Fast Neutron Detector System, based on <sup>242</sup>Pu fission chambers as sensors and including dedicated electronics and data processing systems. Irradiation tests in the BR2 reactor of <sup>242</sup>Pu fission chambers operating in current mode showed that in typical MTR conditions the fission chamber currents are dominated by the gamma contribution. In order to reduce the gamma contribution to the signal, it was proposed to use the fission chambers in Campbelling mode. An irradiation experiment in the BR2 reactor with a <sup>242</sup>Pu and a <sup>235</sup>U fission chamber, both equipped with a suitable cable for measurements in Campbelling mode, proved the effectiveness of the suppression of the gamma-induced signal component by the Campbelling mode: gamma contribution reduction factors of 26 for the <sup>235</sup>U fission chamber and more than 80 for the <sup>242</sup>Pu fission chamber were obtained. The experimental data also prove that photofission contributions are negligibly small. Consequently, in typical MTR conditions the gamma contribution to the fission chamber Campbelling signal can be neglected.
IEEE Transactions on Nuclear Science 05/2011; · 1.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Flux monitoring is of great interest for experimental studies in material testing reactors. Nowadays, only the thermal neutron flux can be monitored on line, e.g., using fission chambers or self-powered neutron detectors. In the framework of the Joint Instrumentation Laboratory between SCK-CEN and CEA, we have developed a fast neutron detector system (FNDS) capable of measuring on line the local high-energy neutron flux in fission reactor core and reflector locations. FNDS is based on fission chambers measurements in Campbelling mode. The system consists of two detectors, one detector being mainly sensitive to fast neutrons and the other one to thermal neutrons. On line data processing uses the CEA depletion code DARWIN in order to disentangle fast and thermal neutrons components, taking into account the isotopic evolution of the fissile deposit. The first results of FNDS experimental test in the BR2 reactor are presented in this paper. Several fission chambers have been irradiated up to a fluence of about 7 × 10(20) n∕cm(2). A good agreement (less than 10% discrepancy) was observed between FNDS fast flux estimation and reference flux measurement.
The Review of scientific instruments 03/2011; 82(3):033504. · 1.52 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Fission chambers are widely used in the nuclear industry. As an example, they play a major role in the control of any fission reactor and are thus regarded as a key component for ensuring their safety. They are also employed in the material testing reactors for monitoring irradiations. We have recently started a research program, the objective of which is to improve the performance of those neutron detectors in terms of lifetime, calibration, and online diagnosis. In this paper, we present several studies carried out in order to model the signal delivered by a fission chamber. First, the simulation of the deposit evolution allowed us to select the most appropriate fissile material for a given spectrum and fluence. Second, we studied the impact of the bias voltage and filling gas characteristics on the charge collection time. Finally, the simulation of a pulse signal prior to amplification showed how it is important to have a satisfactory knowledge of the energy for creating ion pairs to accurately assess the signal in current or Campbelling mode.
IEEE Transactions on Nuclear Science 01/2011; · 1.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: For the on-line monitoring of high fast neutron fluxes in the presence of a strong thermal neutron component, SCK·CEN and CEA are jointly developing a Fast Neutron Detector System, based on <sup>242</sup>Pu fission chambers as sensors and including dedicated electronics and data processing systems. Irradiation tests in the BR2 reactor of <sup>242</sup>Pu fission chambers operating in current mode showed that in typical MTR conditions the fission chamber currents are dominated by the gamma contribution. In order to reduce the gamma contribution to the signal, it was proposed to use the fission chambers in Campbelling mode. An irradiation experiment in the BR2 reactor with a <sup>242</sup>Pu and a <sup>235</sup>U fission chamber, both equipped with a suitable cable for measurements in Campbelling mode, proved the effectiveness of the suppression of the gamma-induced signal component by the Campbelling mode: gamma contribution reduction factors of 26 for the <sup>235</sup>U fission chamber and more than 80 for the <sup>242</sup>Pu fission chamber were obtained. The experimental data also prove that photofission contributions are negligibly small. Consequently, in typical MTR conditions the gamma contribution to the fission chamber Campbelling signal can be neglected.
Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), 2009 First International Conference on; 07/2009
-
[show abstract]
[hide abstract]
ABSTRACT: The Dosimetry Command control and Instrumentation Laboratory (LDCI) at CEA/Cadarache is specialized in the development, design and manufacturing of miniature fission chambers (from 8 mm down to 1.5 mm in diameter). LDCI fission chambers workshop specificity is its capacity to manufacture and distribute special fission chambers with fissile deposits other than U235 (typically Pu242, Np237, U238, Th232). We are also able to define the characteristics of the detector for any in-core measurement requirements: sensor geometry, fissile deposit material and mass, filling gas composition and pressure, operating mode (pulse, current or Campbelling) with associated cable and electronics. The fission chamber design relies on numerical simulation and modeling tools developed by the LDCI. One of our present activities in fission chamber applications is to develop a fast neutron flux instrumentation using Campbelling mode dedicated to measurements in material testing reactors.
Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), 2009 First International Conference on; 07/2009
-
[show abstract]
[hide abstract]
ABSTRACT: Fission chambers are widely used for on-line monitoring of neutron fluxes in irradiation reactors. A selective measurement of a component of interest of the neutron flux is possible in principle thanks to a careful choice of the deposit material. However, measuring the fast component is challenging when the flux is high (up to 10<sup>15</sup> n/cm<sup>2</sup>/s) with a significant thermal component. The main problem is that the isotopic content of a material selected for its good response to fast neutrons evolves with irradiation, so that the material is more and more sensitive to thermal neutrons. Within the framework of the FNDS (Fast Neutron Detector System) project, we design tools that simulate the evolution of the isotopic composition and fission rate for several deposits under any given flux. In the case of a high flux with a significant thermal component, <sup>242</sup>Pu is shown after a comprehensive study of all possibilities to be the best choice for measuring the fast component, as long as its purity is sufficient. If an estimate of the thermal flux is independently available, one can correct the signal for that component. This suggests a system of two detectors, one of which being used for such a correction. It is of very high interest when the detectors must be operated up to a high neutron fluence.
Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), 2009 First International Conference on; 07/2009
-
[show abstract]
[hide abstract]
ABSTRACT: A new data acquisition system dedicated to neutronic experiments in nuclear reactors is presented. Its main purpose is to integrate in a single system all features needed to perform digital and analogic acquisitions, such as kinetics experiments, time correlations of events, fluctuations analysis or pile noise measurements. Moreover, it has been designed to perform complex experiment such as synchronous acquisition or triggered experiments. In order to achieve those goals, it is equipped with two newly developed acquisition cards based on FPGA circuits. They can acquire and process up to 32 digital signals and 8 analogic signals. In digital mode, the system is able to count and time-mark TTL events up to 10 MHz for all channels. In analogic mode, it can sample signals at adjustable frequency and perform pulse height analysis. Finally, the system generates 4 channels of TTL periodical or random signals. One can use those signals for testing purposes or as time reference signals. In this paper, sketches of the main functions are detailed. Then, an experimental result is presented in order to enhance the interest of the time marking mode of the system
Instrumentation and Measurement Technology Conference, 2005. IMTC 2005. Proceedings of the IEEE; 06/2005
-
[show abstract]
[hide abstract]
ABSTRACT: The stopping power of ions in gases can be computed by codes, such as SRIM, based on experimental data and theories. However, no available code has been tailored to deal with the specific properties of fission fragments when interacting with gas. This is, however, of key interest for fission chambers, in which the electric signal results from the ionisation of a gas by fission fragments. We compared experimental data available in the literature with those computed with SRIM. In spite of a underestimation of the energy loss per unit length, SRIM gives qualitatively good results, thus is an useful tool to study the stopping power of fission fragments in gases. However, getting more comprehensive experimental data should be beneficial.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 618:294-297. · 1.21 Impact Factor
-
S. Andriamonje,
S. Aune,
A. Giganon,
I. Giomataris,
J. Pancin,
M. Riallot,
C. Blandin,
S. Breaud, B. Geslot,
C. Jammes,
Y Kadi,
L. Sarchiapone,
G. Ban,
P. Laborie,
J.F. Lecolley,
J.C. Steckmeyer,
J. Tillier,
R. Rosa,
G. Andriamonje
[show abstract]
[hide abstract]
ABSTRACT: Future fast nuclear reactors designed for energy production and transmutation of nuclear wastes need new neutrons detectors able to measure the neutron flux over a large energy range from thermal energies to several MeV. A novel compact and very small detector, named Piccolo-Micromegas has been developed for this purpose. Description of the detector configuration especially dedicated to neutron detection inside nuclear reactor is given. The advantage of this detector over conventional neutron flux detectors and the results obtained with the first prototype are presented.
-
[show abstract]
[hide abstract]
ABSTRACT: The in vessel instrumentation of sodium-cooled fast reactors must deliver measurements that are reliable and easy to interpret over several reactor cycles in order to fulfill the safety requirements. This paper compares, with respect to this requirement, three types of detectors that are widely used in neutron measurements: fission chambers, boron-lined proportional counters, self-powered neutron detectors. We use neutron spectra that are computed for preliminary design of sodium-cooled fast reactor in different representative locations: in diluting tubes within nuclear fuel assemblies, or in the lateral neutron protections. With an evolution code, we compute the expected signal for each type of detector, to assess whether its level is sufficient, and also its evolution over three operating cycles, to examine whether it is compatible with long term measurements. The conclusion is that fission chambers are the only type able to deliver an interpretable signal for a wide dynamic of reactor power and for three or more operating cycles. The two other types are shown to be inadequate.
Annals of Nuclear Energy.
