Search

Symposium on Radiation Measurements and Applications (SORMA), Oakland, CA, MAY 14-17, 2012; International audience; Electron accelerators are intense photoneutron sources for nuclear waste packages characterization and homeland security applications. Moreover, when considering medical accelerators, photoneutrons can cause secondary cancers for patients and also expose hospital staff to deactivation gammas after the irradiation. In this study, we investigate photoneutrons properties according to average emission intensity, energy spectrum and spatial distribution. The latter parameter was measured using an activation detector and the other two parameters were determined by simulation, and then, evaluated by comparing absolute activation simulations and measurements. Our methodology was applied to characterize the photoneutron flux generated by two electron accelerators. Our study has shown that there is a strong probability for photonuclear cross-sections to be undervalued in the energy range studied.

Localization of radioactive sources is a major issue for many applications in the nuclear industry. Gamma imaging is a powerful non-destructive technique, enabling to locate radioactive hot spots contained in a given area and well-adapted to this topic. Industrial gamma cameras have been commercialized by various companies for several years but present some limitations in terms of sensitivity, weight and ease of use in comparison with the requirements of end-users.

The tracking of radiation contamination and distribution has become a high priority in the nuclear cycle industry in order to respect the ALARA principle which is a main challenge during decontamination and dismantling activities. To support this need, AREVA/CANBERRA and CEA LIST have been actively carrying out research and development on a gamma-radiation imager. In this paper we will present the new generation of gamma camera, called GAMPIX. This system is based on the Timepix chip, hybridized with a CdTe substrate. A coded mask could be used in order to increase the sensitivity of the camera. Moreover, due to the USB connection with a standard computer, this gamma camera is immediately operational and user-friendly. The final system is a very compact gamma camera (global weight is less than 1 kg without any shielding) which could be used as a handheld device for radioprotection purposes. In this article, we present the main characteristics of this new generation of gamma camera and we expose experimental results obtained during in situ measurements. Even though we present preliminary results the final product is under industrialization phase to address various applications specifications.

The MOBISIC project, funded by the System@tic Paris-Region cluster, is being developed in the context of local crisis (attack bombing in urban environment, in confined space such as an underground train tunnel etc.) or specific event securing (soccer world cup, political meeting etc.). It consists in conceiving, developing and experimenting a mobile, modular ('plug and play') and multi-sensors securing system. In this project, CEA LIST has suggested different solutions for nuclear risks detection and identification. It results in embedding a CZT sensor and a gamma camera in an indoor drone. This article first presents the different modifications carried out on the UAV and different sensors, and focuses then on the experimental performances.

Previous works on pressurized water reactors show that the nitrogen 16 activation product can be used to measure thermal power. Power monitoring using a more stable indicator than ex-core neutron measurements is required for operational sodium-cooled fast reactors, in order to improve their economic efficiency at the nominal operating point. The fluorine 20 and neon 23 produced by (n,α) and (n,p) capture in the sodium coolant have this type of convenient characteristic, suitable for power measurements with low build-up effects and a potentially limited temperature, flow rate, burn-up and breeding dependence. This method was tested for the first time during the final tests program of the French Phénix sodium-cooled fast reactor at CEA Marcoule, using the ADONIS gamma pulse analyzer. Despite a non-optimal experimental configuration for this application, the delayed gamma power measurement was pre-validated, and found to provide promising results.

Characterization of nuclear waste packages is crucial to optimize waste management (temporary storage, transport, final repository). Passive and active non-destructive methods are well-adapted to this problem and their coupling can be extremely useful in order to optimize data analysis. Photon activation analysis (PAA), based on the photofission process and on the detection of delayed particles emitted after this reaction, is a powerful tool for the analysis of bulky concrete waste packages. Methods developed around PAA allow to locate, identify and quantify the mass of actinides (235U, 238 U, 239Pu) present in a given package in order to estimate its alpha activity. In this article, we present experimental and simulated results obtained in PAA during the characterization of a real nuclear waste package in the SAPHIR facility (Active Photon and Irradiation System). For the first time, several non-destructive methods (passive gamma-ray spectrometry, high-energy radiography) are combined with traditional PAA techniques (altitude scan, global photofission, photofission tomography) in order to optimize the characterization process.

CEA is developing a method to prevent illegal traffic of special nuclear material (SNM) at borders, especially sea ports where millions of containers are transiting every day. This nondestructive method is based on the interrogation of the container by high-energy photon and the subsequent detection of particles emitted after the fission. This technique requires the knowledge of nuclear parameters that have been rarely measured for fission induced by photons. Therefore, we present fundamental measurements of these parameters for uramium-238 and uranium-235. Numerical simulations to assess the SNM detection performances are also reported.

Being able to characterize and classify nuclear waste packages is crucial for an appropriate mode of storage. The alpha-activity due to the presence of actinides inside the packages can be determined using non-destructive active (NDA) methods. CEA-LIST is developing one of those, based on fission induced by photons that allows us to quantify the global mass of actinides in large concrete packages and localize it by the means of a tomography using delayed particles emitted after the fission process.

International audience; In the present study, diameter 5''× 3'' and diameter 2''× 2'' EJ-313 liquid fluorocarbon as well as diameter 2'' × 3'' BaF2 scintillators were exposed to neutrons from a 252Cf neutron source and a Sodern Genie 16GT deuterium-tritium (D+T) neutron generator. The scintillators responses to β− particles with maximum endpoint energy of 10.4 MeV from the n+19F reactions were studied. Response of a diameter 5'' × 3'' BC-408 plastic scintillator was also studied as a reference. The β− particles are the products of interaction of fast neutrons with 19F which is a component of the EJ-313 and BaF2 scintillators. The method of fast neutron detection via fluorine activation is already known as Threshold Activation Detection (TAD) and was proposed for photofission prompt neutron detection from fissionable and Special Nuclear Materials (SNM) in the field of Homeland Security and Border Monitoring.Measurements of the number of counts between 6.0 and 10.5 MeV with a 252Cf source showed that the relative neutron detection efficiency ratio, defined as Epsilon_BaF2 / Epsilon_EJ−313−5'', is 32.0% ± 2.3% and 44.6% ± 3.4% for front-on and side-on orientation of the BaF2, respectively. Moreover, the diameter 5'' EJ-313 and side-on oriented BaF2 were also exposed to neutrons from the D+T neutron generator, and the relative efficiency Epsilon_BaF2 / Epsilon_EJ−313−5'' was estimated to be 39.3%. Measurements of prompt photofission neutrons with the BaF2 detector by means of data acquisition after irradiation (out-of-beam) of nuclear material and between the beam pulses (beam-off) techniques were also conducted on the 9 MeV LINAC of the SAPHIR facility.

Photons with energies above 6 MeV can be used to detect small amounts of nuclear material inside large cargo containers. The method consists in using an intense beam of high-energy photons (bremsstrahlung radiation) in order to induce reactions of photofission on actinides. The measurement of delayed neutrons and delayed gammas emitted by fission products brings specific information on localization and quantification of the nuclear material. A simultaneous measurement of both of these delayed signals can overcome some important limitations due to matrix effects like heavy shielding and/or the presence of light elements as hydrogen. We have a long experience in the field of nuclear waste package characterization by photon interrogation and we have demonstrated that presently the detection limit can be less than one gram of actinide per ton of package. Recently we tried to extend our knowledge to assess the performance of this method for the detection of special nuclear materials in sea and air freights. This paper presents our first results based on experimental measurements carried out in the SAPHIR facility, which houses a linear electron accelerator with the energy range from 15 MeV to 30 MeV. Our experiments were also modeled using the full scale Monte Carlo techniques. In addition, and in a more general frame, due to the lack of consistent data on photonuclear reactions, we have been working on the development of a new photonuclear activation file (PAF), which includes cross sections for more than 600 isotopes including photofission fragment distributions and delayed neutron tables for actinides. Therefore, this work includes also some experimental results obtained at the ELSA electron accelerator, which is more adapted for precise basic nuclear data measurements.

A characterization of the alpha-activity due to the presence of actinides inside nuclear waste packages is necessary to select the best mode of storage. Non-destructive active methods, based on fission process, allow to quantify the global mass of actinides. However, these measurements give no information on the nature of isotopes in most cases. We are currently developing a method to identify actinides (235U, 238U, 239Pu), based on the detection of delayed gammas emitted by fission products. The delayed gamma spectrum can be regarded as a "fingerprint" of the irradiated sample. Qualitative and quantitative analysis of peaks allow an identification of actinides. The main purpose of this paper is twofold. First, basis of this method of differentiation are described. Then, experimental results obtained in fission and photofission are presented, in particular in the case of mixtures containing several actinides.