[en] We used a micro-Raman spectrometer with two different laser excitation sources (514 and 785 nm) and variable laser powers to identify some uranium chemical species contained in airborne particulate matter. In the first part of this paper, we demonstrate that characteristic Raman bands mentioned in the literature for several uranium compounds relevant in the nuclear industry (UO₂, UO₄.(4H₂O), U₃O₈, UO₂F₂ and UF₄) can be identified in particles in the few μm to 30 μm size range. In the second part of the paper, we describe a method to carry out Raman analysis on airborne uranium particles sampled along with a majority of other kinds of particles simply by dabbing adhesive carbon disks on dusty surfaces. This methodology involves an SEM equipped with an energy dispersive X-ray analyser and software for automated detection of particles specifically to locate uranium particles on the substrate before the Raman analysis. Then the sample holder is transferred to the micro-Raman spectrometer and particles are relocated using landmarks and simple geometric calculations. Raman analyses are carried out with the laser that gives the best signal to noise ratio. With such a method particles as small as 5 μm can be efficiently analysed, although most of the smaller particles cannot be analysed due to limited precision of the relocation process. This methodology was successfully applied to 20 particles collected in a nuclear facility.

[en] In the frame of nuclear safeguards, knowledge of the chemical form (stoichiometry) of the uranium compounds present in the micrometric particulate material sampled by wiping surfaces in an inspected nuclear facility may point out the industrial process implemented in the installation. Micro-Raman spectroscopy (MRS) coupled with scanning electron microscopy (SEM) has been used for the first time to analyze micrometer-size particles of various uranium oxides [UO_2, U_3O_8, UO_3, and UO_4.4(H_2O)] deposited on carbon disks. Uranium particles are detected by means of SEM, and Raman analysis is then directly carried out inside the SEM measurement chamber without moving the carbon disk from SEM to MRS. When particles are deposited on appropriate carbon disks (sticky carbon tapes), despite a loss of signal-to-noise ratio of about an order of magnitude with regard to the stand-alone MRS, all uranium oxides are successfully identified in particles by in-SEM Raman analysis, obtaining similar characteristic bands as the ones obtained with the stand-alone MRS. Moreover, with the SEM-MRS coupling, particles as small as 1 μm can be analyzed, whereas, without the SEM-MRS coupling, only particles larger than ∼5 μm are efficiently analyzed, after localization inside the SEM, transfer of the sample holder into the MRS, and relocation of the particles inside the MRS. (authors)

[en] The knowledge of the chemical forms of the uranium in micrometer-size particles recovered inside or around a nuclear facility can tell information about the nuclear processes applied in the facility. For the first time a micro-Raman spectrometer combined with a scanning electron microscope has been used to analyse dust particles containing various uranium oxides. The scanning electron microscope detects the particle containing uranium while the Raman spectra allow the identification of the type of uranium oxide [UO₂ or U₃O₈ or UO₃ or UO₄(H₂O)]. We have demonstrated that the presence of most uranium oxides used in nuclear industry can be detected in micrometer-size dust particles

[en] Thanks to its ability to carry out structural identification of small–size objects, Micro-Raman spectrometry (MRS) is a potentially interesting tool for nuclear forensics. In this communication, application of Raman spectrometry to the fast and non–destructive determination of the chemical composition of various uranium compounds will be presented and discussed. Analysis by MRS can be carried out to minute amounts of samples and to mixtures of various uranium species. Moreover, MRS can be coupled to a scanning electron microscope (SEM) thanks to a coupling device. This interface was designed to obtain topographical information (by SEM imaging), elemental composition (by EDX), and chemical information (by MRS) from the same spot without sample transfer. Different examples of analysis by MRS or SEM–MRS coupling of relevant samples for nuclear forensics will be shown. (author)

[en] In this paper, we present some results of R and D works conducted at CEA to improve on the one side the performance of the techniques already in use for detection of undeclared activities, and on the other side to develop new capabilities, either as alternative to the existing techniques or new methods that bring new information, complementary to the isotopic composition. For the trace analysis of plutonium in swipe samples by ICP-MS, we demonstrate that a thorough knowledge of the background in the actinide mass range is highly desirable. In order to avoid false plutonium detection in the femtogram range, correction from polyatomic interferences including mercury, lead or iridium atoms are in some case necessary. Efforts must be put on improving the purification procedure. Micro-Raman spectrometry allows determining the chemical composition of uranium compound at the scale of the microscopic object using a pre-location of the particles thanks to SEM and a relocation of these particles thanks to mathematical calculations. However, particles below 5 μm are hardly relocated and a coupling device between the SEM and the micro-Raman spectrometer for direct Raman analysis after location of a particle of interest is currently under testing. Lastly, laser ablation - ICP-MS is an interesting technique for direct isotopic or elemental analysis of various solid samples and proves to be a suitable alternative technique for particle analysis, although precision over isotopic ratio measurement is strongly limited by the short duration and irregularity of the signals. However, sensitivity and sample throughput are high and more developments are in progress to validate and improve this method. (author)

[en] Short communication

[en] The safety assessment of Sodium-cooled Fast Reactors (SFR) requires to account for hypothetical severe accidents involving the melting down of the core materials. This paper deals with the modeling of a fuel vaporization transient that might occur in a SFR in case of severe accident. After a nuclear power excursion, some fuel might be molten and vaporized. In this case, the expansion of fuel vapor might generate a mechanical stress on the reactor vessel and structures. Assessing the vessel integrity is of major importance for the reactor design. A fuel vaporization and expansion modeling, which has been simplified using a Dimensional Analysis, is presented. The modeling is implemented in a tool, called DETONa, able to perform fast calculations, of the order of one minute. The vaporized fuel's thermal exchange with the reactor liquid coolant leading to a possible coolant vaporization is simulated by DETONa. The coolant is assumed to be entrained into the fuel vapor. A droplet entrainment model based on Rayleigh-Taylor instabilities associated to their diameter's limitation using Weber stability criterion is proposed. The modeling is validated on experimental results and on code-to-code comparisons. Parametric calculations are conducted on a reactor case. The impact of the initial molten fuel mass, its initial temperature, critical Weber number and radiative heat transfer are investigated. The non-adiabatic modeling and the adiabatic modeling yield results different by 40% in certain cases. DETONa is shown to be sensitive to the fuel initial temperature, the heat transfer coefficient and the Rayleigh-Taylor wavelength, involving variations that can range to 18%. (authors)

[en] The Atalante research facility produces radioactive waste that have to be managed according to specific rules. In particular, solid and liquid wastes need to be transferred to another facility in Marcoule to be evaporated with an alpha activity limit of 16.65 GBq/m"3. The radioactive aqueous nitric acid wastes produced in Atalante must be first decontaminated by removing U, Pu and minor actinides and therefore a dedicated decontamination program for radioactive aqueous nitric acid wastes is implemented in Atalante. In particular, the recovery of americium and curium is obtained by extraction chromatography. TEHDGA (N, N, N', N'-tetra-2-ethylhexyl-3-oxopentane-1,5-diamide), DMDOHEMA ((N,N'-dimethyl-N,N'-dioctyl-hexyl-oxyethyl malonamide) and a mixture of both extractants were impregnated on silica gel and studied. Batch experiments were made to determine the performances of such a process. The weight distribution coefficients (Dw) were determined for Am and Nd. Different kinetic behavior was found with both complexing agents. An effect of nitric acid concentration was observed. For 3 solids, the americium's uptake increases with acidity. Loading capacities by isotherm and Langmuir isotherm are obtained (between 48 mg/g and 94 mg/g). After determining various parameters in batch extraction experiments, the performances of the solid supports were studied in columns. The breakthrough and elution curves were obtained with neodymium (respectively between 12 mg/g and 21 mg/g; 0.17 and 0.27 L/g). Capacity and recovery were optimized with the mixture of DMDOHEMA and TEHDGA. (authors)

[en] It has been reported recently that a higher airborne arsenic level was correlated with higher urinary arsenic concentration and lower serum thyroxin level among urban policemen and rural highway workmen in Italy. The current study was to determine whether exposure to low-level arsenic groundwater (2–22 µg/L) is associated with hypothyroidism among 723 participants (118 male and 267 female Hispanics; 108 male and 230 female non-Hispanic whites, NHW) living in rural West Texas counties. Arsenic and iodine levels in their groundwater used for drinking and or cooking were estimated by the inverse distance weighted (IDW) interpolation technique. Groundwater arsenic was ≥8 µg/L in 36% of the subjects' wells while iodine concentration was <1 µg/L in 91% of their wells. Logistic regression analysis showed that arsenic in groundwater ≥8 µg/L and cumulative arsenic exposure (groundwater arsenic concentration multiplied by the number of years living in the current address) but not groundwater iodine concentration were significant predictors for hypothyroidism among Hispanics (p<0.05) but not NHW after adjusting for covariates such as age, gender, annual household income and health insurance coverage. The ethnic difference may be due to a marginally higher percentage of Hispanics (p=0.0622) who lived in areas with groundwater arsenic ≥8 µg/L compared with NHW. The prevalence of hypothyroidism was significantly higher in Hispanics or NHW of this rural cohort than the national prevalence. Measures should be taken to reduce arsenic in drinking water in order to prevent hypothyroidism in rural areas. - Highlights: • We determined if arsenic exposure is associated with hypothyroidism in rural Texas. • Groundwater arsenic level is associated with hypothyroidism among Hispanics only. • The rate of hypothyroidism in rural Texas was higher than the US general population

[en] Highlights: • Outcome of the France-Japan collaboration on R&D related to fuel discharge. • Study of efficiency of mitigation devices. • Unprotected Loss Of Flow simulation results in terms of mitigation efficiency. • Local calculations around one transfer tube. Sodium-cooled Fast Reactors (SFR) are investigated as future Generation IV reactor concepts. In SFR, the core configuration is not the most reactive during the nominal reactor operation, its geometry change or coolant voiding can induce a reactivity insertion. Within these considerations, mitigation devices should be implemented into the core in order to limit the thermal energy released into the fuel during a severe accident and thereby the possibility to induce mechanical loadings of the reactor structure when vaporized materials expand. Complementary safety devices called Transfer Tubes (TT) are studied in a French concept as an effective mitigation measure of severe accidents to reach a final reactor safe state, even in case of a failure of all shutdown systems including the passive shutdown safety rods. More precisely the TT, with their upper part located in and above the core, cross the core support structure and are linked to the core catcher zone situated in the main vessel bottom. Their purpose is to extract fissile materials from the core zone and secondly to favor the transfer of the molten fuel from the core region to the core catcher in case of severe core damage. The fuel discharge out of the core zone is necessary in order to lower the core reactivity, the relocation into the core catcher is necessary to enable the stabilization, the sub-criticality and the fuel cooling. An extensive work on severe accident calculations and phenomena identification related to fuel discharge through TT was performed. These studies represent the outcome of the work performed in 2014–2019, performed with collaboration of Japanese JAEA and MFBR and Framatome in the framework of the SFR project carried out by CEA. Calculations of fuel discharge were carried out with the mechanistic calculation code SIMMER and the main results are presented in this paper. Firstly, the whole unprotected loss of flow (ULOF) accident sequence was calculated with the SIMMER code. From these calculations, the power and flow evolution were set as boundary conditions for a more detailed model with six fuel assemblies around TT. This model was used to focus on key phenomena and to check impact of design parameter as local bottom restriction inside TT on fuel discharge way.