Dosimétrie par luminescence stimulée optiquement déportée par fibre optique. Etude de capteurs à alumine a pour la dosimétrie du personnel en temps réel

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Characterization of contamination: french analysis of international EMECC campaigns

International audienceThe reduction in collective dose is an important objective for all nuclear plant operators. One of the ways for studying the impact of design and operation parameters is the measurement campaigns of contamination in PWRs. EDF' strategy is based on several levels of measurement: local dose rates give raw information; dose rate index and CZT spectrometry allow an evaluation of the radiological situation of each plant, its evolution and comparison with other plants. For very accurate characterization, EDF performs gamma spectrometry measurements with CEA and its EMECC system, with more than 300 campaigns in EDF plants and also about 70 campaigns in collaboration with other operators. Recent collaboration between EDF and other operators with excellent collective dosimetry resulted in measurements during several Refuelling Outages. The present paper presents results obtained with EDF Energy at Sizewell B Outage 8, ELECTRABEL at Doel 3 Outage 25 and Doel 4 Outage 22 and CNAT at Trillo Outage 21. The paper presents the results in terms of deposited activities and dose rates in RCS and CVCS, and compares them with French PWRs, and especially with Saint-Laurent B1. The specificities of all these plants are identified, to explain the differences in results, either for dose rates, deposited activities or collective dosimetry. All these comparisons will enable EDF and collaborative operators to improve the performance of their own plants

Impact of the coarse indoor non-radioactive aerosols on the background radon progenies' compensation of a continuous air monitor

International audienceThis paper addresses the problem of false positive alarm when using a continuous air monitor (CAM) in decommissioning sites of nuclear facilities. CAMs are used to measure airborne activity and play an important role in the radiation protection of workers likely to be exposed to radioactive aerosols. Monitors usually sample aerosols on a membrane filter. Radioactive particles sampled are detected through the alpha and beta decays that they emit. These latter ionizing particles are measured online by spectrometry thanks to a Passivated Implanted Planar Silicon detector (PIPS). Alpha and beta decays, in this context, come mainly from the natural radon progeny (218Po, 214Pb, and so on) and, in the case of radioactive contamination, also from artificial radionuclides such as 239Pu or 137Cs. The aim of the CAM is to alert the workers when the artificial airborne activity occurs, always considering the presence of a variable background due to the natural particulate airborne activity. The CAM-specific algorithm considers this background dynamically and continuously, often by using a constant parameter. However, non-radioactive aerosols are also sampled on the membrane filter. These latter make the discrimination more difficult as they lead to the deterioration of the alpha-energy spectrum. In this paper, the effect of coarse non-radioactive aerosols on the CAM response is highlighted with four aerosol size-distributions. The evolution of the background is characterized as a function of the aerosol mass sampled, with the example of a simple algorithm. Thus, in this paper, results show a positive correlation of the background with the aerosol mass sampled by the CAM. In addition, results highlight at least two different evolutionary trends according to the aerosol size distribution. An explanation of these evolutions is given by considering the penetration profile of the natural radioactive aerosols in the granular deposit above the CAM filter. The main consequence of these results is that the background could not be considered as proportional to radon progeny as it is currently used

Main Parameters Influencing the Level of Labile Contamination and the Removal Factor

International audienceSeveral nuclear facilities are currently being decommissioned in France, on CEA and EDF sites. The decommissioning process as a whole, with cutting operations and nuclear waste management presents workers with significant risks of exposure. The aim of this study was therefore to improve risk assessments of internal exposure in operations where the main uncertainties are the removal factor and the airborne release factor. A new method is presented to assess the risk of internal exposure and optimize the choice of personal protective equipment to use during nuclear dismantling operations. The main forces and parameters influencing the level of labile contamination and particle resuspension were identified from a literature review and feedback. A manageable set of parameters was then obtained based on literature data and on-site information. The effects of the drying temperature, relative humidity, roughness of the contaminated surface, and wiping pressure were thus investigated on labile contamination and removal factor measurements. Successive wipings with cotton pads were performed on surfaces contaminated with simulated contaminants to estimate the influence of the different parameters. Results highlight the importance of surface roughness over the other considered parameters

Experimental study of particle deposition kinetics in the primary circuit of the CIRENE loop and comparison with OSCAR V1.2 code simulations

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The OSCAR code: modelling and simulation of the corrosion product behaviour under nucleate boiling conditions in PWRs

International audienceThe PWR primary circuit materials are subject to general corrosion leading to metallic elements (mainly Fe, Ni, Cr, Mn, Co) transfer and subsequent ion precipitation and particle deposition processes on the primary circuit surfaces. When deposited on fuel rods, these species are activated by neutron flux. Thus, crud erosion and dissolution processes result in primary coolant activities. During a normal operating cycle in an EDF PWR, the volume activities in the coolant are relatively stable (usually about 10-30 Bq.g-1 in Co-58). During some cycles (depending on fuel management), a significant increase in Co-58 and Cr-51 volume activities can be observed (10 to 100 times the ordinary volume activities). This increase in volume activities is due to local sub-cooled nucleate boiling on the hottest parts of some fuel assemblies. Indeed, it is well known that nucleate boiling enhances the deposition and precipitation processes. Crud growth in boiling conditions is related to different phenomena: Enrichment: concentration increases at crud-coolant interface, Boiling deposition by vaporisation: fluid vaporization at wall results in particle deposition and ion precipitation. As the crud growth, boiling occurs in the crud itself, so do the ion precipitation and deposition of the small particles. Boiling deposition by trapping: some of the small particles trapped at the interface bubble/fluid make deposit when a bubble leaves the wall. Enhanced erosion: turbulences generated by bubbles collapsing close to the wall and spalling above a certain deposit thickness enhance erosion; it results in the release of particle agglomerates.These phenomena have been modelled in the OSCAR V1.3 code. In this article, we present the modelling of these mass transfer mechanisms in boiling conditions and we show that the crud amount on fuel rods and the volume activities in the primary coolant in case of boiling calculated by OSCAR are in accordance with the experimental feedback on French PWRs

Modelling of crud growth phenomena on PWR fuel rods under nucleate boiling conditions

International audiencePWR primary circuit materials undergo general corrosion leading to a release of metallic element release and subsequent process of particle deposition and ion precipitation on the primary circuit surfaces. The species accumulated on fuel rods are activated by neutron flux. Consequently, crud erosion and dissolution induce primary coolant contamination. In French PWRs, 58 Co volume activity is generally low and almost constant (< 30 MBq.m-3) throughout an ordinary operating cycle. In some specific cases, a significant increase in volume activity is observed after the middle of a cycle (100-1000 MBq.m-3 for 58 Co) when conditions for nucleate boiling are locally reached in certain fuel assemblies. Indeed, it is well known that nucleate boiling intensifies the deposition process. The thickness of the crud layer can reach some micrometers in non-boiling areas, whereas it can reach 100 micrometers in boiling areas

The OSCAR code: modelling and simulation of the corrosion product behaviour under nucleate boiling conditions in PWRs

International audienceThe PWR primary circuit materials are subject to general corrosion leading to metallic elements (mainly Fe, Ni, Cr, Mn, Co) transfer and subsequent ion precipitation and particle deposition processes on the primary circuit surfaces. When deposited on fuel rods, these species are activated by neutron flux. Thus, crud erosion and dissolution processes result in primary coolant activities. During a normal operating cycle in an EDF PWR, the volume activities in the coolant are relatively stable (usually about 10-30 Bq.g-1 in Co-58). During some cycles (depending on fuel management), a significant increase in Co-58 and Cr-51 volume activities can be observed (10 to 100 times the ordinary volume activities). This increase in volume activities is due to local sub-cooled nucleate boiling on the hottest parts of some fuel assemblies. Indeed, it is well known that nucleate boiling enhances the deposition and precipitation processes. Crud growth in boiling conditions is related to different phenomena: Enrichment: concentration increases at crud-coolant interface, Boiling deposition by vaporisation: fluid vaporization at wall results in particle deposition and ion precipitation. As the crud growth, boiling occurs in the crud itself, so do the ion precipitation and deposition of the small particles. Boiling deposition by trapping: some of the small particles trapped at the interface bubble/fluid make deposit when a bubble leaves the wall. Enhanced erosion: turbulences generated by bubbles collapsing close to the wall and spalling above a certain deposit thickness enhance erosion; it results in the release of particle agglomerates.These phenomena have been modelled in the OSCAR V1.3 code. In this article, we present the modelling of these mass transfer mechanisms in boiling conditions and we show that the crud amount on fuel rods and the volume activities in the primary coolant in case of boiling calculated by OSCAR are in accordance with the experimental feedback on French PWRs

Optimized high temperature oxidation and cleaning at BUGEY 3

International audienceAs a part of the EDF Source Term Reduction project, an experimental procedure was carried out at BUGEY 3 further to the steam generator replacement. This innovative procedure consists in theory in two complementary phases /1/: Phase 1: a SG tubes optimized oxidation performed during pre-critical hot functional tests (basic and reducing chemistry) aims to generate an as protective as possible inner oxide layer allowing to reduce the later nickel release, Phase 2: a cleaning procedure of the primary circuit performed under acid and reducing chemical conditioning at 170°C intends to dissolve and eliminate the outer oxide layer by a simultaneous purification. The objective of such a procedure is to reduce corrosion products inventory (mainly nickel) generated by the first SG tube oxidation during hot functional tests and first operation months by carrying out an appropriate cleaning procedure. Gains were expected not only on RCS and auxiliary systems contamination, dose rates and thus collective dose but also on next outages duration. The objective of this paper is to describe the process implementation at BUGEY 3: effective procedure put in place, monitoring program (chemistry and dose rate measurements, EMECC campaign) and firsts results

Modelling of crud growth phenomena on PWR fuel rods under nucleate boiling conditions

International audiencePWR primary circuit materials undergo general corrosion leading to a release of metallic element release and subsequent process of particle deposition and ion precipitation on the primary circuit surfaces. The species accumulated on fuel rods are activated by neutron flux. Consequently, crud erosion and dissolution induce primary coolant contamination. In French PWRs, 58 Co volume activity is generally low and almost constant (< 30 MBq.m-3) throughout an ordinary operating cycle. In some specific cases, a significant increase in volume activity is observed after the middle of a cycle (100-1000 MBq.m-3 for 58 Co) when conditions for nucleate boiling are locally reached in certain fuel assemblies. Indeed, it is well known that nucleate boiling intensifies the deposition process. The thickness of the crud layer can reach some micrometers in non-boiling areas, whereas it can reach 100 micrometers in boiling areas