Trapping measurements of volatile iodine by sand bed and metallic filters

International audienceSeries of experimental tests were performed to measure the efficiency of volatile iodine trapping on sand bed filters and metallic filters. These filtering media are used in French nuclear power plants to mitigate releases in case of severe accident. The results show that molecular iodine is more easily trapped than methyl iodide due to its high chemical affinity with stainless steel or with silver and cesium cations included in the filter medium. For methyl iodide, the efficient of trapping is low

Determination of correction factors for alpha activity measurements in the environment (conditions of high dust loading)

Within the framework of a French national monitoring program to survey the man-made radioactivity in the environment, several power plants and research facilities on the territory use environmental air monitors for unwanted releases of radioactive aerosols. High sensitivity and lack of false alarms are all important for environmental air monitors. The project aims to conduct investigations to improve operation of environmental air monitors, particularly under conditions where a lot of nonradioactive dust may be deposited on the filters (conditions of high dust loading). The dust may increase the frequency with which filters must be changed and can lead to an underestimation of the real activity. This underestimation is due to deteriorated alpha energy resolution and response specificity to the radionuclides of interest. In this study, our objective was to find experimental correction factors for the degraded activity measurements taking into account the alpha absorption in the dust loading. © The Author 2010. Published by Oxford University Press. All rights reserved

Experimental and simulation methods to evaluate the alpha self-absorption factors for radioactive aerosol fiber filters

Air sampling for particulate radioactive material involves collecting airborne particles on a filter in order to measure the radioactivity in the environment or in working areas. The amount of alpha radioactivity collected on the sampling filter is frequently determined by global alpha-particles measurements. Several factors can affect the alpha energy while passing through the filter to reach the detector. The most affecting factor on the alpha spectrum degradation is the absorption of alpha particle energies in the filter fibers. The fibers' density can range from 1 to 9 mg cm-2. The counting losses can accordingly be important, and the global activity in the filter can be underestimated. The complexity of the experiments and the diversity of the filter types, filtration conditions as well as detector types used for survey incite us to formulate a numerical model to simulate the correction factors of the degraded activity. Comparisons between experimental and simulated correction factors for a commonly used filter are presented. The good agreement found between experimental and calculated values validates the method in the studied conditions. © 2009 Elsevier Ltd. All rights reserved

Rétention of radioactive methyl iodide in the context of nuclear industry: on the quantification of isotopic exchange contribution inside activated carbons

International audienceIn this paper, the behavior of TEDA and KI impregnated activated carbons (AC) towards the capture of methyl iodide (CH3I) is investigated using complementary methodologies. On the one hand, radioactiveCH3I decontamination factors (DF) were determined at different water vapor contents for variouscommercial activated carbons. A combination between the retention performances and the physicochemical properties is performed to gain insights about the AC influencing parameters on Y-labelled CH3I capture. On the other hand, new experimental methodologies are developed in order to measureboth stable and Y-labelled CH3I breakthrough curves (BTC) for KI or TEDA impregnated AC {T = 20 -30 °C, dry conditions}. These works improve the knowledge about the role played by KI and TEDA. Indeed, TEDA is found to enhance CH3I retention especially under humid conditions and, for the firsttime, the KI contribution is isolated and quantified: the KI action towards 131I is highlighted after the breakthrough phase through an isotopic redistribution mechanism

Rétention of radioactive methyl iodide in the context of nuclear industry: on the quantification of isotopic exchange contribution inside activated carbons

International audienceSince the Fukushima accident, an interest has been renewed for R&D works on radioactive iodine releases mitigation by adsorbents. More particularly, the behavior of KI and TEDA co-impregnated activated carbons (AC) employed within nuclear facilities to trap volatile iodine species (I2/CH3I), is studied. Indeed, uncertainties remain about the influencing parameters and the involved retention mechanisms. We adopted complementary approach based on both experimental and theoretical investigations. Numerous techniques were used to probe the intrinsic AC properties. Moreover, a step-by-step methodology was employed for CH3I retention experiments owing to the complexity of radioactive iodine handling. Batch reactor studies were conducted first towards stable CH3I. These data were useful to probe physisorption and chemisorption phenomena. A specific model was then deduced from these studies to predict breakthrough curves for a non-impregnated AC. Efforts should be nevertheless performed to implement KI and TEDA reactions. Therefore, complex test benches (decontamination factors (DF), breakthrough curves) were developed within the PERSEE facility to study CH3127+131I dynamic adsorption on KI and TEDA simply impregnated AC. These results improve the knowledge about the role played by KI and TEDA. Indeed, TEDA was found to enhance CH3I retention under humid conditions and, for the first time, the KI contribution was isolated and quantified: the KI action towards 131I was highlighted after the breakthrough phase through an isotopic redistribution mechanism. We will attempt to finely quantify the contribution due to isotopic exchange. The challenge is to identify new synthesis strategies promoting this reaction before its kinetic modelling under various conditions

Rétention d’espèces Volatiles d'iode Par Les Charbons Actifs Imprégnés

International audienceThe efficient capture of volatile iodine species (I2, CH3I) potentially released from nuclear facilities is a major issue to improve the nuclear safety. In that respect, activated carbons (AC) have been used for the removal of iodine within ventilation networks of nuclear facilities. More particularly, the commonly used nuclear grade AC are co-impregnated with potassium iodide (KI, 1 wt%) and triethylenediamine (TEDA, < 5 wt%) [1]. However, uncertainties remain about the contribution of the involved retention mechanisms (more particularly, the isotopic exchange for KI-impregnated AC). Hence, the present study aims to gain insights into the importance of this reaction as a comparison with other adsorption mechanisms (physisorption and chemisorption). A specific methodology has been implemented (Fig. 1 (A)). In a first part, the behavior of characterized AC towards the retention of methyl iodide under a large panel of configurations (Fig. 1 (A)) was explored. Preliminary experiments using standardized test methodologies for nuclear grade AC have shown the importance of isotopic exchange phenomenon for the capture of γ-labeled CH3I under humid conditions (T = 20°C, R.H. = 90%, Fig. 1 (B)). The quantification of this reaction has to be assessed by comparing the breakthrough curves obtained in both cases (radioactive and not-radioactive CH3I). Accordingly, a test bench is under development and validation. This talk will describe the used strategies to obtain the first data relevant to the quantification of isotopic exchange phenomena. More precisely, the methodologies, the different test benches as well as the first results showing the importance of this phenomena in the retention of radioactive iodine will be presented

Application of the monte carlo method to study the alpha particle energy spectra for radioactive aerosol sampled by an air filter

An alpha spectrometer including a semi-conductor detector is commonly used for measurements of the emergent alpha particles from an air filter, on which was sampled a radioactive aerosol. The alpha spectrometry and the detection efficiency are necessary input information for real radioactivity measurements. The MCNPX code based on the Monte Carlo method has been applied to simulate the detection process in order to obtain spectrum peaks and determine the detection efficiency for modeled geometry. First simulations with MCNPX have been carried out in order to validate the alpha particle energy spectrometry of an electrodeposited solid source and an initial simulated filter model. Furthermore, to improve our first filter model, the real spatial distribution of radioactive aerosols across the filter thickness, found experimentally, is taken into account in a multi-layer filter model. Such an alpha particle distribution allows achieving an adequate simulation of the filter. Comparison between measured and simulated alpha spectra highlights the good agreement in spectral parameters and in detection efficiency even under different aerosol spatial distributions inside the volume of the filter. © 2009 Health Physics Society

Rétention d’espèces Volatiles d'iode Par Les Charbons Actifs Imprégnés

International audienceThe efficient capture of volatile iodine species (I2, CH3I) potentially released from nuclear facilities is a major issue to improve the nuclear safety. In that respect, activated carbons (AC) have been used for the removal of iodine within ventilation networks of nuclear facilities. More particularly, the commonly used nuclear grade AC are co-impregnated with potassium iodide (KI, 1 wt%) and triethylenediamine (TEDA, < 5 wt%) [1]. However, uncertainties remain about the contribution of the involved retention mechanisms (more particularly, the isotopic exchange for KI-impregnated AC). Hence, the present study aims to gain insights into the importance of this reaction as a comparison with other adsorption mechanisms (physisorption and chemisorption). A specific methodology has been implemented (Fig. 1 (A)). In a first part, the behavior of characterized AC towards the retention of methyl iodide under a large panel of configurations (Fig. 1 (A)) was explored. Preliminary experiments using standardized test methodologies for nuclear grade AC have shown the importance of isotopic exchange phenomenon for the capture of γ-labeled CH3I under humid conditions (T = 20°C, R.H. = 90%, Fig. 1 (B)). The quantification of this reaction has to be assessed by comparing the breakthrough curves obtained in both cases (radioactive and not-radioactive CH3I). Accordingly, a test bench is under development and validation. This talk will describe the used strategies to obtain the first data relevant to the quantification of isotopic exchange phenomena. More precisely, the methodologies, the different test benches as well as the first results showing the importance of this phenomena in the retention of radioactive iodine will be presented

Rétention d’espèces Volatiles d'iode Par Les Charbons Actifs Imprégnés

International audienceThe efficient capture of volatile iodine species (I2, CH3I) potentially released from nuclear facilities is a major issue to improve the nuclear safety. In that respect, activated carbons (AC) have been used for the removal of iodine within ventilation networks of nuclear facilities. More particularly, the commonly used nuclear grade AC are co-impregnated with potassium iodide (KI, 1 wt%) and triethylenediamine (TEDA, < 5 wt%) [1]. However, uncertainties remain about the contribution of the involved retention mechanisms (more particularly, the isotopic exchange for KI-impregnated AC). Hence, the present study aims to gain insights into the importance of this reaction as a comparison with other adsorption mechanisms (physisorption and chemisorption). A specific methodology has been implemented (Fig. 1 (A)). In a first part, the behavior of characterized AC towards the retention of methyl iodide under a large panel of configurations (Fig. 1 (A)) was explored. Preliminary experiments using standardized test methodologies for nuclear grade AC have shown the importance of isotopic exchange phenomenon for the capture of γ-labeled CH3I under humid conditions (T = 20°C, R.H. = 90%, Fig. 1 (B)). The quantification of this reaction has to be assessed by comparing the breakthrough curves obtained in both cases (radioactive and not-radioactive CH3I). Accordingly, a test bench is under development and validation. This talk will describe the used strategies to obtain the first data relevant to the quantification of isotopic exchange phenomena. More precisely, the methodologies, the different test benches as well as the first results showing the importance of this phenomena in the retention of radioactive iodine will be presented