KI and TEDA influences towards the retention of radiotoxic CH3I by activated carbons.

Activated carbons (AC) are widely used within the ventilation networks of nuclear facilities to trap volatile iodine species. In this paper, the performances of various commercial activated carbons towards the trapping of γ-labelled methyl iodide were evaluated in semi-pilot scale under different R.H. according to normalized procedures. A combination between the retention performances and the physico-chemical properties as deduced from several techniques was performed to gain insights about the AC influencing parameters on γ-CH3I capture. Different trends were obtained depending on the impregnant nature and the studied conditions. A high sensitivity of KI/AC towards water vapor was outlined. At R.H. = 40%. The enhancement of water uptake by KI/AC as deduced from water adsorption experiments, leads to decrease the available microporosity for CH3I physisorption, inducing therefore the reduction of performances as a function of KI content at these conditions. At R.H. = 90%, the adsorption mechanism was found to be governed by isotopic exchange reaction since 90% of the microporosity was occupied by water molecules. Therefore, a slight increase of DF was obtained in these conditions. This sensitivity was found to be of a lesser extent for TEDA/AC displaying the highest retention performances whatever the studied condition.

Effects of water vapour and temperature on the retention of radiotoxic CH3I by silver faujasite zeolites.

In this work, Ag/X and Ag/Y faujasite zeolites were evaluated as candidate sorbents for the retention of methyl iodide under conditions close to those expected in a severe nuclear accident. Different categories of tests were conducted from laboratory to semi-pilot scales. First, the effects of temperature and water vapour on the CH3I retention/decomposition mechanism were investigated under lab-scale conditions. More specifically, the CH3I adsorption capacities and the fate of its main decomposition products (oxygenated compounds and alkanes) were measured under dynamic conditions at different temperatures (35, 100 and 250 °C). Then, the decontamination factors of Ag/X and Ag/Y silver faujasites exchanged with different silver contents were monitored according to the time on stream using a very low CH3I concentration (1 ppmv). Finally, a parametric study was conducted at semi-pilot scale using realistic [CH3I]/[H2O] molar ratio ≈ 10-6 and temperatures in the range 20-90 °C. Those experiments were helpful in order to assess the effects of some important parameters relevant to the adsorbents or operating conditions.

Investigations of the MGy dose level radiation effects on the photometric budget of a radiation-hardened CMOS-based camera.

We studied the impact of ionizing radiation at high dose levels (megagray, MGy) on the photometric budget of a radiation-resistant complementary metal oxide semi-conductor (CMOS)-based camera. This is achieved by measuring the radiation-induced degradation of each subpart, namely its illumination system, its optical system, and its CMOS image sensor. The acquired experimental results allow performing a rather realistic simulation of the radiation effects at the system level. Thanks to appropriate mitigation techniques, limited image darkening and color change are obtained at MGy dose levels. The presented results confirm the feasibility of a CMOS-based camera able to resist to MGy dose level of ionizing radiations with an acceptable degradation of the image quality, opening the way to its implementation in the most challenging harsh environments.

Production of reference sources of radioactive aerosols in filters for proficiency testing.

In the framework of the organization of proficiency testing, filters with deposits of 137Cs and 90Sr+90Y radioactive aerosols have been submitted to laboratories for radionuclide measurement. Procedures for the special preparation and characterization of filters have been developed. The different steps of filter preparation, determination of the deposited radionuclide activity and characterization of the homogeneity of these deposits are presented. This method of filter preparation can also be used in the production of secondary standards, whose properties are more adapted to the needs of laboratories measuring radioactivity in filters than are the solid sources that they typically use.

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.