Trapping measurements of volatile iodine by sand bed and metallic filters

Abstract

A series 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 trapping efficiency is low.

Study of the stability of CsI and iodine oxides (IOx) aerosols and trapping efficiency of small aerosols on sand bed and metallic filters under irradiation

“…These rates are compatible with previous publications [32,33,34] on iodine interaction with steel as they are from one to two orders of magnitude higher than the ones expected for electro-polished steel (and for which the interaction of gaseous iodine is expected to much be slower). It is also compatible with the first part of this work [6] for which it was found that, at 100°C and 35% RH, gaseous I2 was retained on the MF with a DF ~ 10 (i.e. 90% retention in 4 hours).…”

“…1) installed on the French NPPs is a PALL® Corporation product [4]. It consists of 92 filtering elements of 800 mm length and 60 mm diameter each [6,11], with a total filtration geometrical surface of 33 m2 These filtering elements, called "cartridges", are made, from the internal to the external parts, by: (1) a perforated internal grid; (2) a metallic weaved supporting layer; (3) a first filtering metallic medium (PFM FH 200); (4) a second filtering medium (PFM 40) and (5) a metallic weaved protective layer (Cf. left parts of Fig.…”

“…If the conditions on the MF and the sand filter are strong enough to lead to the decomposition of IOx and multicomponent iodine aerosols, it is expected that molecular iodine would be one of the main products of the decomposition reactions (organic iodides may also be formed in the sand filter). It was recently found that gaseous I2 (and CH3I) are not well retained neither by the MF (DF(I2) ~ 10, DF(CH3I) = 1) nor by the sand filter (DF(I2, CH3I) ~ 1 [6]. Another result from FUCHIA program [3] (on a scale 1 sand bed filter) was that, even though I2 is not trapped by the sand itself, it could be adsorbed on the steel surfaces of the line and on the deposited aerosols on the steel/sand surfaces, leading to an estimated DF(I2)line ~ 10.…”

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

“…The PERSeE f acilky [20,22] was used in order to extrapolate the behavior of some selected zeolitic sorl'nts towards the capture of methyl iodide at semi-pilot scale, using conditions closer to severe nuclear accident (relative humidity, y-radiation, temperature). A general scheme of this facility is given in Figure S3 (see ESI).…”

“…Attention was paid to ensure a good dispersion of the zeolitic material within the sand in the sample holder. Preliminary studies have shown that the used sand is totally ineffective for the retention of labelled methyl iodide (DF = 1 [20,22]). The different materials to be tested were placed in the upstream stage, giving the possibility to test simultaneously f< ur different solid mixtures {tested zeolite + sand} (Figure 1).…”