Influence of the decontamination of a high radioactive solution from Cesium on analytical performances
Résumé
The high rate of irradiation of certain samples is essentially due to the presence of the $^[137}$Cs. Removing selectively Cs from these samples provides several advantages 1- a weaker dilution to make possible the samples manipulation and to carry out their analyses by techniques usually implanted in glove boxes (ICP-AES, ICP-QMS, radiometry, etc.), 2- a lower detection limit of analyzed elements, 3- a minimization of the Compton effect on gamma spectra.The method of cations / Cs$^+$ separation is very important. It must lead to the highest possible cesium decontamination factor, the quantitative recovery of the other elements and the lowest possible dilution factor of the sample. The implemented method is extraction chromatography using the AMP-PAN resin (ammonium molybdophosphate embedded in polyacrylnitrile). It consists in adding the sample, firstly adjusted at a nitric acidity of 2M on a AMP-PAN column, then in adding a washing solution ([HNO$_3$] = 2M). During these two stages, the cesium is expected to be retained by the chromatographic support whereas the other cations cross the column.The efficiency of this method was tested by comparison of analyses by gamma and alpha spectrometry, by X-ray fluorescence and by ICP-AES realized with a sample, taken in a storage tank of fissions products, before and after its passage on an AMP-PAN column.The results of analyses were very satisfactory. A strong decontamination of the initial sample from $^{137}$Cs (FD > 5.104) and a quasi-quantitative recovery of the other analyzed elements were observed. The gamma spectra showed in particular several radionuclides which were not quantified on the initial sample and led to detection limits twenty times lower.The description of the chromatographic cycle on AM-PAN resin and all the analyses will be presented during this talk.
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