Qualification in a reppresentative environment of an alpha spectrometer prototype operating at ambient air pressure
Résumé
In recent years, the CEA has been working on the development of alpha spectrometry operating at ambient air pressure to improve the in situ radiological characterization of historical waste contaminated with alpha emitters. This non-destructive measurement technique aims, through spectrometric selectivity and the use of a grid collimator, to identify the same radionuclide combinations as alpha spectrometry in a vaccum chamber, namely 239Pu + 240Pu, 241Am + 238Pu and 244Cm. Contrary to a laboratory measurement, the measurement is carried out on smears involving a degradation of the alpha spectrum due to the phenomenon of self-absorption of alpha particles within the contaminant and the sample support. In previous works, a first prototype has been developed and qualified in laboratory with electrodeposited sources. The prototype, designed by Monte Carlo simulation, consists of a grid with a collimation height of 0.5 cm or 0.7 cm and an apothem of 1 mm placed in front of a CAM PIPS detector with an active surface of 2000 mm² or a TCAM PIPS detector with and active surface of 1700 mm². This article presents the results of the tests carried out in order to qualify this prototype in a representative environment. These tests consisted in carrying out measurements in glove box on various smear samples of nuclear waste obtained beforehand using remote manipulators. Different parameters affecting the quality of the measured alpha spectra have been studied such as the type of contaminant sampling support (cellulose, nylon, PTFE or glass microfiber filter, or adhesive support), the conditioning of the samples to avoid contamination of the prototype and the duration of the measurement in order to define a minimum counting statistic. Although the measured alpha spectra are degraded compared to those measured in laboratory on electroplated sources, the qualitative analysis shows that it is possible to identify the three groups of radionuclides of interest, i.e. 239Pu + 240Pu, 241Am + 238Pu and 244Cm. Furthermore, a spectral deconvolution with the COLEGRAM software allowed to obtain quantitative information necessary to estimate the ratio of each radionuclide group to the total alpha emitters for each sample. These results of non-destructive alpha spectrometry measurements are in agreement with the results of radiochemical analysis performed in laboratory. The first results obtained with the alpha spectrometer prototype in a representative environment are promising and allow to consider its future implementation for waste categorization.