Verification of the sampling procedure for waste and industrial material

Abstract

In accordance with ISO/IEC 17025:2017 - General requirements for the competence of testing and calibration laboratories, the laboratory needs to verify its ability to properly perform methods before introducing them, by ensuring it can achieve the required performance (article 7.2.1.5). Also, if a laboratory carries out a sampling of a material, it needs to have a sampling plan and method established (article 7.3.1). In laboratories dealing with radionuclide content testing, the sampling does not affect the testing results directly, but the sampling procedure has to ensure that the taken and later measured sample adequately represents the tested material. In order to verify the sampling procedure for the needs of radiological tests, a sampling of red mud (13 samples) and bauxite ore (6 samples) was conducted in the aluminum factory “Alumina ltd”, Zvornik, Bosnia and Herzegovina in June 2021. In accordance with the established sampling procedure, GPS coordinate and ambient dose rate were recorded for each sample. Samples were prepared in accordance with IAEA, TRS 295 (1989), placed into identical PVC cylindrical boxes and measured by HPGe gamma spectrometer. Spectra of bauxite and red mud were recorded in 10 consecutive measurements for 21000 s and 6000 s, respectively, in order to achieve good statistic. For the purpose of sampling procedure verification, the counting rates per unit mass in the recorded spectra were compared. For each measurements series, the total counts in the spectrum as well as individual energies mean value and standard deviations were calculated. After the measurements were completed, the average of the each individual series mean values and the associated/corresponding standard deviation were calculated. The measurement result of each individual series is considered satisfactory if, taking into account the calculated standard deviation, it is within +/- two standard deviations of the average of the mean values. The obtained results verified the sampling procedure, i.e. it was shown that the applied sampling procedure ensures the representativeness of the bulk material