Abstract
Micro-particles (of μm size) are contaminants in the primary coolant of light water reactors and have their origin in corrosion processes. These micro-particles can be separated by filtration through Nuclear Track Micro Filters (NTMF) with pores having well-defined sizes (e.g. 2 μm). A rapid method for determining the α-activity in the coolant was developed. The α-sources are mostly adsorbed on micro-particles and can be separated by filtration. Afterwards, the activity can be directly measured α-spectrometrically. (90 ± 10) % of the total α-activity of the coolant is retained on the surface of the NTMF. Detailed investigations show differences of the measured α-activity in duplicate samples by a factor of two. Differences of one order of magnitude in the determination of α-activity by the filtration method and by conventional analytical chemistry are also observed. The first difference is caused by inhomogeneity of the coolant itself, and the latter by adsorption of actinides on the sample container surface. Correlations between α-activity due to transuranium elements and γ-activity due to corrosion products were studied over long periods. However, no relationship could be found. The solid particles separated by NTMF were analyzed by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray analysis (EDXA). The chemical composition of these particles shows the usual chemical composition of primary circuit structural materials, but some particles seem to be simple conventional dust (Si, O, Ca. ….). The distribution of α-activity on loaded NTMF samples was investigated by α-autoradiography. Results of these investigations show that the α-emitters are geometrically concentrated, i. c., they form either conglomerates (e.g. colloids) or they arc adsorbed on the surface of micro-particles. Particles identified by autoradiography as carrier of α-emitters were analyzed by EDXA, too.
