Gross alpha determination in radioactive wastes from nuclear power plants using the track registration technique

Low and intermediate level nuclear wastes (ion-exchange resins and evaporator concentrates) essentially contain beta and gamma emitters, with very few alpha emitters. Several techniques may be used to determine gross alpha activity but, in this case, solid-state nuclear track detectors (SSNTDs) are a suitable technique for gross alpha determination because track detectors are not sensitive to beta and gamma emitters. Also, this technique is simple and inexpensive. In this paper, we studied the parameters (background, efficiency and self-absorption) that could affect the gross alpha determination using SSNTDs for both sample preparation methods, the “dry method” with tensioactives and the “wet method”. For the “dry method”, a self-absorption curve for 241Am standard was prepared using a set of varying thickness of sodium salt and for two different tensioactives: Tween®20 and Teg. The results showed that, below 1mg/cm2, the self-absorption factor can be considered similar for both tensioactives and equal to unity. Several detectors for gross alpha determination were compared and we found that the most suitable techniques were ZnS(Ag) solid scintillator and track detectors. Both detectors were used to compare radioactive waste samples. Finally, the proposed methods (“dry method” with Teg tensioactive and “wet method”) using track detectors were tested by analysing the gross alpha activity of several radioactive wastes.