Studies on Important Radionuclides for the Safety of a Radioactive Waste Disposal Site: Correlation Between Easily Measurable Gamma Emitters and Long-Lived Radionuclides

To comply with the regulations laid down by the French safety authorities for a national surface disposal site, one must obtain a good evaluation of the activity of the long-lived nuclides in each individual package. Because this cannot be done on a routine basis by direct nondestructive measurements, experiments are being conducted in France to calculate the activity of long-lived nuclides from the measured activity of “key” nuclides (⁶⁰Co and ¹³⁷Cs). This is achieved through the use of scaling factors and correlation functions that are calculated from the analysis of a limited number of representative waste samples. The first results obtained for some typical French pressurized water reactor radioactive wastes, including ion-exchange resins, evaporator concentrates, and filter cartridges, are presented. Significant correlations are observed for the ⁶³Ni/⁶⁰Co and ⁹⁴Nb/⁶⁰Co nuclide pairs, while ^I4C does not seem to correlate with ⁶⁰Co. A good correlation between ¹³⁷Cs and ⁹⁰Sr is established for resins, while in the case of filters, only a tendency to correlation appears. This evaluation work is only at a preliminary stage, and much improvement of the results presented here is expected from research programs being carried out in this field by Electricité de France, Commissariat a l’Energie Atomique, and the French National Agency for Radioactive Waste Management in cooperation with the Commission of the European Communities.