AbstractsEngineering

Strontium-90 (90Sr) is an anthropogenic contaminant that is present in the environment from spent nuclear fuel, radioactive waste, and atmospheric fallout from nuclear weapon tests and major nuclear incidents. Strontium-90 is one of the most hazardous and radiotoxic radioisotopes, due to its relative long half-life and high mobility in the environment. Because of its significant health hazards, 90Sr needs to be measured accurately. The radioanalytical capabilities for the determination of 90Sr in the environment are challenged by matrix interferences, which often result in less effective, long, and tedious determination methods. Moreover, a number of shortcomings were found in the current seawater 90Sr methods following the Fukushima Daiichi nuclear power accident in March 2011. Thus, the need for effective, rapid, and simple procedures is on-going. In the present dissertation, the advancements in modern technologies were used to minimize some of the gaps in current radioanalytical capabilities used for the determination of 90Sr in water. The present work considered techniques at moderate and low levels of detection, and in each case undertook to produce methodologies with increased speed of analysis and greater efficiency. A triple-to-double coincidence ratio (TDCR) Čerenkov counting technique using a Hidex liquid scintillation counter was developed for the indirect determination of 90Sr from 90Y at equilibrium activity concentrations of 90Sr-90Y. The technique was fast and simple with excellent performance test results. For low level 90Sr determination in water, pre-concentration using semi-selective co-precipitation and highly selective extraction chromatography techniques were used. Freshwater 90Sr was determined directly as well as indirectly from 90Sr-90Y equilibrium activity concentrations. The method employed (1) co-precipitation of freshwater 90Sr-90Y using calcium phosphate in alkaline conditions; (2) sequential purification of 90Sr and 90Y on Sr-Resin® and DGA-N® extraction chromatography columns, respectively; and (3) detection of 90Sr by liquid scintillation assay (LSA) at two different time intervals and that of 90Y using both Čerenkov counting and LSA. Seawater 90Sr was determined indirectly from 90Y at equilibrium activity concentrations of 90Sr-90Y. The method used (1) co-precipitation of seawater 90Y using calcium carbonate and hydrous titanium oxide in alkaline conditions; (2) purification of 90Y on DGA-N® resin; and (3) detection of 90Y using both Čerenkov counting and LSA. The methods’ performance evaluation demonstrated excellent agreement between measured and expected activities of spiked 90Sr-90Y standard solution. Effective implementation of the freshwater method on natural water samples containing a wide range of 90Sr-90Y concentrations was also achieved. Le strontium-90 (90Sr) est un contaminant anthropogénique présent dans l’environnement et provenant de combustible nucléaire usé, de déchets radioactifs, et de retombées atmosphériques des essais d’armements nucléaires et des…