|Acidic destruction of the matrix (HCl, HNO3, H2SO4, HF, aqua regia)|
|Ashing (combustion of organic compounds)|
|Precipitation formation (oxides, sulphides, oxalates, etc.)|
|Ion exchange and extraction chromatography|
|Step-by-step detection of gamma-emitting impurities|
In most disposal facilities the long lived α- and b-emittingradionuclides have the most restrictive inventory limits, because they do not decayappreciably in the lifetime of the facility. These isotopes are called difficult-to-measure (DTM) isotopes, because their activity concentrations are usually several order of magnitude lower than the „bulk” (mostly 60Co + 137Cs), due to a) low formation probability (fission or activation); b) low „escape” probability (from an intact fuel rod); c) low specific activity (as a result oflong half-life). Furthermore, they are either pure alpha/beta emitters or have only very low energy and intensity X-ray or γ-ray lines. As a result, the determination of their concentrations requires a radiochemical separation of various complexity.
Radiochemical separation methods for a large number of DTM isotopes are being developed since the mid 1990s based on the evaporator concentrate samples of Paks NPP, Hungary. Whenever possible, combined methods (for the determination of multiple isotopes from the same aliquot) have been developed for the reduction of unnecessary human radiation exposure, as well as of secondary nuclear waste. The methods listed in the previous sections are more or less “final”, with average chemical yields as high as 55-95%, depending on the sample matrix. In most cases, they can also be applied to spent ion exchange resin and sludge samples as well.
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