Leaching tests result interpretation

There are a great number of leaching tests. The experimental conditions and interpretation of results are dependent on the application context and scientific objectives, as follows ... 

Most leaching tests are performed in a laboratory. Whilst leaching tests are designed and intended to reflect reality, there is a limited amount of data available from field tests which can be used to correlate with those from laboratory tests hence validate their performance in relation to the situation in the field. One of the most common errors in the interpretation of results from leaching tests is to assume that, based on the commonly used shaking test at a liquid to solid ratio of 10 1, the resultant leachant is representative of the concentration of contaminants that will emerge from the base of a deposit of the material tested. Even if it is assumed that the factors such as leachant used, pH and redox are correctly applied in the test, the concentrations of contaminants in the leachate represent an average of the concentration which will be leached... 

The interpretation of the results from leaching tests cannot be carried out without an understanding of the details of the test including those parameters which have been controlled or not controlled, an understanding of how the test conditions relate to reality and an understanding of how the conditions tested may change in the short, medium or long-term. 

The tests of a capsule design may be performed with simulated radioactive material. The term simulated means a facsimile of a radioactive sealed source, the capsule of which has the same construction and is made with exactly the same materials as those of the sealed sonrce that it represents, but contains, in place of the radioactive material, a substance with mechanical, physical and chemical properties as close as possible to those of the radioactive material and containing radioactive material of tracer quantities only. The tracer should be in a form soluble in a solvent which does not attack the capsule. One procedure described in ISO 2919 [1] utilizes either 2 MBq of Sr-90 and Y-90 as soluble salt, or 1 MBq of Co-60 as soluble salt. When possible, shorter lived nnclides should be used. However, if leaching assessment techniqnes are used, care needs to be taken when interpreting the results. The effects of scaling will have to be introduced, the importance of which will depend upon the maximum activity to be contained within the capsule and also the physical form of the intended capsule contents, particularly the solubility of the intended capsule contents as compared with the tracer radionuclide. These problems can be avoided if volumetric leakage tests are used (see paras 603.3 and 603.4). Typically, tests for special form radioactive material are performed on full scale sealed sources or indispersible soUd material because these are not expensive and the results of the tests are easy to interpret. 

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