The Usage of Scaling Factors for Determining Nuclide Content for Clearance or Disposal

The benefits of using validated scaling factors, also denoted nuclide vector or fingerprint, are that the number of samples and analyses for each waste package or item can be significantly reduced. The basis for a validated nuclide vector is however sampling and analyses as well as a theoretical model which includes the connection between measured and non measured nuclides. To develop nuclide vectors, the origin and history of the item/waste package must be sufficiently known. When using a nuclide vector for calculation the nuclide content for a waste package aimed for disposal it is important to communicate with the competent authority and the owner of repository to get acceptance of the theoretical model as well as the list of nuclides. As a nuclide vector for clearance is regulated by the clearance regulations, the nuclides with high clearance levels and low scaling factors will not influence clearance of material and can therefore be screened from the full vector. A screened nuclide vector has limitations in use as the scaling factor will change with time. When time elapse screened nuclides may increase in importance for clearance and it is therefore important to save the original vector and rescreen it if it is to be used later. There are also a few disadvantages of the nuclide vector methodology, the obvious one is that it is easy to become overconfident in the application of the nuclide vector. When the sampling and analyses are evaluated, there will be a distribution in the results and a decision about the level of conservatism in the vector has to be decided. If the dispersion of data is too large the needed conservatism will be too large and render the vector useless. This will be solved by dividing the nuclide vector into two or more nuclide vectors. (author)