Verlag des Forschungszentrums Jülich
JUEL-3806
Standard correction procedures for gamma-ray attenuation are often performed by drum weighing or calculation of corrective factors based on 'simple' assumptions regarding the distribution of density and activity in the waste. In the case of heterogeneous activity and/or matrix distribution uncertainties will be introduced when applying standard correction procedures that can lead to significant errors in the activity determination especially for medium and high density waste combined with low and medium gamma-ray energies (below ca. 500 keV).
The main objective of the R & D project was to develop and test methods that will decrease systematic uncertainties and bias, caused by a lack of information on the activity and matrix distribution, by taking into account the relevant characteristics of the waste package under inspection. For the applicability of the improved gamma assay techniques in routine operation two important requirements were defined: The methods should keep the inspection time in an acceptable range and the implementation into existing systems should be possible without extensive hardware modifications and at reasonable costs.
A modelling software (SOLIDANG, /SCK-1/) was used to calculate the detection efficiency of 'standard' gamma scanning systems which helped to design, evaluate and optimise new scanning techniques. Validation of the simulation software has proven that SOLIDANG can be used as an efficient tool for performance evaluation and optimisation of gamma assay techniques. With this software the quantitative influence of relevant parameters on the assay result was investigated with reduced experimental effort. The results lead to a better understanding of possible sources of bias.
Within the R & D project several advanced NDA-methods have been developed, tested and implemented into prototype assay systems. These techniques involve multi-energy transmission measurements of the drum and special scanning modes which reveal more information about the density and activity distribution inside the drum.
Performance assessment was carried out on well-defined and specially designed mock-up configurations and on selected drums under routine 'field' conditions. The results showed significant improved accuracy for the new developed assay techniques compared to 'conventional' state-of-the-art gamma scanning procedures.
Sanden, Hans-Jürgen; Caspary, Guido; Kroth, Kornelius; Bücherl, Thomas
Optimisation of gamma assay techniques for characterisation of radioactive waste packages
72 S., 2000
Conditioned radioactive waste has to meet the specifications and acceptance criteria defined by national regulatory and management authorities. Gamma scanning is one of the most widely used non-destructive assay techniques for routine quality checking of radioactive waste drums. The result of gamma scanning measurements is strongly influenced by the gamma attenuation in the waste matrix.
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