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Construction and Testing of a Computer Tomography Assembly for Routine Operation

Objective

The decisive criterion for acceptance of radioactive waste packages in an underground repository is the knowledge of the specific activity of the conditioned waste and the total activity of the waste package which in the case of a homogeneous waste matrix is normally straightforward. In the case of shielded structures or inhomogeneous fillings, the calculation must include shielding factors which range from 1 for homogeneous filling to 20. A better estimation of the shielding properties by computer tomography is the aim of this contract. The objective is a direct measurement of the distribution of and m/g or m in shielded structures and heterogeneous fillings of waste drums by attenuation measurement and computer tomography. The application of computer tomography (CT) the g-scanner "GERNOD" will be done in close cooperation with groups in KFA and BAM.
Quality control of radioactive waste packages prior to their disposal in underground repositories can be achieved by either non-destructive or destructive analysis of the waste packages. The decisive criterion for acceptance is knowledge of the specific activity of the conditioned waste and the total activity of the waste package. Determination of the specific activity and total activity is straightforward in the case of a homogeneous waste matrix of densities between 0.1 and 3 g/cm{3}. In the case of shielded structures or inhomogeneous fillings, the calculation must include shielding factors which range from 1 for homogeneous filling to 20. This project aims to produce a better estimation of the shielding properties by computer tomography. The direct objective is a measurement of the distribution of specific and total activity in shielded structures and heterogeneous fillings of waste drums by attenuation measurement and computer tomography. Considerations for an extension of the existing gamma scanner for inclusion of computer tomography and tests for the application of existing software programs on this computer are underway. The literature survey led to a reconsideration of the optimum mechanical layout and the best kind of radiation source.
Work programme:

An existing passive gamma-scanner has been modified to obtain gamma ray screening capability by

- addition of a 7 Ci Co-60 gamma source for transmission measurements
- modification of the turntable for the drum and upgrading the mechanical system for translatory movement.
The installation of a suitable computer tomography system for the examination of samples with uncommon composition and density distribution requires
- the development of tomography software
- the design of technical equipment in order to synchronize mechanical movement, countrate measurements and absorption data transfer to the computer
- the visualisation of density and activity distribution and estimating the total activity of the waste drum.
Comparative test measurements are being carried out
- on dummies with different materials for testing purposes
- on typical waste drums with inner shielding structures

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Forschungszentrum Jülich GmbH
Address
Wilhelm-johnen-straße
52428 Jülich
Germany