Book/Report

FZJ-2019-01276

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Entwicklung und Bau einer Tomographieanlage für Routinemessungen an radioaktiven Abfallfässern zur Qualitätskontrolle

Eifler, P. (Corresponding author)FZJ*

1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21558

Report No.: Juel-3164

Abstract: Governmental regulations require to specify the radioisotopic inventory of radioactive waste containers to be disposed of in a repository. Therefore, a needemerges to thoroughly examine the containers' contents. This paper describes the work performed at the Forschungszentrum Jülich (KFA) to quality controlradioactive waste drums by applying tomography techniques. In particular, a tomography assay system is built which is designed to analyze $\textbf{L}$ow-$\textbf{L}$evel-$\textbf{W}$aste (LLW) contained in 200 liter drums of a maximum surface dose rate of 2 mSv/h. Prior to determining the nuclide inventory of a radioactive waste drum, the measurement of the density distribution by a technique called $\textbf{T}$ransmission $\textbf{C}$omputerized $\textbf{T}$omography (TCT) is applied. In TCT, the drum's attenuation of a $\gamma$-beam radiated by an external source is measured by one or more detectors. The density throughout an observed plane of the drum is then visualized by a density image. Generally, the internal attenuation of the emitted radiation by the sources contained in the drum, cannot be neglected. For this reason, the attenuation coefficients obtained from the transmission measurements, are applied to correct the emission data of the internal sources. Finally, the analysis and visualization of the activity distribution within the drum is carried out by applying the technique of $\textbf{E}$mission $\textbf{C}$omputerized $\textbf{T}$omography (ECT). The setup of the tomography assay system is of the translation-rotational type. Vertical moving tracks are installed in order to examine different horizontal cross sections of the drum. Due to the rather high density of cemented radioactive waste a strong external $\gamma$-source of 259 GBq $^{60}$Co installed within the tomography assay system, is used for transmission measurements (TCT). High count rate measurements of 4 partly attenuated $\gamma$-beams radiated by the $^{60}$Co-source, are accomplished by the use of 4 fast plastic scintillator detectors. The measurement of the comparatively low-active internal radioisotopes contained in the drum, is carried out by 3 Ge-detectors of relatively low count rates, but with high energy resolution for spectroscopic evaluations. The visualization software enables the operator to quantitatively determine the density and activity distribution of the drum's contents by calibrated scales. Reducing the time of measurement is an important aspect to be considered when designing an assay system for routine operation. One major goal of this paper is, therefore, to perform TCT and ECT simultaneously to save costly assay time. Here, a Monte-Carlo-simulation has proven that the detector shielding is adequate to sufficiently keep the scattered TCT $\gamma$-rays from contributing to the ECT detector readings. In addition, the paper describes software improvements on the ECT reconstruction algorithm allowing for quantitative analysis of the radioisotopes. Test measurements on radioactive point and volume sources and on LLW-drums confirm that the mobile tomography assay system has the potential to be a useful tool in nuclear waste management.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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