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Advancements in nuclear waste assay

Curtis, Deborah Claire (2008)
Ph.D. thesis, University of Birmingham.

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The research described in this thesis is directed at advancing the state of the practice of the non-destructive gamma-ray assay of nuclear waste containers. A number of potentially accuracy-limiting issues were identified and addressed, resulting in new developments which were implemented on an instrument prior to entering it into service. A set of Pu reference sources used for experimental data have been studied to determine the internal composition (density and fill height) of the sources to assist with validation of a point kernel model. This model has been used to observe the behaviour of gamma-rays in lumps of fissile material from plutonium over the mass range 0.001g to 350g, for a number of densities corresponding to Pu, PuO\(_2\) and PuF\(_3\). Established lump corrections have been analysed and have been found to produce large over- and under-corrected results for the range of masses. Due to the inadequacies of current techniques, a new Pu self-absorption correction method has been developed using the data from numerical simulations, allowing nature to reveal the correlations rather than traditional approaches based upon approximate models. For a 25g 1cm-high Pu flat-plate of density\(^{-3}\), the developed Pu correction produces a result of (24.9 ± 8.8)g compared to (19.5 ± 0.9)g for the Fleissner 2-line method, and (14.7 ± 0.4)g for the Infinite Energy Extrapolation method. The developed Pu correction method has been extended to the application of uranium lumps in waste matrices, provided the enrichment of the sample is known or may be determined via sophisticated isotopic analysis methods such as MGAU or FRAM. The U self-absorption correction method has been found to produce results within 30% of the true mass of the sample for the lumps studied. An analysis of ‘real drum’ effects has been performed, including the revisiting of the Total Measurement Uncertainty (incorporating the uncertainty components of the new Pu and U self-absorption corrections) and results from known sources placed in artificial inhomogeneous waste matrices assayed inside a Canberra Auto Q2 system.

Type of Work:Ph.D. thesis.
Supervisor(s):Norman, Paul
School/Faculty:Schools (1998 to 2008) > School of Physics & Astronomy
Keywords:NDA, Pu self-absoprtion, plutonium, uranium, TMU, nuclear waste
Subjects:QC Physics
Institution:University of Birmingham
Library Catalogue:Check for printed version of this thesis
ID Code:153
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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