Characterization of waste drums using nonintrusive active and passive computed tomography Page: 4 of 37
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CHARACTERIZATION OF WASTE DRUMS USING
NONINTRUSIVE ACTIVE AND PASSIVE COMPUTED TOMOGRAPHY
G. Patrick Roberson, Harry E. Martz; Daniel J. Decman, David C. Camp
Steven G. Azevedo and Eric R. Keto
Lawrence Livermore National Laboratory
Livermore, CA 94551, USA
We have developed a data acquisition scanner for gamma-ray nondestructive assay
(NDA) active and passive computed tomography (A&PCT) along with associated
computational techniques for image reconstruction, analysis, and display. We are using
this scanner to acquire data sets of mock-waste drums at Lawrence Livermore National
Laboratory (LLNL). In this paper, we discuss some issues associated with gamma-ray
spectroscopy assay, NDA imaging, describe the design and construction of an NDA drum
scanner and report on code development for image reconstruction. We also present
representative A&PCT assay results of well characterized mock-waste drums. These
preliminary results suggest that A&PCT imaging can be used to produce accurate absolute
assays of radioactivity in real-waste drums.
Characterization of mixed (radioactive and hazardous) wastes requires that the identity
and strengths of intrinsic radioactive sources be determined accurately and that all
hazardous (e.g., heavy metals, volatile organic compounds-VOCs-and non-VOCs) and
non-conforming materials (e.g. free liquids, sharp objects, particulates, and pressurized
containers) be identified.[AND91] We are developing both nondestructive evaluation
(NDE) and assay (NDA) methods to meet some of these characterization requirements.
The NDE methods include x-ray real-time radiography (RTR), digital radiography (DR),
and transmission computed tomography (TCT), while the NDA method is gamma-ray
active (A) and passive (P) computed tomography (CT). Here we describe only the NDA
waste-drum characterization research and development (R&D) activities at the Lawrence
Livermore National Laboratory (LLNL). Our NDE activities are described elsewhere in
Current practice within DOE for characterizing nuclear wastes include two
nondestructive assay (NDA) techniques. Passive and active neutron (PAN) interrogation is
an NDA method that determines the amount of spontaneous (passive) and induced (active)
fissionable isotopes present.[CAL86] Segmented gamma-ray spectrometry (SGS) is an
NDA method that measures the amount of only 235U or 239Pu in a waste drum.[SIM90] It
is important to emphasize that these techniques were not developed to assay unknown
wastes but rather to measure large amounts (on the order of grams) of special nuclear
materials given prior knowledge of the radioactive isotopes. Furthermore, these techniques
are applicable only under the assumption that the radioactive sources are uniformly
distributed in a uniformly attenuating matrix. This is typically not the,case for real wastes.
Thus we have been developing a gamma-ray computed tomography technique to resolve
some of these inconsistencies to better assay a waste drum. This new gamma-ray CT
technique is called active and passive CT (A&PCT).
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Roberson, G.P.; Martz, H.E.; Decman, D.J.; Camp, D.C.; Azevedo, S.G. & Keto, E.R. Characterization of waste drums using nonintrusive active and passive computed tomography, article, August 1, 1994; California. (digital.library.unt.edu/ark:/67531/metadc674310/m1/4/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.