Gamma ray scanner systems for nondestructive assay of heterogeneous waste barrels Page: 7 of 16
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We developed some procedures for determining the isotopic distribution of the assay. We
analyze the overall statistical quality of the data and the presence of interference peaks from
other isotopes such as 235U and 237Np. Based on this analysis the procedure can then select
appropriate regions of the spectra for more detailed analyses. In order to support these
concepts we also developed codes that can sum spectra from several slices of A&PCT data in
order to accumulate sufficient statistics for barrels with low radioactive mass.
Analysis of the spectroscopic data from IMPACT includes: (1) summing the data from
each slice; and (2) summing the data for the entire barrel to determine the isotopic ratios for:
238Pu/239Pu 240Pu/239Pu, 241Pu/399Pu, and 241Am/239Pu; and (3) inspecting the 241Pu/239Pu ratio
for each slice to evaluate isotopic homogeneity. Except for the 238Pu/239Pu ratio, the values are
determined from at least two different parts of the gamma-ray spectrum. The isotopic ratios
are then combined with the A&PCT image reconstruction/assay data to calculate the total
alpha curies, thermal power, and fissile gram equivalent for each analysis.
2.4 Performance Measures
One performance objective is to satisfy the Quality Assurance Program Plan (QAPP).[5]
The QAPP identifies the quality of data necessary to meet the specific data quality objectives
associated with the Department of Energy's (DOE) Waste Isolation Pilot Plant (WIPP)
transuranic (TRU) waste characterization program. Two parameters describing the waste
must be determined; the total alpha activity and the activity of the individual isotopes
present. The quality assurance objectives (QAOs) for precision (% relative standard
deviation), accuracy (% recovery), minimum detectable concentration (MDC), completeness,
and total bias are stated in the QAPP. The QAPP requires that each NDA system perform 15
replicate measurements for 4 ranges of waste activity (nominal compliance values are 0.1, 1.0
10, and 160 g WG Pu). Between each measurement the barrel must be completely removed
from the NDA system.
The NDA Performance Demonstration Program (PDP) is designed to help ensure
compliance with the QAPP QAOs.[6] The PDP consists of a series of tests conducted on a
regular frequency and of increasing matrix/source complexity to evaluate the capability for
NDA of TRU waste throughout the DOE complex. Each test is termed a PDP cycle. These
evaluation cycles are blind tests that provide an objective measure of the reliability and
performance of NDA systems. The PDP consists of a set of 208-L barrels and a
configuration that includes provisions to install and physically fasten a matrix in place in
addition to allowing for the convenient external introduction and precise positioning of PDP
standards (radioactive sources) within the barrel volume. The PDP requires only 6 replicate
measurements and removal of the barrel between replicates.
Presently there are 4 barrels: air (no matrix), ethafoam, combustibles and glass. Aluminum
source insert fixtures are provided for each of three insert tube radii: Center or OR, 0.5R and
0.8R, where R is the barrel radius. PDP standard(s) are positioned at desired vertical locations
in the three insert fixtures. Several versions of standards will be used in the program. The
initial standards are weapons-grade (WG) plutonium dioxide (PuO2) uniformly mixed in
diatomaceous earth and then encapsulated in a dual stainless steel cylinder configuration (o.d.:
5 cm, 1:23 cm). Each assembled PDP barrel for every official cycle includes a tamper5
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Martz, H. E.; Roberson, G. P.; Decman, D. J.; Camp, D. C. & Levai, F. Gamma ray scanner systems for nondestructive assay of heterogeneous waste barrels, article, August 1, 1997; California. (https://digital.library.unt.edu/ark:/67531/metadc693863/m1/7/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.