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Integrating Modeling and Monitoring for the Radioactive Waste Management Complex
Roger R. Seitz, James M. McCarthy, and Karen N. Keck
Idaho National Engineering and Environmental Laboratory
P.O. Box 1625, MS 4142
Idaho Falls, ID 83415
Abstract- United States Department of Energy Order 435.1, Radioactive Waste Management, includes requirements for
assessing the long-term performance of radioactive waste disposal facilities and also for environmental monitoring of the
performance of those facilities throughout the time of institutional control. It is also specified that performance assessment
and composite analysis modeling should be integrated with environmental monitoring in order to provide a means to assess
the adequacy of the assumptions that were made for the modeling. This paper describes the development of action levels,
which are expected concentrations at different locations in the subsurface based on modeling conducted for the performance
assessment and composite analysis for the low-level waste disposal facility at the Radioactive Waste Management Complex
at the Idaho National Engineering and Environmental Laboratory. First year comparisons of measured concentrations with
the action levels have shown that migration appears to be occurring at a much lower rate than predicted by the models. This
supports the conclusion that the modeling is conservative and conclusions based on the modeling are likewise conservative.
United States Department of Energy (DOE) Order
435.1, Radioactive Waste Managements, includes
requirements for assessing the long-term performance of
radioactive waste disposal facilities and also for
monitoring of the performance of those facilities
throughout the time of institutional control (100 years
after closure). Long-term compliance with performance
objectives specified in DOE Order 435.1 is demonstrated
using performance assessments (PAs) to address
radiological releases from wastes disposed in a low-level
radioactive waste (LLW) disposal facility and composite
analyses (CAs) to address all potential radiological
sources surrounding a disposal facility in addition to the
disposal facility itself.
DOE Order 435.1 identifies the need to link
environmental monitoring with modeling predictions
from the PA and CA for a given facility. To meet this
requirement, a formal PA/CA monitoring program and
accompanying action levels were developed for the
Radioactive Waste Management Complex (RWMC)
Subsurface Disposal Area (SDA) at the Idaho National
Engineering and Environmental Laboratory (INEEL) (see
Figure 1). Monitoring locations and sampling frequencies
are chosen based on the projected migration pathways and
the potential to exceed the releases projected in the
performance assessment3 and composite analysis4 that
were conducted for the active LLW disposal facility
located in the SDA at the RWMC.
Action levels are essentially thresholds, which are
intended to indicate concentrations at which migration of
radionuclides may be in excess of that predicted for the
PA and CA. Thus, if the action levels are exceeded,
prescribed activities must occur. Examples of responses to
exceeding an action level include:
" immediate notification of the Waste Generator Services
Department at the INEEL,
" immediate evaluation and documentation of the data
" increased sampling frequency at the location where the
action level was exceeded,
" assessment of the need for corrective actions,
" potential reduction in disposal of certain waste streams,
" the potential development of mitigating actions to be
undertaken to restore facility performance.
Action levels are determined for the radionuclides
that significantly contribute to the dose predicted in the
PA and CA. In the vadose zone and aquifer, the emphasis
of monitoring is on mobile radionuclides in the liquid
phase (i.e., C-14, I-129, Cl-36). If migration of
radioactive materials is greater than expected, mobile
radionuclides are most likely to be early indicators.
Carbon-14 was the primary radionuclide of concern in the
assessments, thus C-14 will be used as the example in this
paper. The emphasis of this paper is also on the vadose
zone, because monitoring in the vadose zone will provide
the first indication of a potential problem for the
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Seitz, Roger Ray; Mccarthy, James Michael & Keck, Karen Nina. Integrating Modeling and Monitoring for the Radioactive Waste Management Complex, article, August 1, 2002; [Idaho Falls, Idaho]. (https://digital.library.unt.edu/ark:/67531/metadc890058/m1/2/: accessed April 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.