[Federal Register Volume 70, Number 83 (Monday, May 2, 2005)]
[Notices]
[Pages 22730-22731]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E5-2072]
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NUCLEAR REGULATORY COMMISSION
Draft Report for Comment: ``Documentation and Applications of the
Reactive Geochemical Transport Model RATEQ,'' NUREG/CR-6871
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of availability and request for comments.
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Background: The U.S. Nuclear Regulatory Commission (NRC) uses
environmental models to evaluate the potential release of radionuclides
from NRC-licensed sites. In doing so, the NRC recognizes that, at many
sites, groundwater-related pathways could contribute significantly to
the potential dose received by members of the public. Consequently,
consistent with its mission to protect the health and safety of the
public and the environment, the NRC uses contaminant transport models
to predict the locations and concentrations of radionuclides in soil as
a function of time. Through this notice, the NRC is seeking comment on
documentation of a subsurface transport model developed for the NRC by
the U.S. Geological Survey (USGS) for realistic transport modeling at
sites with complex chemical environments.
Because many radionuclides temporarily attach, or adsorb, to the
surfaces of soil particles, their mobility is reduced compared to that
of compounds that move with the groundwater without interacting with
solid surfaces. As a result, most subsurface-transport models used by
the NRC and its licensees estimate the effects of the anticipated
interactions between radionuclides and solids in the ground. Toward
that end, these subsurface-transport models use a ``distribution
coefficient,'' which is assumed to be constant and reflects the
proportion of radionuclide in the groundwater compared to the
radionuclide associated with the solids in the ground. These
distribution coefficients are widely used, and consequently, the
relevant literature documents ranges of their values for various soil
types and radionuclides. However, the documented ranges can be very
large because the chemical reactions that cause radionuclides to attach
to solids are very sensitive to water chemistry and soil mineralogy. As
a result, uncertainties in the parameters used to characterize the
adsorption of radionuclides in soils have been identified as a major
source of uncertainty in decommissioning, uranium recovery, and
radioactive waste disposal cases evaluated by the NRC.
Surface-complexation and ion-exchange models offer a more realistic
approach to considering soil-radionuclide interactions in performance-
assessment models. These models can also account for variable chemical
environments that might affect such interactions. The subject report,
prepared for the NRC by the USGS, describes the theory, implementation,
and examples of use of the RATEQ computer code, which simulates
radionuclide transport in soil and allows the use of surface-
complexation and ion-exchange models to calculate distribution
coefficients based on actual site chemistry.
The RATEQ code will help the NRC staff define realistic site-
specific ranges of the distribution coefficient values used to evaluate
NRC-licensed sites. In site-remediation cases, such as restoration of
the groundwater aquifer in and around uranium in-situ leach mining
facilities, the RATEQ code can aid in the estimation of restoration
costs by estimating the volume of treatment water needed to restore
sites to acceptable environmental conditions.
[[Page 22731]]
Solicitation of Comments: The NRC seeks comments on the report and
is especially interested in comments on the value of the report to
users who run the RATEQ code and are familiar with the types of complex
chemical environments that complicate many remediation projects.
Comment Period: The NRC will consider all written comments received
before August 12, 2005. Comments received after August 12, 2005, will
be considered if time permits. Comments should be addressed to the
contact listed below.
Availability: An electronic version of the report is available in
Adobe Portable Document Format at http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6871/cr6871.pdf and can be read with
Adobe Acrobat Reader software, available at no cost from http://www.adobe.com. The report and the computer files for the test cases
discussed therein are available at http://wwwrcamnl.wr.usgs.gov/rtm.
Hard and electronic copies of the report are available from the contact
listed below.
FOR FURTHER INFORMATION CONTACT: Dr. John D. Randall, Mail Stop T9C34,
U.S. Nuclear Regulatory Commission, 11545 Rockville Pike, Rockville, MD
20852, telephone (301) 415-6192, e-mail [email protected].
Dated at Rockville, Maryland, this 20th day of April 2005.
For the Nuclear Regulatory Commission.
Cheryl A. Trottier,
Chief, Radiation Protection, Environmental Risk & Waste Management
Branch, Division of Systems Analysis and Regulatory Effectiveness,
Office of Nuclear Regulatory Research.
[FR Doc. E5-2072 Filed 4-29-05; 8:45 am]
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