[Federal Register Volume 70, Number 118 (Tuesday, June 21, 2005)]
[Pages 35743-35744]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E5-3200]



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.



    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

[[Page 35744]]

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 
    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.
    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.

DATES: The NRC will consider all written comments received before 
September 30, 2005. Comments received after September 30, 2005, will be 
considered if it is practical to do so, but the NRC staff is able to 
ensure consideration only for comments received on or before this date. 
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.

U.S. Nuclear Regulatory Commission, 11545 Rockville Pike, Rockville, MD 
20852, telephone (301) 415-6192, e-mail [email protected].

    Dated at Rockville, Maryland, this 10th day of June, 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. E5-3200 Filed 6-20-05; 8:45 am]