EVS Updates its MILDOS-AREA Computer Code used to Evaluate Impacts of Radiological Airborne Emissions and Compliance
The MILDOS-AREA computer code (MILDOS 4) is used to estimate the radiological impacts of airborne emissions from uranium milling facilities. It provides the capability to consider both conventional uranium ore operations and operations associated with in-situ recovery (ISR) facilities. The code was developed by EVS staff for the U.S. Nuclear Regulatory Commission (NRC) for use by license applicants and NRC staff to perform routine radiological impact and compliance evaluations for various uranium recovery operations.
The airborne release of radon and particulates from seven different source types can be analyzed using the MILDOS code. Source types include: (1) point sources (stacks and vents); (2) area sources (ore pads and tailing areas); (3) drying and packaging sources; (4) land application sources; and ISR specific sources, (5) new well field sources; (6) production well field sources; and (7) restoration well field sources.
Plume rise is considered for point sources and for drying and packaging sources. A wind-blown dust (erosion) model is available to address ore pads and tailings piles for area sources. Downwind air concentrations are estimated using a Gaussian plume model with dry and wet deposition to estimate ground concentrations for particulates. The ground concentrations in turn are used to estimate resuspended air concentrations and plant uptake with subsequent consumption by humans and animals. Dose to humans is calculated for the following pathways: inhalation of downwind and resuspended radionuclide air concentrations; external exposure from contaminated ground and air concentrations; and ingestion of plants, meat, and milk.
Releases of particulates explicitly considered are limited to the radionuclides U 238, Th 230, Ra 226, and Pb 210 for the uranium series decay chain, and Th-232, Ra-228, and Th-228 for the thorium series decay chain. Other radionuclides in these series are implicitly accounted for under the secular equilibrium assumption. Gaseous releases are limited to consideration of Rn-222 and Rn-220, plus in growth of decay products.
Version 4.02 Updates
A number of enhancements have been made to the MILDOS code. MILDOS4 is now a 64-bit application which removes the < 2 GB of system memory limit imposed by Windows 32 bit operating systems. Thus, the number of receptors and sources in a scenario considered by the user isn't as constrained, and the reprojection of larger shapefiles is now possible when adding vector files to the map.
Enhancements requested by users also have been added. These include the addition of source/receptor distances and calculated outdoor air Rn-222 equilibrium fractions in the standard output; more consistent ordering of sources and receptors in output listings; and options to allow sorting of the meteorological joint frequency (JFD) data in the user interface, as well as the ability to save the JFD data to a comma-separated values (CSV) file.
A number of map interface enhancements have been made in MILDOS4. Raster (image) layers can now be reprojected to the Universal Transverse Mercator (UTM) projection. This capability allows for the use of data published in other projections, such as National Agriculture Imagery Program (NAIP) orthoimagery, now published in a Web Mercator format by the U.S. Geological Survey. Ruler options have been added to the map control to measure between two points and to measure the area of a polygon. The mouse position on the map can be displayed in meters or in decimal degrees (when in UTM coordinates). The user is now able to specify the exact map location of the first source, (0,0) location, when switching from local to UTM coordinates.
The technical reference and user manual for version 4 of the MILDOS-AREA computer code is provided in the Technical Manual and User's Guide for MILDOS-AREA Version 4 (NUREG/CR 7212). A companion report, MILDOS-AREA Version 4 Computational Verification Report (NUREG/CR-7213), documents the process used to verify the proper operation of the computer code. Additional information, including an addendum to the technical manual for version 4.02, can be found at http://mildos.evs.anl.gov/