RESRAD-OFFSITE is used to assess radiation exposures of a human receptor located on top of or at some distance from soils contaminated with radioactive materials.
RESRAD-OFFSITE inherits and expands upon the objectives of RESRAD-ONSITE. It estimates radiation doses and cancer risks to an individual located on site, i.e., within the boundary of the primary contamination in soil (as considered by RESRAD-ONSITE), off site, or both on site and off site (with a time fraction at each location). It also derives radionuclide soil guideline levels for the primary contaminated area corresponding to a specific dose criterion. Because of the extension to off-site locations, RESRAD-OFFSITE simulates actual exposure conditions more realistically, and can be applied to evaluate more complicated decommissioning conditions (with restriction) and the effectiveness of environmental monitoring.
The modeling approach of RESRAD-OFFSITE is the same as that of RESRAD-ONSITE. The calculation of dose and cancer risk is scenario driven, by activating exposure pathways and using parameter values commensurate with the scenario under consideration. Nine exposure pathways are modeled, as in RESRAD-ONSITE, which include external radiation, inhalation of airborne radionuclides, ingestion of plant foods, meat, milk, water, and aquatic food, incidental ingestion of soil, and inhalation of radon. Unlike RESRAD-ONSITE, which assumes the residence and agricultural fields are collocated with the primary contamination, RESRAD-OFFSITE allows them to be at different locations, each at a specific distance and direction from the primary contamination as well as of specific dimensions. The same option extends to a well and a surface water body, which can be off the center line of the groundwater flow direction. Accumulation of radionuclides due to air deposition and irrigation at off-site locations is also modeled, contributing to radiation exposures of the receptor.
A Gaussian plume model based on area source release was incorporated into RESRAD-OFFSITE to calculate air concentrations at off-site locations. For groundwater transport modeling, in addition to radiological decay and ingrowth, advection, and sorption and desorption between solid and liquid phases in soil, one-dimensional and three-dimensional dispersion are also considered for the unsaturated zones and saturated zone, respectively, and the transport extends beyond the boundary of the primary contamination.
The latest enhancement to the RESRAD-OFFSITE code is the incorporation of a source term model, which allows time-delayed and distributed release of radionuclides to infiltration water and provides options to calculate the release as instantaneous, uniform, or 1st order rate controlled. With this enhancement, the application of RESRAD-OFFSITE is no longer limited to the typical soil contamination for which it was initially designed.
The RESRAD-OFFSITE code maintains most of the features of the RESRAD-ONSITE code, including a user-friendly interface to facilitate data entry, performing calculations, displaying calculation results, and accessing general and context-specific help, the choice of ICRP-38 or ICRP-107 radionuclide transformation database, the selection of dose conversion factors and cancer risk slope factors library, and the specification of a cut-off half-life for defining short-lived associated progenies. In addition to performing deterministic sensitivity analyses, it is capable of performing probabilistic sensitivity analyses and features an interface that steps the user through the probabilistic analysis.
RESRAD-OFFSITE maintains and enhances the functions of RESRAD-ONSITE. It is approved by NRC for use in decommissioning and license termination risk assessment. In addition to typical soil contamination, it can also be applied to evaluate human health and environmental impacts associated with radioactive waste disposal, e.g., the evaluation of post-closure performance of the conceptual disposal facility designs at sites that were considered for the greater-than-class C (GTCC) and GTCC-like low-level wastes. RESRAD-OFFSITE accepts direct input of radionuclide release rates to deeper soils, groundwater aquifer, air, or a surface water body, and can thereby be used with other environmental fate and transport models.
Learn more about the use and applications of RESRAD-OFFSITE at a training workshop at Argonne National Laboratory.