ML110030947
| ML110030947 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 06/30/2004 |
| From: | US Dept of Energy (DOE) |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| Shared Package | |
| ML110030939 | List: |
| References | |
| RAS 19374, 50-293-LR, ASLBP 06-848-02-LR, DOE-EH-4.2.1.4-MACCS2, PWA 00021, jrr | |
| Download: ML110030947 (3) | |
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MACCS2 Computer Code Application Guidance for Documented Safety Analysis Final Report U.S. Department of Energy Office of Environment, Safety and Health 1000 Independence Ave., S.W.
Washington, DC 20585-2040 June 2004
MACCS2 Guidance Report June 2004 Final Report 3.2 Phenomenological Regimes of Applicability The MACCS2 class of atmospheric dispersion codes is based on the Gaussian model of dispersion. As such, these types of computer model are best suited for specific types of conditions. The chief phenomenological regimes that should be considered before applying MACCS2 include:
- Temporal regime - The use of these codes is best suited for "short" duration plumes, ranging trom approximately several minutes to several days.
- Spatial regime - The class of code also does not model dispersion close to the source (less than 100 meters trom the source), especially where the influence of structures or other obstacles is still significant. Dispersion influenced by several, collocated facilities, within several hundred meters of each other should be modeled with care. Similarly, the MACCS2 class of codes should be applied with caution at distances greater than ten to fifteen miles, especially if meteorological conditions are likely to be different from those at the source ofthe release. Long-range projections of dose conditions are better calculated with mesoscale, regional models that are able to account for multiple weather observations. Nevertheless, some applications may require fifty-mile or greater radius analysis to meet requirements, e.g. Environmental Impact Statements (EISs) or Probabilistic Safety Assessments (PSAs).
- Terrain variability - Gaussian models are inherently flat-earth models, and perform best over regions of transport where there is minimal variation in terrain. Because ofthis, there is inherent conservatism (and simplicity) if the environs have a significant nearby buildings, tall vegetation, or grade variations not taken into account in the dispersion parameterization.
- Energetic releases - MACCS2 does not account for momentum-driven releases or those originating trom detonation type events without appreciable post-processing of boundary and initial conditions. Using the latter approach, Steele (1998) has demonstrated a MACCS2-based, segmented methodology for a detonation source term that was found to compare well with observations.
- Thermal buoyancy - In plumes arising from fire-related source terms, the user should exercise caution with the models such as MACCS2 that use the Briggs algorithm. The Briggs approach for accounting for sensible energy in a plume is valid for "open-field" releases (not impacted by buildings and other obstacles), or if used in combination with building wake effects. Appendix C provides a limited sensitivity study of the effects of buoyancy and building wake effects on plume dispersion.
- Dose conversion factor applicability - The user should ensure that the dose conversion factors used in MACCS2 are applicable to the radionuclides in the source term and the physicochemical characteristics. For example, plutonium nitrates and oxides have different time scales for dosimetric effects in the body. Thus, the appropriate lung 3-8
MACCS2 Guidance Report June 2004 Final Report absorption type should be used in the dose conversion factor file used in the MACCS2 run.
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