ACCOUNTING FOR THE NON-RESPIRABLE SOURCE TERM

摘要

The objective of this of this work is to make analysts aware of the potential for overlooking a significant dose contribution from radiological material deposited from a plume. As some DOE sites begin to separate alpha-dominated actinides from gamma-dominated isotopes, it becomes increasingly important to understand how the respirable fraction, deposition velocity, and meteorology (wind speed and stability class) affect dose. When estimating airborne radiological source terms, analysts typically use the source term equation given in DOE HDBK-3010-94 (ST = MAR x DR x ARF x RF x LPF). However, as is briefly mentioned in the Handbook, this is only the respirable source term. Depending on the material and release mechanism, there may be a significant non-respirable fraction of the MAR deposited in the vicinity of the receptor. If the nuclide is an alpha emitter, this is of no concern. However, if it has a large gamma component, dose from ground shine can be significant. Results of this work will demonstrate that when modeling a release that includes a significant gamma component: the entire release (including the non-respirable component) should be included; and, when considering several hours of ground shine, low deposition velocities and stable atmospheric conditions may not be conservative.