Re: Default Surface Contamination Criteria for Th-nat

["Boby Abu-Eid" <BAE@NRC.GOV>]

Dan,



The soil screening values for "Th-232 + C" in NUREG-1757 were developed using a simple and  conservative DandD model and code.  There are currently no practical alpha-emitters screening values for building surfaces.  The main reason is because the DandD model is too simple to account for the inhalation pathway in a realistic fashion.  In addition there are certain sensitive parameters used in DandD that are highly conservative causing the surface screening values to be unrealistically low.  For example, the default resuspension factor, RF, used in DandD code is rather high and staff is currently revising this factor.  In this regard, staff developed draft NUREG-1720 which is on the NRC's website for public comment (http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1720/index.html).  The draft NUREG-1720 proposes to reduce the RF by a factor of approximately 15.  Reduction of the RF by this factor may increase the alpha screening limits by the same factor.  Radsafers!

 may take a look at the draft NUREG-1720 and provide their comments if they wish.



Currently, we endorse RESRAD-BUILD3.1 model/code for deriving site-specific alpha-emitters release limits.   However, use of RESRAD-BUILD may require additional site-specific information or parameters about the facility.  





The above views are those of the writers and may not necessarily represent the official views of the NRC.    



Boby Eid &

Duane Schmidt



Division of Waste Management

Office of Nuclear Material Safety and Safeguards

US Nuclear Regulatory Commission           



>>> "Dan Hoffman" <dhoffman@pangea-group.com> 09/20/02 10:41AM >>>

Has anyone developed a surface release criterion for Th-232 + daughter products using D&D or ResRad to comply with the 25 mrem/yr NRC release limit?  I noted that NUREG 1757 Appendix B has a default screening limit for "Th-232 + C" in soils of 1.1 pCi/g but no surface criteria is published.  



I am curious if the numbers would be close to the Reg Guide 1.86 criteria or not.



Regards,



Dan



Daniel E. Hoffman, CHP,CIH,CSP

Vice President EH&S Services

Pangea Group

743 Spirit 40 Park Dr., Suite 232

Chesterfield, MO 63005

Office 636-519-4877

Mobile 314-707-5606



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