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A little followup to my previous message. I found the spreadsheet used to
make relocation and re-entry calculations, using factors developed by EPA for
radionuclide retention out to 50 years assuming only natural removal processes.
Running through the calculations, I come up with the following:
A deposition of 22.2 uCi/m^2 of Cs-137 will result in a first year
"occupancy" dose of 1 rem.
A deposition of 17.4 uCi/m^2 of Cs-137 will result in a second year
"occupancy" dose of 0.5 rem
A deposition of 8.2 uCi/m^2 of Cs-137 will result in a 0-50
year "occupancy" dose of 5.0 rem.
Don't ask me all the assumptions that went into this calculation ...
because I don't know what they are. I'd have to look in EPA 400. Even certain
individuals in EPA admit that the 50 year calculations may be somewhat suspect,
but I'd venture that any agreed upon cleanup level would be below that 8.2
uCi/m^2 value.
Jim Hardeman
Jim_Hardeman@dnr.state.ga.us
>>> "Nardi, A. Joseph" <nardiaj@WESTINGHOUSE.COM> 2/28/2003 12:42:51 >>> This is really an issue of "How clean is clean enough". When decommissioning a licensed facility we are required to take more effort to chase "the last atom" because of the exposure scenarios that are associated with the development of cleanup criteria. Such decommissioning scenarios should not be considered applicable to the cleanup associated with an act of terrorism particularly in an outdoor environment. It seems to me that one of the considerations that should be thought out now is what would be the appropriate cleanup criteria to be applied in the event of such an act of terrorism. Otherwise we are going to end up with the default criteria. The elements that would be required to establish appropriate criteria might be as follows: * Establish a rational dose criteria to be used in these scenarios. This might be done on a time dependent basis such as the first five years, the second 10 years, etc. * Define a realistic scenario for the dose calculation based on different dirty bomb scenarios. * Establish a model that is based on realistic model parameters, not using the general approach for decommissioning models where the parameters are the 90th percentile or other levels of conservatism. * Use the above to establish reasonably protective cleanup criteria that can be used in such an event before the act rather than trying to develop the criteria in the "heat of the moment". Just my humble opinion A. Joseph Nardi, Supervisory Engineer Westinghouse Electric Company P. O. Box 355 Pittsburgh, PA 15230 Telephone: 412-374-4652 FAX Number: 412-374-3357 email: nardiaj@westinghouse.com John Andrews wrote: > I cleaned up an old spill of Cs-137 once. The material had been cleaned > up years earlier, but residual material remained on some of the > concrete. It had penetrated into the concrete up to one inch in > discrete spots. This indicated to me that actual grains of the spilled > source material remained on the concrete and the cesium was sorbed by > whatever reaction into the concrete. There was low level general > contamination just above backround in adjacent areas indicating > migration from the hot spots. Effective cleaning included jackhammering > or intense needle-gun decon of the spots and scabbling the general areas > to 1/2 inch. > > I would expect the same from any Cs-137 spill. > > John Andrews > Knoxville, Tennessee > > ************************************************************************ > You are currently subscribed to the Radsafe mailing list. To unsubscribe, > send an e-mail to Majordomo@list.vanderbilt.edu Put the text "unsubscribe > radsafe" (no quote marks) in the body of the e-mail, with no subject line. > You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/ > > ************************************************************************ You are currently subscribed to the Radsafe mailing list. To unsubscribe, send an e-mail to Majordomo@list.vanderbilt.edu Put the text "unsubscribe radsafe" (no quote marks) in the body of the e-mail, with no subject line. You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/ |