Re: DCGL Values and ALARA

[Jjblute1@aol.com]

Fritz,

The NRC allows licencees to derive generic screening values according to the 
dose modeling described in NUREG-1549 and NUREG/CR-5512.  They made this 
easier by giving us the DandD code which implements these guidance.  If you 
just download DandD, pick the appropriate scenario (Building Occupancy, 
Building renovation, Resident Farmer) and then pick your nuclides, then run, 
the code will give you screening values (DCGLs).  No other parameters need to 
be altered because the code defaults to parameters that the NRC approves for 
Generic Screening Values.  They tend to be low, however, and that is why 
licensees invest significant effort in changing the default values to more 
realistic and site specific values.

These screening values have been published for buildings (Surface 
Contamination Limits) in the HPS newsletter or Journal, I cant remember which 
or when but I have a copy somewhere and will write to you if I find out.  
Taking these values from publication will give you the confidence that you 
have the right ones, but it really is pretty simple to get them out of the 
code.  The dose modelling gets trickier when you are trying to get more site 
specific DCGLs that the licensee, the regulator, and all other stakeholders 
(including the public) are happy with (or at least will accept - try making 
everyone happy and see where you get).  Also, the DandD code is under a lot 
of scrutiny right now because it gives unreasonably low values for some 
radionuclides under certain scenarios (Cs-137 in soil, i.e. resident farmer 
scenario, is one i think).  Because of this, the NRC has backed down on the 
expectation that licensees use only DandD and not other codes like RESRAD.  
So many licensees are now also using (or are back to using) RESRAD for dose 
modeling.

Also I would like to point out a VERY common misconception, by choosing Reg. 
Guide 1.86 limits for your site, you are NOT necessarily in disagreement with 
MARSSIM.  MARSSIM does not care how you get DCGLs or what they are, it does 
not provide (detailed) guidance on how to derive DCGLs.  As Steven Rima 
points out in his reply to your question on RADSAFE, MARSSIM takes over 
_after_ you have determined the DCGLs.  It provides guidance on how to 
demonstrate compliance with them by performing a Final Status Survey.  I will 
point out again that this is an extremely common misconception.  I think it 
comes about because MARSSIM came out at roughly the same time that the NRC 
came out with the rule requiring a 25 mrem/year dose limit, thus requiring 
licensees to perform dose modeling instead of relying on published limits.  
People now associate dose based limits with MARSSIM.

I hope this info helps you out.  If you have any other questions please 
contact me.

Jim Blute
Duke Engineering & Services
Marlborough MA
978-568-2762
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