[ RadSafe ] RE : Spent fuel and decay

John R Johnson idias at interchange.ubc.ca
Thu Jul 26 17:31:56 CDT 2007


Jim and Mike

I knowl that there was a computer program that gave the isotope 
concentrations in spent fuel as a function of time, and burn up, since the 
spent fuel was removed from the reactor. I don't know what it was called but 
it may be referenced in
DOSE CONVERSION FACTORS USED IN THE CURRENT CANADIAN HIGH LEVEL WASTE 
DISPOSAL ASSESSMENT STUDY

J. R. Johnson

AECL-7869, Radiation Protection Dosimetry 3 No. ½ (1982) 47-50.



John***************
John R Johnson, PhD
CEO, IDIAS, Inc.
Vancouver, B. C.
Canada
(604) 222-9840
idias at interchange.ubc.ca


----- Original Message ----- 
From: "Jim Hardeman" <Jim_Hardeman at dnr.state.ga.us>
To: "Mike (DOH) Brennan" <Mike.Brennan at DOH.WA.GOV>; <radsafe at radlab.nl>
Sent: Thursday, July 26, 2007 3:15 PM
Subject: RE: [ RadSafe ] RE : Spent fuel and decay


> Mike --
>
> Good observation. As I recall, the primary driver for long-term isolation 
> of spent fuel is dose through the groundwater pathway. I'd have to go back 
> and look not only at 10 CFR 63 but EPA's standards, but I believe EPA 
> wants groundwater concentrations of radionuclides to be less than their 
> Maximum Contaminant Level (MCL) over the entire period over which 
> consequences are assessed -- I think that's now up to 100,000 years.
>
> I don't know much about the geology of Washington State, but if your 
> geology is anywhere like Georgia's, you'll find quite a few places that 
> exceed MCL for naturally-occuring radionuclides (Ra-226, Ra-228, uranium 
> being the ones currently regulated -- plus total alpha activity (excluding 
> uranium) and total beta activity) . While the MCL for beta-emitters is 
> based on dose (i.e. 4 mrem/yr assuming 2 liter per day consumption rate), 
> the actual dose from Ra-226, Ra-228 and uranium at MCL concentrations will 
> be substantially greater. The MCL for uranium, for example, is in ug/l (30 
> ug/l as I recall) rather than pCi/l. We've noticed that the U-234 / U-238 
> ratio in groundwater isn't constant, and that the dose associated with a 
> concentration of 30 ug/l can vary considerably based on the U-234 / U-238 
> ratio.
>
> What I'm getting at here is that the regulatory framework for spent fuel 
> actually regulates risk through the groundwater pathway at a value far 
> less than the risk associated with groundwater that might be associated 
> with natural uranium deposits.
>
> My $0.02 worth --
>
>>From the piney woods of northern Michigan (on vacation)
>
>
>
> Jim Hardeman, Manager
> Environmental Radiation Program
> Environmental Protection Division
> Georgia Department of Natural Resources
> 4220 International Parkway, Suite 100
> Atlanta, GA 30354
> (404) 362-2675
> Fax: (404) 362-2653
> Personal fax: (678) 692-6939
> E-mail: Jim_Hardeman at dnr.state.ga.us
>
>
>>>> "Brennan, Mike  (DOH)" <Mike.Brennan at DOH.WA.GOV> 7/26/2007 17:49 >>>
>>From the information I have and the interesting site Leo linked to, I
> agree that driver for activity in the long run is Pu.  I just ran a
> spread sheet looking at the U235-U238-Pu239 ratios and the effect on
> total activity, and it is clear that once the fission fragments have
> decayed away enough (a couple hundred years, more or less) the total
> activity is mostly driven by how much U238 was changed into Pu239, and
> how much of the Pu239 was in turn destroyed by fission.  While these
> numbers would all depend on the original make-up of the fuel and its
> history with a reactor, it seems reasonable to say that the fuel would
> reach its original activity after around 10,000 years (fairly wide band
> "around"), and that it would be low enough activity to handle without
> special precautions several thousand years before then.
>
> All in all, while spent fuel presents non-trivial challenges for
> storage/disposal, the claims that it must be kept isolated for 100,000
> (or 1,000,000, as I heard recently) years is clearly not based on actual
> risk.
>
>
>
> -----Original Message-----
> From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
> Behalf Of Pete_Bailey at fpl.com
> Sent: Thursday, July 26, 2007 10:32 AM
> To: radsafe at radlab.nl
> Subject: [ RadSafe ] RE : Spent fuel and decay
>
>
>> ... how long it takes spent fuel to decay to the Aactivity level it
>> had before going into the reactor?
>
> If by 'activity level', you mean 'curies', one very very long time.
>
>> I realize it is highly dependant on factors such as level of
>> enrichment, amount of burn-up, activation of cladding, etc, and
>> breeding of Pu.
>
> Level of enrichment & 'burn-up'(MWT/MTU) drive the length of time.
> Most activation products (active...of clad) fizz out in  a decade or
> so...
> The breeding of Pu....it ain't there to
> start with (for all intent and purposes), and has mega-year half-life.
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