[ RadSafe ] Global Warming

[Peter Bossew]

Mike,

you are of course right that compared to medium lived radionuclides (like
137Cs, 90Sr etc.; the short lived ones don't make it into a repository
because of long intermediate storage times, 30 years or more for
reprocessing waste), the long-lived ones are trivial, in terms of
activity. If I remember well the activity of spent fuel (incl. actinides)
drops below the activity of the same amount of natural U within less than
10.000 years. For the fission products only, this is within a couple of
100 years.  

My purpose was not to blow up the picture of some devilish spectre looming
for millions of years. Nuclear waste is unpleasant, but similar to many
other nasty industrial wastes. 

Still, consider the following. In particular I and Tc are relatively
mobile, much more than Cs and very much more than U, which makes the
initial activity with which you compare it. This means that the glass
blocks (or whatever matrix is used) should be intact after a couple of
hundred years during which they have been under heavy attack by the decay
of the medium lived radionuclides. So even if the activities of 129I and
99Tc are not higher than the one of the same amout of U, they present a
greater hazard, due to their environmental mobility.

Peter





"Brennan, Mike  (DOH)" <Mike.Brennan at DOH.WA.GOV> writes:
>Hi, Peter.
>
>First, thank you for presenting me with a reason to look at this subject
>again.  It has been a while since I paid more than passing attention to
>fission fragments, and it is an interesting topic, core to some of the
>worst (from a technical aspect, anyway) of the arguments surrounding
>nuclear power.  
>
>>small ?
>>99Tc: 6.05% thermal 235U fission yield
>>135Cs: 6.33%
>>129I: 0.66% only
>>93Zr: 6.30%
>
>OK, so about 1/5th.  Depends, I guess, on your definition of "small".
>On the other hand, if you look at activity when the fuel comes out of
>the reactor, the long lived fission products (LLFP) are by anyone's
>definition a small fraction of the total.  As an example, 135Cs and
>137Cs both account for about 6.3% of the atoms in the fission fragment
>inventory.  Because of the difference in their half lives, however, in
>fresh spent fuel 137Cs produces about 76,000 times as much radiation as
>the 135Cs in the fuel.  The 137Cs decay is also about 4 times as
>energetic.  
>
>I might concede "small" and go up to "modest" on the % of atoms in fresh
>spent fuel that are LLFP.  On the other hand, I would revise the % of
>activity from "small" to "vanishingly small" or "trivial" in comparison
>the short half life fission products.  
>
>I am now uncertain when the total activity of the spent fuel becomes
>less than the total activity of the fuel before going into the reactor,
>but I am pretty confident of two things: (1) It is a long time; long
>enough that I won't be personally concerned, and (2) in a much shorter
>time frame, a couple of hundred years or so, the activity of the fuel
>will have decreased to the point where the greatest danger is from one
>of our less sophisticated descendants taking a length of fuel rod and
>beating someone over the head with it. 
>
>As for transmutation of LLFP, I've seen some articles speculating on it,
>but I frankly don't see the need.  If it happens when spent fuel is put
>in a fast flux reactor to burn more of the fissile material, cool, but I
>just don't see that in and of itself transmutation (with any foreseeable
>tech) is worth the effort.
>
>Thanks again for pointing my attention this way. 
>
>-----Original Message-----
>From: Peter Bossew [mailto:Peter.Bossew at reflex.at] 
>Sent: Wednesday, December 09, 2009 12:04 PM
>To: Brennan, Mike (DOH)
>Cc: radsafe at radlab.nl
>Subject: Re: [ RadSafe ] Global Warming
>
>"Brennan, Mike  (DOH)" <Mike.Brennan at DOH.WA.GOV> writes:
>>There aren't actually a lot more isotopes after the etc.
>
>
>this is true.
>
>
>>, but yes, there
>>are some fission fragments that have long half lives.  However, they
>>represent a small fraction of the inventory of fission products in
>>"fresh" spent fuel, either on an atom basis or an activity basis.  They
>>also generally represent a small fraction, again on an activity or atom
>>basis, of the fissile material that was consumed by the reaction (the
>>exact ratio is dependent on many factors). 
>
>
>small ?
>99Tc: 6.05% thermal 235U fission yield
>135Cs: 6.33%
>129I: 0.66% only
>93Zr: 6.30%
>
>while 99Tc and 129I can be subjected to transmutation (in principle; if
>someone is willing to pay for this), 135Cs and 93Zr cannot, to my
>knowledge.
>
>Has anybody calculated what a system - certainly scientifically
>beautiful,
>on paper -  would cost (e.g. in Euro / MWh) which includes advanced
>reactors, reprocessing of high burn-up fuel, actinide burning,
>transmutation of fission products, and including probably decades of
>development until it works large scale ? Any figures available ?
>
>Peter Bossew
>
>
>
>> In most cases, even with the
>>long lived fission fragments mentioned, somewhere in the 300 to 500
>year
>>range the spent fuel will probably become less radioactive than the
>>fresh fuel was, even including the unused fuel and fissile
>transuranics.
>>It gets even better with reprocessing.
>>
>>So, if the assumption is that radioactive material is bad, and that we
>>need to be willing to sacrifice now in order to protect less
>>technologically sophisticated later generations, it is clear that the
>>ethically sound choice is to use as much uranium as possible now to
>make
>>electricity, so that there will be less radioactive material in the
>>world later.
>>
>>-----Original Message-----
>>From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
>>Behalf Of Peter Bossew
>>Sent: Wednesday, December 09, 2009 3:47 AM
>>To: gstanford at aya.yale.edu
>>Cc: radsafe at radlab.nl
>>Subject: Re: [ RadSafe ] Global Warming
>>
>>George Stanford <gstanford at aya.yale.edu> writes:
>>
>>(...)
>>>
>>>
>>>     Then the only waste would consist of fission 
>>>products, which can be easily isolated in various 
>>>ways for 300 - 500 years, by which time their 
>>>radioactivity has decayed below any reasonable level of concern.
>>
>>(...)
>>
>>129I: half life 1.57e7 a
>>99Tc: 2.11e5 a
>>135Cs: 2.3e6 a
>>etc.
>>
>>
>>Peter Bossew
>>
>>_
>