Re: Radiation Hardness of materials

[Schoenhofer <schoenho@via.at>]

At 13:02 05.12.1996 -0600, you wrote:
>This info is from my previous life as a DOE consultant.
>
>There was some work done in Idaho (INEL) a few years back.  They had some Be
>reflector blocks from the Advanced Test Reactor that required disposal.  The
>blocks were high in H-3 (approx 100,000 Ci each) but the H-3 was typically
>not available for release unless the Be corroded.  The intended disposal
>method was in concrete lined shafts within INEL LLW disposal facility.
> Since, the concrete liner wouldn't prevent water intrusion (and hence
>corrosion) and the fact that the concrete itself also causes corrosion, it
>was decided to provide an additional liner, between the waste form and the
>concrete in the form of seamless, extruded High Density Polyethylene (HDPE)
>pipe.  Since the HDPE had a wall thickness of almost 2", and the top and
>bottoms caps were heat welded, it was thought that this additional liner
>would be a very effective barrier to both the intrusion of water, and if any
>release waste form occured, the release outside the shaft of H-3.
>-----------------------------------------------------------------------

Kelly,

One of the consequences of my subscribing to Radsafe is, that I get to know
about a lot of different problems associated with radionuclides, their
disposal etc. So I learn a lot - as I did now about Be-reflectors loaded
with terrible amounts of tritium and the brittling of plastic. Let me just
mention one thing: The HDPE would hardly prevent the escape of tritium -
tritium is (like iodine) something which will diffuse out of everything and
you will find contamination everywhere and at any place you would not expect
it. Two inches is quite a wall thickness, but since tritium would have had
time enough (until eternity), it would diffuse out. This behaviour seems to
be independent whether tritium is present as HT or HTO. We did some work on
diffusion of tritium from luminous dials through plastic encasing of the
watch to the body. Tritium behaves as if no barrier was present!

As to the question of degradation of plastic due to high doses of radiation
I am not surprised - compare the energy necessary to break C-C bonds and the
energy of for instance Co-60 radiation. Of course the extend of broken bonds
depends on the dose. I would never encapsulate any radionuclide in plastic
to keep it for "eternity". 

Franz
Schoenhofer
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