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Re: Question on Properties of Aluminum at Research Reactor
Paul
My guess is that the Pu-212, Pb-214 and Bi-214 are radon progeny that plated
out from the decay in the water. The Co-60 and Eu-152 could be formed from
neutron capture of trace amounts of cobalt and europium in the water. Co-59
(100% of stable cobalt) and Eu-151 (~50% of stable) europium. This can be
checked by looking for Eu-154. The ration of the capture cross section of
Eu-151/Eu-153 is 5900/320 so the Eu-154 "abundance" will be 320/5900 times
that of Eu-152.
John
_______________________
John R Johnson, PhD
idias@interchange.ubc.ca
----- Original Message -----
From: "Paul E. Benneche" <peb@VIRGINIA.EDU>
To: <radsafe@list.vanderbilt.edu>
Cc: "Paul Benneche" <peb@VIRGINIA.EDU>
Sent: Tuesday, April 22, 2003 10:05 AM
Subject: Question on Properties of Aluminum at Research Reactor
> We are completing the decommissioning work at the University of Virginia
> Nuclear Reactor Facility and are having a few problems with some of the
> enbedded aluminum structure in the reactor pool area.
>
> Over the lifetime of our two megawatt research reactor (1960-1998) the
> aluminum reactor pool gate frame was in constant contact with reactor pool
> water, except for a nine month period in 1968. The rest of the 70,000
> gallon pool was epoxy paint coated concrete. The pool was permanently
> drained about six months ago.
>
> While full, the pool water was always kept very pure, with a conductivity
> between 1 and 3 micromhos/cm. The water was recirculated through a carbon
> filter and a mixed bed demineralizer. It appears that the uncoated
> aluminum may have either absorbed dissolved radionuclides out of the pool
> water or it was manufactured with trace amounts of uranium or thorium
> related radionuclides within the material. These constituents seem to be
> near the surface and can be removed with aggressive cleaning with either
> high pressure water or lye. However, some time after cleaning the
> radionuclides reappear on the surface of the aluminum (detectable at the
> surface with a thin window, large area, gas flow proportional counter, but
> not readily removable). We hypothesize that if there is uranium, thorium
> or some other radionuclide within the aluminum that the cleaning that we
> are doing may be selectively removing shortlived radioactive daughter
> products from the surface that are then returning by building in over time
> from their parent isotope. Note, this gate frame was far enough distant
> from the reactor that there was no possibility of neutron activation of
> the material.
>
> When examined by a long count on a germanium detector the following
> radionuclides were observed above background levels in the gate frame
> material:
>
> Pb-212, Pb-214, Bi-214, Co-60 and Eu-152
>
> The lead and bismuth may be from naturally occurring uranium / thorium
> that may be in the aluminum and the cobalt and europium are activation
> products that may have been "absorbed" out of the water.
>
> Does anyone have any insight as to what we may be observing, as to why we
> can clean the surface of the aluminum but the contamination returns in
> about a month. Any help would be appreciated. Email or call me.
>
> Paul E. Benneche
> University of Va. Reactor Supervisor
> peb@virginia.edu (e-mail)
> 434-982-5440 (work phone)
>
>
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