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Bernie —
Unless you spent many 80+ hour weeks in the RSI decontamination effort as I
did, I would caution you from making snide comments about the findings of the
decontamination effort. I will attempt to address your comments in a
professional manner.
I'm not saying that concrete or dirt will sorb CsCl out of other
substances, such as high-level waste. Certainly you understand the chemical
processes of sorption / desorption. I WAS indicated that not all of the CsCl
will remain dissolved in water, despite its enormous solubility (you could
dissolve the entire 2,000 Ci source we've been talking about, assuming it's
CsCl, in less a liter of water) ... some of will will sorb deep into surfaces,
and be VERY resistant to simple cleaning methods such as rinsing, or even
vigorous cleaning with solvents.
At RSI, CsCl migration into soil was enhanced by expansion joints in the
concrete slab (a standard construction technique) surrounding the pool. The clay
surrounding the pool, however, was well packed, and precluded MOST of the CsCl
from migration more than a few inches into the soil. However, where structures
(such as the pilings around the pool wall) entered the soil, water apparently
ran down interstitial spaces around the surfaces, resulting in contamination to
some depth. I would expect the same thing to happen along pavement joints,
cracks in sidewalks, joints between sidewalks and buildings, etc.
As for your comment about the use of stainless steel tanks, I believe
you'll find that most HLW tanks are in fact carbon steel, not stainless. Despite
this, our friends in DOE keep telling us that it's far more effective to simply
grout tanks in place that to decontaminate them, despite "vigorous attempts" at
decontamination. Savannah River Site (SRS) has already grouted several HLW tanks
removed from service. As for stainless, we have months worth of data from the
RSI cleanup documenting the sorption of CsCl onto stainless steel from
contaminated water, and likewise, the desorption of CsCl back out of the
stainless steel into "relatively clean" water. Ask anybody who's ever shipped
spent fuel in a stainless steel cask whether contamination of the external cask
surface from spent fuel pool water is a problem.
I am not familiar with any Cs tracer tests, but I am familar with the RSI
cleanup, the extent to which CsCl spread through the structure, and the
difficulty of removing that CsCl. I wish it were as simple as hosing the
surfaces off, but unfortunately, it isn't.
Hmm ... I hadn't thought about "tasting" the salt. Does anybody have any
idea how much salt you have to have to actually "taste" the salt? I remember
seeing somewhere an estimate that a grain of NaCl salt is somewhere around 6E-5
g. A "grain" of CsCl might weigh 2-3 times as much ... let's call it 2E-4 g. Is
that enough to taste? If so, and if it were CsCl from a Hanford WESF capsule, it
would contain about 3.6 mCi of Cs-137 ... I don't think I'd be inclined to
try to taste it.
If I remember correctly, the specific activity of 137CsCl in the WESF
capsules from Hanford is about 18 Ci/g ... and it had a pretty good impurity
load in it ... maybe call it 20 Ci/g for relatively pure CsCl. I'm pretty sure I
could put several grams of "salt" in my (small) front yard and not effect the
growth of my "grass" (it's actually more like an experiment in biodiversity!) in
the least ... but if it was CsCl "salt", I don't know that want to be running
back and forth over the grass with a lawnmower <grin> I wouldn't depend on
grass growing or not as being an indicator as to the presence or absence of
CsCl.
As to records on the decontamination of surfaces at RSI, I'm sure that
Chem-Nuclear (the cleanup contractor) has boxes and boxes of survey
results. These survey results document levels of contamination found on a
number of surfaces (e.g., concrete, painted carbon steel, stainless steel)
before any decontamination, and after utilization of a number of decontamination
techniques. The fact that removal of concrete was necessary to address fixed
contamination, in my opinion, speaks volumes as to what sort of efforts might be
required to decontaminate building and road surfaces ... depending, of course,
on what federal, state and local officials and (let's not forget them) the
public agree are "acceptable" levels for decontamination.
The RSI facility was decontaminated in accordance with Reg. Guide 1.86
limits, not to background, as you assert. I'm not aware that the federal
government has established any other cleanup levels that might be applicable to
"terrorist" events. I'm sure that there would be much weeping and gnashing of
teeth over "how clean is clean".
As always, my $0.02 worth ...
Jim Hardeman
>>> BERNARD L COHEN <blc+@pitt.edu> 2/28/2003 9:54:44 >>> On Thu, 27 Feb 2003, Jim Hardeman wrote: > Another aspect of this problem is that part of the CsCl will bind with soil and building materials, such as concrete. --Then to solve the problem with leaking tanks at Hanford, all they had to do was pour in dirt and small pieces of concrete? > One aspect that most folks don't think about is that concrete and even stainless steel are pretty porous, and much of the contamination may be "below surface" ... you clean the surface today, and then come back a week later, and it's crapped up again. The only way to truly remove the bulk of the contamination is to remove that portion of the surface into which the contamination has seeped. CsCl disolved in water will also seep down to soil in expansion joints in roadways, etc. --If it seeps down into soil so rapidly, why doesn't it continue to seep down until it gets so far down that the soil above becomes an effective shield --If stainless steel and concrete are so porous, why are they used for tanks to contain high level waste after reprocessing? --Have there been tests where Cs tracer is spread on materials and they are hosed with water after a brief time? --The enormous quantities of salt we spread on roads for de-icing must result in large quantities splashed onto soil and buildings. A few months later, are they salty? This can easily be tested with one's tongue. Will grass grow on salty soil? > Just as an example, your federal government spent about $45 million cleaning up an industrial facility in Decatur, GA into which approximately 10 Ci of Cs-137 as CsCl had been released --They were trying to reduce radioactivity to background, not just to levels that make the area unsafe. Is there info available on what fraction of the radioactivity was removed by hosing and washing, before starting to remove building materials? |