RE: Steam Generator Contamination

[Glen.Vickers@ucm.com]

This response would have come a little earlier, but I'm a little busy
considering our plant is currently in a steam generator replacement outage.
Composed most of this at home... The question was,

	>Do anyone of you know the level and nuclides of radioactive
contaminants
	>in a steam generator channel head? It would be also appreciated if
you'd
	>let me know where I can get this kind of information for various
types of
	>plants and who is an expert on this. Thanks in advance.

A good source of data would be EPRI radiological surveys performed each
outage.  I know many radiological measurments are performed, but can't
remember if we also performed isotopic analyses of the contamination at the
same time.  

The diaphragm, metal plate between the tensioned manway cover and reactor
coolant, would probably be the ideal item to gather data on.  The
contamination levels on the diaphragm should be consistent with the levels
in the other part of the steam generator bowl/channel head with perhaps an
exception to the bottom of the tube sheet.  The tube sheet will likely have
visible borated deposits and be likely to possess higher contamination
levels.  Radiation measurements of this ~24" diameter diaphragm are
typically taken with an ion chamber in the window open and window closed
position.  I believe the smears of the diaphragm are also measured to
determine contamination levels.  These diaphragms will also generally have
additional radiological surveys performed, because they must later be worked
by personnel.  

With the creation of the "SCO" shipment class for radioactive materials,
many facilities will have good correlation factors for ion chamber readings
to contamination levels.  The factors will vary somewhat, but you should be
able to use an average from a couple of different PWRs and be able to
convert with acceptable error.  I would think two significant figures of
accuracy would be reasonable, not sure about three without further study.  I
would choose PWRs of similar age and model.

Isotopic distribution

We are in the process of cutting out our Westinghouse D-4 steam generators
and I have a little isotopic data available.  We at Braidwood are a four
loop, ~1200 MW plant, and both units came on line in 1987, 1988 time frame.
I have isotopic data from a 100 cm^2 smear in the channel head as well as an
isotopic of blast media used to clean the loops.  I was interested in the
blast media, because it should contain all layers of potential crud built up
over the years.  I was specifically looking for differences in percent
abundance in ratios such as Co-60/Co-58 or others which might infer an
"aged" or built up layer.  I haven't had time to evaluate the data, but here
it is.

Channel head smear, 		Blast Media
160 mrem/hr, (w/o-w/c)*5

	uCi/smear		uCi/g
Cr-51	2.403E0		1.526E-1
Mn-54	1.632E-1		1.483E-1
Co-57	1.669E-2		1.074E-2
Co-58	4.657E0		3.217E0
Fe-59	1.055E-1		2.330E-2
Co-60	6.786E-1		4.157E-1
Zn-65	2.098E-2		9.412E-3
Nb-95	1.795E-1		1.533E-2
Zr-95	9.521E-2		4.584E-3

Notice the presence of every activation product.  I made sure I had enough
activity to get the lower abundance contributors.

Distinct absence of Cs and Sb isotopes.  These tend to be removed by ion
exchange resins.

I'm not sure the smear data is constant from outage to outage.  Each outage
we undergo a curie reduction process known as "Early Boration/Hydrogen
Peroxide" addition.  These processes greatly affect the specific activity of
the coolant.  If all of the species dissolve and precipitate out equally,
then perhaps the ratios might not be influenced that much, but I won't offer
an opinion at this time.  The curie reduction process is also a little
different each time as they try to increase the efficiency of the process
and also complete in a shorter time period.  I could see how a steam
generator could be left with a lot or a little of precipitates without much
surprise.

Once again, go for the EPRI data for steam generators and possibly look at
their curie reduction processes as a side bar.



Sincerely,
Glen Vickers
Braidwood Nuclear Power Station
glen.vickers@ucm.com <mailto:glen.vickers@ucm.com> 

Many more stories about steam generator maintenance...  RP coverage of steam
generator work encompasses every facet of reactor health physics*10.
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