Re: Davis-Besse corrosion?

[Tim <tstead@ntirs.org>]

You are correct in that boric acid is dilluted in the

RCS as a chemical shim for long-term reactivity

management.  It is not a fission product.



As far as steam slicing through the RPV, that would

not explain why the stainless steel was not attacked. 

Also, examination of the surface area of the exposed

carbon steel would clue one in on the destructive

mechanism.



I would think that the steam would cut the head like a

knive instead of essentially carving out a rectangular

area from the head.  In addition, I doubt anyone

washes their eyes with 600 deg. boric acid and as

temperature goes up, so do corrosion rates with many

acids.  I'm not an expert in corrosion mechanics of

carbon steel vs. high temp boric acid so this is just

a guess based on my knowledge of how other acids

behave.



A SEM of the exposed surface of the RPV head would

pretty much answer these types of questions.



Regards,

Tim Steadham



--- Christoph Hofmeyr <chofmeyr@nnr.co.za> wrote:

> Sandy, Radsafers,

> 

> I get the impression that there is a bit of

> questionable information

> being distributed on the Davis-Besse problem.  Since

> when is "The acid

> ... a byproduct of the nuclear fission process

> inside the reactor"?

> Boric acid is a design element of criticality

> control and part and

> parcel of any PWR cooling system. It is also

> difficult to accept that

> the stuff which is mild enough to be used as an

> eyewash has corroded

> through six inches of steel.  At the temperature in

> question, the boric

> acid would tend to dry to a solid in air. The

> question I heard mooted by

> experts is whether a more realistic mechanism would

> not be that the

> steam leak resulted in high pressure steam cutting

> of the metal.  The

> rate of progress of that process could conceivably

> be quite different

> from corrosion.

> Chris Hofmeyr

> chofmeyr@nnr.co.za



__________________________________________________

Do You Yahoo!?

Yahoo! Tax Center - online filing with TurboTax

http://taxes.yahoo.com/

************************************************************************

You are currently subscribed to the Radsafe mailing list. To unsubscribe,

send an e-mail to Majordomo@list.vanderbilt.edu  Put the text "unsubscribe

radsafe" (no quote marks) in the body of the e-mail, with no subject line.

You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/