March 25th, 2011- Issues with seawater in a BWR – Crack growth rate found to be 30 times higher than KAPL paper

From: Csontos. Aladar
To: Klein Paul; Taylor. Robert
Subject: Re: Stress Corrosion Crack Growth Rates of Stainless Steels in Chloride Solutions.docx
Date: Friday, March 25, 2011 2:27:35 PM

Rob,

I agree with Paul that SCC is a secondary issue and only an issue as it allows the core radionuclides a pathway for release. Also, I agree with Paul that my #3 bullet should be caveated with many assumptions/best estimates, so use with caution. I could be wrong, but I thought the bottom RPV penetrations and SRV interals also use susceptible stainless steels.

Paul, as normal, has done a fantastic job pulling us together.

Al

From: Klein, Paul
To: Taylor, Robert
Cc: Csontos, Aladar
Sent: Fri Mar 25 14:14:57 2011
Subject: RE: Stress Corrosion Crack Growth Rates of Stainless Steels in Chloride Solutions.docx

Rob,

To follow up NRC staff’s initial comments on the “Issues with seawater in a BWR” paper, I asked RES to examine the literature to see if the staff could provide a better ballpark estimate of SCC crack growth rates given that we thought the number provided in the paper could underestimate the rate.

I am forwarding Al’s email below to you since you are in a good position to digest the contents while also understanding there are many uncertainties (e.g., we don’t know the actual environment conditions) that can significantly affect stress corrosion crack growth rates. Here’s my take on the information:

1. Our best estimate for crack growth rates, considering the scatter in the existing test data and uncertainties associated with the actual environment, is on the order of 0.030 inches per day or 30 times higher than was in the KAPL paper.

2. I have attached a summary of information compiled by Darrell Dunn related to CGRs in chloride solutions.

3. I have included Al’s points below for some background information, but we should be cautious about trying to draw too many conclusions given the very limited information available.

4. Overall, I think SCC cracking remains a secondary priority given other current issues. Their plan to switch to freshwater injection as soon as possible is also a beneficial change with respect to SCC.

As to be expected Al, Dave Rudland, and Darrell did a great job pulling together and digesting some relevant crack growth rate data.

From: Csontos, Aladar k
Sent: Friday, March 25, 2UI1P-.2:30. .A..M……………..
To: Klein, Paul
Subject: IW: Stress Corrosion Crack Growth Rates of Stainless Steels in Chloride Solutions.docx

Paul,

Here’s Darrell’s writeup on the CGRs. I think we ought to change the 0.001 in/day number that’s in your writeup to reflect a more realistic number based on the attached. With residual stresses in welds, a 0.03in/day number seems more realistic from Tamaki’s 1991 paper. We should at least send this out to folks to see what they think is reasonable.

Other bullets that I wanted to send to you that you can adjust: Boric acid, salt deposits, and 100C saturated brine salt water will lead to degraded
piping, RPV, and other primary loop components over time (within weeks of the initial sea water injection).

Preliminary component integrity calculations with best estimate CGRs found in the peer reviewed literature as a function of stress intensity indicate that throughwall circumferential cracking can occur within 21 days for a 0.5″ thick pipe and 30-59 days for 1″ thick pipe that is contacting the 100C brine water/hydrated salt precipitates on both ID and OD.

The calculations also indicate that many circumferential cracks would arrest prior to growing throughwall, but, may grow throughwall during an aftershock seismic event.

These cracks would lead to some leakage from numerous throughwall cracks and pits, but, without significant pressures, the leaks may be limited.

Nevertheless, this is a fast pathway for further radionuclide release into the environment. Moving from sea water to fresh water may reduce this degradation, however, further degradation will continue even in diluted salt water.

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