ML23109A077

NRC-2022-000160 - Resp 2 - Final, Agency Records Subject to the Request Are Enclosed, Part 1 of 7

ML23109A077
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Issue date:	04/13/2023
From:	NRC/OCIO
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ML23109A075	List: ML23109A076 ML23109A077 ML23109A078 ML23109A079 ML23109A080 ML23109A082 ML23109A083 ML23109A084
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NRC-2022-000160
Download: ML23109A077 (1)

Text

-*om: Mitman, Jeffrey nt: Thursday, June 18, 2009 9:46 AM

. u: Galloway, Melanie

Subject:

RE: Keowee Dam If Duke raised only the Keowee Dam proper, meaning the dam from the spillway on the east to the CCW discharge on the west, they would protect the Keowee power-house which, as you know, is their source of emergency power. They would also protect the switchyard which is their source of offsite power.

If they continued the flood protection further to the west and south to include the Little River portion of the reservoir, they would also prevent failure and flooding at the intake canal structure. This would increase protection against water coming over the dike and onto the yard near the SSF (which is the source of the flooding predicted by the 1992 analysis. Presumably, this added protection would also prevent water from flowing down Highway 130 (what I've been calling the backdoor) onto the yard at the SSF.

A combination of the two above changes would also protect the !(b)(7XFl. (bX3) 16 u s.c. § 8240-l(d)

!(bX7XF>. (bX3):I6 us c . § s24o-l(d) I Under the current design not only is electrical power lost to these systems but the rooms where the pumps are located are physically threatened by water entering the rooms.

With this raising of flood protection Duke could also elevate one or more of the roads and/or bridges onto the site. This would increase the reliability of offsite access during and after any failure.

This buys them much more than simply raising the local flood protection of the SSF. As we've discussed 1ising and/or improving the local SSF flood protection leaves them still dependent on a highly unreliable SSF Nith a failure probability of ~27%). The increased "dam" height reduces the dependency on the SSF because the normal and emergency systems remain available during the transients . In PRA jargon, the increased height reduces the risk importance of the SSF during floods. This appears to add substantially to their defense-in-depth, something that raising the locally SSF flood protection does not achieve.

A couple of comments on this potential solution. I'm not a civil/structural engineer, but this looks like a lengthy and difficult process, especially near the intake canal. There is little room to widen the base of the dike here that would allow them to build a higher dike. Second, the discussion about overtopping becomes even more significant under this potential fix, because in all probability increasing the amount of water and the size of the break at Jocassee, increases the flood height at ONS. This will increase the height of the required dam to protect it against these higher flood heights. For example, currently HEC-RAS is predicting a flood height of

... X3....

l(b... u-s"""c...11f we include overtopping, a larger breach size and a worst case scenario not the conservative realistic 1~...

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flood Duke currently wants to use) they may be looking at a flood of 16 or 3~: 16 U.S.C .S.C Jeff From: Galloway, Melanie Sent: Thursday, June 18, 2009 7:51 AM To: Mitman, Jeffrey

Subject:

Keowee Dam Mike and I were discussing a bit what the lie would hope to gain by raising Keowee. Can you elaborate?

Saving the hydro units? Not flooding the SSF? the turbine building? The switchyard? Any details you can

, rovide would be appreciated. Thanks