Document: NUREG-0800
Document ID: 122fd05c-21bf-4590-a927-328d9ae856bb
Document Type: srp
Title: and 2.4.11.
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340561.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.4.1
CFR Part: 
CFR Title: 

Content:
The applicant proposes one kind of warning scheme for rainfall floods and another type of warning scheme for seismically-induced dam failure floods. For rainfall floods, the first stage (Stage I) of shutdown will begin when sufficient rainfall occurs to yield a projected plant site water level of 697.0 feet above mean sea level'in the winter months (October 1 through April 15) and 703 feet above mean sea level in the summer months (April 16 through September 30). These water levels assure that any additional rain will not produce water levels in excess of 703 feet mean sea level in less than 27 hours. This level provides a two-foot margin (requested by us) so that waves resulting from high winds cannot disrupt flood protection preparation, i.e., cannot exceed plant grade of 705 feet above mean sea level. 2.4.14-3 Rev. 2 - July 1981 Stage I will be maintained until either Stage II begins, or until the applicant determines that floodwaters will not exceed elevation 703 feet above mean sea level at the plant. Stage II shutdown will begin only when enough additional rain has fallen to yield water levels in excess of 703.0 feet above mean sea level. The applicant estimates that required shutdown procedures will take no longer than 24 hours, which allows a three-hour contingency margin. As stated in Section 2.4.4 above, the failure of nine upstream dams either singly or in varying combinations can produce floods over plant grade. Stage I.shutdown will be started upon notification that any one of these dams has failed, and will continue until it has been determined that critical combinations do not exist. At our request, the applicant committed to initiating Stage II shutdown if communica- tions are lost, or if there is no certainty that critical combinations do not exist in such situations. Three communication networks are available to the applicant: (1) the applicant's own microwave network; (2) the applicant's own powerline carrier system; and (3) the commercial Bell