Document: NUREG-0800
Document ID: 9061fdf7-74fc-4c1f-8378-738cfa4a84cb
Document Type: srp
Title: through 2.4.7 and the controlling flood level is selected.  The controlling flood
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070240.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.4.3
CFR Part: 
CFR Title: 

Content:
estimated to be partially diverted to the 21 leveed G and H floodways upstream of the site, with 42,500 m /s (1,500,000 cfs) 3 22 continuing downstream within the levee system past the plant site. The applicant concluded that the PMF could result in overtopping of levees and flooding of the river valley well upstream from the site, thereby causing generally low level flooding in the plant area. The upstream levee overtopping and resulting valley flow during such an event would reduce the flow in the main levee channel adjacent to the site to levels equal to or less than those that would exist during a PDF. We conclude that the combination of a runoff-type flood less severe than a PMF, but more severe than a PDF, and a coincident levee break in the vicinity of the site could occur before water approaches levee grade upstream. A failure or levee breach, when the levee is full to design capacity 3 feet (1 m or 3 ft) below the top of the levee adjacent to the site plus the effects of any 23 coincident wind-generated wave activity), would result in a higher water surface at the DRAFT Rev. 4 - April 1996 2.4.2-8 plant than a PMF spread over the valley as a result of levee failures upstream. At our request, the applicant evaluated various modes of levee failure in the vicinity of the plant. One of the conditions postulated is that of a flood, approaching the severity of a PMF, causing a massive failure of the upstream left bank levee along the G floodway, resulting in flooding around the plant, coincident with a failure of the levee adjacent to the plant site. The applicant estimated the resulting water level at the plant would reach elevation 22.5 feet 6.9 m (22.5 ft) MSL for this case. The case of an instantaneous levee failure 24 adjacent to the plant, with no upstream levee failure, resulted in an estimated water level of 24.6 feet 7.5 m (24.6 ft) MSL. Based upon this evaluation, the staff concludes that, 25 in order to meet the requirements of General Design Criterion