ML19221A957
| ML19221A957 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-02.4.4, NUREG-75-87, NUREG-75-87-2.4.4, SRP-02.04.04, SRP-2.04.04, NUDOCS 7907120050 | |
| Download: ML19221A957 (7) | |
Text
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/,e U.S. NUCLEAR REGULATORY COMMISSION f>w( l S iMpf STANDARD REVJEW PLAN
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OFFICE OF NUCLEAR REACTOR REGULATION SECTION 2.4.4 POTENTIAL DAM FAILURES (SElsMICALLY-INDUC[D)
REVIEW RESPONSIBILITIES Primcry - Hydrology and Meteorology Branch (HMB)
Secondary - None I.
/dEAS OF REVIEW In this section of the safety analysis report (SAR) the hydrogeologic cesign basis is developed to ass;re consideratica in plant design of any potential hazard to the safety-related facilities due to the failure of upstream and downstream water contrn1 structures from seismic causes. The areas of review include consideration of flood waves (bores) f am severe breaching of upstream dams and the potential loss of water supply due to failure of a downstream dam, domino-type failurts of dams, landslides, and effects of sediment deposition and erosion.
When data are 9rovided to show that seismic events will not cause failures of upstream dams that could produce the governing flood at the plant, this section may contain additional data and other information to support a contention that the dams are equivalent to seismic Category I structures and will survive a local equivalent of the safe shutdown earthquake (SSE) or will survive the operating basis earthquake (OBE). In such cases the Geosciences Branch (GB) and Structural Engineering Branch (SEB), as necessary, will evaluate the data necessary to justify such a classification. GB and SEB review proce-dures are outlired in the appropriate geosciences and structural SRP sections. The balance of this SRP section applies to the hydrologic analyses of non seismic Catagory I u*s ar,d U Mc cry I 'kms that could be af fected by floodwaves caused by upstream failures of the non seismic Category 1 dan Where analyses are piovided in support of either a conclusion that a probable maximum flood (PMF) should be the design basis flood for a stream, or that a postulated or arbitrarily assumed seismic 311y-induced flood is the design basis flood for a stream, the areas of review consist of the following:
1.
Conservatism of modes of assumed dam failure and deposition of debris downstream.
2.
Consideration of full flood control reservoirs.
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3.
Conservatism of downstream flow rates and levels depending on whether failure is postulated with an equivalent SSE coincident with a 25 year flood, or an OBE coincident with a standard project flood (SPF). An SPF is considered to be about torty percent of a PMF.
4.
Flood wave attenuation i.o downstream dams, or to the site, whichever would be encountered first.
5.
Potential for mutiple dam failures; flood wave effects and ootential for failure of downstream dams.
6.
Hydraulic failure of downstream dams induced by upstream failures.
7.
Dynamic effects on exposed plant facilities of possible bores.
8.
Conservatism (see item 3 above) of ambient flow conditions for downstream dam failures that can influe" ? safety-related water supplies.
9.
Applicability and conservatism of models used to predict the effects of dam failure floods.
!I.
ACCEPTANCE CRITERIA The staff will review the applicant's analyses and independently assess the coincident river flows at the site and at the dams being analyzed. The acceptable " worst conditicas" to t,e postulated for analysis of upstream f ailures are: (1) dam able to withstand SSE (equivalent to seismic Category I structures)--assume no failures; (2) dam failure caused by SSE-~ assume dam failure coincident with 25 year flood and 2 year extreme windspeed at the site; and (3) dam failure caused by OBE--assume dam failure coincident with SPF and 2 year extreme windspeed at the site. The < plicant's estimates (which may include landslide-induced failures) of the flood discharge resulting from the " worst conditions" should be no more than 5 percent less conservative than the staff's estimates to be acceptable. If the applicant's estimates differ by more than 5 percent, the applicant should fully document and justify its estimates or act.ept the staff's estimates and redesign applicable flood protection.
For SAR Section 2.4.4.1 (Dam Failure Permutations): The location of dams and potentially "likely" or severe modes of failure must be identified. The potential for multiple, seismically-induced dam failures and the domino failure of a series of dams must be discussed. Approved models of the Corps of Engineers and the Tennessee Valley Authority are used to predict the downstream water levels resulting from a dam breach (Refs. 4, 8, 13, 14 and 15). First-time use of other models will require complete model description 9
mm Rev. 1 2.4.4-2
and documentation. Acceptance of the model (and subsequent analyses) is based on the staff review of model theory, available verification, and application. A determination of the peak flow rate and water level at the site for the worst possible combination of dam failures and a summary analysis (that substantiates the condition as the critical permuta-tion) must be presented, along with a descriptic (and the bases) of all coefficients and methods used. Also, the etsects of other concur _nt events on plant safety, such as blockage of the river and waterborne missiles, must be considered.
For SAR Sections 2.4.4.2 (Unsteady flow Analysis of Potential Dam Failures) and 2.4.4.3 (Water level at Plant 3ite): The effects of coincident and antecedent flood flows (or low flows for downstream s'cuctures) on initial pool levels must be cor.sidered. Use of the methods given in Ref(rences 1 or 3 is acceptable for determination of initial pool levels.
Dependir.g upon estimated failure modes and the elevation difference between plant grade and normal river levels, it may be acceptable to use conservative simplified procedures to estimate flo'd levels at the site. Where calculated flood levels using simplified methods are at or above plant grade and using assumptions which cannot be demonstrated as conserva-tive, it will be necessary to use unsteady flow methods to develop flood levels at the site.
References 8 and 9 are acceptable methods; however, other programs would be accept-able with proper documentation and justification. Computations, coefficients, and methods used to establish the water level at the site for tne most critical dam failures must be summarized. Coincident wind generated wave activity should be considened in a manner similar to that discussed in SRP Sectior 2.4.3.
Appropriate sections of the guides described belcw are used by the staff to determine the acceptability of the applicant's data and analyses. Regulatory Guide 1.59 provides guidance for estimating the design lasis for flooding considering the worst single phenomena and combination of less severe phenomena. Regulatory Guide 1.135 describes methods for deter-mining normal water levels. (All estimated water levels should be referenced to normal or mean water levels.) Regulatory Gu;de 1.29 identifies the safety related structures, systems, and components, and Regulatory Guide 1.102 describes acceptable flood protection to prevent the safety related facilities from being adversely affected.
III. REVIEW PROCEDURES The conservatism of the applicant's estimates of flood potential and low water levels f rom seismically-induced structure failures is judged against the criteria indicated in subscction II above. An analysis is performed using simplified, conservative procadures (such an instantaneous failure, coincident SPF flows, minimal flood wave attenuation, and extrapolated site discharge-rating curves). Techniaues for such analyses are identified in standard hydraulic design references and text books, such as those listed in the reference section. If no potential flood problem exists, the staff safety evaluation report (SER) input is written accordingly. If the simplified analysis indi-cates a potential flooding problem, the analysis is repeated using a more refined tech-nique which may include time rate of failure and hydrometeorologically compatible storm 145 2 %
2.4.4-3 Rev-I
centerings. Detailed failure models, such as those of the Corps of Engineers and the Tennessee Valley Authority, are utilized to identify the outflows from varicus failure mooes. Models of the Corps of Engineers or the Tennessee Valley Authority are used to w
identify the outflow characteristics and resultant water level at the site (Refs. 4, 8, 13, 14 and 15).
The staff will develop a position based on the analyses performed; resolve.
if possible, differences between the applicant's and staff's estimates; and write the E R input accordingly.
The above reviews are performed only when applicable to the site or site region. Some items of review may be done on a generic basis.
IV.
EVALUATION FINDINGS For construction permit (CP) reviews, the findings will summarize th( applicant and staff evaluations of the design basis maximum and minimum water levels caused by seismically-induced dam failures. If the applicant's estimates are within acceptable margins (described in subsection II), staff concurrence in the applicant's estimates will be stated. If the applicant's est; mates are not within acceptable margins, and if the plant may be adversely af fected, a occ.itior, requiring use of the staf f bases will be stated. If no seismically-induced dam failure review was undertaken at the construction permit stage (of the scope described), this fact will be indicated.
For operating license (OL) reviews of cases for which detailed seismically-induced dam failure analyses were made during the CP review, the CP-stage conclusions will be refer-
- enced, in addition, any further review done to reaffirm the.aximum or minimum water levels based on any new information will be described and the results and conclusions stated.
Sample statements for CP reviews follow:
"The distance (more than 300 miles) to upstream reservoirs of an?reciable size is such that the staff assessment loads to the conclusirn that their arbitrarily assumed failure, under NRC criteria of reasonably postulated combinations of floods and earthquakes, would not constitute a threat to the plant worse than that due to a severe runoff-type flood or to hurricane-induced surge.
" Dam failure caused ' worst case' floods were evaluated by the applicant based upon failures with consideration of only the location and sizes of upstream impoundments, and not on inherent capability of such structures to resist earthquakes, volcanic activity and severe landslide-induced floods. The most severe flo'd of this kind was estimated based upon an ;ssumed catastrophic failuce of Dam A some 420 miles upstream.
The peak flow at the site from such a flood was estimated to be 3,000,000 cfs.
This flow is estimated to occur about two days after the dam failure and reach elevation 41 feet MSL. Smaller dams or, the river between Dam A and the site were also evaluated for such a flood and, it was concluded, would probably also fail.
O Rev. 1 2.4.4-4 mo
centerings. Detailed failure models, such as those of the Corps of Engineers and the Tennessee Valley Authority, are utilized to identify the outflows from various failure modes. Models of the Corps of Engineers or the Tennessee Valley Authority are used to identify the outflow characteristics and resultant water level at the site (Refs. 4, 8, 13, 14 and 15).
The staff will develop a position based on the analyses performed; resolve, if pcssible, differences between the applic6nt's and staff's estimates; and write the SER input accordingly.
The above reviews are performed only when applicable to the site or site region. Some items of review may be done on a generic basis.
IV.
EVALUAf!ON FINDINGS For construction permit (CP) reviews, the findings will summarize the appl'
_ and staff evaluations of the design basis maximum and minimum water levels caused by seismically-induced dam failures, if the applicant's estimates are within acceptable margins (described in subsection II), staff concurrence in the applicant's estimates will be stated.
If the applicant's estimates are not within acceptable margins, and if the plant may be adversely affected, a position requiring use of the staff basos will be stated.
If no seismically-induced dam failure review was undertaken at the construction permit stage (of the scope described), this fact will be indicated.
For operating license (OL) reviews of cases for which detailed seismically-induced dam failure analyses were made during the CP review, the CP stage conclusions will be refer-enced.
In addition, any further review done to reaffirm the maximum or minimum water levels based on any new information will be describad and the results and conclusions stated.
Sample statements for CP reviews follow:
"The distance (more than 300 miles) to upstream reservoirs of appreciable size is such that the staff assessment leaA to the conclusion that their arbitrarily assumed failure, under NRC criteria of reasonably postulated combinations of floods and earthquakes, would not constitute a threat to the plant worse than that due to a severe runoff-type flood or to hurricane-induced surge.
" Dam failure caused ' worst case' floods were evaluated by the applicant based upon failures with consideration of only the location and sizes of upstream impoundments, and not on inherent capability of such structures to resist earthquakes, volcanic activity and severe landslide-induced floods. The most severe flood of this kind was estimated based upon an assumed catastrophic failure of Dam A some 420 miles upstream.
The peak flow at the site from such a flood was estimated to be 3,000,000 cfs.
This flow is estimated to occur about two days after the dam failure and reach elevation 41 feet MSL. Smaller dams on the river between Dam A and the mite were also evaluated for such a flood and, it was concluded, would probably also fail.
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13.
W. A.
Thomas, "A Method for Analyzing Effects of Dam Failures in Design Studies,"
Corps of Engineers Hydrologic Engineering Center, Davis California (for presentation at the ASCE Hydraulics Division Specialty Conference, Cornell University, Aegust 1972).
14.
" Flow Through a Breached Dam," Military H'arology Bulletin No. 9, C: ps of Engineers (1957).
15.
" Floods Resulting From Suddenly Breached Dams, Conditions of High Resistance,"
Misc. Paper No. 2-374, Report 2, Corps of Engineers (1961).
16.
Bureau of Reclamation, " Flood Routing," Chapter 6/0 in " Flood Hydrology," Part 6 in
" Water Studies," Volume IV, U.S. Department of the Interior (1947).
17.
Regulatory Guide 1.70, " Standard Format ar.d Conter.t of Safety Analysis Reports for Nuclear Power Plants."
18.
Regulatory Guide 1.59, " Flood Design Basis for Nuclear Power Plants."
19.
ANSI N170, " Standards for Determining Design Basis Flooding at Power Reactor Sites" (1976).
20.
Regulatory Guide 1.29, " Seismic Design Classification."
21.
Regulatory Guide 1.102, " Flood Protection for Nuclear Power Plants."
22.
Regulatory Guide 1.135, " Normal Water Levels and Discharge at Nuclear Power Plants."
23.
10 CFR Part 100, Appendix A, " Seismic and Geologic Siting Criteria for Nuclear Power Plants. "
Rev. I 2.4.4-6 1A f, ff I4J J()
Figure 2.4.4-1 STANDARD REVIEW PLAN SECTION 2.4.4 SEISMICALLY - INDUCED FLOODS Review location and sizes of upstream and immediately downstream dams using SAR & other available dam descriptions.
Determine which structures (I or more) are hydro'ogically controlling based on size and location.
Perform quicky " pull the plug" analyses assuming half PMP, minimal flood wave attenuation, and extrapolated site rating curve.
Compare "quicky" estimate with applicant's analysis &
!ocation and elevations of saf ety-related f acili' ies.
NO Decide on whether potential flood problem exists.
YES Request missing data.
Perform refined "quicky" analysis.
Evaluate answers & undertake detailed analysis of contiolling cases using conceptual models of failures, hydraulic analyses of outflow characteristics and computarized models (corps of engrs.)
of unsteady flow, HEC-1, HEC-2, and others.
Develop staff positions.
Attempt to resolve differences with applicant thru LPM.
Write SER input 9
145 303 2.4.4-7