Regulatory Guide 1.135
| ML003740143 | |
| Person / Time | |
|---|---|
| Issue date: | 09/30/1977 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-1.135 | |
| Download: ML003740143 (5) | |
U.S. NUCLEAR REGULATORY COMMISSION
4 REGULATORY GUIDE
,
OFFICE OF STANDARDS DEVELOPMENT
REGULATORY GUIDE 1.135 NORMAL WATER LEVEL AND DISCHARGE AT NUCLEAR POWER PLANTS
A. INTRODUCTION
General Design Criterion 2, "Design Bases for Protection Against Natural Phenomena," of Appen dix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Licensing of Produc tion and Utilization Facilities," requires that struc tures, systems, and components important to safety be designed to withstand the effects of natural phenomena such as floods, tsunami, and seiches without loss of capability to perform their safety functions. Criterion 2 also requires that design bases for these structures, systems, and components reflect:
1. Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding region, with sufficient margin for the limited accuracy and quan tity of the historical data and the period of time in which the data have been accumulated,
2. Appropriate combinations of the effects,,of n*6 mal and accident conditions with the effectsof the'.
natural phenomena, and
...
3. The importance of the safety furfons i6 be per formed.
Paragraph 100.1 r bftOCFR Part 100, "Reactor Site Criteria." requi t'*
[k., ysical characteristics of the site, Inc]
I
ei lo&g'
meteorology, geology, and hydro y, b k e-into account in determining the ac .
ta
'ty o ',site for a nuclear power reactor.
Th uide sets forth methods acceptable to the NRC
f for determining normal ground and sur face wat r levels and surface water discharges for use in analyses of the. effect of design basis natural and accidental events on structures and systems at nuclear power plants. This guide also suggests data sources and acceptable methods for determining such water levels and discharges.
B. DISCUSSION
Some structures and systems
.. 'Mnost nuclear power plants are continually suif o
uctuating live loads that result from variions i ound water levels, discharges -ld a
Is isn'treams, or water levels in lakes anid uctures that ex tend below grousd surfac~nto the local ground water aquifer*-(o1ý`
1
A
ifers must withstand the resulting hydftaticýressti'e. Structures that are af fected b1:.zurfhceý*atetdischarges and levels include damss, 6*-.,*a;
aters, canals, and intake and dis cl*4e s*c*.cids. In considering the effects of design bas eientsiuch as earthquakes, tornadoes, and hur ricwsnt&;and the effects of design basis accidental e*ffVw,
'ts such as plane crashes, transportation acci
"."dents, explosions, fires, and loss-of-coolant accidents (LOCAs), the designer must include in his calcula tions the loads caused by the water level (or dis charge), as well as the load on the structure or system caused by the design basis event being considered.
This water level (or discharge) is referred to in this guide as the normal water level (or discharge).
Since the design basis events have a very low probability of occurrence, the water level (or dis charge) used in combination with the design basis event need not represent a condition with low Design basis events are those natural events that there is virtually no risk of exceeding, such as the Probable Maximum Hurricane, Safe Shutdown Earthquake, and other natural events of similar low probability of occurrence, and accidental events, such as ex plosions, plane crashes, and fires.
USNRC REGULATORY GUIDES
Comments should be sent to the Secretary of the Commission. US. Nuclear Regu Regulatory Guides are issued to describe and make available to the public methods latory Commission, Washington. D.C.
20555, Attention.
Docketing and Service acceptable to the NRC staff of implementing specific parts of the Commission's Branch.
regulations, to delineate techniques used by the staff in evaluating specific problems or postulated accidents, or to provide guidance to applicants. Regulatory Guides The guides are issued n the following ten broad divisions are not substitutes for regulations, and compliance with them is riot required
1. Power Reactors
6. Products Methods and solutions different from those set out in the guides will be accept-
2. Research and Test Reactors
7. Transportation able if they provide a basis for the findings requisite to the issuance or continuance
3. Fuels and Materials Facilities
8. Occupational Health of a permit or license by the Commission.
4. Environmental and Siting
9. Antitrust Review B. Materials and Plant Protection tO. Generat Comments and suggestions for improvements in these guides are encouraged at all times, and guides will be revised, as appropriate, to accommodate comments and Requests for single copies of issued guides (which may be reproduced) or for place.
to reflect new information or experience.
However, comments on this guide,if ment on an automatic distribution list for single copies uf future guides in specific received within about two months after its issuance, will be particularly useful in divisions should be made in writing to the US. Nuclear Regulatory Commision.
evaluating the need for an early revision.
Washington, D.C.
20555, Attention:
Director. Division of Document Control.
September 1977
probability of occurrence. As used in this guide, the term normal water level (or discharge) means that water level (or discharge) that has a probability of ap proximately 0.5 of occurrence at the time of interest.
Some design basis events may actually consist of a series of events such as an earthluake followed by one or more aftershocks. This fact is important if the earthquake could affect the normal water level (or discharge) and result in a different water level (or dis charge) when the aftershocks occur. For example, the initial earthquake could affect an underdrain system to lower ground water levels at tjhe time of the aftershocks. Similarly, a dam failure caused by the in itial earthquake could substantially change the dis charge in a river at the time of the aftershocks. Under such conditions, the normal water level (or discharge)
should be assumed only at the time of the initial event, and the water level (or discharge) during the aftershocks should be determined by analysis of the effect of the initial event.
1. Seasonal Occurrence of Design Basis Events Earthquakes, plane crashes, transportation acci dents, explosions, fires, and LOCAs may occur at any time. However, water levels (or discharges) may vary considerably during any year. Accordingly, when determining normal water levels (or discharges) for these events by the methods recommended in this guide, water levels (or discharges) for the entire year should be considered.
On the other hand, floods, hurricanes, and tor nadoes are seasonal in most parts of the United States. In determining normal water levels (or dis charges) for these seasonal events, such seasonality should be taken into account. For example, tor nadoes do not generally occur during the winter months in the northern states. Therefore, the normal water level (or discharge) to be considered with tor nado effects should be derived only from data for those months in which tornadoes may be expected to occur.
Similarly, in Florida hurricanes have been recorded in virtually every month, but they are more likely to occur during the late summer and early fall, which is coincidentally the period of the year in which high water levels (or discharges) are most likely to oc cur. Accordingly, for this type of seasonal variation, the normal water level (or discharge) should be deter mined only for that period of the year during which the event is most likely to occur or for the ap propriate period as indicated by studies of the area.
Floods are seasonal in many parts of the United States. While the surface water levels (or discharges)
addressed in this guide are not applicable to floods, it is quite possible that the influence of flood levels on normal ground water levels must be considered.
The following discussions of various water bodies assume that the seasonality of the design events are properly taken into account.
2. Nontidal Streams Data on stream discharge rates are readily available for thousands of stream-gaging stations operated by the U.S. Geological Survey; U.S. Army Corps of Engineers; Bureau of Reclamation; other Federal, State, and local agencies; power companies;
and other organizations. Most such data are in the form of mean daily discharges for varying periods of record. Hydrology textbooks contain acceptable standard methods for transposing these data from the gaging stations to the plant site. Thus, relatively reliable information on stream discharge may be ob tained for a plant site located on a nontidal stream.
Short-term discharge data are also frequently col lected at the sites and should be used to verify the transposed data.
A period of record of at least 50 years is desirable for use in determining the normal water level and dis charge at sites on nontidal streams. For many loca tions, however, such long-term records do not exist.
In such cases, periods of record of at least 12 years may be acceptable if it can be demonstrated that the period used includes major wet and dry periods.
Where shorter-term data or no data exist, records should be estimated on the basis of weather records and records for other streams in the region. In all cases, watershed development conditions anticipated during the plant lifetime should be considered.
For nontidal streams, the median discharge will be considered the normal discharge. The median dis charge may be determined as the 50% point on a flow-duration curve2 (discharge vs. percent of days when indicated discharge was equalled or exceeded).
Acceptable methods of constructing a flow-duration curve are outlined in many publications, e.g., U.S.
Geological Survey Water-Supply Paper
1542-A,
"Flow Duration Curves," 1959.1 It would be desirable to determine the normal water level on nontidal streams by similar means, i.e.,
use of a stage-duration curve (water level vs. percent of days when indicated level was equalled or ex ceeded). However, stages (water levels) at gaging sta tions are not as readily available as are the cor
2 The U. S. Geological Survey computes data for most of their gaging stations from which a flow-duration curve may be plotted.
It should be noted, however, that such a curve will cover only the period of record available for the gaging station.
' Copies are available from the Branch of Distribution, U.S.
Geological Survey, 1200 South Eads Street, Arlington, VA 22202.
1.135-2
responding discharge data. Therefore, the NRC staff will accept, as the normal water level, the water level corresponding to the normal discharge. Computation of the normal water level by this method requires the establishment of the relationship between river level and discharge (the rating curve) and the application of that relationship to the normal discharge. If the stream has a movable bed, allowance should be made for shifting of the rating curve.
3. The Great Lakes The levels of some of the Great Lakes have shown upward or downward trends over long periods. For example, Lake Michigan-Huron has shown a slight downward trend over a period of more than 100
years. Such trends should be taken into account in determining the normal level. An acceptable procedure is to adjust the last 50 years of data for the indicated trend before determining the median level.
This adjusted 50-year median level should be con sidered as representing the normal level.
Lunar tides in the Great Lakes may be ignored because their size is negligible.
Because of the size of the Great Lakes, their water levels change very slowly. Therefore, it is not neces sary to determine the normal water level from daily data. Mean monthly values are of sufficient accuracy.
The Detroit District, U.S. Army Corps of Engineers, collects and publishes monthly data on the levels of the Great Lakes.
4. Unregulated Lakes As used in this guide, the term unregulated lakes means those natural lakes whose outlets are virtually uncontrolled by dams or other structures and those natural lakes that are not appreciably affected by diversions into or out of the lake. Regulatedlakes are discussed as reservoirs in this guide.
A median level based on 50 years of data is accep table as the normal water level. This level can be determined from long-term records of the lake level.
If only short-term records are available, they may be extended by estimating longer-term data on the basis of records for other lakes, stream discharge and ground water data, and weather records. As with nontidal streams, a shorter record may be acceptable if it can be demonstrated that major wet and dry periods are included. As with the Great Lakes, if a trend can be identified, the data should be adjusted for this trend. Consideration should also be given to potential changes in water use that could significantly alter this median.
In many cases, mean monthly data may be used to compute the median level. However, a study should be made to determine whether the median based on mean monthly records is sufficiently accurate or whether mean daily data should be used. Such a study could consist of computing medians for a short period (e.g., two or three years) from both monthly and daily information and comparing the results.
5. Regulated Lakes and Reservoirs At their outlets many lakes have dams or other regulating structures, which in effect convert the lake into a reservoir. Regulated lakes are therefore addres sed as reservoirs in this guide.
Most reservoirs have at least one level designated as "normal pool" elevation. For some reservoirs, more than one elevation, usually varying with the time of the year, may be considered normal pool.
Those reservoirs that have reserved flood control space are frequently of this type. For example, a reservoir in the Sierra Nevada of California might have a given normal pool level for the July-to November period, followed by a November-to December period when the level must be drawn down to accommodate potential flood runoff, and a December-to-June period when the level must be kept as closely as possible to the drawndown level but may rise to as high as the top of the flood control pool.
Normal water level should be considered the nor mal pool level of the reservoir, with due considera tion for variations in normal pool level during the year. If the reservoir includes flood control storage, the median of the flood control pool levels for the life of the reservoir should be considered normal for events that are likely to occur during the flood season.
Records of levels of regulated lakes and reservoirs are usually collected by the operator of the reservoir.
In some cases, these data are published by the U. S.
Geological Survey, U.S. Army Corps of Engineers, or other Federal, State, or local agencies.
6. Oceans A complete tide cycle averages 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> 25 minutes at most points on the shores of the .United States.
Because of this relatively rapid rate of change of ocean levels, the duration of the design basis event should be considered. Most such events are of short duration, ranging from essentially instantaneous (e.g., plane crashes, explosions, and most transporta tion accidents) to a few seconds or minutes (e.g.,
earthquakes, tornadoes, and some transportation ac cidents). However, hurricanes and fires may last suf ficiently long to span the entire tidal range from low to high.
For short duration events, the median tide level may be considered as the normal water leve
l. For
5-3
longer duration events, however, it is probable that the tide will be above (or below) the median level for at least part of the time of the occurrence of the event.
For these events, therefore, median higher high tide or median lower low tide (see discussion below)
should be used as the normal. The choice of median higher high tide or median lower low tide will depend on the event being considered. For example, hur ricane winds blowing seaward from land will lower the level of the ocean (setdown). If this will have an effect on a safety-related water supply, the normal water level should be the median lower low tide.
High and low tides do not consistently reach the same levels. The two high tides during a complete 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 50-minute cycle at some locations are of dif ferent heights, as are the two low tides. The higher of the two high tides is designated as higher high tide and the lower of the two low tides as lower low tide.
Other cyclic variations have also been identified.
Tidal heights vary during each lunar month from spring (high) to neap (low) range. The tidal range also has a cyclic variation of somewhat more than 19 years. In addition, tidal heights are affected by varia tions in barometric pressure and by wind. These meteorological phenomena cause the principal dif ferences between predicted and recorded tidal heights.
In order to ensure that these variations are con sidered, normal tide levels should be computed from a continuous record of at least 20 years.
A long-term tide record is not available at the exact location of many nuclear power plant sites. Usually, however, a short-term record will have been collected at the site. In this case, the short-term record may be extended by correlation with one or more records for nearby long-term tide stations.
Records of tidal heights are collected and main tained by several agencies but principally by the National Oceanic and Atmospheric Administration (NOAA) in the Department of Commerce. This agency regularly estimates mean high tide or mean higher high tide, primarily for coastal locations. Data for other locations may be estimated, using the rela tions given in tide tables, by interpolation.
7.- Estuaries Both freshwater runoff and lunar tides affect water levels in estuaries. Most estuaries are gaged by the U.S. Geological Survey, National Oceanic and At mospheric Administration, U.S. Army Corps of Engineers, or others. A stage-duration curve should be used to estimate the median water level as the nor mal water level. This procedure may be used for loca tions upstream and downstream from the site with the normal water level at the site estimated by inter polation.
A period of record of 20 years (to account for cyclic tidal variations) is acceptable if it can be demonstrated that the period includes major wet and dry periods.
8. Ground Water Normal ground wa'ýýr level should be the median level over a 20-year period. This length of record will not be available at most sites for nuclear power plants. However, most sites will have one or more short-term records of a year or two. The staff will ac cept extension of these short-term records by correla tion with longer records in the region. The effect of future changes in water use should be considered.
The U.S. Geological Survey collects and publishes records for thousands of observation wells throughout the United States and may advise where other data in the region may be obtained.
For those sites at which the applicant plans to lower the ground water level permanently by use of an underdrain system, either pumped or gravity flow, the staff will accept, as normal, the anticipated lower water level for which the system is designed.
Ground water levels to be used for soil liquefaction analyses will be discussed in a regulatory guide now under preparation on liquefaction.
C. REGULATORY POSITION
Analyses of the capability of safety-related struc tures, systems, and components to resist combina tions of loading conditions often require identifica tion of normal water levels or discharges. For the purposes of this guide, normal water level (or dis charge) means the water level (or discharge) that can be expected at the time of occurrence of design basis natural or accidental events.' Subject to the excep tions below, the normal water level (or discharge) will generally be the median water level (or discharge),
i.e., that water level (or discharge) that will be equal led or exceeded 50% of the time.
1. Seasonal Occurrence of Design Basis Events If the design basis event under consideration is seasonal, the normal water level (or discharge) should be determined for that part of the year in which the event is likely to occur.
2. Nontidal Streams The normal discharge should be the median dis charge based on a period of mean daily discharge record, preferably at least 50 years in length. The nor mal water level should be either (a) the median mean daily water level based on a record of preferably at least 50 years or (b) the water level corresponding to
' See Footnote 1.
1.135-4
normal discharge, including consideration of shifting rating curves for streams with movable beds. A
shorter period of record (not less than 12 years) is ac ceptable if longer records do not exist and it can, be demonstrated that the period used includes major wet and dry periods.
3. The Great Lakes Normal water level should be the median mean monthly level based on the latest 50 years of record, with suitable adjustment for demonstrated long-term trends.
4. Unregulated Lakes (Other Than the Great Lakes)
Normal water level should be the median based preferably on 50 years of data. Unless it can be demonstrated that the median based on mean monthly levels is sufficiently accurate, mean daily data should be used. If long-term trends can be iden tified, the 50-year median should be adjusted for these trends. A shorter period of record (not less than
12 years) is acceptable if longer records do not exist and it can be demonstrated that the period used in cludes major wet and dry periods.
5. Regulated Lakes and Reservoirs Normal water level should be the designated nor mal pool elevation. There may be different designated normal pool elevations at different times of the year. If the reservoir contains flood control space, the normal water level during the flood season should be the median of the flood levels attained dur ing the life of the reservoir.
6. Oceans For events of short duration (a half hour or less),
normal water level should be the median tide based on a 20-year period of record. If the event may have a longer duration, normal water level should be the me dian higher high tide or median lower low tide based on a 20-year period of record. Choice of higher high or lower low tide should be the most conservative for the event being considered and its consequences.
7. Estuaries Normal water level should be the median level based on a 20-year period of record. For longer duration events, median higher high or lower low tide based on a 20-year period of record should be sub stituted for median tide level.
8. Ground Water Normal ground water level should be the median level based on 20 years of data. If permanent lower ing of the ground water level by using underdrains is planned, normal level should be the design lowered level.
9. Availability of Data If the minimum periods of record specified in the foregoing positions are not available, standard methods may be used to transpose or extend the available data. Full explanations of the methods used for such procedures should be furnished.
D. IMPLEMENTATION
The purpose of this section is to provide informa tion to applicants regarding the NRC staffs plans for using this regulatory guide.
Except in those cases in which the applicant proposes an acceptable alternative method for com plying with specified portions of the Commission's regulations, the method described herein will be used in the evaluation of submittals for construction per mit applications docketed after May 1, 1978, unless this guide is revised as a result of suggestions from the public or additional staff review.
If an applicant wishes to use this regulatory guide in developing submittals for applications docketed on or before May 1, 1978, the pertinent portions of the application will be evaluated on the basis of this guide.
1.135-5