Regulatory Guide 1.102
| ML003740308 | |
| Person / Time | |
|---|---|
| Issue date: | 09/30/1976 |
| From: | Office of Nuclear Regulatory Research |
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| -nr RG-1.102 Rev 1 | |
| Download: ML003740308 (5) | |
U.S. NUCLEAR REGULATORY COMMISSION
REGULATORY GUIDE
OFFICE OF STANDARDS DEVELOPMENT
Revision 1 September 1976 REGULATORY GUIDE 1.102 FLOOD PROTECTION FOR NUCLEAR POWER PLANTS
A. INTRODUCTION
General Design Criterion 2, "Design Bases for Protec tion .Against Natural Phenomena," of Appendix A,
"General Design Criteria for Nuclear Power Plants," to
10 CFR Part 50, "Licensing of Production and Utiliza tion Facilities," requires that structures, systems, and components important to safety be designed to with stand the effects of natural phenomena such as floods, tsunami, and seiches without loss of capability to performntheir safety functions. Criterion 2 also requires that the design bases for these structures, systems, and components reflect:
1. Appropriate consideration of the most severe natural phenomena that have been historically reported for the site and surrounding region, with sufficient margin for the limited accuracy and quantity of the
2 historical data and the period of time in which the data have been accumulated;
2. Appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena; and
3. The importance of the safety functions to be performed.
Paragraph 100.10(c) of 10 CFR Part 100, "Reactor Site Criteria," requires that physical characteristics of the site, including seismology, meteorology, geology, and hydrology, be taken into account in determining the acceptability of a site for a nuclear power reactor.
Appendix A, "Seismic and Geologic Siting Criteria for Nuclear Power Plants,"
identifies the investigations necessary for a detailed study of seismically induced floods and water waves.
The appendix requires that design bases for seismically induced floods and water waves take into consideration the results of geologic and seismic investigations and that these design bases be taken into account in the design of the nuclear power plant.
Regulatory Guide 1.59, "Design Basis Floods for Nuclear Power Plants," describes acceptable methods of determining the design basis flood conditions that nuclear power plants located on sites along streams must withstand without loss of safety-related functions. It also discusses the phenomena producing comparable design basis floods for coastal, estuary, and Great Lakes sites. The guide states that examples of the type of flood protection to be provided for nuclear power plants will be the subject of a separate regulatory guide.
This guide describes types of flood protection accept able to the NRC staff for the safety-related structures, systems, and components identified in Regulatory Guide
1.29.* In addition, this guide describes acceptable
"Regulatory Guide 1.29, "Seismic Design Classification," Identi fies structures, systems; and components of light-water-cooled nuclear power plants that should be designed to withstand the effects of the Safe Shutdown Earthquake and remain func tionaL These structures, systems, andI components- are those necessary to ensure (1) the integrity of the reactor coolant pressure boundary, (2) the capability to shut down the reactor and maintain it in a safe shutdown condition, or (3) the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures comparable to the guideline exposures of 10 CFR Part 100. These structures, systems, and components should also be designed to withstand conditions resulting from the design basis flood and remain functional.
It is expected that safety-related structures, systems, and components of other types of nuclear power plants will be identified in futur6 regulatory guides. In the interim, Regula tory Guide 1.29 should be used as guidance when identifying safety-related structures, systems, and components of other types of nuclear power plants that need to be protected from floods by methods such as those suggested in this guide.
USNRC REGULATORY GUIDES
Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission. Washington. D.C. U5.
Attention: Dockoting end Regulatory Guides we issued to describe and make available to the public secesection.
methods aiceptable to the NRC staff of Implementing specific parts of the Commission's regulations, to delineate techniques used by the staff in ovalu- The guides are issued in the following ton broad divisions:
sting specific problems Or postulated accidents. or to provide guidance to appli cents. Regulatory Guides are not substitutes for regulations, and compliance I. Power Reactors S. Products with them is not required. Methods and solutions different from those set out in
2. Research and Test Reactors
7. Transportation the guides will be acceptable if they provide a basis for the findings requisite to
3. Fuels and Materials Facilities S. Occupational Health the issuance or continuance of a permit or license by the Commission.
4. Environmentel and Siting
9. Antitrust Review Comments and suggestions for improvements in these guides are encouraged S. Materials and Plant Protection
10. General at all times. and guides will be revised. as appropriate. to accommodate com ments and to reflect new information or experience. This guide was revised as a Copies of pub4ished guides may be obtained by written request indicating the result of substantive comments received from the public and additional st&ff divisions desired to the U.S. Nuclear Regulatory Commission. Washington. D.C.
review.
2=5. Attention: Director. Office of Standards Development.
methods of protecting nuclear power plants from the effects of Prbbable Maximum Precipitation (PMP) falling directly on the site.*
B. DISCUSSION
Nuclear power plant structures, systems, and com ponents important to safety should be designed to withstand, without loss of capability to perform their safety functions, the most severe flood conditions that can reasonably be postulated to occur at a site as a result of severe hydrometeorological conditions, seismic ac tivity, or both. The flood protection features necessary to protect the safety-related structures, systems, and components should be designed for the range of precipi tation, wind, and seismically induced flood conditions identified in Regulatory Guide 1.59. The water-induced effects, both static and dynamic, on the flood protection features are considered to constitute normal environ mental forces for use in the design of such features. The forces are developed from the hydrologic engineering analysis of the flood conditions.
For purposes of this guide, the Design Basis Flooding Level (DBFL) is defined as the maximum water eleva tion attained by the controlling flood, including coinci dent wind-generated wave effects. The wind-generated wave component of elevation is generally controlled by fetch and water depth and may differ at locations around the plant. Further distinction must be made between estimates of"structural" effects (i.e., static and dynamic forces) and flooding or inundation effects.
Additionally, the controlling flood event may be differ ent for evaluating structural effects than for evaluating inundation effects. For example, the Probable Maximum Flood (PMF) may produce the highest water level and static forces on a given structure, but the total static and dynamic forces on the structure may be greater during a smaller (in elevation) flood wave from the seismically induced failure of an upstream dam.
For structural purposes, the significant wave height is used; for inundation considerations, the one-percent wave height Is used. Sgniflcant wave height (HA) is the average of the highest one-third of wind-generated waves In a representative -.pectrum. One-percent wave height (HI), sometimes erroneously called the mximum wye height, is the average of the highest 1 percent of
- iwind-generated waves in a representative spectrum. Use of the relation H1 = 1.67Hs is acceptable for determin Iing the one-percent wave height.
- Suggested criteria for the consideration of localized severe precipitation are contained it Section 2.4.2.3 of Regulatory Guide 1.70, "Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants." The definition of Probable Maximum Precipitation Is contained in "Regulatory Guide 1.59.
- 'Lne# indicate substantive changes from previous Issue.
Methods of flood protection for nuclear power plants fall into one of the following three types (ocal flooding induced by severe local precipitation will be discussed later):
1. Dry Site The plant is built above the DBFL, and therefore safety-related structures, systems, and components are not affected by flooding.
2. Exterior Barrier Safety-related structures, systems, and components are protected from inundation and static and dynamic forces thereof by engineered features external to the immediate plant area. Such features may, when properly designed and maintained, produce the equivalent of a dry site, although care must be taken to ensure that safety-related structures, equipment, and components are not adversely affected by the differential hydraulic head.
3. Incorporated Barrier Safety-related structures, systemsi and components are protected from inundation and static and dynamic effects by engineered features in the structure/
environment interface.
Regulatory Position 2 of Regulatory Guide 159 provides that those structures, systems, and components necessary for safe shutdown and maintenance thereof should be protected against the DBFL. The position also suggests that, if sufficient warning time Is shown to be available to bring the plant to a safe shutdown condi tion, some of the other safety-related structures, sys tems, and components identified in Regulatory Guide
1.29 do not require protection against a flood as severe as the DBFL Use of this method of protection as an acceptable alternative requires development of emer gency procedures and technical specifications. Substanti ation of the adequacy of the time available will require, in part:
I. Estimating the time required to bring the plant from full-power operation to a safe shutdown mode.
2. Establishing the warning indicators that will initi ate shutdown procedures. Flood stage and rate of rise are common and generally acceptable indicators. How ever, sites along streams downstream from the conflu ence of major tributaries may require an assessment of flooding potential from floods that are less than the PMF, but could exhibit faster rates of rise than the PMF.
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3. Documenting that sufficient time will remain after the warning for the safe shutdown to be accomplished before water-.can flood any safety-related structures, systems, or components.
The regulatory positions of this guide identify several key items to be considered in developing acceptable flood-related emergency procedures.
Local PMP may produce flooding at sites otherwise considered'immune from flooding. The intensity of this rainfall and the usual design of the drainage system may result in ponding in the plant yard that could produce the DBFL. Also, roofs may receive more precipitation than the roof drains are designed to discharge.
Final plant grading is usually designed to cause ponded water to flow away from safety-related build ings. IEven so, some temporary ponding is to be expected. Such ponding is generally accommodated by locating penetrations above the level of temporary ponding. Plant structures, systems, and components subject to ponding are also subject to the static and dynamic forces of the ponded water. These forces are usually less, however, than the forces from other design basis events.
C. REGULATORY POSITION
1. The following paragraphs provide working defini tions of the various types of flood protection acceptable to the NRC staff.
a. Dry Site The dry site may be the result of natural terrain or it may be constructed using engineered fill. The latter type refers to the "plant island" concept, rather than the minor fill used to dress plant grade. When fill is required to raise the plant access level above design basis flood conditions, the fill is safety related and must be protected from flood effects in the same manner as safety-related dams, dikes, etc.
b. Exterior Barriers
(1) Levee. "A dike or embankment to protect land from inundation."
Levees are generally earthen structures, trapezoidal in cross section, and protected from erosion by armor on the face exposed to waves and current..
(2) Seawall or Floodwall. "A structure separat ing land and water areas, primarily designed to prevent erosion and other damage due to wave action."*
Seawalls are massive structures designed to take the full impact of the design wave. The seawall dissipates wave energy by throwing the water upward and downward.
The upward deflection may result in wind-blown over topping; the downward deflection can cause severe erosion at the toe of the seawall.
(3) Bulkhead Similar to a seawall. The prime purpose is to restrain the land area. A bulkhead should not be'used where it may be subject to direct wave attack.
(4) Revetment. "A facing of stone, concrete, etc., built to protect a scarp, embankment, or. shore structure against erosion by wave action or currents."*
Revetments are alternatives to seawalls and bulkheads.
They protect the shore from direct wave attack by absorbing the wave energy in their interstices and on the surface of the revetment material. In this regard, riprap is more effective than smoother surfaces. Wave runup on the revetment is a function of incident wave height, revetment slope, and the nature of the revetment material. Rough surfaces reduce runup. When riprap is used, the placement of the material is critical to the effectiveness of the feature. Filling of the interstices with finer material destroys much of the energy absorbing capabilities of the installation and may result in overtopping a structure that is otherwise adequate to prevent such overtopping.
(5) Breakwater. "A structure protecting a shore area, harbor, anchorage, or basin from waves."
Breakwaters may be connected to the shore or may be located entirely offshore. Wave energy is dissipated in the same manner as it is by revetments. Offshore breakwaters are used principally to reduce the wave effects that might otherwise reach safety-related struc tures, facilities, or components. Shore-connected break waters may serve the same purpose and also may be used to train discharge or intake water flow paths to limit recirculation.
c. Incorporated Barriers Protection is provided by special design of walls and penetration closures. Walls are usually reinforced concrete designed to resist the static and dynamic forces of the DBFL and incorporate special waterstops at construction joints to prevent inleakage. Penetrations include personnel access, equipment access, and through wall piping. Pipe penetrations are usually sealed with
- Definition from the U.S. Army Coastal Engineering Research Center, "'Shore Protection Manual," Kingman Building, Fort Belvoir, Virginia 22060. Copies may be obtained from the Superintendent of Documents, U.S. Government Printing Of fice, Washington, D.C. 20402.
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special rubber boots and flanges. Personnel access closures that have been found acceptable include sub marine doors and hatches. The hydraulic and seismic'
design bases for all types of closures, including water stops, boots, and flanges, are the same as for the wall (i.e., water tightness and resistance to static and dynamic forces). In addition, the doors should open outward to ensure closure if the door is inadvertently opened during the flood event. Additionally, the plant should be designed and operated to keep doors necessary for flood protection closed during normal operation. Penetrations thit are too large to close with a single door (e.g.,
equipment and fuel loading access) generally require stop logs or flood panels for closure. The design bases for these features are the same as above, as is the need to maintain them normally in a closed position.
Temporary flood barriers, such as sandbags, plastic sheeting, portable panels, etc., which must be installed prior to the advent of the DBFL, are not acceptable for issuance of a construction permit. How ever, unusual circumstances could arise after constriic tion that would warrant consideration of such barriers.
One example of unusual circumstances that might justify use of temporary barriers is a post-construction change in the flood-producing characteristics of the drainage area, as discussed in Regulatory Position 3 of Regulatory Guide 1.59, "Design Basis Floods for Nuclear Power Plants." In such circumstances, and with strong justifica.
tion, the staff may accept temporary barriers.
2. Past experience suggests the need for guidance in establishing the shutdown technical specifications or emergency operating procedures necessary to utilize Regulatory Position 2 of Regulatory Guide 1.59. The following should be used in establishing the necessary procedures:
a. Stage (elevation)-time relations should be devel oped using the appropriate flood hydrograph (with coincident wind-generated wave effects) and site char.
acteristics. River sites downstream from the confluence of major tributaries may require assessment of the flood'
potential from less severe flood events that may exhibit faster rates of rise than the PMF.
b. The flood stage, including design basis wind generated wave effects and the time of occurrence within the flood event, at which any safety-related structure, system, or component (as defined in Regula.
tory Guide 1.29) may become degraded or inoperative should establish the completion time for all shutdown procedures.
c. Estimates of the time required for safe shut.
down should be based on average rather than best-time operator performance. This time interval should be less Sthan the time for occurrence of the event in Regulatory Position 2.b to establish the limiting values of the selected warning indicators. The procedures should consider the total DBFL; however, the indicators (usu.
ally flood stage and rate of rise) should be based on the stillwater level (i.e., DBFL less wind-generated wave effects). This precludes the masking of flood potential by less than design basis wind at the time of observation.
d. A communication system should be established to alert both onsite and offsite company personnel of flood conditions that may require subsequent shut down of the plant. Such a system may use offsite facilities and services, such as upstream river gages and flood forecasting services, as well as direct communica tion between onsite and offsite company personnel.
e. The procedures in 2.c should specify that onsite plant personnel will initiate a safe shutdown on their own volition when the limiting values of the indicators are attained. Only those warning systems located at the site and under control of plant personnel should be needed to determine the limiting values of the indica tors.
3. Analysis supporting the invulnerability of safety related structures, systems, and components from the effects of local PMP should be performed using the point rainfall value of the PMP for the site area.
a. Regulatory Guide 1.59 provides guidance on obtaining PMP estimates. An analysis of the estimated depth of ponding in the plant area should also be made.
b. Roofs are usually provided with drains designed to discharge precipitation intensities considerably less than that of the PMP. The following methods of preventing undesirable buildup of standing water on the roofs of safety-related buildings have been found accept able to the NRC staff:
(1) The parapets (a common architectural fea ture of nuclear power plant structures) may be deleted on one or more sides of the building. This is the most common method.
(2) The parapet height may be limited to preclude buildup of water in excess of the structural capacity of the roof for design loads.
(3) Scuppers may be installed through the parapets to discharge the standing water over the edge of the building.
(Note that limiting the parapet height or lip of the scupper to, for example, 6 inches above the roof will not necessarily limit the depth of water on the roof to 6 inches. Consideration should be given to the hydraulic head necessary to initiate flow.)
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c. The load induced by the maximum depth of standing water on the roofs (including antecedent or coincident snow or ice) during the design basis event
1 should be less than the structural capacity of the roof for design loads, and the discharge capacity of roof drains should be compared with the design basis dis charge.
0. IMPLEMENTATION
The purpose of this section is to provide information to license applicants and licensees regarding the NRC
staff's plans for using this regulatory guide.
This guide reflects current NRC staff practice. There fore, except in those cases in which the license applicant or licensee proposes an acceptable alternative method for complying with specified portions of the Commis sion's regulations, the method described herein is being and will continue to be used in the evaluation of submittals for operating license or construction permit applications until this guide is revised as a result of suggestions from the public or additional staff review.
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