L-22-272, Supplement to License Amendment Request to Revise the Methodology Used for Flood Hazard Analysis (EPID L-2021-LLA-0067) and Withdrawal of Exemption Requests (EPIDs L-2021-LLE-0022 and L-2021-LLE-0023)

Supplement to License Amendment Request to Revise the Methodology Used for Flood Hazard Analysis (EPID L-2021-LLA-0067) and Withdrawal of Exemption Requests (EPIDs L-2021-LLE-0022 and L-2021-LLE-0023)

ML22350A798
Person / Time
Site:	Perry
Issue date:	12/16/2022
From:	Penfield R Energy Harbor Nuclear Corp
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-2021-LLE-0023, L-2021-LLE-0022, L-2021-LLA-0067, L-22-272
Download: ML22350A798 (1)

Text

energy harbor Energy Harbor Nuclear Corp.

Perry Nuclear Power Plant IO Center Road P.O. Box 97 Perry, Ohio 44081 Rod L. Penfield 440-280-5382 Site Vice President, Perry Nuclear December 16, 2022 L-22-272 10 CFR 50.90 10 CFR 50.12 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUBJECT:

Perry Nuclear Power Plant, Unit No. 1 Docket No. 50-440, License No. NPF-58 Supplement to License Amendment Request to Revise the Methodology Used for Flood Hazard Analysis (EPID L-2021-LLA-0067) and Withdrawal of Exemption Requests

{EPIDs L-2021-LLE-0022 and L-2021-LLE-0023)

By letter dated April 7, 2021 [Agencywide Documents Access and Management System (ADAMS) Accession No. ML21106A027], Energy Harbor Nuclear Corp. submitted to the Nuclear Regulatory Commission (NRC) a license amendment request (LAR) for the Perry Nuclear Power Plant, Unit No. 1 (PNPP) to revise the Updated Safety Analysis Report (USAR) to change the methodology used for analysis of flooding hazards and drainage within the local intense precipitation (LIP) domain and reflect the results from the new analysis. Based on the new analysis, a new flood hazard protection scheme was also proposed for PNPP. In addition, Energy Harbor Nuclear Corp. requested exemptions in accordance with 10 CFR 50.12 to credit non-safety related protection features including: (1) permanent (passive) and temporary (deployable) flood barriers, and (2) the use of the plant storm drain system in mitigation of flood levels during a LIP event.

By letter dated June 1, 2022 (ADAMS Accession No. ML22152A180), Energy Harbor Nuclear Corp. submitted a supplement to the LAR that added new Technical Specification (TS) 3. 7.11, Flood Protection. The supplement also provided an updated no significant hazards consideration for the LAR, which did not change the conclusion.

On October 31, 2022, a telephone conference was held with Energy Harbor Nuclear Corp. personnel and NRC staff to discuss the two exemption requests associated with the LAR. As a result of this discussion, it was determined that the exemptions were not needed. Therefore, Energy Harbor Nuclear Corp. hereby withdraws both exemption

Perry Nuclear Power Plant L-22-272 Page 2 requests and provides the attached updated USAR pages impacted by the addition of TS 3.7.11. The text of USAR Section 2.4 was the only area impacted. Therefore, updated mark-ups of the proposed USAR Section 2.4 is provided in Attachment 1 with a retyped version provided in Attachment 2.

This supplement does not affect the no significant hazards consideration previously provided by letter dated June 1, 2022.

There are no regulatory commitments contained in this submittal. If there are any questions, or if additional information is required, please contact Mr. Phil H. Lashley, Manager - Fleet Licensing, at 330-696-7208.

I declare under penalty of perjury that the foregoing is true and correct. Executed on December -1..f:p_, 2022.

tt:

Sincerely, Attachments:

1. Proposed Updated Safety Analysis Report Section 2.4 Text Pages (Mark-Ups; for Information Only)

2. Proposed Updated Safety Analysis Report Section 2.4 Text Pages (Retyped; for Information Only) cc: NRC Region Ill Administrator NRC Resident Inspector NRR Project Manager Executive Director, Ohio Emergency Management Agency, State of Ohio (NRC Liaison)

Utility Radiological Safety Board

Attachment 1 L-22-272 Proposed Updated Safety Analysis Report Section 2.4 Text Pages (Mark-Ups; for Information Only)

(73 pages follow)

Information Only (Section 2.4) 2.4 HYDROLOGIC ENGINEERING 2.4.1 HYDROLOGIC DESCRIPTION 2.4.1.1 Site and Facilities The Perry Nuclear Power Plant is located in Lake County, Ohio, approximately seven miles northeast of Painesville. The southern plant site boundary line is 3,100 feet from the shoreline of Lake Erie on the west side of the site and 8,000 feet on the east side. Grade elevations in the immediate plant area prior to plant construction varied between 620.0 feet and 623.0 feet based upon the USGS datum.

The maximum monthly average level of record for Lake Erie is 575.4 feet (USGS) (Reference 61); therefore, no problems of site flooding exists owing to the nature of the sitedue to elevated lake levels.

The construction of the plant resulted in some minor changes in local drainage patterns, runoff characteristics and in the diversion of one small streammodification of two streams located on the plant property.

Final topography is shown in <Figure 2.14-3> and an aerial photograph of the site, prior to plant construction, is shown in <Figure 2.1-4>.

Protection is provided for safety-related structures, exterior systems and access equipment against flooding from Lake Erie, surface runoff and local intense precipitation. This is accomplished by location, arrangement and design of these structures, systems and equipment, and flood protection features as discussed in the following sections.

2.4.1.2 Hydrosphere Lake Erie, the major hydrologic feature of this location, will provide cooling water for the plant. The lake will not influence the surface water characteristics of the site since the mean lake level is in excess of 40 feet below plant grade.

Revision 12 2.4-1 January, 2003

Information Only In the vicinity of the site, the coastal watershed is drained by several small streams. These streams have cut deep channels as they approach the lake in the otherwise flat terrain of this region. The width of this coastal watershed in the site area is approximately 4.5 miles with the ground falling away sharply to the south of the ridge into the Grand River Basin.

Topographically, the site lies in the Old Lake-bed Region of northeast Ohio.

Two nameless, parallel streams run close to the plant area. The larger stream, called the Major Stream, has a drainage basin of 7.1644 square miles (Reference 70) and runs northwestward within 1,000 feet of the southwest corner of the plant. The smaller stream, called the Diversion Stream, which has a drainage area of only 0.7659 square mile (Reference 71), borders the plant area to the east and north. The drainage areas are shown in <Figure 2.4-1>. The smaller stream was originally diverted prior to construction and had been historically referred to as the Minor Stream. The name change to the Diversion Stream coincides with a post-construction modification (Reference 75) to divert the stream further to the east. A portion of the originally engineered channel of the Minor Stream remains located between the plant area and the Diversion Stream. This section of the stream no longer functions as a traditional stream. The Remnant Minor Stream, as it is now named, functions as a drainage swale located entirely within the Local Intense Precipitation (LIP) domain.

The safety-related structures of the plant are located within the drainage basin of the small stream which was diverted to border the final plant area to the east onlybetween the watersheds of the adjacent streams. The site is not subject to flooding from surface runoff originating from either streams drainage basin. Site drainage ultimately is directed to Lake Erie either directly or via the following notable drainage paths: ESW Swale, Remnant Minor Stream, Major Stream, the Barge Slip, and the Northwest Impoundment.

Revision 12 2.4-2 January, 2003

Information Only No recorded data exists for either of the adjacent streams, or any similar stream in the general area of the site. However, base flow estimates made during site visits indicate that the average flow for the largerMajor and smallerDiversion streams would be approximately 5 cfs and 10.78 cfs, respectively (Reference 70 and Reference 71).

Older local inhabitants living on Lockwood and Center Roads did not recall either the Major or Minor sStreams level overtopping Center Road. High water marks on the headwalls of the preexisting Center Road bridge over the major stream indicated that the maximum depth at this point had been approximately four feet. The smaller stream previously passed through a 4-foot by 5-foot rough stone culvert under Center Road.

There are no users of water from the minorMajor or Diversion sStreams.

The only user of surface water from the major stream is the Neff Perkins Corporation which intermittently withdraws water from a pond near the downstream end. Use of groundwater is discussed in

<Section 2.4.13>. Possible Revision 12 2.4-2 January, 2003

Information Only contamination of groundwater is also discussed in <Section 2.4.13> and the degree of contamination as assessed in that section will also apply to both streams.

Lake Erie has an area of 9,970 square miles and is only slightly larger than Lake Ontario, which has the smallest surface area of any of the Great Lakes. It is the shallowest of the lakes, with a maximum depth of 210 feet and an average depth of 58 feet. Also, Lake Erie has the smallest volume, 110 cubic miles (Reference 1).

The lake is about 241 miles long with a maximum width of 57 miles. The long axis of the lake lies in a general northeast-southwest direction.

The drainage basin of Lake Erie, including Lake St. Clair, is about 29,650 square miles. The mean annual flow from the Detroit River at the western head of the lake is 178,000 cfs which accounts for about 90 percent of the inflow into Lake Erie. The mean annual outflow into Lake Ontario is about 194,000 cfs through the Niagara River and about 8,000 cfs through the Welland Canal (Reference 1).

Lake Erie level records have been maintained by the Lake Survey Center (NOAA) since 18591860 (Reference 61). As shown in <Figure 2.4-2>, tThe average level is 572.3 feet above mean sea level, mean tide, New York City, which is the USGS datum. The 1973 monthly levels were exceptionally high, setting a new maximum monthly mean level of 575.4 feet (USGS) in June, 1973 (Reference 61). The lowest average monthly recorded level was 569.3 feet (USGS) in February, 1936 (Reference 61). Corresponding levels relative to the 1955 International Great Lakes Datum (IGLD 55) are 1.9 feet less. The Lake Erie Low Water Datum (LWD) is at Elevation 570.5 feet (USGS) and Elevation 568.6 feet (IGLD) (Reference 2). Vertical datum conversion values applicable to the site are provided on <Figure 2.4-2>.

Minimum lake levels usually occur in February when precipitation throughout the Great Lakes drainage basin is being stored in the form Revision 14 2.4-3 October, 2005

Information Only of ice and snow. Maximum levels occur in mid-summer when the full effect of Revision 14 2.4-3 October, 2005

Information Only the runoff from the drainage basin is felt. Fluctuations of several feet, but of short duration, are caused by wind effects. Northerly winds raise lake levels in the plant area, while winds from the south and east tend to lower the lake levels (Reference 3).

2.4.2 FLOODS 2.4.2.1 Flood History No records of flooding in the plant area of the site exist, either from the two adjacent streams draining the coastal watershed, or from Lake Erie. The terrain is relatively flat and gently sloping toward the lake. The soil is relatively permeable and contains sand layers in the upper reaches of the drainage area. The ground surface in much of the catchment area is forested with a heavy mulch ground cover. Due to the flat terrain, permeable upper soil layers and the small catchment areas

<Section 2.4.1.2>, it is unlikely that this location has ever been subjected to flooding or is likely towill experience severe flooding from surface runoff in the future.

2.4.2.2 Flood Design Considerations The probability of any flooding in the area of the site is exceptionally low. The storm drainage system for the plant was designed to prevent flooding during the Probable Maximum Flood (PMF).

The site area is passively protected from probable maximum flood hazards originating from Lake Erie and the adjacent streams. Studies discussed in <Section 2.4.3> have shown that even if a PMF is experienced, the streams will be contained within their naturalrespective channelsdrainage basins with no site impact except for the overtopping of the crossings at Lockwood Road and the plant main access road, which would temporarily prevent road access. The presence of a natural, high ridgeTopography along the rightplant-side bank of the major stream will preclude flooding of the site by the PMF, allowing the plant to continue uninterrupted operation. Diversion Revision 12 2.4-4 January, 2003

Information Only Stream PMF is prevented from reaching the site by the presence of an earthen berm located between the streams engineered channel and the Remnant Minor Stream channel, allowing the plant to continue uninterrupted operation.

Revision 12 2.4-4 January, 2003

Information Only Flooding from Lake Erie is extremely improbable. Final grade elevations in the immediate plant area vary from 617 to 620 feet (USGS). This is about 45 feet above the maximum monthly mean lake level of 575.4 feet (USGS) (Reference 61). Surge flooding is described in <Section 2.4.5>. Runup occurring coincidentally with the probable maximum setup would extend to about Elevation 607.9 feet on the bluff at the lake shore (Reference 65). This runup would still be about 12 feet below the 620 foot (USGS) plant grade elevation.

The controlling flood hazard is the Local Intense Precipitation (LIP) event. LIP water levels impacting the site are a result of the sites drainage capacity during significant precipitation events as discussed in <Section 2.4.2.3>. Protection of safety-related facilities, systems, and equipment is discussed in <Section 2.4.2.3>,

<Section 2.4.10> and <Section 2.4.14>.

External flood hazards and protection for PNPP are developed using the guidance of <Regulatory Guide 1.59> and <Regulatory Guide 1.102>.

Flood hazards are determined using the guidance of (Reference 81),

which is referenced by Appendix A of <Regulatory Guide 1.59>. For all off-site flood hazards, PNPP complies with Regulatory Position C.1 of

<Regulatory Guide 1.59>. For these hazards, PNPP is fully passively protected by topography and exterior barriers are defined in

<Regulatory Guide 1.102>. For the LIP hazard, PNPP employs an approach more closely aligned with Regulatory Position C.2 of <Regulatory Guide 1.59> with protection provided via a combination of permanent and temporary incorporated barriers as defined in <Regulatory Guide 1.102>.

PNPP does not comply with Regulatory Position C.2.d of <Regulatory Guide 1.59> in that structures required to reach and maintain cold shutdown are not fully passively protected. These structures, like all safety-related structures and nonsafety-related structures that communicate with safety-related structures, are passively protected up to and including the effects of the Standard Project Storm (SPS) as derived and evaluated in (Reference 72) and (Reference 82),

respectively. For hazards exceeding the SPS up to and including the Probable Maximum Precipitation event of the LIP domain which is shown Revision 12 2.4-5 January, 2003

Information Only in <Figure 2.4-82>, protection features are deployed via operator action as discussed in <Section 2.4.10> and <Section 2.4.14>.

Flood protection features are treated as non-safety related, non-seismic and are therefore not controlled under the PNPP Quality Assurance Program.

2.4.2.3 Effects of Local Intense Precipitation The plant site is drained by three separate storm drainage systems, two draining to the west and the third draining to the east. The entire storm drainage system is as shown by <Figure 2.4-3>. The entire site area is subdivided into discrete subbasins, each having storm water inlets referred to as catch basins.

Peak flows to all catch basins are based on the Rational Formula which does not account for complications in the runoff processes, neglects the advantages of storage, and assumes a steady-state flow condition.

The 6-hour Probable Maximum Precipitation (PMP) of 26.7 inches for the site was distributed into hourly intensities as described in

<Section 2.4.3>. The maximum hourly rainfall of 13.1 inches per hour will be occurring during the first hour.

Three values of rainfall intensity were used in the Rational Formula based on this most intense hourly value and the type of area from which the flows originated. The values used are:

a. Rainfall intensity of 4.1 inches/hour for roof downspout systems leading directly into a catch basin; this value was used because the roof systems are structurally designed to hold 9 inches of water, and therefore, the downspouts were sized to discharge 4.1 inches/hour.

Revision 12 2.4-5 January, 2003

Information Only

b. Rainfall intensity of 9.1 inches/hour for roof areas with scupper overflows along the sides; this value was used since any rainfall intensity greater than the downspout capacity of 4 inches/hour will pass through the scupper overflows.

c. Rainfall intensity of 7.1 inches/hour for all overland flow calculations; this value was used because total depth of 6 inches is allowed to build up over the entire plant site.

In case of complete blockage of roof downspouts, building scuppers have been sized to alleviate water from a PMP event. Water level on the roofs will not exceed the maximum loading limit of 16.25.

In addition, runoff coefficients of 0.25 for the general site area and 0.90 for roof top areas and pavements are used for the design of the system.

Sizing of storm drainage pipes is based upon basic hydraulic theory employing entrance, exit and friction losses. Tailwater conditions were assumed to exist at each pipe based on the previous downstream pipes headwater calculation. The final outlet of each storm drainage subsystem was assumed to have no downstream tailwater restrictions.

Storm water flows overland for no more than 300 feet before it reaches a catch basin. Subbasin gradients are 0.5 percent or greater.

In case of complete blockage of the storm drainage system, the plant site has been graded so that overland drainage will occur away from the plant site buildings and will not allow the accumulated storm water to exceed Elevation 620-6.

Revision 19 2.4-6 October, 2015

Information Only The area surrounding the plant site is traversed by an inner perimeter road which, for the most part, is at Elevation 620-4 (the exceptions are at the northwest plant site corner, where it dips to Elevation 616-11, and the area directly east of the intermediate building, where it dips to Elevation 619-6). The railroad enters the plant buildings at Elevation 620-6, although it has been lowered to Revision 19 2.4-6a October, 2015

Information Only Elevation 620-2 (in the vicinities of catch basins W-7 and E-5) so that excess storm water adjacent to the buildings on the east and west sides can be discharged to lower areas.

As a result, overland flow will begin once the ponding has reached an elevation of 620-4 (based on all centerline roadway elevations being the same). Assuming the worst case (i.e., complete blockage of the site storm drainage system and using peak discharge from the most intense hour of the PMP), the resulting increase in surface elevation of water flowing over the surrounding roads and railroads (acting as weirs) would not exceed one inch. This ponding elevation of 620-5 will have no adverse affect upon safety class equipment because the floors at plant grade are set at Elevation 620-6.

As the water overflows the inner perimeter road and access railroad at Elevation 620-4, the storm water will be carried away by several large drainage swales including:

a. The large swale between the two cooling towers carries water away to the east.

b. The swale south of the Unit 2 cooling tower carries water to the southeast.

c. A major portion of the plant site overland flow at the north area will be carried away by the previously mentioned low area at the northwest corner into the barge unloading ramp area.

The Local Intense Precipitation domain comprises the site property bordered to the north by Lake Erie, to the east by the Diversion Stream and to the west and south by the Major Stream. The LIP domain is shown by <Figure 2.4-82>. All safety related buildings are located within the LIP domain. The LIP event is based on a front-loaded Probable Maximum Precipitation event as described in <Section 2.4.3.1>.

Surface drainage is provided by a combination of overland drainage features and the sites non-safety related storm drain system which is Revision 12 2.4-7 January, 2003

Information Only shown on <Figure 2.4-3>. Site topography provides overland runoff to several notable drainage features including the Major Stream, Remnant Minor Stream via the ESW Swale, the Barge Slip, Northwest Impoundment, and Lake Erie. Additionally, three separate subsurface storm drainage systems (East, West and South System) assist in surface drainage. Site topography and the storm drain system are designed to reduce the effects of the LIP flooding event. The controlling flood levels impacting the site are a result of the limitations of the sites surface drainage capabilities during the LIP event (Reference 66). The site surface drainage ability is largely influenced by site topography and ground cover type; location and dimensions of above grade objects, structures and buildings; roof drainage and storage; surface drainage features; and subsurface storm drain systems.

Due to drainage limitations, floodwater depths have the potential to impact safety-related structures and non-safety related structures that communicate with safety related structures. The flood protection requirements needed to protect safety-related facilities, systems, and equipment from this event are identified in <Section 2.4.10>.

Safety and non-safety building roofs are drained by a combination of roof pitch, roof drains, parapet openings and scuppers. The drainage on the roofs is controlled to ensure that water depths developed during the LIP rainfall do not exceed the structural capacity of the roof (Reference 67). In case of complete blockage of roof downspouts on safety related buildings, building scuppers and parapet openings have been sized to ensure roofs will not exceed the maximum allowable loading limits.

Analysis of the LIP event is based on a front-loaded precipitation event distributed into hourly intensities as described in

<Section 2.4.3.1>. The peak rainfall intensity of 13.19 inches per hour will occur during the first hour and total precipitation of 34.72 inches occurs over 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> (Reference 68). Analysis of the LIP event assumes a concurrent discharge of the ESW Swale as well as a failure of the Diversion Stream berm. The LIP analysis also assumes Revision 12 2.4-7 January, 2003

Information Only maximized boundary conditions for the Major Stream, Diversion Stream and Lake Erie. These conservative assumptions and inputs ensure the LIP analytical results are bounding of any potential event combination.

Therefore, no combined events need to be postulated for PNPP.

Analysis of the LIP event is performed using a two-dimensional transient (unsteady state) volume conservation model (Reference 66).

Delineation of the computational domain is based on knowledge of the Remnant Minor Stream, Major Stream, Lake Erie and Diversion Stream watersheds and topographic dividing features. The entire Remnant Minor Stream watershed is included in the LIP domain as it functions as a drainage swale for a large portion of the east side of the plant site.

The LIP domain, depicted in <Figure 2.4-82>, is discretized into uniform grid cells for runoff analysis.

The LIP flood model simulates precipitation runoff effects over complex topography through a numerical approximation of the Shallow Water Equations and accounts for the complications in runoff. The model solves a set of partial differential equations (Saint-Venants Equation) using the second-order Newton-Raphson tangent finite difference method. Appropriate two-dimensional runoff coefficients are specified based on landcover type. Buildings, structures and security features are appropriately represented in the LIP domain model. The LIP flooding model also incorporates the plant roof and storm drain systems providing discharge analyses for these systems. The conduits modeled in the storm drain system are analyzed using the Manning Equation for gravity flow conditions and transitions to the Darcy-Weisbach Equation when pressurized flow conditions exist. Allowances are included for debris on catch basin openings and within the storm drain piping. LIP modeling is captured in (Reference 66).

The effects of the LIP event on building roofs is evaluated to ensure the structural capacity of buildings is not exceeded (Reference 67).

This analysis considers the cascading effects of roof drainage from higher roof elevations to the locations where scuppers, roof drains or parapet openings discharge on lower roof elevations. For safety Revision 12 2.4-7 January, 2003

Information Only related buildings, this is determined through the capacity of building scuppers and parapet openings. For those roofs of non-safety buildings that function as an environmental interface for a safety related building, evaluation is provided (Reference 67). A non-safety building is considered an environmental interface to a safety related building if external floodwaters would enter the safety related building if the existence of all or part of the non-safety building was removed. The roof pitch, drains, and scuppers on non-safety roofs are designed to ensure that the effective loading of high-water levels does not exceed the structural capacity of the structure. Similar to the safety related buildings, the non-safety roof analysis includes consideration of the cascading effects of roof drainage from higher roof elevations at the locations where scuppers, roof drains or parapet openings discharge on lower roof elevations.

2.4.2.3.1 Non-LIP Precipitation Events Additional analysis of the LIP domain is provided for less significant precipitation events including the Standard Project Storm (SPS) and Probable Maximum Winter Precipitation (PMWP) events. The precipitation data for these events are provided in <Section 2.4.3.1>. The runoff analyses for these events utilize the same underlying methodology described above for the LIP event. The effects of the SPS is determined in (Reference 82). Modeling techniques for the plant storm drain system for LIP effects are retained in the SPS modeling.

The effects of the PMWP with concurrent snowmelt is determined in (Reference 78). This analysis assumes portions of the computational domain are maintained generally clear of snowpack due to normal operational activities. In these areas, a seasonally adjusted one-hour precipitation event of one-year recurrence interval is applied as an antecedent snowfall condition. The remainder of the computational domain is assumed to have a probable maximum snowpack present. The cool-season analysis models a portion of the storm drain system; (Reference 78) omits catch basin inlets which are located under the probable maximum snowpack. Only those catch basins located in areas Revision 12 2.4-7 January, 2003

Information Only routinely cleared of snowfall are credited with removing overland runoff. Other modeling techniques for the plant storm drain system for LIP effects are retained in the PMWP modeling.

2.4.3 PROBABLE MAXIMUM FLOOD (PMF) ON STREAMS AND RIVERS In accordance with Appendix A of <Regulatory Guide 1.59> and the applicable sections of (Reference 55), the procedures and data of the U.S. Army Corps of Engineers (Reference 4) and the U.S. Bureau of Reclamation (Reference 5) were used to calculate effective Probable Revision 12 2.4-7 January, 2003

Information Only Maximum Floods for the two streams mentioned in the preceding sections.

The calculated PMF for the mMajor sStream was found to be 31,25032,760 cfs (Reference 70), and for the minorDiversion sStream 7,0004,330 cfs (Reference 71), at their outfalls into Lake Erie.

<Figure 2.4-4> and <Figure 2.4-5> show the hydrographs generated for the PMF of both streams. <Figure 2.4-4A> and <Figure 2.4-5A> show the inundation profiles of the Major Stream and Diversion Stream, respectively.

2.4.3.1 Probable Maximum Precipitation The Probable Maximum Precipitation (PMP) for areas from 10 to 1,000 square miles east of the 105th Meridian has been derived by the Corps of Engineers and is presented in Hydrometeorological Report 33 (Reference 4). For the Perry site, the PMP for the 6-hour, 12-hour, 24-hour and 48-hour storms are 26.726.91, 28.829.21, 31.832.43, and 33.934.73 inches, respectively (Reference 68).

The following tabulation provides a further breakdown of the 6-hour PMP made according toHydrometeorological Report 33 (Reference 4) does not provide methods to determine precipitation data for time intervals less than six hours. Guidance for obtaining hourly rainfall interval intensities is provided in procedures outlined by the U.S. Bureau of Reclamation (Reference 5) and U.S. Army Corps of Engineers (Reference 6):. A front-loaded event sequence is used for LIP domain analysis. A mid-loaded event sequence is used for Rivers and Streams analyses as reflected in the following tables (Reference 68). Total precipitation values are the same; only the temporal distribution differs between LIP and Rivers and Streams analyses.

Hour

__1 2 3 4 5 6

a. U.S. Bureau of Reclamation Procedure (Reference 5)

Cumulative Revision 12 2.4-8 January, 2003

Information Only Percentage of 6-hr rain 49 64 75 84 92 100 Cumulative Rainfall, in. 13.1 17.1 20.0 22.4 24.6 26.7 Incremental Rainfall, in. 13.1 4.0 2.9 2.4 2.2 2.1 Revision 12 2.4-8 January, 2003

Information Only

b. U.S. Army Corps of Engineers Procedure (Reference 6)

Cumulative Percentage of 6-hr rain 10 22 37 75 89 100 Cumulative Rainfall, in. 2.7 5.9 9.8 20.0 23.8 26.7 Incremental Rainfall, in. 2.7 3.2 3.9 10.2 3.8 2.9 Comparison of the cumulative rainfall values and peak incremental rainfall for the two methods shows that the U.S. Bureau of Reclamation Procedure (item a) to be more conservative for every hour. It was, therefore, used as a basis for the flood calculations.

DesignBasisProbableMaximumPrecipitationLocalIntensePrecipitation

Time 1HR 2HR 3HR 4HR 5HR 6HR 12HR 24HR 48HR

Incremental

Rainfall 13.19 4.03 2.96 2.42 2.16 2.15 2.30 3.22 2.30

(inches)

Cumulative

Rainfall 13.19 17.22 20.18 22.60 24.76 26.91 29.21 32.43 34.73

(inches)

DesignBasisProbableMaximumPrecipitationRiversandStreams

Time 1HR 2HR 3HR 4HR 5HR 6HR 12HR 24HR 48HR

Incremental

Rainfall 2.15 2.42 2.96 13.19 4.03 2.16 2.30 3.22 2.30

(inches)

Cumulative

Rainfall 2.15 4.57 7.53 20.72 24.75 26.91 29.21 32.43 34.73

(inches)

Cool-season cumulative precipitation and snowmelt values are determined in (Reference 69) to have peak intensity of 3.63 inches/hour and a 48-Revision 12 2.4-9 January, 2003

Information Only hour total of 26.58 inches. Probable Maximum Winter Precipitation data is obtained from (Reference 4) for the months of December, January and February, consistent with the cool-season months described in

<Section 2.3.1.2.5>. Cool-season event combinations are obtained from (Reference 55). For PNPP a conservative snowmelt contribution is determined in (Reference 69) by assuming an inexhaustible snowpack.

Snowmelt rates are determined using the guidance of (Reference 83). By comparison, the all-season event is bounding of the cool-season event.

The all-season event is therefore used as the basis for streams and rivers analyses. Cool-season analysis for the LIP domain is discussed in <Section 2.4.2.3.1>. The cool-season event sequence is provided below.

ProbableMaximumWinterPrecipitationandSnowmelt

Time 1HR 2HR 3HR 4HR 5HR 6HR 12HR 24HR 48HR

Incremental

Rainfall+

3.63 1.28 1.01 0.87 0.81 0.79 0.61 0.43 0.39

Snowmelt

(inches)

Cumulative

Rainfall+

3.63 4.91 5.92 6.79 7.59 8.39 12.02 17.22 26.58

Snowmelt

(inches)

Standard Project Storm precipitation values are determined in (Reference 72) to have peak intensity of 3.747 inches/hour and a 24-hour total of 13.00 inches. Derivation of the Standard Project Storm is performed using the guidance of (Reference 6). By comparison, the all-season event is bounding of the Standard Project Storm event. The all-season event is therefore used as the basis for streams and rivers analyses. Standard Project Storm analysis for the LIP domain is discussed in <Section 2.4.2.3.1>. The Standard Project Storm event sequence is provided below.

Revision 12 2.4-9 January, 2003

Information Only StandardProjectStorm

Time 6HR 12HR 13HR 14HR 15HR 16HR 17HR 18HR 24HR

Incremental

Rainfall 0.560 1.600 0.986 1.183 1.479 3.747 1.380 1.085 0.980

(inches)

Cumulative

Rainfall 0.560 2.160 3.146 4.329 5.808 9.555 10.935 12.020 13.000

(inches)

2.4.3.2 Precipitation Losses To increase the conservatism of the results, 100 percent antecedent saturation of the basins and no losses were assumed for any of the precipitation hazards described herein.

2.4.3.3 Runoff and Stream Course Models Runoff was determined according to curve No. 100 of Figure A-4, Page 542 of (Reference 5).Flood elevations for the Major and Diversion Streams are determined for the PMF peak runoff using the standard step method (steady state modeling) as described in (Reference 48) and in accordance with (Reference 55), (Reference 70), and (Reference 71).

PMF peak runoffs are determined by application of triangular synthetic unit hydrographs, as described in (Reference 5) using the all-season precipitation event provided in <Section 2.4.3.1>. However, fFor conservatism the PMP was assumed to fall on fully saturated terrain, with 100 percent runoff. The size of the streams drainage basins is described in <Section 2.4.1.2>. Coefficients used in the stream course models are described in <Section 2.4.3.5>. The PMF flow hydrographs for the Major Stream and the Diversion Stream are presented in

<Figure 2.4-4> and <Figure 2.4-5>, respectively.

No stream course modeling is provided for the effects of the Standard Project Storm or cool-season events as discussed in <Section 2.4.3.1>

since the all-season event is considered bounding with fully passive protection provided for Major and Diversion streams flood hazards.

Revision 12 2.4-9 January, 2003

Information Only The Remnant Minor Stream is not evaluated as a traditional stream or river. Instead, the Remnant Minor Stream is incorporated into the two-dimensional LIP domain model since the Remnant Minor Stream serves as a topographic drainage swale and does not function as a traditional stream. This allows the channel to respond dynamically (unsteady state analysis) as part of the LIP event.

2.4.3.4 Probable Maximum Flood Flow The probable maximum flood flow hydrograph for the mMajor and minorDiversion sStreams at their outfalls into Lake Erie are presented in <Figure 2.4-4> and <Figure 2.4-5>, respectively. These hydrographs correspond to the incidence of the PMP. Other factors such as surges or upstream dam Revision 12 2.4-9 January, 2003

Information Only failures will not affect the streams PMF. The PMFs flow for both streams were calculated with the rain data given in <Section 2.4.3.1>

and the procedures outlined in Pages 73 through 82 of (Reference 5).

2.4.3.5 Water Level Determinations

<Figure 2.4-6> and <Figure 2.4-8> show the bed elevation and PMF surface profiles for the mMajor and minorDiversion sStreams, respectively. Surface profiles were determined according to the standard step method utilizing Mannings formula. The Manning coefficient of friction was assumed to be equal to 0.100 for the portions of the existing stream bed and overbanks, and equal to 0.024 for the trapezoidal sections used in the relocated stream bedengineered streamcourse. At each stream station a cross section was drawn and the area of flow and hydraulic radius were calculated for a range of elevations. The stations and correspondingprofiles and cross sections are shown on <Figure 2.4-7>, <Figure 2.4-8>, <Figure 2.4-9><Figure 2.4-8a>, <Figure 2.4-10>, and <Figure 2.4-11>. Commencing at the first station upstream of the lake, trial and error procedures were followed until the hydraulic gradient required to produce the PMF flow was obtained. The elevation determined from the hydraulic gradient described above became the first point of the profile and the whole procedure was then repeated for the next upstream station. Successive repetitions were made until the PMF profile could be drawn

<Figure 2.4-6> and <Figure 2.4-8>.The steady state analysis computes water surface profiles from one cross section to the next by solving the Energy equation with an iterative procedure called the Standard Step Method. The Standard Step Method begins computations with the downstream boundary condition for subcritical flow. The unknown water surface elevation at the upstream cross section is first assumed by applying the downstream water depth. The corresponding conveyance and velocity head are determined for the applied water surface elevation.

The friction slope between the two cross sections is then computed and used to solve the energy head loss between the two cross sections. The Energy equation is then solved to determine the water surface elevation at the upstream cross section. The solved water surface elevation is Revision 12 2.4-10 January, 2003

Information Only compared with the initial assumed elevation and iterations are repeated until numerical values converge. PMF surface profiles are provided in

<Figure 2.4-6> for the Major Stream (Reference 70) and <Figure 2.4-8>

for the Diversion Stream (Reference 71).

Based on the large flow areas at each structure, Tthe Major Stream water surface profiles during the PMF were calculated under the assumption that the plant access road, rail line bridge, and the sediment control dams placed across the streams remained intact/open during the event. The Diversion Stream outfall culvert and Major Streams Contractor Access Road culvert were modeled as blocked during PMF conditions. Furthermore, a discharge coefficient of 3.00 was used for calculating the depth of the PMF passing over the broad crested weirs formed either by the access road or the sedimentation dam crestsby inline structures.

Trial and error procedures were again employed for the weir and culvert flow computations. The maximum PMF water surface elevation (WSE) along the Major Stream occurs upstream of the plant access road for the PMFand was founddetermined to be 624.0 feet until this surface Revision 12 2.4-10 January, 2003

Information Only met the normal depth of flow in the existing stream. The existing natural ridge along the right bank of the stream is at a maximum elevation of 630-0 (approximate).approximately 633.1 ft NGVD29 Perry Local Datum (PLD). The WSE at the Plant Access Road was determined to be 633 ft PLD (Reference 70). The maximum PMF WSE along the Diversion Stream is approximately 627 ft PLD at the upstream end of the modeled stream course (Reference 71). For both the Major Stream and Diversion Stream, topography plant-side of the stream course ensures the PMF inundation profile does not reach plant structures. This includes the natural ridge along the Major Stream and the earthen berm along the plant side bank of the Diversion Stream. The minimum freeboard for either stream exceeds one foot (Reference 70, Reference 71). ThisThe PMF flow elevation water surface elevation will safely passexceeds the bottom of beneath the railroad bridge; however, analysis shows the bridge remains intact during PMF conditions (Reference 73).

As no recorded data exists, no correlation is possible between the results obtained and floods on record. For added conservatism, the flow for each reach of both streams was considered to be equal to the corresponding PMF flow at the outfall to Lake Erie.

2.4.3.6 Coincident Wind Wave Activity Wind wave activity is of no concern with the flood conditions in these small streams as previously discussed.

2.4.4 POTENTIAL DAM FAILURES, SEISMICALLY INDUCED Presently there are no impoundments upstream of the plant, and since the drainage basins of the two streams passing through the site are small and the terrain is quite flat, it is unlikely there will be any impoundments in the future. Therefore, seismically-induced dam failure is not included as a design condition.

2.4.4.1 Dam Failure Permutations Revision 12 2.4-11 January, 2003

Information Only This section is not applicable to PNPP.

2.4.4.2 Unsteady Flow Analysis of Potential Dam Failures This section is not applicable to PNPP.

2.4.4.3 Water Level at Plant Site This section is not applicable to PNPP.

Revision 12 2.4-11 January, 2003

Information Only center of the lake reach 102 mph. The temporal variation in setup height over the remaining storm period is plotted in the hydrograph shown in <Figure 2.4-28>. The spatial profile of the lake surface at maximum deflection is plotted in <Figure 2.4-29>.

It should be noted that these values do not reflect corrections for pressure differences or precipitation. With an antecedent water level of 575.4 feet (USGS), a precipitation value of 0.5 feet, a pressure correction of 0.3 feet, and a wind setup of 4.30 feet, the total maximum stillwater surface level at the plant site was computed to be 580.5 feet (USGS) (Reference 61).

Wind velocities for the PMS were generated at three hour intervals for ten stations around the periphery of Lake Erie using the techniques discussed in <Section 2.4.5.1>. <Figure 2.4-26> shows the locations of the ten stations. <Figure 2.4-30> and <Figure 2.4-31> show variations of wind speed and direction for the two stations (20,1) and (40,1) adjacent to the site and the two stations (20,21) and (40,21) north of the site, respectively.

indicates the site setup winds at these stations. The wind speed for the stations adjacent to the site averages above 70 mph for a period of 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />. During the same period the wind speeds for the stations across the lake from the site average 80 mph or above with a maximum of 110 mph being reached at the center of the lake. 2.4.5.3 Wave Action The wind field used to determine the probable maximum setup was also used to find the concurrent wave action. As discussed in <Section 2.4.5.1>, this wind field was defined at ten stations located around the lake to give complete meteorological coverage of Lake Erie. A study of the critical fetch direction showed that the fetch lengths were approximately the same for winds directed toward the site from Revision 12 2.4-21 January, 2003 Information Only The setup of the lake level causes the pumps to operate at a higher than normal flow rate since the static head is reduced. With these wave induced variations in the pump chamber water level, no problem exists in meeting the flow requirement described in <Section 9.2.1>. 2.4.5.5 Protective Structures 2.4.5.5.1 Shoreline Recession 2.4.5.5.1.1 Summary Since plant grade is approximately 45 feet above the normal lake level and there are no safety-related structures within 380 feet of the lake shoreline (toe of bluff), damage to the shoreline bluff by an individual storm would not affect the operation or the safety of the PNPP. Data presented herein shows that the range of bluff recession in the vicinity of the emergency service water pumphouse has been less than 2 feet per year since 1937. Erosion of the shoreline bluff is caused by groundwater seepage and direct runoff on the upper portions of the bluff, and by wave attack and runup at the lower portions. To monitor the combined effect of shoreline recession and bluff erosion, a semiannual (Spring and Fall) survey is being made at six profile locations established at regular intervals along the shoreline. This survey will continue on a semiannual basis from 1984 through 1989, at which time it will be continued on an annual basis (spring) for the life of the plant (Reference 74). <Figure 2.4-32> shows the exact locations of the survey lines. The sections that follow describe the bluff recession process. 2.4.5.5.1.2 Introduction This section presents the findings of shoreline erosion studies and investigations for a 6,000 foot reach of the Lake Erie shoreline north Revision 12 2.4-24 January, 2003 Information Only locally as much as 1,500 feet offshore. The lake bottom north of the site boundary is irregular but generally slopes at about 2.5 feet per 100 feet for the first 300 feet offshore, decreasing to about 5 feet in 1,000 feet for the next 4,000 feet or more. 2.4.5.5.1.4 Nature of Bluff Erosion The principal factors affecting shoreline recession are variations in Lake Erie levels, wind (storm waves), water seepage and frost action. The composition and degree of compaction of the bluff materials are limiting factors in the rate of recession. Widespread slumping of the upper half of the bluff is the most prevalent bluff feature in the vicinity of the site. Slumping within the lacustrine and upper till deposits is caused mainly by groundwater seepage forces and frost action. Undercutting and removal of slump material by wave action complete the cycle of bluff recession. 2.4.5.5.1.5 Wind, Littoral Drift and Beaches Local storms are the main cause of significant wave action. The shoreline at the site is subjected to waves from the southwest through the north to the northwest. Winds from the southwesterly direction set up the prevailing littoral current from the west to the east. Generally, the west to east direction of littoral drift results in accretion of sand at the west side and the depletion of material to the east side of structures projecting from the shore. There are, however, no projecting permanent structures along the shoreline boundary of the site. The nearest suchoff-site structure is located near the northwest corner of the site boundary on the former Neff Perkins property. This structure, a sheet piled water conveyance channel, projects into Lake Erie about 135 feet. With the exception of the small beach northwest of the site, beaches along the shore in the study area are narrow, short in length and frequently transitory or submerged. Revision 12 2.4-28 January, 2003 Information Only 2.4.5.5.1.6 Lake Levels Shoreline erosion is noticeably influenced by lake levels and the related storm waves. High levels allow the waves to directly contact the toe of bluff while waves from low lake levels are dissipated by wider beaches. Lake levels vary with climatic conditions which affect evaporation and inflows. Minimum lake levels usually occur in February and maximum levels occur in mid-summer. The maximum seasonal fluctuation is nearly three feet, but long term cycles of fluctuation, resulting from wet and dry periods are as much as eight feet. Predictions of future lake levels are difficult to make. However, future long term cycles of fluctuation are not expected to differ significantly from those presented in <Figure 2.4-33>. <Figure 2.4-34> presents monthly recorded mean lake levels, from 1904 to 1979, which show short and long term trends. Long term annual fluctuations are shown in <Figure 2.4-33>. The 1973 mean level of Lake Erie was about fourfive feet above the Lake Erie Low Water Datum (LWD) established at 570.5 feet (USGS) above mean tide at New York City; that mean level was at the peak of a high lake level cycle (Reference 61). Reducing lake levels to a common datum for the various years studied was not possible because dates (day and month) were not always given on the property survey information. 2.4.5.5.1.7 Effects of Ice Almost every year, ice forms along the shore of Lake Erie. In winters with sustained periods of sub-zero temperatures, the entire lake freezes over; during the winter months, wave action upon the beach and the shoreline bluff is minimal or non-existent due to the buildup of ice along the shoreline. However, freezing and thawing of the groundwater seepage produces a detrimental effect on the bluff face that contributes to the rate of bluff erosion. Revision 12 2.4-29 January, 2003 Information Only The total top of bluff change indicated by <Figure 2.4-35> for a 2,000 foot central reach of shoreline northwest of the plant ranges from 20 to 85 feet (<1 to 2 ft/yr) from 1937 to 1972 (35 years). For the same period, total top of bluff recession of reaches to the west and east of the central section ranged from 1 to 3 ft/yr and 4 to 5 ft/yr, respectively. Fluctuations of Lake Erie <Figure 2.4-34> indicate long term mean lake levels from 1934 were on an up cycle, peaking in 1952 and again in 1973 (Reference 61). A correlation of larger changes in bluff erosion during periods of high lake levels could not be evaluated with certainty due to lack of data, but high lake levels undoubtedly have a significant effect. shows annual recession rates relative to 1972 for each of the twelve erosion monitoring lines <Figure 2.4-32> and is summarized below: Range (Ft/Yr) of Top of Bluff Recession Relative to 1972 Section 1937 1957 1964 West (J-I-H-G) 1-3 2-6 3-7 Central (F-L-K-A-B) <1-2 1-5 1-7 East (C-D-E) 4-5 5 4-5 It should be remembered that the bluff erosion is a two-step process. One step is wave action on the lower till which forms the toe of the bluff. As previously discussed, the location of the toe of bluff is the factor that will determine the need for bluff protection. The other step is the random occurrence of localized slumping induced by groundwater seepage and frost action. Although a single slump (at Profile Line C between 10/72 and 4/73) indicated a significant change of 33 feet in the top of bluff location, future movement at the slumped location most likely will not occur again until the toe of bluff has receded to a point where most of the slumped material has been removed. The more recent comparisons (1957 and 1964) show the effects of the random slumping process on the relative top of bluff recession rates. Revision 12 2.4-31 January, 2003 Information Only in the spring and fall of each year. The first complete profiles were taken in November, 1973, and are presented in <Figure 2.4-38>. Readings of the net changes in the bluff, at two year intervals, taken to date are also shown in <Figure 2.4-38>. summarizes the recession rates for the profiles shown in <Figure 2.4-38> using profile information through September, 1978. In general, between 1972 and 1978, the top of bluff erosion rate varied (from <1 to 2 ft/yr) within the central shoreline reach. The eastern end of the central reach receded at about 7 ft/yr during this relatively short (six-year) period. This same area receded only 2 ft/yr between 1876 and 1978. The eastern and western tops of bluff receded from 2 to 6 ft/yr and 5 to 9 ft/yr, respectively, between 1972 and 1978. Again, the long term (1876 to 1978) top of bluff recession rates were 2 to 3 ft/yr and 1 to 4 ft/yr for the eastern and western reaches, respectively. In addition, the 1975 aerial survey was examined to assure that excessive erosion of the bluff did not take place between the ground survey profile lines. shows that the shorter the time interval investigated, the greater is the recession rate for that time interval. This is due to significant, localized slumps being averaged over a relatively short time period. However, these short term, localized slumps are part of the overall recession cycle; in addition, they are attributable to the sustained high lake levels which peaked in 1975 and, therefore, allowed wave attack to undermine the toe of bluff during the high lake level period. The entire recession process is time and water level dependent; i.e., it occurs in a stop-start sequence, and should be averaged over a long period of time to obtain meaningful results. 2.4.5.5.1.10 Man Made Effects of Erosion With the exception of the potential future bluff protection described later in this section and the interim protection discussed in <Section 2.4.5.5.9>, no permanent structures exist on the bluff. Revision 12 2.4-34 January, 2003 Information Only Grading and clearing of the site were performed in such a manner that surface runoff was controlled and erosion minimized. The closest building structure (service water pumphouse) to the bluff is approximately 280 feet away. This structure is founded on shale rock well below the overlying glacial deposits. Controlled blasting (instrumentally monitored) was conducted during construction of PNPP. AnTwo interim revetments, described in <Section 2.4.5.5.9>, hashave been built along the shoreline of the plant property. Protection is provided along the shoreline from the Remnant Minor Stream discharge to the Northwest Storm Impoundment Spillway. Protection is also provided at the outfall of the Diversion Stream. These two features are not continuous. Changes in littoral drift accretion and depletion along the shoreline forming the north site boundary is not expected to change greatly as a result of possible future industrial development to the east and west of the site boundary. Both the State and Federal agencies play an active role in restricting construction of new structures projecting into Lake Erie that might affect littoral drift patterns or increase the rate of shoreline recession of neighboring shoreline property. Additionally, periodic inspections of unprotected areas ensure excessive erosion does not occur (Reference 74). 2.4.5.5.2 Maximum Allowable Shoreline Recession <Section 2.5.5> describes the point to which bluff recession could progress without threatening the function of safety class structures. Bluff protection will be installed if the retreat closely approaches this limit. 2.4.5.5.3 Protective Measures 2.4.5.5.3.1 Protective Measures Description If the shoreline retreat becomes threatening to the safety-related structures, the shoreline will be protected by a suitable permanent Revision 12 2.4-35 January, 2003 Information Only construction that will protect the face and toe of the bluff. Final design and permit applications for the shoreline permanent protection construction will be initiated when the lake shoreline (toe of bluff) Revision 12 2.4-35 January, 2003 Information Only has receded to a point 250 feet away from the closest safety class structure (emergency service water pumphouse). However, if the State of Ohio or the Federal Government develops an area-wide plan for shoreline protection that includes the plant, CEI will fully cooperate in implementing the plan on its property. The protective construction (Reference 29) (Reference 39) considers grading of the shoreline bluff and construction of a permanent protective revetment. Interim protective measures are described in <Section 2.4.5.5.9>.

a. Bluff Grading Prior to installation of the shoreline protective revetment, the bluff will be graded to the dimensions shown in <Figure 2.4-39>.

The bluff grading will be as follows:

1. Prior to the placement of the protective revetment, the bluff will be graded to a 2:1 slope between Elevation 555 feet (USGS) and Elevation 605 feet (USGS).

2. After the 2:1 grading is finished, a 10-foot wide berm will be cut at Elevation 605 feet (USGS).

3. After the berm is finished, further grading of the bluff to a 3:1 slope is required between Elevation 605 feet (USGS) and the top of the bluff.

b. Protective Revetment The maximum wave runup, corresponding to the 9.7-foot high maximum wave breaker height (Reference 31) breaking on the rough 2:1 slope of the protective revetment, is found in (Reference 22) to be 16.4 ft. The wave runup would therefore reach Elevation 596.9 feet (USGS) when the lake is at Elevation 580.5 feet (USGS) i.e., maximum stillwater level PMS (Reference 61). However, it should be pointed out Revision 12 2.4-36 January, 2003

Information Only that the freeboard between the top of the protective revetment, located at Elevation 605.0 feet (USGS), and the maximum wave breaker height runup is 8.1 feet. Therefore, it is not expected that the wave runup produced by the PMS will ever overtop the crest of the revetment. The shoreline protective revetment will protect a section of the lake shoreline approximately 2,000 feet long, comprised of the distance between the entrance to the barge unloading area and the outlet of the Remnant mMinor sStream diversion. Extension to the outfall of the Diversion Stream will also be evaluated. The protective revetment as shown in <Figure 2.4-39> will offer sufficient protection to the emergency service water pumphouse. The shoreline protective revetment will be a rubble mound structure composed of the following layers of material:

1. The first layer is a permeable plastic fabric sheet, which is placed on the lake bed and over the area cut to the 2:1 slope.

2. On top of the permeable plastic fabric a 2-foot thick gravel filter blanket will be placed, as specified and shown in

<Figure 2.4-39>.

3. The filter will be covered with two layers of 1,000 to 2,000 pound quarry stones fitted into the gravel material.

4. The two layers of large quarry stones will be surmounted by two layers of heavy armor stones having a weight of between 6 and 10 tons. The heavy armor stones will not only be randomly placed over the sloped surface, but will become an integral part of the protective toe of the rubble mound protection. The toe protection will extend 47 feet into the lake and will be founded on weathered bedrock at approximate Elevation 555.0 feet.

Revision 12 2.4-37 January, 2003 Information Only environmental impact report. This is required for any structure that will be built in Lake Erie below Elevation 572.8 feet IGLD (574.7 feet USGS).

b. Shore erosion permit This permit will be issued by the Ohio Department of Natural Resources and requires detailed drawings of the proposed shoreline protection structures.

2.4.5.5.4 (Deleted) 2.4.5.5.5 (Deleted) 2.4.5.5.6 Barge Slip A nonsafety-related barge slip was constructed northwest of the plant along the southern shoreline of Lake Erie. It is located in the general area incised by the mMinor sStream where it originally entered the Lake (prior to plant construction). An approach channel (averaging about seven feet in depth) was dredged from the lake to the barge slip. Lake dredging was performed to initially open the channel and then as required to maintain the opening prior to barge deliveries. Dredged material was disposed of on the plant site. The barge slip was constructed of steel sheet piling with tie-backs. The lake end of the barge slip was constructed about 30 feet south of the 1972 shoreline, with sheet pile wings being constructed toward the shoreline. To protect the side slopes and shoreline at the lake end of the barge slip, a rubble mound protective revetment structure was installed along the shoreline, extending 50 and 80 feet, respectively, east and west of Revision 12 2.4-41 January, 2003 Information Only 2.4.5.5.7 Northwest Sediment Control Dam A nonsafety-related sediment control earthen dam and associated concrete spillway were constructed at the northwest corner of the plant site. The toe of the spillway is approximately 90 feet south of the 1975 shoreline. The channel bottom between the spillway toe and the shoreline is protected by 2-foot-6-inch thick dumped riprap placed over a 1-foot-3-inch thick gravel filter. 2.4.5.5.8 Remnant Minor Stream and Diversion ChannelStream Outlets The mMinor sStream, which originally entered the lake at the present barge slip location, was diverted east of the plant site prior to plant construction. The channel outfall to the lake was constructed using 96 inch diameter corrugated metal pipe installed over a layer of 500 to 8,000 pound dumped stone riprap. The pipe was terminated at the sheet piling protection installed along the lake shoreline in front of the plant site. In 2015, the Diversion Stream was installed to further route streamflow east of the plant, increasing the conveyance capacity of the streamcourse (Reference 75). The Diversion Stream intercepts the Minor Stream and routes streamflow through a trapezoidal engineered channel, discharging to Lake Erie. Following installation of the Diversion Stream, the Remnant Minor Stream (consisting of the construction-era engineered channel) functions only as a swale path for the Local Intense Precipitation domain. The outfall of the Diversion Stream is provided with a 48-inch pipe discharging to an armor stone revetment along the shoreline, discussed in <Section 2.4.5.5.9>. The outfall is sized for the streamflow resulting from a 100-year recurrence interval storm; flowrates in excess of this will overtop the outfall and flow directly to Lake Erie. 2.4.5.5.9 Interim Shore Protection In the early spring of 1975, significant shore erosion was observed at three localized areas of the plant site in the vicinity of site construction operations. These accelerated erosion rates were directly Revision 12 2.4-43 January, 2003 Information Only attributed to the sustained high lake levels which peaked in 1975 and which allowed wave attack to undermine the toe of the bluff during the high lake level period. In 1983, a rock protected sheet pile breakwall was erected. This sheet pile breakwall protects the section of the lake shoreline approximately 2,200 feet long, composed of the distance between the entrance to the barge unloading area and the outlet of the Remnant mMinor sStream diversion as shown in <Figure 2.4-39A>. In 1992, the temporary sunken barges were removed and the interim revetment was extended 1300 feet west to the northwest storm impoundment spillway as shown in <Figure 2.4-39A>. The design of the extension was essentially the same as the original 2200 foot revetment. Revision 12 2.4-43 January, 2003 No change proposed. Included for context. The breakwall was constructed in the following manner:

1. A sheet pile breakwall was driven along a line approximately 25 feet out into the lake from the toe of the sloped bluff.

The sheet piling was cut off at approximate Elevation 580-3. Whaler was bolted to the piling.

2. The shore side of the breakwall was finished as follows:

(a) Filter cloth was installed against the sheet piling. (b) A causeway was formed of clean sandstone and concrete fill to Elevation 576-0. (c) An underlayer of 2 to 14 inches of sandstone was installed to Elevation 577-0. (d) Armor stones were installed to Elevation 579-0.

3. The lake side of the breakwall was finished as follows:

(a) Filter cloth was placed on the lake bottom approximately 9-0 out from sheet piling. (b) Armor stones were placed on filter cloth at an approximate slope of one to one to an elevation of approximately 577-0.

d. The eastern end of the breakwall was gradually curved into the shoreline and the lake side armor stones were installed up to the top of the sheet piling. The western end of the breakwall was curved into the shoreline at the east edge of the northwest storm impoundment spillway and the lakeward side was protected by armor stone placed at the base of the spillway.

Revision 12 2.4-44 January, 2003 Information Only The top of the bluff should stabilize at approximately 300 feet from the emergency service water pumphouse. Therefore, this breakwall will provide significant protection to the shoreline and to the emergency service water pumphouse. In 2015, as part of the Diversion Stream installation, an armor stone revetment was installed at the outfall of the Diversion Stream. The armor stone revetment protects approximately 100 feet of shoreline and exceeds the requirements of Technical Report No. 4 (Reference 22) (Reference 76). The revetment consists of a toe stone layer of four to five-ton stone and an armor stone layer of two to four-ton stone. The revetment begins below the lake surface and extends up the bluff to areas impacted by wave runup; the armor stone extends up to the base of the Diversion Stream culvert, approximate Elevation 589.6 ft PLD (Reference 77). The Diversion Stream revetment is depicted in <Figure 2.4-39B>. 2.4.6 PROBABLE MAXIMUM TSUNAMI FLOODING Since the site is located on Lake Erie, an inland lake, tsunami occurrence is not applicable. The Lake Survey Center (NOAA) has found no evidence of earthquake related seiches. 2.4.7 ICE EFFECTS 2.4.7.1 Regional Ice Formation History Lake Erie, the shallowest of the Great Lakes, is also the most thermally variable. It reacts rapidly to seasonal temperature changes and can build an appreciable ice cover in a comparatively short time (Reference 33). As winter progresses, ice on Lake Erie spreads from west to east. In mid-December, ice begins to form in the extreme western portion of Lake Erie. It spreads eastward, partially aided by a prevailing west wind, until the beginning of March when the eastern end of the lake is Revision 12 2.4-45 January, 2003 Information Only completely ice covered. At this time, the probability of ice cover in the site area exceeds 76 percent (Reference 32). The ice disappears from the western and central portions of Lake Erie by the end of March and by mid-April only a small area near Buffalo, New York, is still ice covered (Reference 33). Available information indicates that the critical period for ice development in the site area is from mid-February through mid-March with ice block formation prevalent during the spring ice breakup. Revision 12 2.4-45 January, 2003 Information Only The intake structures are protected against the impact of ice islands by 10 vertical reinforced concrete caissons, each 6 or 7 feet in diameter, placed in a 70-foot diameter circle around each of the submerged intake structures. The spacing between the caissons is such that the intake water approach velocity will not be increased. The three foot diameter discharge nozzle is encased in a 17-foot diameter reinforced concrete caisson for protection against the ice loads produced by the impact of a floating ice island crushing against the structure. <Figure 3.8-67> and <Figure 3.8-68> show details of caissons for the intake and discharge structures. 2.4.7.4 Ice Flooding Ice flooding cannot occur because of the high bluffs between the buildings and the lake. Also, safety-related onshore buildings are set back from the top of the 45-foot high bluff to preclude ice forces being a problem. Ice-induced flooding from the adjacent streams is not a concern. The base flow of the streams is 5 cfs or less per <Section 2.4.1.2> which precludes formation of appreciable ice blockage in the stream channels. The probable maximum winter precipitation (PMWP) rainfall is bounded by the all-season rainfall as presented in <Section 2.4.3.1>. The effects of the PMWP on the Local Intense Precipitation (LIP) domain is discussed in <Section 2.4.2.3.1>. 2.4.8 COOLING WATER TUNNELS AND OFFSHORE STRUCTURES 2.4.8.1 Cooling Water Tunnels Service and cooling water for PNPP will be obtained from Lake Erie at approximately 2,600 feet offshore and carried to the plant site through a 10-foot diameter intake tunnel located in the underlying bedrock. The water is then returned to the lake through a similar discharge tunnel of shorter length. Short tunnels of the same diameter are used Revision 12 2.4-47 January, 2003 Information Only near the shore facilities to tap the cooling water tunnels for the emergency service water system. Tunnel locations are shown on <Figure 3.8-65> and <Figure 3.8-66>. A discussion of the tunnel function is given in <Section 2.4.11.6> and <Section 9.2.1>. Revision 12 2.4-47 January, 2003 Information Only A three-foot diameter discharge was chosen as the best design for environmental protection. Details of the analysis are given in (Reference 36). The design of the diffuser discharge structure is shown in <Figure 3.8-67>. 2.4.9 CHANNEL DIVERSIONS This section is not applicable to PNPP since no cooling water channels exist from which flow could be diverted. 2.4.10 FLOODING PROTECTION REQUIREMENTS Four prospective sources of flooding exist at the Perry site: Lake Erie to the north of the plant, intense local precipitation, and flooding by two small, namelessthe Major sStreams which borders the site to the eastwest and south, flooding from the Diversion Stream which borders the site to the east, and flooding within the local intense precipitation domain due to direct precipitation events. All flooding sources are mitigated with unique flooding protection to ensure that floodwaters do not adversely impact safety related structures, systems and components. Protection is provided in the form of Exterior Barriers and Incorporated Barriers as defined in <Regulatory Guide 1.102>. 2.4.10.1 Lake Erie Flood Hazards <Section 2.4.5> and <Section 2.4.7> discuss the possibility of flooding caused by the probable maximum surge including wave runup and ice conditions in the lake. The plant grade is sufficiently high to greatly reduce the probability of general site floodingabove lake hazards that plant land structures are protected from floodwaters and related forces. The peak water surface elevation (WSE), including wave runup is 607.9 ft PLD as provided in <Section 2.4.2.2>. This is well Revision 12 2.4-50 January, 2003 Information Only below the nominal ground-level floor elevation of plant structures of 620.5 ft PLD. As such, flooding from Lake Erie is not a concern. On the intake side of the cooling water systems, all safety-related pumps and equipment will be located above Elevation 586-6 (USGS) in the emergency service water pumphouse. This elevation allows approximately three feet of freeboard over the simultaneous occurrence of the probable maximum setup, the maximum monthly mean lake level of record, and the associated oscillation of the pump chamber water level due to wave action over either the main or alternate submerged offshore intake structure. Plant flooding by intense local precipitation is prevented by the design of the storm drainage and roof drainage systems. For details, see <Section 2.4.2.3>.No emergency procedures are required for Lake Erie flood hazards. 2.4.10.2 Major Stream Flood Hazards The Major Stream probable maximum flood (PMF) inundation area is shown in <Figure 2.4-4a>. As shown in this figure, the streamflow resulting from a probable maximum precipitation (PMP) event is confined to the Major Streams drainage basin and does not encroach on plant safety-related structures or nonsafety-related structures that communicate with safety-related structures. The Major Stream is an engineered feature external to the plant area designed to protect the site from inundation and functions as an Exterior Barrier as described in <Regulatory Guide 1.102>. Plant Structures, Systems and Components are passively protected from the Major Stream flood hazards for all events up to and including the PMP by the channel capacity and topographic features segregating the Major Streams drainage basin from the local intense precipitation (LIP) domain. The PMF discussed herein is based on the precipitation event provided in <Section 2.4.3.1> which bounds the standard project storm (SPS) and Revision 12 2.4-50 January, 2003 Information Only probable maximum winter precipitation (PMWP) events provided in <Section 2.4.3.1>. No emergency procedures are required for Major Stream flood hazards. 2.4.10.3 Diversion Stream Flood Hazards The Diversion Stream probable maximum flood (PMF) inundation area is shown in <Figure 2.4-5a>. As shown in this figure, the streamflow resulting from a probable maximum precipitation (PMP) event is confined to the Diversion Streams drainage basin and does not encroach on plant safety-related structures or nonsafety-related that communicate with safety-related structures. The Diversion Stream is provided with an earthen embankment (berm) which functions as an extension of the channels west bank. The top of the Diversion Stream berm is above the peak water surface elevation (WSE) during the Diversion Stream PMF. The Diversion Stream and berm are engineered features external to the plant area designed to protect the site from inundation and functions as an Exterior Barrier as described in <Regulatory Guide 1.102>. Plant Structures, Systems and Components are passively protected from the Diversion Stream flood hazards for all events up to and including the PMP by the channel capacity and berm which segregates the Diversion Streams drainage basin from the local intense precipitation (LIP) domain. A failure of the Diversion Stream berm is postulated within the analysis for the LIP event (Reference 66). Guidance for determining the breach profile and size, as well as resulting breach flow rate, is determined using the guidance of the U.S. Army Corps of Engineers (Reference 84) (Reference 85). As such, any failure of the Diversion Stream berm is inherently bounded by the protection discussed for the LIP event. The PMF discussed herein is based on the precipitation event provided in <Section 2.4.3.1> which bounds the standard project storm (SPS) and Revision 12 2.4-50 January, 2003 Information Only probable maximum winter precipitation (PMWP) events provided in <Section 2.4.3.1>. No emergency procedures are required for Diversion Stream flood hazards. 2.4.10.4 Local Intense Precipitation Domain Flood Hazards As discussed in <Section 2.4.2.3>, effects from the Local Intense Precipitation (LIP) result in the controlling flood event for the site. The LIP event results in water levels which exceed door thresholds and wall penetrations. For the LIP hazard, flood protection is provided in the form of incorporated barriers as defined in <Regulatory Guide 1.102>. Protection is provided for safety-related buildings and nonsafety-related buildings which communicate with safety-related buildings. These incorporated barriers provide protection for safety-related structures, systems, and components. For the LIP hazard, both permanent and temporary (removable) incorporated barriers are utilized. Permanent incorporated barriers consist of safety-related building exteriors, steel closure plates, and concrete and aluminum flood walls. With the exception of the safety related building exteriors and closure plates at the Emergency Diesel Generator (EDG) overflow flame arrestors, the permanent incorporated barriers are nonsafety-related and are not within the scope of the PNPP Quality Assurance Program. Typical depictions of the concrete and aluminum flood walls are shown in <Figure 2.4-78> and <Figure 2.4-79>, respectively. Buildings protected by these features are depicted in <Figure 2.4-77>. Temporary incorporated barriers are provided in the form of removable flood panels (flood stop logs) which are also nonsafety-related and not within the scope of the PNPP Quality Assurance Program. These barriers are utilized at plant doorways which create openings in the otherwise continuous protection provided by the walls discussed above. These removable barriers, certified to the requirements of ANSI Standard Revision 12 2.4-50 January, 2003 Information Only ANSI/FM-2510, are generally stored in a central location and deployed in accordance with plant procedures. In some cases, where there is minimal impact on normal plant operation and no impact on personnel egress, these temporary incorporated barriers may be pre-deployed. As discussed in detail in <Section 2.4.14>, operator action is initiated by receipt of meteorological forecast, discussed in <Section 2.4.10.5>, of forthcoming significant precipitation. Typical depictions of the concrete and aluminum flood walls are shown in <Figure 2.4-78> and <Figure 2.4-79>, respectively. Typical examples of the removable incorporated barriers are depicted in <Figure 2.4-80> and <Figure 2.4-81>. All incorporated barriers are designed for the entire range of flood forces (Reference 79). This includes the hydrodynamic forces resulting from the flooded condition (including fluid velocities) and the forces resulting from flood-born missile impact. Deployment of flood protection features for the LIP hazard is incorporated into plant off-normal instructions. Lesser precipitation hazards for the LIP domain, up to and including the standard project storm (SPS) and probable maximum winter precipitation event (with concurrent snowmelt), are mitigated using permanent passive protection which requires no operator action. Consistent with other flood protection features, these protection features barriers are nonsafety-related and are not within the scope of the PNPP Quality Assurance Program. These features include the walls discussed above, closure plates, ramps and raised thresholds. No emergency procedures for barrier deployment are required for SPS or PMWP effects. 2.4.10.5 Meteorological Forecast Warning Using the guidance of (Reference 88), PNPP utilizes a two-tier meteorological alert to initiate deployment of the temporary barriers discussed in <Section 2.4.10.4> (Reference 89). The first-tier warning Revision 12 2.4-50 January, 2003 Information Only is set to 2.1 inches of precipitation in a 24-hour period. This event corresponds to a one-year recurrence interval precipitation event. The second-tier warning is set to 1.9 inches of precipitation in a one-hour period. This event corresponds to an approximately 18-year recurrence interval event. Compared to the Standard Project Storm (SPS) event for which fully passive protection is provided, which has a peak hourly intensity of 3.747 inches per hour as discussed in <Section 2.4.3.1>, sufficient overlap is provided to account for uncertainties associated with meteorological forecast limitations. Meteorological forecasting is provided by an external service which is implemented by certified meteorologists. The forecasting employs an ensemble technique using diversified inputs. Input models are obtained from the National Blend of Models (NBM) and Weather Prediction Center (WPC). The NBM provides Quantitative Precipitation Forecasts (QPF) which the WPC provides Probabilistic Quantitative Precipitation Forecasts (PQPF). A 95th percentile confidence value is selected for the ensemble forecasting method per the guidance of (Reference 88). QPF forecasting provides a medium range forecast monitoring five days into the future. PQPF forecasting provides a short-range forecast monitoring 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> into the future. The lower tier warning does not require any specific action by plant personnel. This alert instead serves to initiate heightened awareness thus allowing plant personnel to conservatively take any necessary preemptive actions. The higher alert serves as the entry condition for a Technical Specification Limiting Condition of Operation (LCO) and initial condition for entry condition for off-normal instructions which includes deployment of temporary flood barriers. Revision 12 2.4-50 January, 2003 Information Only 80 mph for approximately 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />. For station (20,21), the wind direction varies from 340 to 310 degrees during the maximum wind period. For station (40,21), the wind direction varies from 340 to 320 in this period. The total distance that these winds travel over water is approximately 56 miles. The computed setdown hydrograph for the site during the period of the PMS is shown in <Figure 2.4-63>. With the 4.043 foot maximum setdown, the minimum water surface elevation at the plant site would be 563.36 feet IGLD (565.26 feet USGS) (Reference 90). This is based on an antecedent water elevation of 567.4 feet (IGLD) (Reference 61), the minimum monthly level of record. The wave action coincident with this setdown was determined by procedures described in Technical Report No. 4 (Reference 22). Using an average 90 mph offshore, over water wind of unlimited duration with a 30 percent reduction to account for land effects in the nearshore zone, the Bretschneider method gives a 2.6 foot significant wave height and a 4.7 second period. Since the alternate intake (normal discharge structure) is closer to shore, the wave heights would be less than at the normal intake structure. 2.4.11.2.2.3 One-Dimensional Model for Setdown Surge The analysis of the lake setdown surge at the plant site was made using the one-dimensional model described in Technical Report No. 4 (Reference 22), and briefly characterized in <Section 2.4.5.2.2>. The probable maximum setdown was computed with this method using a fetch defined by a line connecting grid points (36,3) (plant site) and (36,21) <Figure 2.4-26>. <Figure 2.4-63> shows the hydrographs of computed setdown at the site for the PMS setdown wind data. Note that the curve does not reflect any adjustment for lake volume balance, pressure or precipitation. The maximum setdown shown on this curve is 4.03 feet (122.95 cm) (Reference 90). Revision 14 2.4-55 October, 2005 Information Only Volume adjustment was made on the basis of Equation 2.4-1. <Figure 2.4-29> summarizes the results of the volume computations for both the setup and setdown cases at the time of their peak occurrence. The pressure adjustments were made by looking at the PMS pressure data and choosing the maximum pressure difference between adjacent stations across the lake. For both the PMS setup and setdown cases, the maximum pressure difference was found to be 10 mb # 10 cm of water. No precipitation adjustment was included for the setdown case since it would only reduce the setdown and would not be indicative of the most conservative case. 2.4.11.3 Historical Low Water Two gauges have provided data for the study of the variation in surface elevation of Lake Erie. The Cleveland gauge has a period of record for monthly and annual means dating back to 1860, with instantaneously recorded data since 1904. The gauge at Erie has continuous data from 1960 to the present. A third gauge at Ashtabula, installed in 1954, has been neglected for extended periods since its installation and much of the data recorded by this gauge is incomplete and unreliable due to malfunction of the gauge and its recording mechanism. <Figure 2.4-2> reveals that the mean lake level has a cyclic variation. At Cleveland, the minimum monthly mean level of record was 567.4 feet IGLD (569.3 feet USGS) recorded in December 1934February 1936. The minimum recorded instantaneous level was 565.71 feet IGLD (567.61 feet USGS), which occurred on February 4, 1936. The maximum seiche setdown for each year was computed by subtracting the minimum instantaneous lake level from the mean level for the month in which it occurred. The peak setdown at Cleveland for the period of record was -3.04 feet, occurring December 8, 1927. At Erie, the minimum monthly mean level was 568.27 feet IGLD (570.17 feet USGS) for December 1964 and the minimum recorded Revision 14 2.4-56 October, 2005 Information Only instantaneous level was 566.00 feet IGLD (567.90 feet USGS), which occurred on March 10, 1964. The peak seiche setdown at Erie for the period of record is -2.90 feet, occurring March 10, 1964. A frequency study of seiche setdown and minimum monthly mean stages was made for both the Cleveland and Erie gauges. The results obtained are shown in <Figure 2.4-64> and <Figure 2.4-65>, respectively. Log Pearson Type III and Linear Gumbel distributions are presented for each case. Comparison of the seiche setdown curves in these figures shows that at a particular frequency the seiche at Erie exceeds that at Cleveland. This is felt to be attributable to dissimilar lengths of gauge records and topography in the vicinity of the gauging stations. 2.4.11.4 Future Controls There are three hydrologic features which influence the site: Lake Erie and the two small, namelessadjacent streams which border the site. The safety-related structures are located outside the drainage basin of the larger (major)both streams. No developments are foreseen for the streams as the meanbase flow of each is less than 105 cfs or less, and except for intermittent withdrawal by an adjacent industry from the downstream end of the major stream, the only use is for drainage. These streams are only used for drainage purposes. Lake Erie drains into Lake Ontario via the Niagara River and is also connected to Lake Ontario by the Welland Canal. The Niagara River has two major control structures for power generation before reaching Niagara Falls. The upstream east channel has also been channelized for navigational purposes. However, no new developments involving control structures are envisioned. The Welland Canal is approximately 26.5 miles long and has 8 locks capable of raising ocean-going vessels 326 feet from Lake Ontario to Lake Erie. A more complete description of the canal may be found in Revision 12 2.4-57 January, 2003 Information Only <Section 2.4.11.6>. A section of the canal is being straightened between Miles 23.8 and 15 (Mile 23.8 is approximately 4 miles from the Lake Erie end). The new cross section will have a bottom width of 350 feet compared with 192 feet in the existing channel. The depth of the new channel will be 30 feet, three feet deeper than the present system it will replace. For reasons outlined in the <Section 2.4.11.6>, it is considered most unlikely that any developments of the canal will influence the surface elevation of Lake Erie. 2.4.11.5 Plant Requirements As described in <Section 2.4.11.2>, the probable minimum lake level at Perry is Elevation 565.26 feet (USGS). With the inverts of the intake ports at an average elevation of 552.65 feet, inflow of sufficient cooling water during this period is assured. The corresponding water level in the emergency service water pump chamber would be at Elevation 562.09 feet. During this condition, water for the emergency service water system could also be supplied by the alternate intake system discussed in <Section 2.4.5.4> and <Section 9.2.5>. The crown and invert elevations of the diffuser nozzle of the discharge structure are 555.8 and 552.8 feet (USGS), respectively. The available 12.2-foot submergence over the diffuser nozzle would prevent air entrainment due to the inflow velocity (approximately 15.85 fps through the nozzle). The minimum water level in the emergency service water pumphouse will occur during the hot standby condition when only the emergency service water systems are operating. At the probable minimum lake level with coincident wave action, the level in the emergency service water pump chamber for this condition will be Elevation 562.09 feet (USGS) (Reference 91). With the invert of the chamber at Elevation 537.0 feet, the 10-foot minimum Revision 12 2.4-58 January, 2003 No change proposed. Included for context. loss of 326 feet. With no inflow to Lake Erie and discharge occurring through the Niagara River and the canal, it would take 350 days for the lake level to drop 5 feet from 573.00 feet IGLD (574.90 feet USGS) to 568.00 feet IGLD (569.90 feet USGS). Further conservatism in this estimate was gained by using the initial outflow head (the outflow for a lake level of 573.00 feet IGLD) rather than a falling head relationship for both the canal and the river for the whole head increment. The result of this conservative evaluation shows that a total failure of the Welland Canal lock system will not compromise the safety of the plant. The likelihood of such a failure is remote due to the redundancy of protective devices and the structural enormity of the system. Service and makeup water for the power plant will be obtained from Lake Erie approximately 2,600 feet offshore and carried to the plant through a 10-foot diameter intake tunnel; after passing through the plant, the water will be returned to the lake through a similar discharge tunnel. Two short tunnels of 10 feet diameter, shown in <Figure 3.8-65>, intersect the main cooling water tunnels near the shore facilities. Their only purpose is to draw cooling water for the emergency service water pumphouse, either from the intake or the discharge tunnel. Normally, as explained in this section and <Section 3.8.4> and <Section 9.2.1>, the intake tunnel supplies water to both the emergency service water pumphouse and the service water pumphouse. In the unlikely event of a complete blockage of the intake structure or intake tunnel, water for the emergency service system must be drawn from the discharge tunnel. During this time, the heated effluent from the service water system will be discharged onshore and will flow by gravity down to the lake shoreline. Discharge will be through the Safety Class 3 standpipe on the downstream side of the heat exchangers, as shown on <Figure 9.2-1> and discussed in Revision 12 2.4-60 January, 2003 Information Only <Section 9.2.1>. The water will discharge outside the auxiliary building onto the ground. The slopes and elevations are set so that the flow will be away from the plant, across the road and down a graded swale between the cooling towers to the diverted stream <Figure 2.4-3>. The water will flow down to the stream and discharge into Lake Erie (Reference 86). A longitudinal profile throughThe topography of the emergency service water alternate discharge area (Remnant mMinor sStream diversion channel) is depictedcan be seen in <Figure 2.4-83> and shows the elevations of the flow paths through the stream to the lake. Flow through all paths for both units will result in a total flow to the stream of approximately 50,000 gpm initially, which will be reduced to 25,000 gpm in a short period of time. These flow rates represent original plant design (two units). Since then, Unit 2 has been abandoned. As a result, the actual total flow exiting the ESW standpipes will be much less. In addition, the required ESW flow rates for Unit 1 have been analytically decreased to values less than those originally specified (reference <Figure 9.2-1(3)> for the required ESW system flow rates). The contours of the site will be set to provide a depressed area east of the auxiliary buildings <Figure 2.4-3>. This depressed area will slope away from the plant buildings, over the road and through the swale to the Remnant mMinor sStream. Elevations of the depressed areas will be such that no water exiting the plant under this unlikely event will flow back to the plantresult in flooding of the facility. This is confirmed via analysis captured in (Reference 86). The main intake structures shown on <Figure 3.8-65> and <Figure 3.8-67> consist of two independent intake heads that are each connected to a six foot diameter shaft. The two vertical shafts convey the water into the 10-foot diameter intake tunnel shown in <Figure 3.8-65> and <Figure 3.8-66>. The intake heads are circular in plan and are covered with a velocity cap placed at a minimum of 13.3 feet below the low water datum (LWD), as shown in <Figure 3.8-67>. Inflow is through Revision 13 2.4-61 December, 2003 Information Only vertical openings around the periphery of the intake heads. The discharge Revision 13 2.4-61 December, 2003 No change proposed. Included for context. structure, shown in <Figure 3.8-65> and <Figure 3.8-67>, consists of one 3-foot diameter diffuser nozzle encased in a 17-foot diameter protective concrete caisson, the top of which is 12.2 feet below LWD. The intake and discharge structures are located approximately 2,600 feet and 1,700 feet, respectively, offshore. Approximately 1,550 feet of horizontal separation exists between the two structures. Revision 13 2.4-61a December, 2003 No change proposed. Included for context. construction has been observed to be less than 500 feet <Section 2.5.4>, a distance well within the project site boundaries. The radius of influence will not be altered significantly after construction. Thus, the effects on groundwater during construction and throughout the plant life will not extend beyond the project site. 2.4.13.3 Accident Effects The groundwater movement in the general area of the plant <Figure 2.4-66> is to the north toward Lake Erie. As previously stated, the gradient ranges from 12 to 26 ft/mile. Additional withdrawals by future users will be significantly limited by the shallow thickness of the aquifer and the low transmissibility. Local domestic wells outside the exclusion radius are up-gradient from the plant site and will not be affected by the power plant. The low permeability of the glaciolacustrine deposits and of the shale bedrock, together with the low groundwater gradients toward the lake, would severely restrict the movement of water which might contain radioactive particles. Additionally, clay, the main constituent of the soil, has the potential for absorbing radioactive contaminants (Reference 25). An accidental release of radioactive contamination into the ground at the site is considered to be highly unlikely because of the extensive precautions taken to preclude such an accident. Postulating an accidental release of radioactive materials occurring at the radwaste building of the PNPP, the pumps installed in the pumping manholes of the pressure relief underdrain system will be manually shut off, allowing groundwater to build up to Elevation 590.0 feet within the underdrain system and discharge via the gravity drains to the emergency service water pumphouse and eventually into Lake Erie. In addition, radiation monitors located in the gravity discharge manholes, will automatically stop the service and backup underdrain pumps upon detection of high radioactivity <Section 11.5>. A discussion of postulated radioactive release is included in <Section 15.7>. Revision 13 2.4-71 December, 2003 Information Only Further, assuming an accidental release of radioactive materials was to occur at the radwaste building and was to assume a travel path through the soils, the estimated transit time to the point of discharge into Lake Erie is 25 years if the groundwater was allowed to return to Elevation 620.0. The maximum groundwater velocity would likely occur within the lacustrine deposits (upper 25 feet) as the underlying tills are relatively impervious. Coefficient of permeability K calculated from field testing within lacustrine materials ranged between 1.2 x 10-4 cm/sec and 4.2 x 10-7 cm/sec, as discussed in <Section 2.5.4>. The hydraulic gradient was determined from differences in gravitational groundwater levels between the radwaste building and the future protected bluff slope, and the shortest distance between these points. Groundwater levels measured in proximity to the radwaste building (Boring 1-45) averaged about Elevation 620.0. Near the edge of the bluff, the static groundwater level range occurs at around Elevation 616.0. The Perry site has been graded to approximate Elevation 620.0 PLD. The small streamnatural watercourse of the Minor Stream, located between the plant and the bluff, has beenwas relocated a trapezoidal engineered channel to the eastand. tThe abandoned channel has been filled with compacted soils to Elevation 620.0. The maximum difference in groundwater levels expected between the plant and the bluff after completion of the site grading is conservatively estimated at 12 feet; however, the readjusted piezometric slope after grading will likely be much less. The minimum groundwater transit distance will occur when the 1979 bluff, which is approximately 1,010 feet from the radwaste building, has receded about 200 feet <Figure 2.4-39>. On the assumption that 200 feet of recession will actually occur during the life of the PNPP, a conservative distance of 800 feet has been used for establishing the groundwater gradient. For Revision 13 2.4-72 December, 2003 Information Only In order to continuously monitor and detect significant amounts of radioactive concentrations discharging from the underdrain system, as a result of the postulated event, radiation monitors are located inside each of the two gravity discharge system manholes at the north end of the Unit 1 heater bay, at locations where the underdrain pump effluent travels through the gravity drain system. Details of the radiation monitor are discussed in <Section 11.5>. The offsite effects of a hypothetical release, due to a seismic event, of radioactive liquids to the environs is described in <Section 15.7>. 2.4.13.5.4 Maintenance and Testing Normal routine maintenance will be performed on the mechanical and electrical portions of the system. The manholes and gravity discharge pipes will be inspected annually to iensure that all parts of the system, including the porous piping, are in operating condition. Any blockage in the porous concrete periphery drain pipes will be cleared by mechanical or other suitable means. The following periodic tests will be performed to ensure continuous satisfactory performance of the system.

a. Continuity Test This test will be performed semiannually for the first five years of operation and annually thereafter. The objective of the test is to verify that water will build up and draw down at the monitoring points, to establish that the underdrain system can reduce the hydrostatic pressure on building foundations to the desired level.

Revision 16 2.4-92 October, 2009 Information Only

c. Long Term Performance of the Porous Concrete Underdrain System The long term performance of the porous concrete pressure relief underdrain system is evaluated as follows:

1. Tornados Tornados will not affect the operation of the underdrain system because it is underground. However, the manhole covers are exposed but are not considered missile proof because a missile entering the top of a manhole would not totally obstruct the flow of water in the manhole.

2. Earthquakes The system is a Seismic Category I system. The seismic design and analysis for the gravity discharge pipe is discussed in <Section 2.4.13.5.1>. The seismic design and analysis for manholes is discussed in <Section 3.8.4>.

3. PMP (Probable Maximum Precipitation)

The effect of PMP on the underdrain system is negligible. Around the nuclear island buildings, the ground surface will be paved with asphalt, concrete, or backfilled with relatively impervious Class B fill of excavated lower till soils. The rate of infiltration through the Class B fill is calculated to be less than 3 gpm and the effect on the underdrain system is insignificant. Revision 13 2.4-97 December, 2003 Information Only velocity and transport capability of groundwater to erode either Chagrin shale or lower till are negligible. The durability of the shale and its ability to resist subaqueous disintegration and decomposition have been documented by slaking tests and are discussed in <Section 2.5.4>. Lower till is nondispersive as demonstrated by the pinhole and soil conservation service laboratory dispersion test <Section 2.5.4>. The association of lower till and Chagrin shale properties, coupled with their demonstrated ability to withstand subsurface weathering and erosion during the Recent Epoch, show that no basis exists for assuming a subsurface erosion potential. A conspicuous absence at the Perry site of montmorillonite-type clays, which are characteristically detected in overburden and bedrock undergoing subsurface erosion as well as extensive surface erosion, is considered significant positive evidence in further refutation of this potential.

d. Potential of the Underdrain System to Drain Water From Lake Erie or Along Plant Piping Systems All piping except the underdrain system gravity flow discharge pipes running from the main plant buildings to the emergency service water pumphouse are designed and installed above Elevation 595.0 (i.e., approximately 20 feet above the mean monthly high water level for Lake Erie of 575.4 per

<Section 2.4.1.1>). The gravity discharge lines enter the emergency service water pumphouse at invert Elevation 579.0 which is approximately four feet above mean monthly high lake level. This ensures that no man-made flow path will exist between the pumphouses and the main plant buildings. Revision 12 2.4-110 January, 2003 Information Only The lowest discharge points from any of the 13 deep plant manholes of the porous concrete underdrain system are at manholes No. 8 and 9 which have pipe invert elevations of 582.6 and 583.5, respectively <Figure 2.4-69>. Since these gravity discharge pipe inverts are above the maximum lake setup due to the PMS (580.5), no backflow from the lake can occur through the Emergency Service Water Pumphouse into the porous concrete underdrain system. The mean monthly high water level for Lake Erie is Elevation 575.04 (Reference 61) which is seven feet above the groundwater level of 568.0 maintained in the underdrain system. Because the plant is 800 feet from the lake, the possibility of seepage from the lake into the underdrain was considered. Geologic mapping of the foundation area was conducted, and open fractures were grouted. None were seepage sources. In this way, all possible drainage paths from the lake into the underdrain systems were sealed. Underground piping systems, which enter the main plant buildings, were set in bedding materials of granular material which have a higher permeability than the lacustrine soil through which the pipes run, and hence, provide a potential flow path for groundwater into the underdrain system. In order to prevent this flow, at two separate locations special bedding and backfill material were used around all external pipes where they enter the Class A fill at the plant buildings. The special bedding and backfill material is low permeability Class B fill. The quantity that can flow through the backfill and bedding was included in the calculation of total groundwater flow into the underdrain system. The flow postulated through the pipe bedding material would not increase the calculated inflow to the underdrain system because that calculation assumes a saturated soil. Revision 14 2.4-111 October, 2005 Information Only

e. Infiltration Due to Rainfall, Surface Spills or Lawn Sprinkling A layer of impervious Class B soil was placed over the Class A fill to reduce the amount of seepage possible from infiltration at the surface. Such seepage could result from either rainfall, surface spills, or lawn irrigation.

All underdrain system manholes have gasketed, watertight covers installed at the surface. The covers are normally locked or bolted in a closed position. The 24 outside manholes (two manholes constructed inside buildings) have heavy duty gray cast iron covers. In paved areas, the covers are installed at grade. In unpaved areas, the covers are up to six inches above grade.These covers ensure minimal, if any, inleakage occurs into the underdrain system due to rainfall, surface spills or lawn sprinkling. In the event of the rupture or leakage of an onsite reservoir (e.g., cooling tower basins and industrial waste lagoons), the discharge will generally drain overland away from the plant into neighboring streams and thus to Lake Erie. The area surrounding the plant is drained by a catch basin storm drainage systemalso provided with a nonsafety-related storm drain system which will immediately collect all surface water approaching the plant and assist in drainage of the powerblock area. Because of the impermeable nature of the surface materials, there will not be sufficient time available to allow significant infiltration into the permanent underdrain system. summarizes the major onsite storage facilities excluding the cooling tower basins. Roofs of all buildings are drained to the storm water drainage system which discharges into naturalthe Major and Remnant Minor sStreams that feed into Lake Erie. Rainfall on paved and unpaved Revision 21 2.4-112 October, 2019 Information Only areas around the main plant buildings is directed by surface grading to catch basins which also discharge into the generally routed by topography or the storm water drainage system away from the plant. Rainwater or lawn Revision 21 2.4-112 October, 2019 No change proposed. Included for context. sprinkling water that falls on unpaved areas and percolates into the backfill material around the main plant buildings will add an insignificant amount to the flow in the pressure-relief underdrain system.

f. Seepage Increase Due to Excavation Heave due to elastic rebound was not known to have induced micro-fracturing of a surficial zone of the shale upon excavation unload. This phenomenon would have been expected to slightly increase the secondary porosity of the surficial shale zone and the corresponding permeability thereof. The amount of permeability increase cannot be quantified because of the limited depth influence and the negligible effect if any, of induced micro-fracturing. Any such increase did not influence seepage quantities derived from the shale during construction, because no seepages from the shale were detected.

Upon imposition of plant loads, the shale recompressed, reversing the heave deformation. The effect of the reloading closed much, if not all, of the micro-heave fractures and restored the unexcavated shale permeability. While the secondary porosity of the shale in a localized area might have increased due to micro-fracturing, the quantity of flow through this zone would not increase because the surrounding, sound, unfractured shale would still control the flow rate.

g. Pressure Distribution Within the Porous Concrete Blanket Under Design Flow Conditions Under normal conditions, practically all of the groundwater inflow is collected by the porous concrete and 12-inch porous pipes around the perimeter of the drainage system. It then flows to the pumped Revision 12 2.4-113 January, 2003

Information Only a seismic related failure of non-Category I structures without compromising the full operating capability of the redundant permanent dewatering system. 2.4.13.5.6 Controlled Low Strength Material (CLSM) Controlled Low Strength Material (CLSM) may be used as a replacement for Class B and Class C fill, and as a replacement for Class A fill when the Class A fill was used as bedding and backfill for buried piping and ductbanks only, and not as part of the Plant Underdrain system, or as a foundation for safety-related buildings or structures. Since the CLSM is equivalent to or better than Class B fill in bearing capacity and impermeability, this change has no effect on the results of USAR <Section 2.4.13.5.1> and <Section 2.4.13.5.5>. 2.4.14 TECHNICAL SPECIFICATION AND EMERGENCY OPERATION REQUIREMENTS Safety-related facilities at PNPP are protected as described in the preceding sections. Therefore, emergency protective measures and attendant technical specifications are not required.The only external flooding hazard which requires operator action to protect the Structures, Systems and Components (SSCs) required to achieve and maintain cold shutdown is the LIP event which represents the bounding external flood hazard for PNPP as determined in (Reference 66). Operator action is required only for precipitation hazards which exceed the Standard Project Storm (SPS). Operator action is limited to the deployment of nonsafety-related removable incorporated barriers in the form of flooding stop logs. The requirements and guidance for this action is incorporated into plant off-normal instructions. The action is limited to the placing of the stop logs at pre-determined locations. This involves sliding the stop logs into pre-installed end channels and securing the panels with compression clamps. This action is completed without the need for hand tools. Revision 12 2.4-117 January, 2003 Information Only Entry into the plant off-normal instructions is initiated by a meteorological forecast warning which is discussed in detail in <Section 2.4.10.5>. This action is required by PNPPs Technical Specifications as discussed in <Regulatory Guide 1.102>. The alert provides approximately 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of warning which grossly bound the estimated deployment duration of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. This ensures the barriers can be deployed well in advance of the onset of a flooded condition. If barriers are not deployed in the timeframe allotted by the Technical Specification Limiting Condition of Operation, a plant shutdown is initiated. 2.4.15 LIST OF PERSONS AND AGENCIES INTERVIEWED The following is a listing, by sections, of individuals and agencies whose assistance was elicited during preparation of the Hydrologic Engineering discussions: <Section 2.4.5.2> Dr. L. Bajorunas, Director, Great Lakes Research Center, NOAA, Detroit, Michigan. Mr. Elmer Kulp, Acting Chief, Vertical Control Section, Lake Survey Center, NOAA, Detroit, Michigan. Revision 12 2.4-117 January, 2003 Information Only

56. Pree, H. L., Jr., Ashtabula and Conneaut Creek Basins, and Adjacent Lake Erie Tributaries, Ohio Department of Natural Resources, Division of Water, 1960.

57. DeWiest, Roger J. M., Geohydrology, John Wiley and Sons, Inc., New York, 1967.

58. Todd, D. K., Groundwater Hydrology, John Wiley and Sons, Inc., New York, 1959.

59. Woodward-Cylde Consultants letter of November 01, 1981, to Gilbert Associates, Inc. Ref: See page Estimate.

60. Gilbert Associates Inc. Calculation 26:12, Perry Emergency Service Water Pumphouse - Stability Analysis, Revision 0 (Retained as Perry Calculation 26:12.000, Revision 0).

61. PNPP Calculation 50:74.000, Lake Erie Water Levels.

62. Not Used

63. Not Used

64. Not Used

65. PNPP Calculation DX-1.5.1, Lake Erie Surge Study - Surge Analysis.

66. PNPP Calculation 50:64.000, PNPP Site Modifications Local Intense Precipitation (Design Basis).

Revision 14 2.4-126 October, 2005 Information Only

67. PNPP Calculation 50:65.000, Evaluation of Structural Roof Capacity for USAR Described PMP Event.

68. PNPP Calculation 50:71.000, Design Basis Maximum Precipitation (PMP) Determination.

69. PNPP Calculation 50:79.000, Probable Maximum Winter Precipitation (PMWP, Cool-Season PMP) and Snowmelt Contribution (Design Basis).

70. PNPP Calculation 50:72.000, Design Basis Major Stream Probable Maximum Flood (PMF).

71. PNPP Calculation 50:73.000, Design Basis Diversion Stream Probable Maximum Flood (PMF).

72. PNPP Calculation 50:75.000, Design Basis Standard Project Storm (SPS) Determination.

73. PNPP Calculation 21:02.000, Misc. Yard Structures - Railroad Bridge.

74. PNPP Procedure EMARP-0005, Monitoring Shoreline Recession and Bluff Erosion.

75. PNPP Engineering Change Package 13-0802, Major/Minor Stream Modification.

76. PNPP Calculation 50:68.000, Perry Nuclear Power Plant (PNPP)

Diversion Stream Design Basis Shore Protection Analysis.

77. PNPP Drawing 744-0177-00012, Stream Relocation Outfall Profile -

Stream Outfall. Revision 14 2.4-126 October, 2005 Information Only

78. PNPP Calculation 50:80.000, Effects of Cool-Season Probable Maximum Winter Precipitation (PMWP) Event.

79. PNPP Calculation 50:77.000, Evaluation of Flood Barriers.

80. PNPP Calculation 21:21.000, Hydrogen Water Chemistry Tank Foundations and Miscellaneous Equipment Foundations.

81. ANSI Standard ANS-N170-1976-ANS-2.8, American National Standards for Determining Design Basis Flooding at Power Reactor Sites.

82. PNPP Calculation 50:76.000, PNPP Design Basis Standard Project Storm (SPS) Rainfall Effects.

83. U.S. Army Corps of Engineers Snow Hydrology, June 1956.

84. U.S. Army Corps of Engineers Guidelines for Calculating and Routing a Dam-Break Flood, RD-5, Hydrologic Engineering Center, January 1977.

85. U.S. Army Corps of Engineers Guidelines for Corps Dams, RD-13, Hydrologic Engineering Center, June 1980.

86. PNPP Calculation 50:82.000, ESW Swale Discharge Flooding Evaluation.

87. PNPP Calculation 50:83.000, Mixed Bed Tank Discharge Evaluation.

88. NEI 15-05, Warning Time for Local Intense Precipitation Events, Revision 6, April 2015, Nuclear Energy Institute.

89. PNPP Calculation 50:85.000, Precipitation Hazard Alert Evaluation.

Revision 14 2.4-126 October, 2005 Information Only

90. PNPP Calculation DX-1.5.0, Lake Erie Surge Levels - Lake Level Studies - PMS.

91. PNPP Calculation DX 1.1.2, Emergency Service Water Pumphouse Water Levels.

Revision 14 2.4-126 October, 2005 Attachment 2 L-22-272 Proposed Updated Safety Analysis Report Section 2.4 Text Pages (Retyped; for Information Only) (58 pages follow) Information Only 2.4 HYDROLOGIC ENGINEERING 2.4.1 HYDROLOGIC DESCRIPTION 2.4.1.1 Site and Facilities The Perry Nuclear Power Plant is located in Lake County, Ohio, approximately seven miles northeast of Painesville. The southern plant site boundary line is 3,100 feet from the shoreline of Lake Erie on the west side of the site and 8,000 feet on the east side. Grade elevations in the immediate plant area prior to plant construction varied between 620.0 feet and 623.0 feet based upon the USGS datum. The maximum monthly average level of record for Lake Erie is 575.4 feet (USGS) (Reference 61); therefore, no problems of site flooding exists due to elevated lake levels. The construction of the plant resulted in changes in local drainage patterns, runoff characteristics and in the modification of two streams located on the plant property. Final topography is shown in <Figure 2.4-3> and an aerial photograph of the site, prior to plant construction, is shown in <Figure 2.1-4>. Protection is provided for safety-related structures, exterior systems and access equipment against flooding from Lake Erie, surface runoff and local intense precipitation. This is accomplished by location, arrangement and design of these structures, systems and equipment, and flood protection features as discussed in the following sections. 2.4.1.2 Hydrosphere Lake Erie, the major hydrologic feature of this location, will provide cooling water for the plant. The lake will not influence the surface water characteristics of the site since the mean lake level is in excess of 40 feet below plant grade. Revision 2.4-1 Information Only In the vicinity of the site, the coastal watershed is drained by several small streams. These streams have cut deep channels as they approach the lake in the otherwise flat terrain of this region. The width of this coastal watershed in the site area is approximately 4.5 miles with the ground falling away sharply to the south of the ridge into the Grand River Basin. Topographically, the site lies in the Old Lake-bed Region of northeast Ohio. Two parallel streams run close to the plant area. The larger stream, called the Major Stream, has a drainage basin of 7.44 square miles (Reference 70) and runs northwestward within 1,000 feet of the southwest corner of the plant. The smaller stream, called the Diversion Stream, which has a drainage area of only 0.59 square mile (Reference 71), borders the plant area to the east. The drainage areas are shown in <Figure 2.4-1>. The smaller stream was originally diverted prior to construction and had been historically referred to as the Minor Stream. The name change to the Diversion Stream coincides with a post-construction modification (Reference 75) to divert the stream further to the east. A portion of the originally engineered channel of the Minor Stream remains located between the plant area and the Diversion Stream. This section of the stream no longer functions as a traditional stream. The Remnant Minor Stream, as it is now named, functions as a drainage swale located entirely within the Local Intense Precipitation (LIP) domain. The safety-related structures of the plant are located between the watersheds of the adjacent streams. The site is not subject to flooding from surface runoff originating from either streams drainage basin. Site drainage ultimately is directed to Lake Erie either directly or via the following notable drainage paths: ESW Swale, Remnant Minor Stream, Major Stream, the Barge Slip, and the Northwest Impoundment. Revision 2.4-2 Information Only No recorded data exists for either of the adjacent streams. However, base flow estimates indicate that the average flow for the Major and Diversion streams would be approximately 5 cfs and 0.78 cfs, respectively (Reference 70 and Reference 71). Older local inhabitants living on Lockwood and Center Roads did not recall either the Major or Minor Streams level overtopping Center Road. High water marks on the headwalls of the preexisting Center Road bridge over the major stream indicated that the maximum depth at this point had been approximately four feet. The smaller stream previously passed through a 4-foot by 5-foot rough stone culvert under Center Road. There are no users of water from the Major or Diversion Streams. Use of groundwater is discussed in <Section 2.4.13>. Possible Revision 2.4-2a Information Only contamination of groundwater is also discussed in <Section 2.4.13> and the degree of contamination as assessed in that section will also apply to both streams. Lake Erie has an area of 9,970 square miles and is only slightly larger than Lake Ontario, which has the smallest surface area of any of the Great Lakes. It is the shallowest of the lakes, with a maximum depth of 210 feet and an average depth of 58 feet. Also, Lake Erie has the smallest volume, 110 cubic miles (Reference 1). The lake is about 241 miles long with a maximum width of 57 miles. The long axis of the lake lies in a general northeast-southwest direction. The drainage basin of Lake Erie, including Lake St. Clair, is about 29,650 square miles. The mean annual flow from the Detroit River at the western head of the lake is 178,000 cfs which accounts for about 90 percent of the inflow into Lake Erie. The mean annual outflow into Lake Ontario is about 194,000 cfs through the Niagara River and about 8,000 cfs through the Welland Canal (Reference 1). Lake Erie level records have been maintained by the Lake Survey Center (NOAA) since 1860 (Reference 61). The average level is 572.3 feet above mean sea level, mean tide, New York City, which is the USGS datum. The 1973 monthly levels were exceptionally high, setting a new maximum monthly mean level of 575.4 feet (USGS) in June, 1973 (Reference 61). The lowest average monthly recorded level was 569.3 feet (USGS) in February, 1936 (Reference 61). Corresponding levels relative to the 1955 International Great Lakes Datum (IGLD 55) are 1.9 feet less. The Lake Erie Low Water Datum (LWD) is at Elevation 570.5 feet (USGS) and Elevation 568.6 feet (IGLD) (Reference 2). Vertical datum conversion values applicable to the site are provided on <Figure 2.4-2>. Minimum lake levels usually occur in February when precipitation throughout the Great Lakes drainage basin is being stored in the form Revision 2.4-3 Information Only of ice and snow. Maximum levels occur in mid-summer when the full effect of Revision 2.4-3a Information Only the runoff from the drainage basin is felt. Fluctuations of several feet, but of short duration, are caused by wind effects. Northerly winds raise lake levels in the plant area, while winds from the south and east tend to lower the lake levels (Reference 3). 2.4.2 FLOODS 2.4.2.1 Flood History No records of flooding in the plant area of the site exist, either from the two adjacent streams draining the coastal watershed, or from Lake Erie. The terrain is relatively flat and gently sloping toward the lake. The soil is relatively permeable and contains sand layers in the upper reaches of the drainage area. The ground surface in much of the catchment area is forested with a heavy mulch ground cover. Due to the flat terrain, permeable upper soil layers and the small catchment areas <Section 2.4.1.2>, it is unlikely that this location has ever been subjected to flooding or will experience severe flooding from surface runoff in the future. 2.4.2.2 Flood Design Considerations The probability of any flooding in the area of the site is exceptionally low. The site area is passively protected from probable maximum flood hazards originating from Lake Erie and the adjacent streams. Studies discussed in <Section 2.4.3> have shown that even if a PMF is experienced, the streams will be contained within their respective drainage basins with no site impact except for the overtopping of the crossing at the plant main access road, which would temporarily prevent road access. Topography along the plant-side bank of the major stream will preclude flooding of the site by the PMF, allowing the plant to continue uninterrupted operation. Diversion Stream PMF is prevented from reaching the site by the presence of an earthen berm located between the streams engineered channel and the Remnant Minor Stream channel, allowing the plant to continue uninterrupted operation. Revision 2.4-4 Information Only Flooding from Lake Erie is extremely improbable. Final grade elevations in the immediate plant area vary from 617 to 620 feet (USGS). This is about 45 feet above the maximum monthly mean lake level of 575.4 feet (USGS) (Reference 61). Surge flooding is described in <Section 2.4.5>. Runup occurring coincidentally with the probable maximum setup would extend to about Elevation 607.9 feet on the bluff at the lake shore (Reference 65). This runup would still be about 12 feet below the 620 foot (USGS) plant grade elevation. The controlling flood hazard is the Local Intense Precipitation (LIP) event. LIP water levels impacting the site are a result of the sites drainage capacity during significant precipitation events as discussed in <Section 2.4.2.3>. Protection of safety-related facilities, systems, and equipment is discussed in <Section 2.4.2.3>, <Section 2.4.10> and <Section 2.4.14>. External flood hazards and protection for PNPP are developed using the guidance of <Regulatory Guide 1.59> and <Regulatory Guide 1.102>. Flood hazards are determined using the guidance of (Reference 81), which is referenced by Appendix A of <Regulatory Guide 1.59>. For all off-site flood hazards, PNPP complies with Regulatory Position C.1 of <Regulatory Guide 1.59>. For these hazards, PNPP is fully passively protected by topography and exterior barriers are defined in <Regulatory Guide 1.102>. For the LIP hazard, PNPP employs an approach more closely aligned with Regulatory Position C.2 of <Regulatory Guide 1.59> with protection provided via a combination of permanent and temporary incorporated barriers as defined in <Regulatory Guide 1.102>. PNPP does not comply with Regulatory Position C.2.d of <Regulatory Guide 1.59> in that structures required to reach and maintain cold shutdown are not fully passively protected. These structures, like all safety-related structures and nonsafety-related structures that communicate with safety-related structures, are passively protected up to and including the effects of the Standard Project Storm (SPS) as derived and evaluated in (Reference 72) and (Reference 82), respectively. For hazards exceeding the SPS up to and including the Probable Maximum Precipitation event of the LIP domain which is shown Revision 2.4-4a Information Only in <Figure 2.4-82>, protection features are deployed via operator action as discussed in <Section 2.4.10> and <Section 2.4.14>. Flood protection features are treated as non-safety related, non-seismic and are therefore not controlled under the PNPP Quality Assurance Program. 2.4.2.3 Effects of Local Intense Precipitation The Local Intense Precipitation domain comprises the site property bordered to the north by Lake Erie, to the east by the Diversion Stream and to the west and south by the Major Stream. The LIP domain is shown by <Figure 2.4-82>. All safety related buildings are located within the LIP domain. The LIP event is based on a front-loaded Probable Maximum Precipitation event as described in <Section 2.4.3.1>. Surface drainage is provided by a combination of overland drainage features and the sites non-safety related storm drain system which is shown on <Figure 2.4-3>. Site topography provides overland runoff to several notable drainage features including the Major Stream, Remnant Minor Stream via the ESW Swale, the Barge Slip, Northwest Impoundment, and Lake Erie. Additionally, three separate subsurface storm drainage systems (East, West and South System) assist in surface drainage. Site topography and the storm drain system are designed to reduce the effects of the LIP flooding event. The controlling flood levels impacting the site are a result of the limitations of the sites surface drainage capabilities during the LIP event (Reference 66). The site surface drainage ability is largely influenced by site topography and ground cover type; location and dimensions of above grade objects, structures and buildings; roof drainage and storage; surface drainage features; and subsurface storm drain systems. Due to drainage limitations, floodwater depths have the potential to impact safety-related structures and non-safety related structures that communicate with safety related structures. The flood protection Revision 2.4-5 Information Only requirements needed to protect safety-related facilities, systems, and equipment from this event are identified in <Section 2.4.10>. Safety and non-safety building roofs are drained by a combination of roof pitch, roof drains, parapet openings and scuppers. The drainage on the roofs is controlled to ensure that water depths developed during the LIP rainfall do not exceed the structural capacity of the roof (Reference 67). In case of complete blockage of roof downspouts on safety related buildings, building scuppers and parapet openings have been sized to ensure roofs will not exceed the maximum allowable loading limits. Analysis of the LIP event is based on a front-loaded precipitation event distributed into hourly intensities as described in <Section 2.4.3.1>. The peak rainfall intensity of 13.19 inches per hour will occur during the first hour and total precipitation of 34.72 inches occurs over 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> (Reference 68). Analysis of the LIP event assumes a concurrent discharge of the ESW Swale as well as a failure of the Diversion Stream berm. The LIP analysis also assumes maximized boundary conditions for the Major Stream, Diversion Stream and Lake Erie. These conservative assumptions and inputs ensure the LIP analytical results are bounding of any potential event combination. Therefore, no combined events need to be postulated for PNPP. Analysis of the LIP event is performed using a two-dimensional transient (unsteady state) volume conservation model (Reference 66). Delineation of the computational domain is based on knowledge of the Remnant Minor Stream, Major Stream, Lake Erie and Diversion Stream watersheds and topographic dividing features. The entire Remnant Minor Stream watershed is included in the LIP domain as it functions as a drainage swale for a large portion of the east side of the plant site. The LIP domain, depicted in <Figure 2.4-82>, is discretized into uniform grid cells for runoff analysis. The LIP flood model simulates precipitation runoff effects over complex topography through a numerical approximation of the Shallow Water Revision 2.4-6 Information Only Equations and accounts for the complications in runoff. The model solves a set of partial differential equations (Saint-Venants Equation) using the second-order Newton-Raphson tangent finite difference method. Appropriate two-dimensional runoff coefficients are specified based on landcover type. Buildings, structures and security features are appropriately represented in the LIP domain model. The LIP flooding model also incorporates the plant roof and storm drain systems providing discharge analyses for these systems. The conduits modeled in the storm drain system are analyzed using the Manning Equation for gravity flow conditions and transitions to the Darcy-Weisbach Equation when pressurized flow conditions exist. Allowances are included for debris on catch basin openings and within the storm drain piping. LIP modeling is captured in (Reference 66). The effects of the LIP event on building roofs is evaluated to ensure the structural capacity of buildings is not exceeded (Reference 67). This analysis considers the cascading effects of roof drainage from higher roof elevations to the locations where scuppers, roof drains or parapet openings discharge on lower roof elevations. For safety related buildings, this is determined through the capacity of building scuppers and parapet openings. For those roofs of non-safety buildings that function as an environmental interface for a safety related building, evaluation is provided (Reference 67). A non-safety building is considered an environmental interface to a safety related building if external floodwaters would enter the safety related building if the existence of all or part of the non-safety building was removed. The roof pitch, drains, and scuppers on non-safety roofs are designed to ensure that the effective loading of high-water levels does not exceed the structural capacity of the structure. Similar to the safety related buildings, the non-safety roof analysis includes consideration of the cascading effects of roof drainage from higher roof elevations at the locations where scuppers, roof drains or parapet openings discharge on lower roof elevations. Revision 2.4-6a Information Only 2.4.2.3.1 Non-LIP Precipitation Events Additional analysis of the LIP domain is provided for less significant precipitation events including the Standard Project Storm (SPS) and Probable Maximum Winter Precipitation (PMWP) events. The precipitation data for these events are provided in <Section 2.4.3.1>. The runoff analyses for these events utilize the same underlying methodology described above for the LIP event. The effects of the SPS is determined in (Reference 82). Modeling techniques for the plant storm drain system for LIP effects are retained in the SPS modeling. The effects of the PMWP with concurrent snowmelt is determined in (Reference 78). This analysis assumes portions of the computational domain are maintained generally clear of snowpack due to normal operational activities. In these areas, a seasonally adjusted one-hour precipitation event of one-year recurrence interval is applied as an antecedent snowfall condition. The remainder of the computational domain is assumed to have a probable maximum snowpack present. The cool-season analysis models a portion of the storm drain system; (Reference 78) omits catch basin inlets which are located under the probable maximum snowpack. Only those catch basins located in areas routinely cleared of snowfall are credited with removing overland runoff. Other modeling techniques for the plant storm drain system for LIP effects are retained in the PMWP modeling. 2.4.3 PROBABLE MAXIMUM FLOOD (PMF) ON STREAMS AND RIVERS In accordance with Appendix A of <Regulatory Guide 1.59> and the applicable sections of (Reference 55), the procedures and data of the U.S. Army Corps of Engineers (Reference 4) and the U.S. Bureau of Reclamation (Reference 5) were used to calculate effective Probable Revision 2.4-7 Information Only Maximum Floods for the two streams mentioned in the preceding sections. The calculated PMF for the Major Stream was found to be 32,760 cfs (Reference 70), and for the Diversion Stream 4,330 cfs (Reference 71), at their outfalls into Lake Erie. <Figure 2.4-4> and <Figure 2.4-5> show the hydrographs generated for the PMF of both streams. <Figure 2.4-4A> and <Figure 2.4-5A> show the inundation profiles of the Major Stream and Diversion Stream, respectively. 2.4.3.1 Probable Maximum Precipitation The Probable Maximum Precipitation (PMP) for areas from 10 to 1,000 square miles east of the 105th Meridian has been derived by the Corps of Engineers and is presented in Hydrometeorological Report 33 (Reference 4). For the Perry site, the PMP for the 6-hour, 12-hour, 24-hour and 48-hour storms are 26.91, 29.21, 32.43, and 34.73 inches, respectively (Reference 68). Hydrometeorological Report 33 (Reference 4) does not provide methods to determine precipitation data for time intervals less than six hours. Guidance for obtaining hourly rainfall interval intensities is provided in procedures outlined by the U.S. Bureau of Reclamation (Reference 5). A front-loaded event sequence is used for LIP domain analysis. A mid-loaded event sequence is used for Rivers and Streams analyses as reflected in the following tables (Reference 68). Total precipitation values are the same; only the temporal distribution differs between LIP and Rivers and Streams analyses. Design Basis Probable Maximum Precipitation Local Intense Precipitation Time 1 HR 2 HR 3 HR 4 HR 5 HR 6 HR 12 HR 24 HR 48 HR Incremental Rainfall 13.19 4.03 2.96 2.42 2.16 2.15 2.30 3.22 2.30 (inches) Cumulative Rainfall 13.19 17.22 20.18 22.60 24.76 26.91 29.21 32.43 34.73 (inches) Revision 2.4-8 Information Only Design Basis Probable Maximum Precipitation Rivers and Streams Time 1 HR 2 HR 3 HR 4 HR 5 HR 6 HR 12 HR 24 HR 48 HR Incremental Rainfall 2.15 2.42 2.96 13.19 4.03 2.16 2.30 3.22 2.30 (inches) Cumulative Rainfall 2.15 4.57 7.53 20.72 24.75 26.91 29.21 32.43 34.73 (inches) Cool-season cumulative precipitation and snowmelt values are determined in (Reference 69) to have peak intensity of 3.63 inches/hour and a 48-hour total of 26.58 inches. Probable Maximum Winter Precipitation data is obtained from (Reference 4) for the months of December, January and February, consistent with the cool-season months described in <Section 2.3.1.2.5>. Cool-season event combinations are obtained from (Reference 55). For PNPP a conservative snowmelt contribution is determined in (Reference 69) by assuming an inexhaustible snowpack. Snowmelt rates are determined using the guidance of (Reference 83). By comparison, the all-season event is bounding of the cool-season event. The all-season event is therefore used as the basis for streams and rivers analyses. Cool-season analysis for the LIP domain is discussed in <Section 2.4.2.3.1>. The cool-season event sequence is provided below. Probable Maximum Winter Precipitation and Snowmelt Time 1 HR 2 HR 3 HR 4 HR 5 HR 6 HR 12 HR 24 HR 48 HR Incremental Rainfall + 3.63 1.28 1.01 0.87 0.81 0.79 0.61 0.43 0.39 Snowmelt (inches) Cumulative Rainfall + 3.63 4.91 5.92 6.79 7.59 8.39 12.02 17.22 26.58 Snowmelt (inches) Standard Project Storm precipitation values are determined in (Reference 72) to have peak intensity of 3.747 inches/hour and a 24-hour total of 13.00 inches. Derivation of the Standard Project Storm is performed using the guidance of (Reference 6). By comparison, the Revision 2.4-9 Information Only all-season event is bounding of the Standard Project Storm event. The all-season event is therefore used as the basis for streams and rivers analyses. Standard Project Storm analysis for the LIP domain is discussed in <Section 2.4.2.3.1>. The Standard Project Storm event sequence is provided below. Standard Project Storm Time 6 HR 12 HR 13 HR 14 HR 15 HR 16 HR 17 HR 18 HR 24 HR Incremental Rainfall 0.560 1.600 0.986 1.183 1.479 3.747 1.380 1.085 0.980 (inches) Cumulative Rainfall 0.560 2.160 3.146 4.329 5.808 9.555 10.935 12.020 13.000 (inches) 2.4.3.2 Precipitation Losses To increase the conservatism of the results, 100 percent antecedent saturation of the basins and no losses were assumed for any of the precipitation hazards described herein. 2.4.3.3 Runoff and Stream Course Models Flood elevations for the Major and Diversion Streams are determined for the PMF peak runoff using the standard step method (steady state modeling) as described in (Reference 48) and in accordance with (Reference 55), (Reference 70), and (Reference 71). PMF peak runoffs are determined by application of triangular synthetic unit hydrographs, as described in (Reference 5) using the all-season precipitation event provided in <Section 2.4.3.1>. For conservatism the PMP was assumed to fall on fully saturated terrain, with 100 percent runoff. The size of the streams drainage basins is described in <Section 2.4.1.2>. Coefficients used in the stream course models are described in <Section 2.4.3.5>. The PMF flow hydrographs for the Major Stream and the Diversion Stream are presented in <Figure 2.4-4> and <Figure 2.4-5>, respectively. Revision 2.4-9a Information Only No stream course modeling is provided for the effects of the Standard Project Storm or cool-season events as discussed in <Section 2.4.3.1> since the all-season event is considered bounding with fully passive protection provided for Major and Diversion streams flood hazards. The Remnant Minor Stream is not evaluated as a traditional stream or river. Instead, the Remnant Minor Stream is incorporated into the two-dimensional LIP domain model since the Remnant Minor Stream serves as a topographic drainage swale and does not function as a traditional stream. This allows the channel to respond dynamically (unsteady state analysis) as part of the LIP event. 2.4.3.4 Probable Maximum Flood Flow The probable maximum flood flow hydrograph for the Major and Diversion Streams at their outfalls into Lake Erie are presented in <Figure 2.4-4> and <Figure 2.4-5>, respectively. These hydrographs correspond to the incidence of the PMP. Other factors such as surges or upstream dam Revision 2.4-9b Information Only failures will not affect the streams PMF. The PMF flow for both streams were calculated with the rain data given in <Section 2.4.3.1> and the procedures outlined in Pages 73 through 82 of (Reference 5). 2.4.3.5 Water Level Determinations <Figure 2.4-6> and <Figure 2.4-8> show the bed elevation and PMF surface profiles for the Major and Diversion Streams, respectively. Surface profiles were determined according to the standard step method utilizing Mannings formula. The Manning coefficient of friction was assumed to be equal to 0.100 for the portions of the existing stream bed and overbanks, and equal to 0.024 for the trapezoidal sections used in the engineered streamcourse. The profiles and cross sections are shown on <Figure 2.4-8a>, <Figure 2.4-10>, and <Figure 2.4-11>. The steady state analysis computes water surface profiles from one cross section to the next by solving the Energy equation with an iterative procedure called the Standard Step Method. The Standard Step Method begins computations with the downstream boundary condition for subcritical flow. The unknown water surface elevation at the upstream cross section is first assumed by applying the downstream water depth. The corresponding conveyance and velocity head are determined for the applied water surface elevation. The friction slope between the two cross sections is then computed and used to solve the energy head loss between the two cross sections. The Energy equation is then solved to determine the water surface elevation at the upstream cross section. The solved water surface elevation is compared with the initial assumed elevation and iterations are repeated until numerical values converge. PMF surface profiles are provided in <Figure 2.4-6> for the Major Stream (Reference 70) and <Figure 2.4-8> for the Diversion Stream (Reference 71). Based on the large flow areas at each structure, the Major Stream water surface profiles during the PMF were calculated under the assumption that the plant access road, rail line bridge, and the sediment control dams placed across the streams remained intact/open during the event. The Diversion Stream outfall culvert and Major Streams Contractor Revision 2.4-10 Information Only Access Road culvert were modeled as blocked during PMF conditions. Furthermore, a discharge coefficient of 3.00 was used for calculating the depth of the PMF passing over the broad crested weirs formed by inline structures. The maximum PMF water surface elevation (WSE) along the Major Stream occurs upstream of the plant access road and was determined to be approximately 633.1 ft NGVD29 Perry Local Datum (PLD). The WSE at the Plant Access Road was determined to be 633 ft PLD (Reference 70). The maximum PMF WSE along the Diversion Stream is approximately 627 ft PLD at the upstream end of the modeled stream course (Reference 71). For both the Major Stream and Diversion Stream, topography plant-side of the stream course ensures the PMF inundation profile does not reach plant structures. This includes the natural ridge along the Major Stream and the earthen berm along the plant side bank of the Diversion Stream. The minimum freeboard for either stream exceeds one foot (Reference 70, Reference 71). The PMF flow elevation exceeds the bottom of the railroad bridge; however, analysis shows the bridge remains intact during PMF conditions (Reference 73). As no recorded data exists, no correlation is possible between the results obtained and floods on record. For added conservatism, the flow for each reach of both streams was considered to be equal to the corresponding PMF flow at the outfall to Lake Erie. 2.4.3.6 Coincident Wind Wave Activity Wind wave activity is of no concern with the flood conditions in these small streams as previously discussed. 2.4.4 POTENTIAL DAM FAILURES, SEISMICALLY INDUCED Presently there are no impoundments upstream of the plant, and since the drainage basins of the two streams passing through the site are small and the terrain is quite flat, it is unlikely there will be any Revision 2.4-11 Information Only impoundments in the future. Therefore, seismically-induced dam failure is not included as a design condition. 2.4.4.1 Dam Failure Permutations This section is not applicable to PNPP. 2.4.4.2 Unsteady Flow Analysis of Potential Dam Failures This section is not applicable to PNPP. 2.4.4.3 Water Level at Plant Site This section is not applicable to PNPP. Revision 2.4-11a Information Only center of the lake reach 102 mph. The temporal variation in setup height over the remaining storm period is plotted in the hydrograph shown in <Figure 2.4-28>. The spatial profile of the lake surface at maximum deflection is plotted in <Figure 2.4-29>. It should be noted that these values do not reflect corrections for pressure differences or precipitation. With an antecedent water level of 575.4 feet (USGS), a precipitation value of 0.5 feet, a pressure correction of 0.3 feet, and a wind setup of 4.30 feet, the total maximum stillwater surface level at the plant site was computed to be 580.5 feet (USGS) (Reference 61). Wind velocities for the PMS were generated at three hour intervals for ten stations around the periphery of Lake Erie using the techniques discussed in <Section 2.4.5.1>. <Figure 2.4-26> shows the locations of the ten stations. <Figure 2.4-30> and <Figure 2.4-31> show variations of wind speed and direction for the two stations (20,1) and (40,1) adjacent to the site and the two stations (20,21) and (40,21) north of the site, respectively. indicates the site setup winds at these stations. The wind speed for the stations adjacent to the site averages above 70 mph for a period of 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />. During the same period the wind speeds for the stations across the lake from the site average 80 mph or above with a maximum of 110 mph being reached at the center of the lake. 2.4.5.3 Wave Action The wind field used to determine the probable maximum setup was also used to find the concurrent wave action. As discussed in <Section 2.4.5.1>, this wind field was defined at ten stations located around the lake to give complete meteorological coverage of Lake Erie. A study of the critical fetch direction showed that the fetch lengths were approximately the same for winds directed toward the site from Revision 2.4-21 Information Only The setup of the lake level causes the pumps to operate at a higher than normal flow rate since the static head is reduced. With these wave induced variations in the pump chamber water level, no problem exists in meeting the flow requirement described in <Section 9.2.1>. 2.4.5.5 Protective Structures 2.4.5.5.1 Shoreline Recession 2.4.5.5.1.1 Summary Since plant grade is approximately 45 feet above the normal lake level and there are no safety-related structures within 380 feet of the lake shoreline (toe of bluff), damage to the shoreline bluff by an individual storm would not affect the operation or the safety of the PNPP. Data presented herein shows that the range of bluff recession in the vicinity of the emergency service water pumphouse has been less than 2 feet per year since 1937. Erosion of the shoreline bluff is caused by groundwater seepage and direct runoff on the upper portions of the bluff, and by wave attack and runup at the lower portions. To monitor the combined effect of shoreline recession and bluff erosion, a semiannual (Spring and Fall) survey is being made at six profile locations established at regular intervals along the shoreline. This survey will continue on a semiannual basis from 1984 through 1989, at which time it will be continued on an annual basis (spring) for the life of the plant (Reference 74). <Figure 2.4-32> shows the exact locations of the survey lines. The sections that follow describe the bluff recession process. 2.4.5.5.1.2 Introduction This section presents the findings of shoreline erosion studies and investigations for a 6,000 foot reach of the Lake Erie shoreline north Revision 2.4-24 Information Only locally as much as 1,500 feet offshore. The lake bottom north of the site boundary is irregular but generally slopes at about 2.5 feet per 100 feet for the first 300 feet offshore, decreasing to about 5 feet in 1,000 feet for the next 4,000 feet or more. 2.4.5.5.1.4 Nature of Bluff Erosion The principal factors affecting shoreline recession are variations in Lake Erie levels, wind (storm waves), water seepage and frost action. The composition and degree of compaction of the bluff materials are limiting factors in the rate of recession. Widespread slumping of the upper half of the bluff is the most prevalent bluff feature in the vicinity of the site. Slumping within the lacustrine and upper till deposits is caused mainly by groundwater seepage forces and frost action. Undercutting and removal of slump material by wave action complete the cycle of bluff recession. 2.4.5.5.1.5 Wind, Littoral Drift and Beaches Local storms are the main cause of significant wave action. The shoreline at the site is subjected to waves from the southwest through the north to the northwest. Winds from the southwesterly direction set up the prevailing littoral current from the west to the east. Generally, the west to east direction of littoral drift results in accretion of sand at the west side and the depletion of material to the east side of structures projecting from the shore. The nearest off-site structure is located near the northwest corner of the site boundary on the former Neff Perkins property. This structure, a sheet piled water conveyance channel, projects into Lake Erie about 135 feet. With the exception of the small beach northwest of the site, beaches along the shore in the study area are narrow, short in length and frequently transitory or submerged. Revision 2.4-28 Information Only 2.4.5.5.1.6 Lake Levels Shoreline erosion is noticeably influenced by lake levels and the related storm waves. High levels allow the waves to directly contact the toe of bluff while waves from low lake levels are dissipated by wider beaches. Lake levels vary with climatic conditions which affect evaporation and inflows. Minimum lake levels usually occur in February and maximum levels occur in mid-summer. The maximum seasonal fluctuation is nearly three feet, but long term cycles of fluctuation, resulting from wet and dry periods are as much as eight feet. Predictions of future lake levels are difficult to make. However, future long term cycles of fluctuation are not expected to differ significantly from those presented in <Figure 2.4-33>. <Figure 2.4-34> presents monthly recorded mean lake levels, from 1904 to 1979, which show short and long term trends. Long term annual fluctuations are shown in <Figure 2.4-33>. The 1973 mean level of Lake Erie was about five feet above the Lake Erie Low Water Datum (LWD) established at 570.5 feet (USGS) above mean tide at New York City; that mean level was at the peak of a high lake level cycle (Reference 61). Reducing lake levels to a common datum for the various years studied was not possible because dates (day and month) were not always given on the property survey information. 2.4.5.5.1.7 Effects of Ice Almost every year, ice forms along the shore of Lake Erie. In winters with sustained periods of sub-zero temperatures, the entire lake freezes over; during the winter months, wave action upon the beach and the shoreline bluff is minimal or non-existent due to the buildup of ice along the shoreline. However, freezing and thawing of the groundwater seepage produces a detrimental effect on the bluff face that contributes to the rate of bluff erosion. Revision 2.4-29 Information Only The total top of bluff change indicated by <Figure 2.4-35> for a 2,000 foot central reach of shoreline northwest of the plant ranges from 20 to 85 feet (<1 to 2 ft/yr) from 1937 to 1972 (35 years). For the same period, total top of bluff recession of reaches to the west and east of the central section ranged from 1 to 3 ft/yr and 4 to 5 ft/yr, respectively. Fluctuations of Lake Erie <Figure 2.4-34> indicate long term mean lake levels from 1934 were on an up cycle, peaking in 1952 and again in 1973 (Reference 61). A correlation of larger changes in bluff erosion during periods of high lake levels could not be evaluated with certainty due to lack of data, but high lake levels undoubtedly have a significant effect. shows annual recession rates relative to 1972 for each of the twelve erosion monitoring lines <Figure 2.4-32> and is summarized below: Range (Ft/Yr) of Top of Bluff Recession Relative to 1972 Section 1937 1957 1964 West (J-I-H-G) 1-3 2-6 3-7 Central (F-L-K-A-B) <1-2 1-5 1-7 East (C-D-E) 4-5 5 4-5 It should be remembered that the bluff erosion is a two-step process. One step is wave action on the lower till which forms the toe of the bluff. As previously discussed, the location of the toe of bluff is the factor that will determine the need for bluff protection. The other step is the random occurrence of localized slumping induced by groundwater seepage and frost action. Although a single slump (at Profile Line C between 10/72 and 4/73) indicated a significant change of 33 feet in the top of bluff location, future movement at the slumped location most likely will not occur again until the toe of bluff has receded to a point where most of the slumped material has been removed. The more recent comparisons (1957 and 1964) show the effects of the random slumping process on the relative top of bluff recession rates. Revision 2.4-31 Information Only in the spring and fall of each year. The first complete profiles were taken in November, 1973, and are presented in <Figure 2.4-38>. Readings of the net changes in the bluff, at two year intervals, taken to date are also shown in <Figure 2.4-38>. summarizes the recession rates for the profiles shown in <Figure 2.4-38> using profile information through September, 1978. In general, between 1972 and 1978, the top of bluff erosion rate varied (from <1 to 2 ft/yr) within the central shoreline reach. The eastern end of the central reach receded at about 7 ft/yr during this relatively short (six-year) period. This same area receded only 2 ft/yr between 1876 and 1978. The eastern and western tops of bluff receded from 2 to 6 ft/yr and 5 to 9 ft/yr, respectively, between 1972 and 1978. Again, the long term (1876 to 1978) top of bluff recession rates were 2 to 3 ft/yr and 1 to 4 ft/yr for the eastern and western reaches, respectively. In addition, the 1975 aerial survey was examined to assure that excessive erosion of the bluff did not take place between the ground survey profile lines. shows that the shorter the time interval investigated, the greater is the recession rate for that time interval. This is due to significant, localized slumps being averaged over a relatively short time period. However, these short term, localized slumps are part of the overall recession cycle; in addition, they are attributable to the sustained high lake levels which peaked in 1975 and, therefore, allowed wave attack to undermine the toe of bluff during the high lake level period. The entire recession process is time and water level dependent; i.e., it occurs in a stop-start sequence, and should be averaged over a long period of time to obtain meaningful results. 2.4.5.5.1.10 Man Made Effects of Erosion With the exception of the potential future bluff protection described later in this section and the interim protection discussed in <Section 2.4.5.5.9>, no permanent structures exist on the bluff. Revision 2.4-34 Information Only Grading and clearing of the site were performed in such a manner that surface runoff was controlled and erosion minimized. The closest building structure (service water pumphouse) to the bluff is approximately 280 feet away. This structure is founded on shale rock well below the overlying glacial deposits. Controlled blasting (instrumentally monitored) was conducted during construction of PNPP. Two interim revetments, described in <Section 2.4.5.5.9>, have been built along the shoreline of the plant property. Protection is provided along the shoreline from the Remnant Minor Stream discharge to the Northwest Storm Impoundment Spillway. Protection is also provided at the outfall of the Diversion Stream. These two features are not continuous. Changes in littoral drift accretion and depletion along the shoreline forming the north site boundary is not expected to change greatly as a result of possible future industrial development to the east and west of the site boundary. Both the State and Federal agencies play an active role in restricting construction of new structures projecting into Lake Erie that might affect littoral drift patterns or increase the rate of shoreline recession of neighboring shoreline property. Additionally, periodic inspections of unprotected areas ensure excessive erosion does not occur (Reference 74). 2.4.5.5.2 Maximum Allowable Shoreline Recession <Section 2.5.5> describes the point to which bluff recession could progress without threatening the function of safety class structures. Bluff protection will be installed if the retreat closely approaches this limit. 2.4.5.5.3 Protective Measures 2.4.5.5.3.1 Protective Measures Description If the shoreline retreat becomes threatening to the safety-related structures, the shoreline will be protected by a suitable permanent Revision 2.4-35 Information Only construction that will protect the face and toe of the bluff. Final design and permit applications for the shoreline permanent protection construction will be initiated when the lake shoreline (toe of bluff) Revision 2.4-35a Information Only has receded to a point 250 feet away from the closest safety class structure (emergency service water pumphouse). However, if the State of Ohio or the Federal Government develops an area-wide plan for shoreline protection that includes the plant, CEI will fully cooperate in implementing the plan on its property. The protective construction (Reference 29) (Reference 39) considers grading of the shoreline bluff and construction of a permanent protective revetment. Interim protective measures are described in <Section 2.4.5.5.9>.

a. Bluff Grading Prior to installation of the shoreline protective revetment, the bluff will be graded to the dimensions shown in <Figure 2.4-39>.

The bluff grading will be as follows:

1. Prior to the placement of the protective revetment, the bluff will be graded to a 2:1 slope between Elevation 555 feet (USGS) and Elevation 605 feet (USGS).

2. After the 2:1 grading is finished, a 10-foot wide berm will be cut at Elevation 605 feet (USGS).

3. After the berm is finished, further grading of the bluff to a 3:1 slope is required between Elevation 605 feet (USGS) and the top of the bluff.

b. Protective Revetment The maximum wave runup, corresponding to the 9.7-foot high maximum wave breaker height (Reference 31) breaking on the rough 2:1 slope of the protective revetment, is found in (Reference 22) to be 16.4 ft. The wave runup would therefore reach Elevation 596.9 feet (USGS) when the lake is at Elevation 580.5 feet (USGS) i.e., maximum stillwater level PMS (Reference 61). However, it should be pointed out Revision 2.4-36

Information Only that the freeboard between the top of the protective revetment, located at Elevation 605.0 feet (USGS), and the maximum wave breaker height runup is 8.1 feet. Therefore, it is not expected that the wave runup produced by the PMS will ever overtop the crest of the revetment. The shoreline protective revetment will protect a section of the lake shoreline approximately 2,000 feet long, comprised of the distance between the entrance to the barge unloading area and the outlet of the Remnant Minor Stream. Extension to the outfall of the Diversion Stream will also be evaluated. The protective revetment as shown in <Figure 2.4-39> will offer sufficient protection to the emergency service water pumphouse. The shoreline protective revetment will be a rubble mound structure composed of the following layers of material:

1. The first layer is a permeable plastic fabric sheet, which is placed on the lake bed and over the area cut to the 2:1 slope.

2. On top of the permeable plastic fabric a 2-foot thick gravel filter blanket will be placed, as specified and shown in

<Figure 2.4-39>.

3. The filter will be covered with two layers of 1,000 to 2,000 pound quarry stones fitted into the gravel material.

4. The two layers of large quarry stones will be surmounted by two layers of heavy armor stones having a weight of between 6 and 10 tons. The heavy armor stones will not only be randomly placed over the sloped surface, but will become an integral part of the protective toe of the rubble mound protection. The toe protection will extend 47 feet into the lake and will be founded on weathered bedrock at approximate Elevation 555.0 feet.

Revision 2.4-37 Information Only environmental impact report. This is required for any structure that will be built in Lake Erie below Elevation 572.8 feet IGLD (574.7 feet USGS).

b. Shore erosion permit This permit will be issued by the Ohio Department of Natural Resources and requires detailed drawings of the proposed shoreline protection structures.

2.4.5.5.4 (Deleted) 2.4.5.5.5 (Deleted) 2.4.5.5.6 Barge Slip A nonsafety-related barge slip was constructed northwest of the plant along the southern shoreline of Lake Erie. It is located in the general area incised by the Minor Stream where it originally entered the Lake (prior to plant construction). An approach channel (averaging about seven feet in depth) was dredged from the lake to the barge slip. Lake dredging was performed to initially open the channel and then as required to maintain the opening prior to barge deliveries. Dredged material was disposed of on the plant site. The barge slip was constructed of steel sheet piling with tie-backs. The lake end of the barge slip was constructed about 30 feet south of the 1972 shoreline, with sheet pile wings being constructed toward the shoreline. To protect the side slopes and shoreline at the lake end of the barge slip, a rubble mound protective revetment structure was installed along the shoreline, extending 50 and 80 feet, respectively, east and west of Revision 2.4-41 Information Only 2.4.5.5.7 Northwest Sediment Control Dam A nonsafety-related sediment control earthen dam and associated concrete spillway were constructed at the northwest corner of the plant site. The toe of the spillway is approximately 90 feet south of the 1975 shoreline. The channel bottom between the spillway toe and the shoreline is protected by 2-foot-6-inch thick dumped riprap placed over a 1-foot-3-inch thick gravel filter. 2.4.5.5.8 Remnant Minor Stream and Diversion Stream Outlets The Minor Stream, which originally entered the lake at the present barge slip location, was diverted east of the plant site prior to plant construction. The channel outfall to the lake was constructed using 96 inch diameter corrugated metal pipe installed over a layer of 500 to 8,000 pound dumped stone riprap. The pipe was terminated at the sheet piling protection installed along the lake shoreline in front of the plant site. In 2015, the Diversion Stream was installed to further route streamflow east of the plant, increasing the conveyance capacity of the streamcourse (Reference 75). The Diversion Stream intercepts the Minor Stream and routes streamflow through a trapezoidal engineered channel, discharging to Lake Erie. Following installation of the Diversion Stream, the Remnant Minor Stream (consisting of the construction-era engineered channel) functions only as a swale path for the Local Intense Precipitation domain. The outfall of the Diversion Stream is provided with a 48-inch pipe discharging to an armor stone revetment along the shoreline, discussed in <Section 2.4.5.5.9>. The outfall is sized for the streamflow resulting from a 100-year recurrence interval storm; flowrates in excess of this will overtop the outfall and flow directly to Lake Erie. 2.4.5.5.9 Interim Shore Protection In the early spring of 1975, significant shore erosion was observed at three localized areas of the plant site in the vicinity of site construction operations. These accelerated erosion rates were directly Revision 2.4-43 Information Only attributed to the sustained high lake levels which peaked in 1975 and which allowed wave attack to undermine the toe of the bluff during the high lake level period. In 1983, a rock protected sheet pile breakwall was erected. This sheet pile breakwall protects the section of the lake shoreline approximately 2,200 feet long, composed of the distance between the entrance to the barge unloading area and the outlet of the Remnant Minor Stream as shown in <Figure 2.4-39A>. In 1992, the temporary sunken barges were removed and the interim revetment was extended 1300 feet west to the northwest storm impoundment spillway as shown in <Figure 2.4-39A>. The design of the extension was essentially the same as the original 2200 foot revetment. Revision 2.4-43a Information Only The top of the bluff should stabilize at approximately 300 feet from the emergency service water pumphouse. Therefore, this breakwall will provide significant protection to the shoreline and to the emergency service water pumphouse. In 2015, as part of the Diversion Stream installation, an armor stone revetment was installed at the outfall of the Diversion Stream. The armor stone revetment protects approximately 100 feet of shoreline and exceeds the requirements of Technical Report No. 4 (Reference 22) (Reference 76). The revetment consists of a toe stone layer of four to five-ton stone and an armor stone layer of two to four-ton stone. The revetment begins below the lake surface and extends up the bluff to areas impacted by wave runup; the armor stone extends up to the base of the Diversion Stream culvert, approximate Elevation 589.6 ft PLD (Reference 77). The Diversion Stream revetment is depicted in <Figure 2.4-39B>. 2.4.6 PROBABLE MAXIMUM TSUNAMI FLOODING Since the site is located on Lake Erie, an inland lake, tsunami occurrence is not applicable. The Lake Survey Center (NOAA) has found no evidence of earthquake related seiches. 2.4.7 ICE EFFECTS 2.4.7.1 Regional Ice Formation History Lake Erie, the shallowest of the Great Lakes, is also the most thermally variable. It reacts rapidly to seasonal temperature changes and can build an appreciable ice cover in a comparatively short time (Reference 33). As winter progresses, ice on Lake Erie spreads from west to east. In mid-December, ice begins to form in the extreme western portion of Lake Erie. It spreads eastward, partially aided by a prevailing west wind, until the beginning of March when the eastern end of the lake is Revision 2.4-45 Information Only completely ice covered. At this time, the probability of ice cover in the site area exceeds 76 percent (Reference 32). The ice disappears from the western and central portions of Lake Erie by the end of March and by mid-April only a small area near Buffalo, New York, is still ice covered (Reference 33). Available information indicates that the critical period for ice development in the site area is from mid-February through mid-March with ice block formation prevalent during the spring ice breakup. Revision 2.4-45a Information Only The intake structures are protected against the impact of ice islands by 10 vertical reinforced concrete caissons, each 6 or 7 feet in diameter, placed in a 70-foot diameter circle around each of the submerged intake structures. The spacing between the caissons is such that the intake water approach velocity will not be increased. The three foot diameter discharge nozzle is encased in a 17-foot diameter reinforced concrete caisson for protection against the ice loads produced by the impact of a floating ice island crushing against the structure. <Figure 3.8-67> and <Figure 3.8-68> show details of caissons for the intake and discharge structures. 2.4.7.4 Ice Flooding Ice flooding cannot occur because of the high bluffs between the buildings and the lake. Also, safety-related onshore buildings are set back from the top of the 45-foot high bluff to preclude ice forces being a problem. Ice-induced flooding from the adjacent streams is not a concern. The base flow of the streams is 5 cfs or less per <Section 2.4.1.2> which precludes formation of appreciable ice blockage in the stream channels. The probable maximum winter precipitation (PMWP) rainfall is bounded by the all-season rainfall as presented in <Section 2.4.3.1>. The effects of the PMWP on the Local Intense Precipitation (LIP) domain is discussed in <Section 2.4.2.3.1>. 2.4.8 COOLING WATER TUNNELS AND OFFSHORE STRUCTURES 2.4.8.1 Cooling Water Tunnels Service and cooling water for PNPP will be obtained from Lake Erie at approximately 2,600 feet offshore and carried to the plant site through a 10-foot diameter intake tunnel located in the underlying bedrock. The water is then returned to the lake through a similar discharge tunnel of shorter length. Short tunnels of the same diameter are used Revision 2.4-47 Information Only near the shore facilities to tap the cooling water tunnels for the emergency service water system. Tunnel locations are shown on <Figure 3.8-65> and <Figure 3.8-66>. A discussion of the tunnel function is given in <Section 2.4.11.6> and <Section 9.2.1>. Revision 2.4-47a Information Only A three-foot diameter discharge was chosen as the best design for environmental protection. Details of the analysis are given in (Reference 36). The design of the diffuser discharge structure is shown in <Figure 3.8-67>. 2.4.9 CHANNEL DIVERSIONS This section is not applicable to PNPP since no cooling water channels exist from which flow could be diverted. 2.4.10 FLOODING PROTECTION REQUIREMENTS Four prospective sources of flooding exist at the Perry site: Lake Erie to the north of the plant, flooding by the Major Stream which borders the site to the west and south, flooding from the Diversion Stream which borders the site to the east, and flooding within the local intense precipitation domain due to direct precipitation events. All flooding sources are mitigated with unique flooding protection to ensure that floodwaters do not adversely impact safety related structures, systems and components. Protection is provided in the form of Exterior Barriers and Incorporated Barriers as defined in <Regulatory Guide 1.102>. 2.4.10.1 Lake Erie Flood Hazards <Section 2.4.5> and <Section 2.4.7> discuss the possibility of flooding caused by the probable maximum surge including wave runup and ice conditions in the lake. The plant grade is sufficiently above lake hazards that plant land structures are protected from floodwaters and related forces. The peak water surface elevation (WSE), including wave runup is 607.9 ft PLD as provided in <Section 2.4.2.2>. This is well below the nominal ground-level floor elevation of plant structures of 620.5 ft PLD. As such, flooding from Lake Erie is not a concern. Revision 2.4-50 Information Only On the intake side of the cooling water systems, all safety-related pumps and equipment will be located above Elevation 586-6 (USGS) in the emergency service water pumphouse. This elevation allows approximately three feet of freeboard over the simultaneous occurrence of the probable maximum setup, the maximum monthly mean lake level of record, and the associated oscillation of the pump chamber water level due to wave action over either the main or alternate submerged offshore intake structure. No emergency procedures are required for Lake Erie flood hazards. 2.4.10.2 Major Stream Flood Hazards The Major Stream probable maximum flood (PMF) inundation area is shown in <Figure 2.4-4a>. As shown in this figure, the streamflow resulting from a probable maximum precipitation (PMP) event is confined to the Major Streams drainage basin and does not encroach on plant safety-related structures or nonsafety-related structures that communicate with safety-related structures. The Major Stream is an engineered feature external to the plant area designed to protect the site from inundation and functions as an Exterior Barrier as described in <Regulatory Guide 1.102>. Plant Structures, Systems and Components are passively protected from the Major Stream flood hazards for all events up to and including the PMP by the channel capacity and topographic features segregating the Major Streams drainage basin from the local intense precipitation (LIP) domain. The PMF discussed herein is based on the precipitation event provided in <Section 2.4.3.1> which bounds the standard project storm (SPS) and probable maximum winter precipitation (PMWP) events provided in <Section 2.4.3.1>. No emergency procedures are required for Major Stream flood hazards. Revision 2.4-50a Information Only 2.4.10.3 Diversion Stream Flood Hazards The Diversion Stream probable maximum flood (PMF) inundation area is shown in <Figure 2.4-5a>. As shown in this figure, the streamflow resulting from a probable maximum precipitation (PMP) event is confined to the Diversion Streams drainage basin and does not encroach on plant safety-related structures or nonsafety-related that communicate with safety-related structures. The Diversion Stream is provided with an earthen embankment (berm) which functions as an extension of the channels west bank. The top of the Diversion Stream berm is above the peak water surface elevation (WSE) during the Diversion Stream PMF. The Diversion Stream and berm are engineered features external to the plant area designed to protect the site from inundation and functions as an Exterior Barrier as described in <Regulatory Guide 1.102>. Plant Structures, Systems and Components are passively protected from the Diversion Stream flood hazards for all events up to and including the PMP by the channel capacity and berm which segregates the Diversion Streams drainage basin from the local intense precipitation (LIP) domain. A failure of the Diversion Stream berm is postulated within the analysis for the LIP event (Reference 66). Guidance for determining the breach profile and size, as well as resulting breach flow rate, is determined using the guidance of the U.S. Army Corps of Engineers (Reference 84) (Reference 85). As such, any failure of the Diversion Stream berm is inherently bounded by the protection discussed for the LIP event. The PMF discussed herein is based on the precipitation event provided in <Section 2.4.3.1> which bounds the standard project storm (SPS) and probable maximum winter precipitation (PMWP) events provided in <Section 2.4.3.1>. No emergency procedures are required for Diversion Stream flood hazards. Revision 2.4-50b Information Only 2.4.10.4 Local Intense Precipitation Domain Flood Hazards As discussed in <Section 2.4.2.3>, effects from the Local Intense Precipitation (LIP) result in the controlling flood event for the site. The LIP event results in water levels which exceed door thresholds and wall penetrations. For the LIP hazard, flood protection is provided in the form of incorporated barriers as defined in <Regulatory Guide 1.102>. Protection is provided for safety-related buildings and nonsafety-related buildings which communicate with safety-related buildings. These incorporated barriers provide protection for safety-related structures, systems, and components. For the LIP hazard, both permanent and temporary (removable) incorporated barriers are utilized. Permanent incorporated barriers consist of safety-related building exteriors, steel closure plates, and concrete and aluminum flood walls. With the exception of the safety related building exteriors and closure plates at the Emergency Diesel Generator (EDG) overflow flame arrestors, the permanent incorporated barriers are nonsafety-related and are not within the scope of the PNPP Quality Assurance Program. Typical depictions of the concrete and aluminum flood walls are shown in <Figure 2.4-78> and <Figure 2.4-79>, respectively. Buildings protected by these features are depicted in <Figure 2.4-77>. Temporary incorporated barriers are provided in the form of removable flood panels (flood stop logs) which are also nonsafety-related and not within the scope of the PNPP Quality Assurance Program. These barriers are utilized at plant doorways which create openings in the otherwise continuous protection provided by the walls discussed above. These removable barriers, certified to the requirements of ANSI Standard ANSI/FM-2510, are generally stored in a central location and deployed in accordance with plant procedures. In some cases, where there is minimal impact on normal plant operation and no impact on personnel egress, these temporary incorporated barriers may be pre-deployed. As discussed in detail in <Section 2.4.14>, operator action is initiated by receipt of meteorological forecast, discussed in <Section 2.4.10.5>, Revision 2.4-50c Information Only of forthcoming significant precipitation. Typical depictions of the concrete and aluminum flood walls are shown in <Figure 2.4-78> and <Figure 2.4-79>, respectively. Typical examples of the removable incorporated barriers are depicted in <Figure 2.4-80> and <Figure 2.4-81>. All incorporated barriers are designed for the entire range of flood forces (Reference 79). This includes the hydrodynamic forces resulting from the flooded condition (including fluid velocities) and the forces resulting from flood-born missile impact. Deployment of flood protection features for the LIP hazard is incorporated into plant off-normal instructions. Lesser precipitation hazards for the LIP domain, up to and including the standard project storm (SPS) and probable maximum winter precipitation event (with concurrent snowmelt), are mitigated using permanent passive protection which requires no operator action. Consistent with other flood protection features, these protection features barriers are nonsafety-related and are not within the scope of the PNPP Quality Assurance Program. These features include the walls discussed above, closure plates, ramps and raised thresholds. No emergency procedures for barrier deployment are required for SPS or PMWP effects. 2.4.10.5 Meteorological Forecast Warning Using the guidance of (Reference 88), PNPP utilizes a two-tier meteorological alert to initiate deployment of the temporary barriers discussed in <Section 2.4.10.4> (Reference 89). The first-tier warning is set to 2.1 inches of precipitation in a 24-hour period. This event corresponds to a one-year recurrence interval precipitation event. The second-tier warning is set to 1.9 inches of precipitation in a one-hour period. This event corresponds to an approximately 18-year recurrence interval event. Compared to the Standard Project Storm (SPS) event for which fully passive protection is provided, which has a peak hourly Revision 2.4-50d Information Only intensity of 3.747 inches per hour as discussed in <Section 2.4.3.1>, sufficient overlap is provided to account for uncertainties associated with meteorological forecast limitations. Meteorological forecasting is provided by an external service which is implemented by certified meteorologists. The forecasting employs an ensemble technique using diversified inputs. Input models are obtained from the National Blend of Models (NBM) and Weather Prediction Center (WPC). The NBM provides Quantitative Precipitation Forecasts (QPF) which the WPC provides Probabilistic Quantitative Precipitation Forecasts (PQPF). A 95th percentile confidence value is selected for the ensemble forecasting method per the guidance of (Reference 88). QPF forecasting provides a medium range forecast monitoring five days into the future. PQPF forecasting provides a short-range forecast monitoring 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> into the future. The lower tier warning does not require any specific action by plant personnel. This alert instead serves to initiate heightened awareness thus allowing plant personnel to conservatively take any necessary preemptive actions. The higher alert serves as the entry condition for a Technical Specification Limiting Condition of Operation (LCO) and initial condition for entry condition for off-normal instructions which includes deployment of temporary flood barriers. Revision 2.4-50e Information Only 80 mph for approximately 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />. For station (20,21), the wind direction varies from 340 to 310 degrees during the maximum wind period. For station (40,21), the wind direction varies from 340 to 320 in this period. The total distance that these winds travel over water is approximately 56 miles. The computed setdown hydrograph for the site during the period of the PMS is shown in <Figure 2.4-63>. With the 4.03 foot maximum setdown, the minimum water surface elevation at the plant site would be 563.36 feet IGLD (565.26 feet USGS) (Reference 90). This is based on an antecedent water elevation of 567.4 feet (IGLD) (Reference 61), the minimum monthly level of record. The wave action coincident with this setdown was determined by procedures described in Technical Report No. 4 (Reference 22). Using an average 90 mph offshore, over water wind of unlimited duration with a 30 percent reduction to account for land effects in the nearshore zone, the Bretschneider method gives a 2.6 foot significant wave height and a 4.7 second period. Since the alternate intake (normal discharge structure) is closer to shore, the wave heights would be less than at the normal intake structure. 2.4.11.2.2.3 One-Dimensional Model for Setdown Surge The analysis of the lake setdown surge at the plant site was made using the one-dimensional model described in Technical Report No. 4 (Reference 22), and briefly characterized in <Section 2.4.5.2.2>. The probable maximum setdown was computed with this method using a fetch defined by a line connecting grid points (36,3) (plant site) and (36,21) <Figure 2.4-26>. <Figure 2.4-63> shows the hydrographs of computed setdown at the site for the PMS setdown wind data. Note that the curve does not reflect any adjustment for lake volume balance, pressure or precipitation. The maximum setdown shown on this curve is 4.03 feet (122.95 cm) (Reference 90). Revision 2.4-55 Information Only Volume adjustment was made on the basis of Equation 2.4-1. <Figure 2.4-29> summarizes the results of the volume computations for both the setup and setdown cases at the time of their peak occurrence. The pressure adjustments were made by looking at the PMS pressure data and choosing the maximum pressure difference between adjacent stations across the lake. For both the PMS setup and setdown cases, the maximum pressure difference was found to be 10 mb 10 cm of water. No precipitation adjustment was included for the setdown case since it would only reduce the setdown and would not be indicative of the most conservative case. 2.4.11.3 Historical Low Water Two gauges have provided data for the study of the variation in surface elevation of Lake Erie. The Cleveland gauge has a period of record for monthly and annual means dating back to 1860, with instantaneously recorded data since 1904. The gauge at Erie has continuous data from 1960 to the present. A third gauge at Ashtabula, installed in 1954, has been neglected for extended periods since its installation and much of the data recorded by this gauge is incomplete and unreliable due to malfunction of the gauge and its recording mechanism. <Figure 2.4-2> reveals that the mean lake level has a cyclic variation. At Cleveland, the minimum monthly mean level of record was 567.4 feet IGLD (569.3 feet USGS) recorded in February 1936. The minimum recorded instantaneous level was 565.71 feet IGLD (567.61 feet USGS), which occurred on February 4, 1936. The maximum seiche setdown for each year was computed by subtracting the minimum instantaneous lake level from the mean level for the month in which it occurred. The peak setdown at Cleveland for the period of record was -3.04 feet, occurring December 8, 1927. At Erie, the minimum monthly mean level was 568.27 feet IGLD (570.17 feet USGS) for December 1964 and the minimum recorded Revision 2.4-56 Information Only instantaneous level was 566.00 feet IGLD (567.90 feet USGS), which occurred on March 10, 1964. The peak seiche setdown at Erie for the period of record is -2.90 feet, occurring March 10, 1964. A frequency study of seiche setdown and minimum monthly mean stages was made for both the Cleveland and Erie gauges. The results obtained are shown in <Figure 2.4-64> and <Figure 2.4-65>, respectively. Log Pearson Type III and Linear Gumbel distributions are presented for each case. Comparison of the seiche setdown curves in these figures shows that at a particular frequency the seiche at Erie exceeds that at Cleveland. This is felt to be attributable to dissimilar lengths of gauge records and topography in the vicinity of the gauging stations. 2.4.11.4 Future Controls There are three hydrologic features which influence the site: Lake Erie and the two adjacent streams which border the site. The safety-related structures are located outside the drainage basin of both streams. No developments are foreseen for the streams as the base flow of each is 5 cfs or less. These streams are only used for drainage purposes. Lake Erie drains into Lake Ontario via the Niagara River and is also connected to Lake Ontario by the Welland Canal. The Niagara River has two major control structures for power generation before reaching Niagara Falls. The upstream east channel has also been channelized for navigational purposes. However, no new developments involving control structures are envisioned. The Welland Canal is approximately 26.5 miles long and has 8 locks capable of raising ocean-going vessels 326 feet from Lake Ontario to Lake Erie. A more complete description of the canal may be found in Revision 2.4-57 Information Only <Section 2.4.11.6>. A section of the canal is being straightened between Miles 23.8 and 15 (Mile 23.8 is approximately 4 miles from the Lake Erie end). The new cross section will have a bottom width of 350 feet compared with 192 feet in the existing channel. The depth of the new channel will be 30 feet, three feet deeper than the present system it will replace. For reasons outlined in the <Section 2.4.11.6>, it is considered most unlikely that any developments of the canal will influence the surface elevation of Lake Erie. 2.4.11.5 Plant Requirements As described in <Section 2.4.11.2>, the probable minimum lake level at Perry is Elevation 565.26 feet (USGS). With the inverts of the intake ports at an average elevation of 552.65 feet, inflow of sufficient cooling water during this period is assured. The corresponding water level in the emergency service water pump chamber would be at Elevation 562.09 feet. During this condition, water for the emergency service water system could also be supplied by the alternate intake system discussed in <Section 2.4.5.4> and <Section 9.2.5>. The crown and invert elevations of the diffuser nozzle of the discharge structure are 555.8 and 552.8 feet (USGS), respectively. The available 12.2-foot submergence over the diffuser nozzle would prevent air entrainment due to the inflow velocity (approximately 15.85 fps through the nozzle). The minimum water level in the emergency service water pumphouse will occur during the hot standby condition when only the emergency service water systems are operating. At the probable minimum lake level with coincident wave action, the level in the emergency service water pump chamber for this condition will be Elevation 562.09 feet (USGS) (Reference 91). With the invert of the chamber at Elevation 537.0 feet, the 10-foot minimum Revision 2.4-58 Information Only <Section 9.2.1>. The water will discharge outside the auxiliary building onto the ground. The slopes and elevations are set so that the flow will be away from the plant, across the road and down a graded swale between the cooling towers to the diverted stream <Figure 2.4-3>. The water will flow down to the stream and discharge into Lake Erie (Reference 86). The topography of the emergency service water alternate discharge area (Remnant Minor Stream) can be seen in <Figure 2.4-3>. Flow through all paths for both units will result in a total flow to the stream of approximately 50,000 gpm initially, which will be reduced to 25,000 gpm in a short period of time. These flow rates represent original plant design (two units). Since then, Unit 2 has been abandoned. As a result, the actual total flow exiting the ESW standpipes will be much less. In addition, the required ESW flow rates for Unit 1 have been analytically decreased to values less than those originally specified (reference <Figure 9.2-1(3)> for the required ESW system flow rates). The contours of the site will be set to provide a depressed area east of the auxiliary buildings <Figure 2.4-3>. This depressed area will slope away from the plant buildings, over the road and through the swale to the Remnant Minor Stream. Elevations of the depressed areas will be such that no water exiting the plant under this unlikely event will result in flooding of the facility. This is confirmed via analysis captured in (Reference 86). The main intake structures shown on <Figure 3.8-65> and <Figure 3.8-67> consist of two independent intake heads that are each connected to a six foot diameter shaft. The two vertical shafts convey the water into the 10-foot diameter intake tunnel shown in <Figure 3.8-65> and <Figure 3.8-66>. The intake heads are circular in plan and are covered with a velocity cap placed at a minimum of 13.3 feet below the low water datum (LWD), as shown in <Figure 3.8-67>. Inflow is through vertical openings around the periphery of the intake heads. The discharge Revision 2.4-61 Information Only Further, assuming an accidental release of radioactive materials was to occur at the radwaste building and was to assume a travel path through the soils, the estimated transit time to the point of discharge into Lake Erie is 25 years if the groundwater was allowed to return to Elevation 620.0. The maximum groundwater velocity would likely occur within the lacustrine deposits (upper 25 feet) as the underlying tills are relatively impervious. Coefficient of permeability K calculated from field testing within lacustrine materials ranged between 1.2 x 10-4 cm/sec and 4.2 x 10-7 cm/sec, as discussed in <Section 2.5.4>. The hydraulic gradient was determined from differences in gravitational groundwater levels between the radwaste building and the future protected bluff slope, and the shortest distance between these points. Groundwater levels measured in proximity to the radwaste building (Boring 1-45) averaged about Elevation 620.0. Near the edge of the bluff, the static groundwater level range occurs at around Elevation 616.0. The Perry site has been graded to approximate Elevation 620.0 PLD. The natural watercourse of the Minor Stream, located between the plant and the bluff, was relocated a trapezoidal engineered channel to the east. The abandoned channel has been filled with compacted soils to Elevation 620.0. The maximum difference in groundwater levels expected between the plant and the bluff after completion of the site grading is conservatively estimated at 12 feet; however, the readjusted piezometric slope after grading will likely be much less. The minimum groundwater transit distance will occur when the 1979 bluff, which is approximately 1,010 feet from the radwaste building, has receded about 200 feet <Figure 2.4-39>. On the assumption that 200 feet of recession will actually occur during the life of the PNPP, a conservative distance of 800 feet has been used for establishing the groundwater gradient. For Revision 2.4-72 Information Only In order to continuously monitor and detect significant amounts of radioactive concentrations discharging from the underdrain system, as a result of the postulated event, radiation monitors are located inside each of the two gravity discharge system manholes at the north end of the Unit 1 heater bay, at locations where the underdrain pump effluent travels through the gravity drain system. Details of the radiation monitor are discussed in <Section 11.5>. The offsite effects of a hypothetical release, due to a seismic event, of radioactive liquids to the environs is described in <Section 15.7>. 2.4.13.5.4 Maintenance and Testing Normal routine maintenance will be performed on the mechanical and electrical portions of the system. The manholes and gravity discharge pipes will be inspected annually to ensure that all parts of the system, including the porous piping, are in operating condition. Any blockage in the porous concrete periphery drain pipes will be cleared by mechanical or other suitable means. The following periodic tests will be performed to ensure continuous satisfactory performance of the system.

a. Continuity Test This test will be performed semiannually for the first five years of operation and annually thereafter. The objective of the test is to verify that water will build up and draw down at the monitoring points, to establish that the underdrain system can reduce the hydrostatic pressure on building foundations to the desired level.

Revision 2.4-92 Information Only

c. Long Term Performance of the Porous Concrete Underdrain System The long term performance of the porous concrete pressure relief underdrain system is evaluated as follows:

1. Tornados Tornados will not affect the operation of the underdrain system because it is underground. However, the manhole covers are exposed but are not considered missile proof because a missile entering the top of a manhole would not totally obstruct the flow of water in the manhole.

2. Earthquakes The system is a Seismic Category I system. The seismic design and analysis for the gravity discharge pipe is discussed in <Section 2.4.13.5.1>. The seismic design and analysis for manholes is discussed in <Section 3.8.4>.

3. PMP (Probable Maximum Precipitation)

The effect of PMP on the underdrain system is negligible. Around the nuclear island buildings, the ground surface will be paved with asphalt, concrete, or backfilled with relatively impervious Class B fill of excavated lower till soils. The rate of infiltration through the Class B fill is calculated to be less than 3 gpm and the effect on the underdrain system is insignificant. Revision 2.4-97 Information Only velocity and transport capability of groundwater to erode either Chagrin shale or lower till are negligible. The durability of the shale and its ability to resist subaqueous disintegration and decomposition have been documented by slaking tests and are discussed in <Section 2.5.4>. Lower till is nondispersive as demonstrated by the pinhole and soil conservation service laboratory dispersion test <Section 2.5.4>. The association of lower till and Chagrin shale properties, coupled with their demonstrated ability to withstand subsurface weathering and erosion during the Recent Epoch, show that no basis exists for assuming a subsurface erosion potential. A conspicuous absence at the Perry site of montmorillonite-type clays, which are characteristically detected in overburden and bedrock undergoing subsurface erosion as well as extensive surface erosion, is considered significant positive evidence in further refutation of this potential.

d. Potential of the Underdrain System to Drain Water From Lake Erie or Along Plant Piping Systems All piping except the underdrain system gravity flow discharge pipes running from the main plant buildings to the emergency service water pumphouse are designed and installed above Elevation 595.0 (i.e., approximately 20 feet above the mean monthly high water level for Lake Erie of 575.4 per

<Section 2.4.1.1>). The gravity discharge lines enter the emergency service water pumphouse at invert Elevation 579.0 which is approximately four feet above mean monthly high lake level. This ensures that no man-made flow path will exist between the pumphouses and the main plant buildings. Revision 2.4-110 Information Only The lowest discharge points from any of the 13 deep plant manholes of the porous concrete underdrain system are at manholes No. 8 and 9 which have pipe invert elevations of 582.6 and 583.5, respectively <Figure 2.4-69>. Since these gravity discharge pipe inverts are above the maximum lake setup due to the PMS (580.5), no backflow from the lake can occur through the Emergency Service Water Pumphouse into the porous concrete underdrain system. The mean monthly high water level for Lake Erie is Elevation 575.4 (Reference 61) which is seven feet above the groundwater level of 568.0 maintained in the underdrain system. Because the plant is 800 feet from the lake, the possibility of seepage from the lake into the underdrain was considered. Geologic mapping of the foundation area was conducted, and open fractures were grouted. None were seepage sources. In this way, all possible drainage paths from the lake into the underdrain systems were sealed. Underground piping systems, which enter the main plant buildings, were set in bedding materials of granular material which have a higher permeability than the lacustrine soil through which the pipes run, and hence, provide a potential flow path for groundwater into the underdrain system. In order to prevent this flow, at two separate locations special bedding and backfill material were used around all external pipes where they enter the Class A fill at the plant buildings. The special bedding and backfill material is low permeability Class B fill. The quantity that can flow through the backfill and bedding was included in the calculation of total groundwater flow into the underdrain system. The flow postulated through the pipe bedding material would not increase the calculated inflow to the underdrain system because that calculation assumes a saturated soil. Revision 2.4-111 Information Only

e. Infiltration Due to Rainfall, Surface Spills or Lawn Sprinkling A layer of impervious Class B soil was placed over the Class A fill to reduce the amount of seepage possible from infiltration at the surface. Such seepage could result from either rainfall, surface spills, or lawn irrigation.

All underdrain system manholes have gasketed, watertight covers installed at the surface. The covers are normally locked or bolted in a closed position. The 24 outside manholes (two manholes constructed inside buildings) have heavy duty gray cast iron covers. These covers ensure minimal, if any, inleakage occurs into the underdrain system due to rainfall, surface spills or lawn sprinkling. In the event of the rupture or leakage of an onsite reservoir (e.g., cooling tower basins and industrial waste lagoons), the discharge will generally drain overland away from the plant into neighboring streams and thus to Lake Erie. The area surrounding the plant is also provided with a nonsafety-related storm drain system which will collect surface water approaching the plant and assist in drainage of the powerblock area. Because of the impermeable nature of the surface materials, there will not be sufficient time available to allow significant infiltration into the permanent underdrain system. summarizes the major onsite storage facilities excluding the cooling tower basins. Roofs of all buildings are drained to the storm drain system which discharges into the Major and Remnant Minor Streams that feed into Lake Erie. Rainfall on paved and unpaved areas around the main plant buildings generally routed by topography or the storm drain system away from the plant. Rainwater or lawn Revision 2.4-112 Information Only a seismic related failure of non-Category I structures without compromising the full operating capability of the redundant permanent dewatering system. 2.4.13.5.6 Controlled Low Strength Material (CLSM) Controlled Low Strength Material (CLSM) may be used as a replacement for Class B and Class C fill, and as a replacement for Class A fill when the Class A fill was used as bedding and backfill for buried piping and ductbanks only, and not as part of the Plant Underdrain system, or as a foundation for safety-related buildings or structures. Since the CLSM is equivalent to or better than Class B fill in bearing capacity and impermeability, this change has no effect on the results of USAR <Section 2.4.13.5.1> and <Section 2.4.13.5.5>. 2.4.14 TECHNICAL SPECIFICATION AND EMERGENCY OPERATION REQUIREMENTS Safety-related facilities at PNPP are protected as described in the preceding sections. The only external flooding hazard which requires operator action to protect the Structures, Systems and Components (SSCs) required to achieve and maintain cold shutdown is the LIP event which represents the bounding external flood hazard for PNPP as determined in (Reference 66). Operator action is required only for precipitation hazards which exceed the Standard Project Storm (SPS). Operator action is limited to the deployment of nonsafety-related removable incorporated barriers in the form of flooding stop logs. The requirements and guidance for this action is incorporated into plant off-normal instructions. The action is limited to the placing of the stop logs at pre-determined locations. This involves sliding the stop logs into pre-installed end channels and securing the panels with compression clamps. This action is completed without the need for hand tools. Entry into the plant off-normal instructions is initiated by a meteorological forecast warning which is discussed in detail in Revision 2.4-117 Information Only <Section 2.4.10.5>. This action is required by PNPPs Technical Specifications as discussed in <Regulatory Guide 1.102>. The alert provides approximately 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of warning which grossly bound the estimated deployment duration of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. This ensures the barriers can be deployed well in advance of the onset of a flooded condition. If barriers are not deployed in the timeframe allotted by the Technical Specification Limiting Condition of Operation, a plant shutdown is initiated. 2.4.15 LIST OF PERSONS AND AGENCIES INTERVIEWED The following is a listing, by sections, of individuals and agencies whose assistance was elicited during preparation of the Hydrologic Engineering discussions: <Section 2.4.5.2> Dr. L. Bajorunas, Director, Great Lakes Research Center, NOAA, Detroit, Michigan. Mr. Elmer Kulp, Acting Chief, Vertical Control Section, Lake Survey Center, NOAA, Detroit, Michigan. Revision 2.4-117a Information Only

56. Pree, H. L., Jr., Ashtabula and Conneaut Creek Basins, and Adjacent Lake Erie Tributaries, Ohio Department of Natural Resources, Division of Water, 1960.

57. DeWiest, Roger J. M., Geohydrology, John Wiley and Sons, Inc., New York, 1967.

58. Todd, D. K., Groundwater Hydrology, John Wiley and Sons, Inc., New York, 1959.

59. Woodward-Cylde Consultants letter of November 01, 1981, to Gilbert Associates, Inc. Ref: See page Estimate.

60. Gilbert Associates Inc. Calculation 26:12, Perry Emergency Service Water Pumphouse - Stability Analysis, Revision 0 (Retained as Perry Calculation 26:12.000, Revision 0).

61. PNPP Calculation 50:74.000, Lake Erie Water Levels.

62. Not Used

63. Not Used

64. Not Used

65. PNPP Calculation DX-1.5.1, Lake Erie Surge Study - Surge Analysis.

66. PNPP Calculation 50:64.000, PNPP Site Modifications Local Intense Precipitation (Design Basis).

Revision 2.4-126 Information Only

67. PNPP Calculation 50:65.000, Evaluation of Structural Roof Capacity for USAR Described PMP Event.

68. PNPP Calculation 50:71.000, Design Basis Maximum Precipitation (PMP) Determination.

69. PNPP Calculation 50:79.000, Probable Maximum Winter Precipitation (PMWP, Cool-Season PMP) and Snowmelt Contribution (Design Basis).

70. PNPP Calculation 50:72.000, Design Basis Major Stream Probable Maximum Flood (PMF).

71. PNPP Calculation 50:73.000, Design Basis Diversion Stream Probable Maximum Flood (PMF).

72. PNPP Calculation 50:75.000, Design Basis Standard Project Storm (SPS) Determination.

73. PNPP Calculation 21:02.000, Misc. Yard Structures - Railroad Bridge.

74. PNPP Procedure EMARP-0005, Monitoring Shoreline Recession and Bluff Erosion.

75. PNPP Engineering Change Package 13-0802, Major/Minor Stream Modification.

76. PNPP Calculation 50:68.000, Perry Nuclear Power Plant (PNPP)

Diversion Stream Design Basis Shore Protection Analysis.

77. PNPP Drawing 744-0177-00012, Stream Relocation Outfall Profile -

Stream Outfall. Revision 2.4-126a Information Only

78. PNPP Calculation 50:80.000, Effects of Cool-Season Probable Maximum Winter Precipitation (PMWP) Event.

79. PNPP Calculation 50:77.000, Evaluation of Flood Barriers.

80. PNPP Calculation 21:21.000, Hydrogen Water Chemistry Tank Foundations and Miscellaneous Equipment Foundations.

81. ANSI Standard ANS-N170-1976-ANS-2.8, American National Standards for Determining Design Basis Flooding at Power Reactor Sites.

82. PNPP Calculation 50:76.000, PNPP Design Basis Standard Project Storm (SPS) Rainfall Effects.

83. U.S. Army Corps of Engineers Snow Hydrology, June 1956.

84. U.S. Army Corps of Engineers Guidelines for Calculating and Routing a Dam-Break Flood, RD-5, Hydrologic Engineering Center, January 1977.

85. U.S. Army Corps of Engineers Guidelines for Corps Dams, RD-13, Hydrologic Engineering Center, June 1980.

86. PNPP Calculation 50:82.000, ESW Swale Discharge Flooding Evaluation.

87. PNPP Calculation 50:83.000, Mixed Bed Tank Discharge Evaluation.

88. NEI 15-05, Warning Time for Local Intense Precipitation Events, Revision 6, April 2015, Nuclear Energy Institute.

89. PNPP Calculation 50:85.000, Precipitation Hazard Alert Evaluation.

Revision 2.4-126b Information Only

90. PNPP Calculation DX-1.5.0, Lake Erie Surge Levels - Lake Level Studies - PMS.

91. PNPP Calculation DX 1.1.2, Emergency Service Water Pumphouse Water Levels.

Revision 2.4-126c