ML14059A233

From kanterella
Jump to navigation Jump to search
Response to Request for Additional Information on Flooding Hazard Reevaluation Report
ML14059A233
Person / Time
Site: Callaway Ameren icon.png
Issue date: 02/28/2014
From:
Ameren Missouri, Union Electric Co
To:
Document Control Desk
Shared Package
ML14059A231 List:
References
ULNRC-06081
Download: ML14059A233 (58)
v • d • e


Text

Enclosure to ULNRC-06081 Page 1 of 58 Response to Request for Additional Information Flooding Hazard Reevaluation Report Union Electric Company Callaway Plant, Unit 1 Docket No. 50-483 Response to RAI Questions

Enclosure to ULNRC-06081 Page 2 of 58 TABLE OF CONTENTS PAGE RAI-1 ..................................................................................................................................1 RAI-2 ..................................................................................................................................2 RAI-3 ..................................................................................................................................3 RAI-4 ...................................................................................................................................5 RAI-5 ...................................................................................................................................6 RAI-6 ...................................................................................................................................9 RAI-7 ...................................................................................................................................9 RAI-8 .................................................................................................................................10 RAI-9 .................................................................................................................................11 RAI-10 ...............................................................................................................................11 RAI-11 ...............................................................................................................................14 RAI-12 ...............................................................................................................................15 RAI-13 ...............................................................................................................................15 RAI-14 ...............................................................................................................................17 RAI-15 ...............................................................................................................................18 References ..........................................................................................................................20 Attachment 1 - Tables Attachment 2 - Figures Appendix A - Electronic Files CEC Unit 1 i RAI Docket No. 50-483, Rev 0

Enclosure to ULNRC-06081 Page 3 of 58 RAI 1: Local Intense Precipitation Flooding In order to review the evaluation of local intense precipitation (LIP), the NRC staff requests additional information regarding the HEC-HMS subbasins shown in FHRR Figure 3-3. Specifically, please provide: (a) discussion of the delineation of subbasins for the LIP evaluation, (b) electronic versions of digital elevation models, (c) input and output files from the application of ArcHydro, and (d) ArcGIS shapefiles used in modeling of LIP. Please also provide electronic versions of the HEC-HMS input files for all scenario runs.

Response to RAI 1, Part a:

Fifty-one subbasins are delineated within a 354-acre (0.55 square mile) area including the plant site and adjacent land for the hydrologic modeling necessary to evaluate Local Intense Precipitation (LIP) flooding. The subbasins are delineated in ArcHydro (ESRI, 2011) within ArcGIS (ESRI, 2009) using the U.S. Geological Survey (USGS) Digital Elevation Model (DEM) data obtained from the USGS website (USGS, 2012), using the Sink Prescreening, Sink Evaluation, and Sink Selection tools as necessary.

A 20,000 square-foot threshold, or minimum catchment area, is used in ArcHydro to avoid the delineation of drainage areas smaller than approximately 1/2 acre, and to obtain a reasonable number of subbasins. Some of the resulting Sink Drainage Area (SinkDA) polygons are merged to create larger catchments to more closely match site drainage patterns.

The resolution of the USGS DEM is 5-feet (ft) by 5-ft (USGS, 2012), which is sufficient to show site grading, including berms and road embankments, and the then-existing Vehicle Barrier System (VBS) alignments. A comparison of the subbasins delineated in ArcGIS, with aerial photography of the site, shows that the boundaries of the subbasins generated for the hydrologic model align with existing roads and structures, confirming the accuracy of the automated delineation process.

Further processing of the DEM data provide the following information for each subbasin:

Contributing drainage area Stage-storage relationship Perimeter length and profile CEC Unit 1 1 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 4 of 58 Peak runoff rates from each subbasin are calculated using United States Army Corps of Engineers (USACE) HEC-HMS (USACE, 2010a) model by utilizing the Probable Maximum Precipitation (PMP) rainfall hydrographs for input, and Snyder unit hydrographs to represent the rainfall-runoff process (refer to Response to RAI 10).

Maximum ponding elevations are subsequently determined in a HEC-RAS model (USACE, 2010b) using steady-state input hydrographs (the peak runoff rate from the HEC-HMS runs). The hydraulics of runoff in the HEC-RAS model are represented in terms of an interconnected network of Storage Areas (SA) with stage-storage characteristics determined from subbasin topography. The SA connections are modeled as flow over broad crested weirs, using the subbasin perimeter profile data to determine the weir length and geometry (refer to Response to RAI 5 for additional discussion).

Response to RAI 1, Part b:

The requested DEM files are submitted in Attachment 1, as summarized in Table 1-1.

Response to RAI 1, Part c:

The requested ArcHydro input and output files are submitted in Attachment 1, as summarized in Table 1-1.

Response to RAI 1, Part d:

The requested ArcGIS shapefiles and HEC-HMS input files for all scenarios are submitted in Attachment 1, as summarized in Table 1-1.

RAI 2: Local Intense Precipitation Flooding Please provide a digital image showing the subbasin delineation overlaid on a satellite (or aerial photo) image of the site or a plant layout map. For example, a similar image is provided in the NRC Library as part of Figure 2-1 from RIZZO Calculation package 12-4939 F-02.

Response to the Request for Additional Information:

The requested imagery is provided on Figure 2-1.

CEC Unit 1 2 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 5 of 58 Figure 2-2 shows the numerical label for each subbasin to allow for referencing of the runoff, and stage output values provided in the body of this set of responses.

RAI 3: Local Intense Precipitation Flooding (a) Please provide justification, based on a sensitivity analysis, of whether or not the 6-hr probable maximum precipitation (PMP) scenario used in the LIP analyses bounds the effects of LIP in comparison with alternative duration PMP scenarios, such as 12-hr, 48-hr, and 72-hr PMP values. (b) The bounding LIP scenario(s) should be determined based on the severity of the flood level as well as the inundation duration. (c) Please describe the rationale for evaluating LIP using a temporal rainfall distribution in which the peak rainfall intensity occurs at the beginning of the PMP event and decreases thereafter. (d)

In addition, please describe which rainfall distribution results in the larger water height at the site.

Response to RAI 3, Part a The LIP flooding analysis for the flood hazard reevaluation study is based on conservative modeling assumptions consistent with the NRCs Hierarchical Hazard Assessment (HHA) methodology presented in Appendix B of NUREG/CR-7046 (NRC, 2011).

The 6-hour (hr) PMP hyetograph, with five-minute intervals (Figure 3-1) is utilized as the meteorological input to the HEC-HMS model of RIZZO Calculation 12-4939 F02, using PMP depths determined by using the Hydrometeorological Report HMR-52 methodology (NWS, 1982) as summarized in Table 3-1. The peak runoff rate modeled in HEC-HMS for each subbasin is used as an input to the associated SA in the HEC-RAS model.

For the sensitivity analysis, the PMP hyetographs are developed for the 12-hr, 48-hr, and 72-hr PMP events using the same HMR-52 methodology (NWS, 1982) as used for the 6-hr PMP event reported in the Flood Hazard Reevaluation Report (FHRR). Table 3-2 provides the cumulative and incremental rainfall depths associated with durations from 5 to 4,320 minutes, which includes the 6-, 12-, 48-, and 72-hr duration events.

Because the first five-minute PMP depth (and associated rainfall intensity) computed in HMR-52 is the same for storms of all durations, the peak runoff rates associated with individual subbasins are also identical for storms of all durations (as opposed to total runoff volumes which do change with the duration). As an example, this is shown for Subbasin 30 (which contains parts of the powerblock) on Figure 3-2.

CEC Unit 1 3 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 6 of 58 Table 3-3 lists the HEC-HMS simulated peak runoff rates for the PMP events for the four durations in question with the maximum rainfall intensities occurring early in the event (a one minute time step is used in anticipation of RAI 11). As expected, the peak runoff rate is the same for each of the PMP durations, (i.e., the 6-hr PMP scenario bounds the effects of the LIP event for the specified alternative durations).

The HEC-HMS input and output files for the sensitivity study in response to RAI 3, Part a on rainfall duration are provided in RIZZO Calculation 12-4939 F-20.

Response to RAI 3, Part b The LIP depths calculated for the FHRR are based on time-varying PMP rainfall inputs to HEC-HMS and quasi-steady state simulations in HEC-RAS. The peak runoff rates, determined for each subbasin in the HEC-HMS simulations, are used as constant-value input to each storage area node in the HEC-RAS model for the determination of the maximum ponding depth. Steady-state simulations are generally more conservative than the unsteady-state simulations. For the FHRR purposes, the steady-state simulation, combined with the assumption that no losses occur during the PMP event, bound the flood level per the HHA process. Consequently, flood durations are not computed using the quasi-steady simulations since the safety related structures and buildings are not impacted for the least conservative scenario in the HEC-RAS model in RIZZO Calculation 12-4939 F03 per the HHA approach. Therefore, only the peak stage simulated in the model scenarios is used to evaluate flood severity.

Transient simulations, using the full HEC-HMS runoff hydrographs, are run in HEC-RAS to provide estimates of the duration of any flooding for the response to RAI 3, Part b, as summarized in Table 13-1.

Response to RAI 3, Part c A rainfall distribution with the highest rainfall intensities early in the event is used in Calculation 12-4939 F-02 (RIZZO, 2013a) as shown on Figure 3-1. This is similar to the rainfall distribution used for the example LIP investigation provided in Appendix B of NRC NUREG/CR-7046 (NRC, 2011, Figure B-5).

RIZZO Calculation 12-4939 F-20 (RIZZO, 2014) is developed to document a sensitivity study of the location of the peak rainfall. For more information refer to RAI 3, Part d.

CEC Unit 1 4 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 7 of 58 Response to RAI 3, Part d The impact on peak water surface elevations, within the powerblock resulting from alternate locations of the peak rainfall intensity within the PMP hyetograph, is evaluated by running simulations with 1) a front-loaded PMP (i.e., with the peak rainfall intensity at the start of the event), and 2) a centrally loaded PMP (i.e., with the peak rainfall intensity at the center of the storm event, as shown on Figure 3-3). HEC-RAS Scenario 5 (RIZZO, 2013b) is used for the simulations with the peak runoff coefficient, Cp, set to 0.4 and VBS openings unblocked. Anticipating RAI 4 and RAI 11, a one-minute time step is used for both simulations.

The results from these simulations are compared in Table 3-4. The centrally-loaded PMP simulation resulted in a maximum increase in the peak water stage of 0.66 ft at SA 1114, raising the water surface elevation to 824.73 ft. At Subbasin No. 30, which contains safety-related Structures, Systems and Components (SSCs), the change in the peak stage is 0.24 ft, resulting in a maximum water surface elevation of 840.56 ft.

The HEC-HMS and HEC-RAS input and output files for the sensitivity study on temporal distribution of rainfall are provided in RIZZO Calculation 12-4939 F-20 (RIZZO, 2014).

RAI 4: Local Intense Precipitation Flooding (a) Please state the time step of the incremental PMP (for example, 5 minutes), along with a justification for its use, associated with modeling the runoff generation from the PMP event discussed in FHRR Section 3.2.1.1 (esp. Figure 3-2). (b) Also, please provide a sensitivity analysis of the selected time step.

Response to RAI 4, Part a:

A time step of five minutes is used to describe the rainfall used in the HEC-HMS model simulations in RIZZO Calculation 12-4939 F-02 (RIZZO, 2013a). A five minute time interval is also selected from the control specification menu in the HEC-HMS model.

The minimum time of concentration (Tc) (i.e., Tc = [0.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />

  • 60 minutes/hour]/0.6) is ten minutes.

So, the selected time-step of the incremental PMP and the HEC-HMS time interval of five minutes is equal to or less than 1/2 of the time of concentration for all subbasins. Therefore, the five-minute time step is refined enough to capture the changes in the runoff.

CEC Unit 1 5 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 8 of 58 Response to RAI 4, Part b:

A separate simulation using a one-minute time interval to address RAI 4 is conducted in RIZZO Calculation 12-4939 F-20 (RIZZO, 2014). The peak runoff using the one-minute and five-minute time intervals are compared in Table 4-1.

The HEC-HMS simulated peak runoff rates using the one-minute time interval are used in HEC-RAS simulations for the sensitivity run. The peak water surface elevations using the one-minute and five-minute time intervals are listed in Table 4-2. In the area of the powerblock, simulated peak stage at Subbasin 30 (where the powerblock is located) is increased from 840.17 ft to 840.32 ft. The floor elevations of buildings containing safety-related SSCs within the powerblock are 840.50 ft.

The HEC-HMS and HEC-RAS input and output files for the evaluation of model sensitivity to the size of the incremental PMP time step, and the Excel File listing the results of the simulations are provided in RIZZO Calculation 12-4939 F-20 (RIZZO, 2014).

RAI 5: Local Intense Precipitation Flooding A. Please provide the following information related to the HEC-HMS LIP flood modeling discussed in the FHRR Section 3.2.1.3:

a. Description of the "quasi-steady-state" approach stated in the calculation package F-03 for determining LIP flood elevations.
b. Discussion of the approaches to delineate overland flow pathways within the site, and assumptions in routing of flow between HEC-HMS subbasins.
c. Description of the basis for assigning HEC-HMS parameter values, such as the weir coefficient and Manning's roughness coefficient.

B. Please clarify the following inconsistencies related to the HEC-HMS LIP flood modeling:

a. The FHRR states (on page 13) that time of concentration was used to calculate lag time, but calculation package F-03 indicates that the lag time was calculated from subbasin parameters and was used to estimate time of concentration.
b. The FHRR and the calculation packages contain two different descriptions of LIP Scenario 1. FHRR Section 3.2.1.2 and calculation package F-02 describe a Scenario 1 that included calculation of runoff using the Rational Runoff Transformation Method, while FHRR Section 3.2.1.3 and calculation package F-03 indicate that HEC-HMS output was used in the evaluation of flood elevations for Scenario 1.

CEC Unit 1 6 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 9 of 58 Response to RAI 5, Part A-a:

The term quasi-steady-state approach is used to refer to the combination of HEC-HMS, and HEC-RAS simulations used to obtain maximum water surface levels within the Callaway Energy Center (CEC) powerblock for the FHRR.

The runoff within each subbasin is simulated in HEC-HMS in Calculation 12-4939 F-02 (RIZZO, 2013a) using the PMP rainfall hydrographs developed input and Snyder Unit Hydrographs to represent the rainfall-runoff process in Calculation 12-4939 F-01(RIZZO, 2013c).

The peak runoff rates for each subbasin are used as steady-state input hydrographs to each SA in an unsteady HEC-RAS simulation. The hydraulics of runoff in the HEC-RAS model are represented in terms of an interconnected network of SAs. The stage-storage characteristics are determined from subbasin topography. The SA connections between adjacent subbasins are modeled as flow over broad crested weirs, using the subbasin perimeter profile data to determine the weir length and geometry.

This conservative approach is used to determine if safety related structures are impacted by the local intense precipitation. One advantage of this approach over the traditional HEC-RAS modeling using hydraulic cross sections is that it does not restrict the flow to a predetermined direction. For the FHRR, this approach is considered conservative. Note that to respond to RAI Nos.1 through 10, new simulations are performed using unsteady-state simulations (RIZZO, 2014).

Response to RAI 5, Part A-b:

The longest flow paths are delineated using the DEM and aerial photography in ArcGIS. In some cases, (e.g., Subbasin 58) the longest flow path ends at a conveyance element represented in HEC-RAS. The flow between subbasins is not represented in HEC-HMS; HEC-HMS is only used to develop the runoff hydrographs. The routing between subbasins, and along conveyance channels, is carried out using HEC-RAS.

Response to RAI 5, Part A-c:

As indicated in response to RAI 5 Part A-b flow routing is done in HEC-RAS, so, neither weir coefficients, nor Mannings roughness coefficients are required for the HEC-HMS simulations.

CEC Unit 1 7 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 10 of 58 Flow routing is done in the HEC-RAS model, with each subbasin treated as an SA. Internal storage, within a subbasin, has to be filled before excess water can flow into an adjacent subbasin or reach. Flow between subbasins (i.e., storage areas) is controlled by broad-crested weirs used to simulate flow over a relatively short overland flow across drainage divides. The topographic elevations along the subbasin divides are used to describe the variation in elevations along the weir crest separating subbasins.

A weir coefficient of 2.63 is used to represent overland weirs between subbasins in the HEC-RAS models. This is a reasonable value of the coefficient for a broad-crested weir discharging under low heads (Brater & King, 1996). The weir coefficient for the outflow from Catchment No. 58, which contains the Ultimate Heat Sink (UHS) storage pond, is set to 2.65, as used in the Final Safety Analysis Report (FSAR) (Ameren Missouri, 2012).

Five channels draining the site (Figure 8-1 of RAI 8) are represented as reaches in the HEC-RAS simulations using cross-sections developed from the DEM. A Mannings roughness of 0.035 is selected to represent these reaches. This value is at the high end of the range reported for excavated or dredged channels that are reasonably well maintained (Brater & King, 1996).

Response to RAI 5, Part B-a:

Page 13 of the FHRR does not clearly state that the time of concentration (which is defined as the travel time from the hydraulically furthermost point in a subbasin to its outlet) was used to calculate the lag time, which is an input parameter for the Snyder Unit Hydrograph option in HEC-HMS (for more information on the selection of the Snyder Unit Hydrograph, refer to RAI 10). Actually, lag time, which is defined as the time from the centroid of the excess rainfall hyetograph to the centroid of direct runoff, and is assumed to be 60 percent of the time of concentration (USACE, 2000), was calculated directly from subbasin parameters, as discussed in RIZZO Calculation 12-4939 F-02 (RIZZO, 2013a).

The lag time in hours, tp, was calculated using Equation 1 (USACE, 2000, p. 54):

(Equation 1)

Where, Cl is a unit conversion coefficient (1 for the English system),

Ct is the catchment shape coefficient, L is the longest flow path across the catchment, in feet, and Ll is the length of the flow path running from the outfall to the centroid of the catchment.

CEC Unit 1 8 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 11 of 58 Response to RAI 5, Part B-b:

LIP Scenario 1, referred to in FHRR Section 3.2.1.2, provides the most conservative estimate of peak discharge by discounting any rainfall losses or attenuation of runoff.

In RIZZO Calculation 12-4939 F-02 (RIZZO, 2013a), the peak discharge for Scenario 1 is calculated using the Rational Runoff Method (Chow et al., 1988) with the runoff coefficient set equal to 1.0, and the constant intensity set equal to the peak five-minute intensity for the PMP.

In RIZZO Calculation 12-4939 F-03 (RIZZO, 2013b) the peak runoff for Scenario 1, which corresponds to Scenario 2 in RIZZO Calculation 12-4939 F-02 (RIZZO, 2013a), is obtained from a HEC-HMS simulation with no rainfall losses or rainfall-runoff transformation, utilizing the complete PMP rainfall hyetograph.

The FHRR is correct. Scenario 1 in RIZZO Calculation 12-4939 F-03 (RIZZO, 2013b) is based on running the flow rates developed for Scenario 2 in RIZZO Calculation 12-4939 F-02 (RIZZO, 2013a).

RAI 6: Local Intense Precipitation Flooding Please provide the electronic version of the HEC-RAS input files, including the HEC-GeoRAS files, related to the local intense precipitation flood analyses.

Response RAI 6:

The requested HEC-GeoRAS files and HEC-RAS input files are attached in Appendix A, as summarized in Table 6-1.

RAI 7: Local Intense Precipitation Flooding Information provided in RIZZO Calculation 12-4939 F-03 (RIZZO, 2013b) indicates that the mean sea level (MSL) datum used in the current design basis at the Callaway Energy Center site apparently is based on NGVD 29, while NAVD 88 is the datum for the new HEC-RAS analysis. The calculation package states that it is conservative to treat NAVD 88 and MSL as equivalent, but the package does not explain why this is conservative. Please clarify the basis for concluding that this equivalency is a conservative assumption.

CEC Unit 1 9 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 12 of 58 Response RAI 7:

The National Geodetic Vertical Datum of 1929 (NGVD29) elevation values, referred to as mean sea level (MSL) are approximately 0.02 ft lower than the North American Vertical Datum of 1988 (NAVD

88) elevation values at the CEC site. The North American Vertical Datum Conversion (VERTCON) website (NOAA, 2013) is used to define the difference in elevation between NGVD 1929 and NAVD
88. A PDF showing the conversion of topographic features from the VERTCON website is provided in Appendix A (i.e., file CallawayEnergy_NAVDvsNGVD.pdf).

The NAVD88 elevations used in the HEC-RAS model (RIZZO, 2013b) are 0.02 ft higher than would be obtained with the model completely converted to NGVD29 elevations. This indicates that the simulated peak stages using HEC-RAS are 0.02 ft higher than would occur if all elevations listed in the HEC-RAS simulation (RIZZO, 2013b) were reduced by 0.02 ft. Therefore, simulated water levels are conservatively high.

RAI 8 Local Intense Precipitation Flooding In order to evaluate the licensee's analysis of water elevations resulting from LIP, the NRC staff needs additional information on the licensee's determination of the Manning's n roughness coefficient. Please provide descriptions of the terrain conditions of areas where overland flow would occur and the rationale for selecting a value (or values) for Manning's n roughness coefficient for these areas.

Response to RAI 8:

As described in the response to RAI 5, Part A-c, each model subbasin is treated as an SA in the HEC-RAS model (RIZZO, 2013b). Because overland flow is not simulated within the SAs, there was no parameterization of roughness within the SA. Roughness is parameterized for the conveyance reaches in the model.

Five channels draining the site (Figure 8-1) are represented as reaches in the HEC-RAS simulations (RIZZO, 2013b) using cross-sections developed from the DEM. A Mannings roughness of 0.035 is selected to represent these reaches. This value is at the high end of the range reported for excavated or dredged channels that are reasonably well maintained (Brater & King, 1996).

CEC Unit 1 10 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 13 of 58 RAI 9 Local Intense Precipitation Flooding Please provide a description of how the Vehicle Barrier System (VBS) was treated in the licensee's LIP model(s). The FHRR states that the VBS location affected the delineation of subbasin boundaries for modeling of LIP and that the most conservative simulation (Scenario 1) treated openings in the VBS as blocked, while the other scenarios represented these openings as open to flow. Calculation package F-03, provided in the NRC Library, contains an image showing the locations of closed and open VBS barrier openings and it contains a table listing the dimensions of the openings, but the image resolution is too low for interpretation and the identifiers in the table are not referenced to the figure.

Response RAI 9:

An ArcGIS shapefile for the VBS barrier alignment and the location of the openings between the units are provided in Appendix 1 in the response to RAI 6 (Table 6-1).

The VBS was reported to be 41 inches high and to have 41-inch openings at specified locations along its length (Ameren Missouri, 2012). The results of HEC-RAS simulations with the VBS openings blocked were used to identify locations of flood water accumulation against the VBS. If these locations included VBS openings greater than 30 inches in width, they were then represented as unblocked in subsequent simulations. Each VBS alignment is associated with the outfall weir for an SA node. Table 9-1 provides a list of the number of openings along each segment of the VBS perimeter with VBS openings which are used for those simulations with VBS openings represented. Figure 9-1 shows the location of the SA connections referenced in Table 9-1. Figures 9-2 through 9-12 show the profiles for each of the connecting weirs with the VBS openings un-blocked.

RAI 10 Local Intense Precipitation Flooding (a) For the LIP Scenarios 2 through 5 described in the FHRR Section 3.2.1.2, please provide an explanation of why the modification to the conservative assumptions (e.g.,

assumptions regarding the state of the VBS and values of runoff coefficients required by the Snyder Runoff Transformation Method) made in the low-order LIP scenario (e.g.,

Scenario 2 versus Scenario 3, and so on) provides a conservative assessment. (b)

Additionally, provide a description of the basis for selecting the Snyder Runoff Transformation Method to perform runoff transformations in Scenarios 3 through 6, and (c) describe whether this method provides a conservative assessment of the effects of local intense precipitation on this site.

CEC Unit 1 11 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 14 of 58 Response to RAI 10 Part a:

All the scenarios represented in HEC-RAS model (RIZZO, 2013b) for the FHRR are conservative in that:

A peak runoff rate, rather than a time varying rate, is used in the simulations Using a quasi-steady state condition in the HEC-RAS simulations means that no initial storage within the subbasins acts to reduce runoff rates or peak stages The simulation of peak runoff rates in HEC-HMS does not include rainfall losses The hydrologic parameters used for each of the scenarios are summarized in Table 10-1.

In RIZZO Calculation 12-4939 F-02 (RIZZO, 2013a), Scenario 1 provides the most conservative results per the HHA approach. No transformation of the rainfall is provided in the HEC-HMS model, so rainfall rates in inches per hour are converted to runoff rates in cubic feet per second (cfs) without attenuation. All openings in the VBS structures are blocked for the weirs connecting storage areas in the HEC-RAS model.

For Scenario 2 in RIZZO Calculation 12-4939 F-02 (RIZZO, 2013a), there is no transformation of rainfall as in Scenario 1, but the VBS openings are no longer blocked, providing a greater discharge for each stage. Following the HHA approach (NRC, 2011), Scenarios 3, 4, and 5 are even less conservative since the peak discharges estimated in HEC-HMS include runoff transformation with the Snyder Unit Hydrograph, which reduce peak flow rates in proportion to adjustments of the parameters Cp and Ct.

The following guidelines with respect to selection of the Snyder Unit Hydrograph parameters are provided in the HEC-HMS technical reference manual (USACE, 2000): Bedient and Huber (1992) report that Ct [Equation 1 in the response to RAI 5] typically ranges from 1.8 to 2.2, although it has been found to vary from 0.4 in mountainous areas to 8.0 along the Gulf of Mexico. Similarly, the Cp typically varies between 0.4 and 0.8....

Lower values of Cp result in lower estimates of peak discharge, as can be seen from the unit response to rainfall, presented here as Equation 2 (USACE, 2000, p. 53, rearranging Eq. [32]):

640 (Equation 2)

CEC Unit 1 12 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 15 of 58 where, Up = peak of the standard Unit Hydrograph, in cfs A = watershed area, in square miles Cp = UH peaking coefficient, dimensionless tp = basin lag, determined from Equation 1, in hours The value of Ct is set equal to 0.4 for all simulations as a conservative assumption to maximize flood levels at the plant. This is outside the typical range as noted above. This leads to a lower estimate of tp (Equation 1), resulting in higher estimates of peak discharge (Equation 2) and, consequently, conservative estimates of maximum water surface elevaiton.

The HEC-HMS simulations for Scenarios 3, 4 and 5 use Cp values of 0.7, 0.5, and 0.4, respectively.

Therefore the simulated peak runoff discharge, calculated in HEC-HMS, decreases with each of these simulations (Table 13-1).

A sensitivity study on the transfotmation method was conducted as part of this response (RIZZO, 2014).

Refer to RAI 10, Part b for more information.

Response to RAI 10, Part b:

For the licensing calculation (Ameren Missouri, 2012), the Soil Conservation Service (SCS) curve number method was used to estimate runoff losses, and the Clark Unit Hydrograph method was used to transform excess rainfall to runoff. For the hydrologic modeling carried out for the FHRR, runoff losses are conservatively set to zero per the HHA approach, and lacking any information for calibration, the Snyder Unit Hydrograph was selected over the Clark Unit Hydrograph because of its simpler parameterization, i.e., lag time is calculated in terms of lengths that can be measured, leaving only the basin coefficient, Ct, and the peak runoff coefficient, Cp, to be calibrated or estimated in the absence of calibration data (USACE, 2000).

Following the HHA approach, the peak runoff coefficient for the Snyder hydrograph transformation varied between simulations conducted for the FHRR, decreasing the level of conservatism with each Scenario, as discussed in the response to RAI 10, Part a.

A sensitivity study is conducted to examine the impact of the transformation method of the peak runoff rates (RIZZO, 2014). In RIZZO Calculation 12-4939 F-20 it was found that the peak flow rates for the Snyder method were comparable to the SCS method when a Cp coefficient of 0.7 was used (Table 10-2).

CEC Unit 1 13 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 16 of 58 Therefore it is concluded that the Snyder Unit Hydrograph provides acceptable results for the estimating peak runoff.

Response to RAI 10, Part c:

The level of conservatism in estimating peak runoff with the Snyder Unit Hydrograph depends on the value of the peak runoff coefficient selected, with higher values of the coefficient giving higher peak runoff rates.

For example, for Subbasin 30, where the powerblock is located, the peak runoff rate calculated with the Snyder Unit Hydrograph method is 74.5cfs, 111.1cfs, and 152.9cfs for values of Cp equal to 0.4, 0.5, and 0.7, respectively (RIZZO, 2013a, Table 7-3), giving maximum water surface elevations of 840.50 ft, 840.71 ft, and 841.16 ft, respectively (RIZZO, 2013b, Table 7-1).

RAI 11: Local intense Precipitation Flooding Results associated with the LIP flood modeling presented in the NRC Library indicate that the HEC-HMS model reported error messages for some subbasins for Scenario 5. Please provide a description of the effects of the reported errors on model results, and either a justification to demonstrate the acceptability of the model results for LIP Scenario 5, or a reanalysis that does not have errors.

Response to RAI 11:

No error messages were printed. The HEC-HMS model cannot run if errors are found in the run.

However, warning messages are printed for the Scenario 5 simulation indicating that the program did not converge for the estimation of the unit hydrograph. The warning message indicates that the value of Cp is slightly modified from 0.400 to approximately 0.402, with a corresponding increase in tp (e.g.,

from approximately 0.1 to 0.124 for Subbasins 17, 18, 19, and 21).

With the HEC-HMS model time interval change from five minutes to one-minute (RIZZO, 2014); the warning messages are not displayed. As indicated in response to RAI 4, there is an increase in simulated peak stage when the time step is decreased from five-minutes to one-minute. For instance, in the area of the powerblock, the simulated peak stage at Subbasin 30 increases from 840.17 ft for a five-minute time interval to 840.50 ft for a one-minute time interval, which is equal to the design site grade elevation.

CEC Unit 1 14 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 17 of 58 RAI 12: Local Intense Precipitation Flooding The FHRR Section 3.2.1.4 states that areas of ponding other than the ultimate heat sink (UHS) retention pond have insufficient fetch distances to generate wind-wave activity with the potential to affect structures, systems, and components. This rationale is not sufficient to explain the reason for not considering potential wind-wave activity for subbasin 22. FHRR Figures 3-3 and 3-4 shows that subbasin 22 has a larger maximum dimension (and, thus, could be expected to have a larger fetch distance) than the UHS retention pond, as well as a higher LIP-associated water level. Please provide either a reanalysis of LIP flooding with wind effects or the rationale for not considering the wind effects from subbasin 22.

Response to RAI 12:

Waves associated with the two-year wind speed are calculated for Subbasin 58 (which contains the UHS) in Calculation 12-4039 F-04 (RIZZO, 2013d) because the pump station located at the edge of the UHS is a safety-related SSC. No wave calculations were made for the excavated area within Subbasin 22 because it is a temporary condition.

The simulations for the FHRR utilize stage-storage data for Subbasin 22 based on the then-existing topography (i.e., with the open excavation). To evaluate the effect of the proposed fill within Subbasin 22, the storage-area relation for that subbasin is adjusted to account for the proposed finished grade elevations in the location of the present excavated area, as shown in Drawing 1484040010-C-CVL-008 Rev. 1, Callaway ISFSI Project DCP-02 Finish Grade and Stormwater Plan (Stone & Webster, 2014).

A sensitivity run incorporating the hydrologic impact of the proposed earthwork has been run for this RAI response, as summarized in Table 13-1 (Sensitivity Run B-3). The change in the stage-storage relationship for Subbasin 22 resulted in a decrease in its maximum stage from 839.78 ft to 839.53 ft, with no impact on peak stages in the adjacent Subbasin 30.

RAI 13: Need for the Integrated Assessment Please confirm whether or not an integrated assessment will be submitted within 2 years of the submittal of the FHRR. Also, clarify which flood hazard mechanisms will be included in the Integrated Assessment, if applicable.

CEC Unit 1 15 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 18 of 58 Response to RAI 13:

During a public meeting on September 25, 2012, the NRC staff identified criteria for deciding whether an integrated assessment is needed by classifying the results of flood hazard reevaluation studies into the following four scenarios:

1. Scenario I- Reevaluated Hazard is bounded by design basis: If the flood levels and the associated effects are completely bounded by the design basis, an integrated assessment is not necessary.
2. Scenario II- Only local intense precipitation is not bounded by the design basis: If the local intense precipitation is the only portion of the reevaluated hazard that is not bounded by the current design basis, the licensee can limit the evaluation to only the site drainage.
3. Scenario III- All permanent and passive flood protection: If all flood protection is permanently installed and passive, a licensee may show that existing condition is reliable and has margin under the reevaluated hazard. If the results of this evaluation do not show that the flood protection is reliable and has margin, a full integrated assessment is necessary and should be submitted within two years of submitting the hazard report.
4. Scenario IV- Integrated assessment is required: If none of the above scenarios are applicable, the licensee would need to perform a full integrated assessment.

The FHRR does not specifically indicate the intention of developing an integrated assessment since the least conservative HEC-RAS simulation, per the HHA approach, does not exceed the floor elevation of the buildings containing safety related structures. As discussed above, a series of quasi-steady state sensitivity runs with HEC-HMS and HEC-RAS are made for utilizing a range of values for the runoff parameter, Cp, in the Snyder Unit Hydrograph used in HEC-HMS. The resulting peak stages at Subbasins 22 and 30, for these runs, are provided for reference as base runs A, B, and C in Table 13-1. The peak stage in Subbasin 30 is at, or above the site grade elevation of 840.5 ft for base runs B and C, with values of 840.5 ft and 840.7 ft, respectively.

Sensitivity analyses carried out in support of responses to RAIs presented above indicate a small increase in peak stages with adjustments to the size of the time step and position of the peak rainfall intensity within the PMP hyetograph, as shown in Table 13-1 for Sensitivity Runs A-1, A-2, and B-1, with values of 840.17 ft, 840.32 ft, and 840.66 ft, respectively.

Additional simulations, with a transient HEC-RAS model, are run as part of the HHA approach using front-end and centrally loaded PMP hyetographs. The results of the more refined modeling show no inundation within the powerblock area for the range of the runoff parameter used in the base runs, as shown in Table 13-1 for Sensitivity Runs A-4, B-3, and C-1, with stages of 840.24 ft, 840.34 ft, CEC Unit 1 16 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 19 of 58 and 840.40 ft, respectively. Using the unsteady runs, as part of the HHA approach, reduces the flood level below the floor elevation (i.e., 840.5 ft) for even for the most conservative scenario (i.e., Cp = 0.7, with a one-minute time step and a centered PMP hyetograph) in comparison to the quasi-steady state simulations reported for the FHRR.

A sensitivity analysis of the impact of transformation method on the peak flow rate showed that modeling the rainfall runoff process with the SCS method resulted in peak runoff values comparable to using a Cp of 0.7 for the Snyder method. Therefore, the estimate of peak runoff is conservative and reasonable for the computation of the LIP. As mentioned above, the quasi-steady state simulation in HEC-RAS for a Cp of 0.7 (Sensitivity Run Base C in Table 13-1) shows a flood level of 840.66 ft (i.e.,

higher than 840.5 ft). However, the unsteady state simulation of the same case (per the HHA approach) shows that the flood level is 840.4 ft (i.e., lower than 840.5 ft).

Based on the fact that transient hydraulic analysis based on conservative estimates of runoff indicates peak stages are lower than the flood elevation of buildings containing safety related structures (i.e.,

840.50 ft), and considering further conservatism in modeling topographic surfaces, it is concluded that an integrated assessment is not required for the CEC site.

RAI 14: Hazard Input for the Integrated Assessment Enclosure 2 of the NRC's 50.54(f) letter dated March 12, 2012, requests the licensee to perform an integrated assessment of the plant's response to the reevaluated hazard if the reevaluated flood hazard is not bounded by the current design basis. Flood scenario parameters from the flood hazard reevaluation serve as the input to the integrated assessment. To support efficient and effective evaluations under the integrated assessment, the NRC staff will review flood scenario parameters as part of the flood hazard reevaluation and document results of the review as part of the staff assessment of the flood hazard reevaluation.

If an integrated assessment will be performed (see RAI 13 above), then please provide the applicable flood event duration parameters (see definition and Figure 6 of the Guidance for Performing an Integrated Assessment, JLD-ISG-2012-05 (NRC, 2012) associated with mechanisms that trigger an integrated assessment using the results of the flood hazard reevaluation. This includes, as applicable, the warning time the site will have to prepare for the event (e.g., the time between notification of an impending flood event and arrival of floodwaters on site) and the period of time the site is inundated for the mechanisms that are not bounded by the current design basis. Also, please provide the basis or source of information for the flood event duration, which may include a description of relevant CEC Unit 1 17 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 20 of 58 forecasting methods (e.g., products from local, regional, or national weather forecasting centers) and/or timing information derived from the hazard analysis.

Response to RAI 14:

The least conservative (quasi-) steady-state simulation in the FHRR as part of the HHA approach does not provide an estimate of flood duration because the safety related structures are not flooded; only the peak stage simulated in the model scenarios is used to evaluate their severity.

Transient modeling, performed for this response to RAIs, does not show inundation within the powerblock for the range of runoff parameters utilized and discussed above in the body of the RAI response.

RAI 15: Hazard Input for the Integrated Assessment Enclosure 2 of the NRC's 50.54(f) letter dated March 12, 2012, requests the licensee to perform an integrated assessment of the plant's response to the reevaluated hazard if the reevaluated flood hazard is not bounded by the current design basis. Flood scenario parameters from the flood hazard reevaluation serve as the input to the integrated assessment. To support efficient and effective evaluations under the integrated assessment, the NRC staff will review flood scenario parameters as part of the flood hazard reevaluation and document the results of the review as part of the staff assessment of the flood hazard reevaluation.

If an integrated assessment will be performed (see RAI 13 above), please provide a summary of the flood height and associated effects, as defined in Section 9 of JLD-ISG-2012-05, (NRC, 2012) for mechanisms that trigger an Integrated Assessment. This includes the following quantified information for each mechanism, as applicable:

Flood height, Wind waves and run-up, Hydrodynamic loading, including debris, Effects caused by sediment deposition and erosion (e.g., flow velocities, scour),

Concurrent site conditions, including adverse weather, Groundwater ingress, and Other pertinent factors.

CEC Unit 1 18 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 21 of 58 Response to RAI 15:

HEC-RAS modeling indicates some ponding within the power block for quasi-steady state simulations using the most conservative runoff parameterization and no inundation for transient simulations over the entire range of runoff parameters, discounting the possibility of significant wave action.

The mechanisms that would trigger an Integrated Assessment would be the simulated flood height and wind waves and run-up. The remaining mechanisms are not evaluated for the FHRR because the least conservative scenario did not show ponding per the HHA process. The transient modeling conducted to respond to the above RAIs also did not show ponding at the powerblock (See Tables 10-2 and 13-1).

The 10 CFR 50.54(f) letter did not identify groundwater ingress as an effect associated with flooding, nor does NUREG/CR-7046. This is not one of the hazards outlined in Attachment 1 to Enclosure 2 of the letter. In the letter, the NRC provides examples of the other effects, Examples of other effects include dynamic wave effects, scouring, and debris transportation.

Sediments associated with the PMF and dynamic loads generated by waves were noted by the NRC in a public meeting held April 11, 2013 (i.e., after preparation of the FHRR) between the NRC and Nuclear Energy Institute. The NRC expressed, during the public meeting, that flooding hazard reevaluation reports will be reviewed considering the comparison methodology shown in Table 15-1. This requires the quantification of dynamic loads and debris loads, if water levels for the LIP event exceed floor elevation of buildings containing safety related structures.

Based on an assessment that LIP flood levels would not reach 840.50 ft, these additional considerations are screened out qualitatively.

CEC Unit 1 19 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 22 of 58

References:

1. Ameren Missouri, 2012, Final Safety Analysis Report (FSAR), Callaway Energy Center Unit 1, Revision OL-19a, July 2012.
2. Brater and King, 1996, Handbook of Hydraulics for the Solution of Hydraulic Engineering Problems, Sixth Edition. McGraw-Hill Book Company. New York, New York.
3. Chow et al, 1988, Chow, Maidment, and Mays, Applied Hydrology, McGraw-Hill Book Company, 1988.
4. ESRI, 2009, Environmental Systems Research Institute (ESRI), Arc GIS ArcMap 9.3.1 Build 4000 Computer Program.
5. ESR1, 2011, Environmental Systems Research Institute (ESRI), ArcHydro 9 v. 2.05. January 5, 2011.
6. ESRI, 2014, Environmental Systems Research Institute (ESRI), ArcGIS Imagery, Website:

<http://www.arcgis.com/home/item.html?id=a5fef63517cd4a099b437e55713d3d54>, Date of Publication: January 16, 2012, Date Accessed: February 22, 2014.

7. NOAA, 2013, National Oceanic and Atmospheric Administration (NOAA), VERTCON:

Orthometric Height Conversion, Website: <http://www.ngs.noaa.gov/cgi-bin/VERTCON/vert_con.prl>, Date Accessed: January 5, 2013.

8. NRC, 2011, United States Nuclear Regulatory Commission (NRC), Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, PNNL-20091, NRC Job Code N6575, Washington DC, November 2011.
9. NRC, 2012, United States Nuclear Regulatory Commission (NRC), JLD-ISG-2012-05, Guidance for Performing the Integrated Assessment for External Flooding, November 30, 2012.
10. NRC, 2013, United States Nuclear Regulatory Commission (NRC), Email from Ed Miller to Jim Riley, April 11, 2013, Available at Website:

< http://pbadupws.nrc.gov/docs/ML1311/ML13113A429.pdf>, Date Accessed: October 23, 2013.

11. NWS, 1982, National Weather Service (NWS), Hydrometeorological Report No. 52 (HMR-52):

Probable Maximum Strom Computation (Eastern U.S.), August, 1982.

12. RIZZO 2013a, Paul C. Rizzo Associates, Inc. (RIZZO), Local Drainage Discharge Rates, Revision 1, RIZZO Calculation 12-4939 F-02, February 5, 2013.
13. RIZZO 2013b, Paul C. Rizzo Associates, Inc. (RIZZO), Callaway Local PMP HEC-RAS Simulation, Revision 0, RIZZO Calculation 12-4939 F-03, February 6, 2013.
14. RIZZO 2013c, Paul C. Rizzo Associates, Inc. (RIZZO), Site Specific PMP for Callaway Energy Center Unit 1, Revision 0, RIZZO Calculation 12-4939 F-1, January 11, 2013.

CEC Unit 1 20 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 23 of 58

15. RIZZO 2013d, Paul C. Rizzo Associates, Inc. (RIZZO), Statistical Analysis of Wind Speed, Revision 1, RIZZO Calculation 12-4939 F-04, February 4, 2013.
16. RIZZO 2014, Paul C. Rizzo Associates, Inc. (RIZZO), Callaway Energy Center Flood Hazard Reevaluation Report - NRC RAI Response, Revision 0, RIZZO Calculation 12-4939 F-20, February 24, 2014.
17. Stone & Webster, 2014, Callaway ISFSI Project DCP-02 Finish Grade and Stormwater Plan, Drawing No. 1484040010-CVL-008, Revision 1, January 20, 2014.
18. USACE, 2000, United States Army Corps of Engineers (USACE), Hydrologic Modeling System HEC-HMS, Technical Reference Manual, March 2000.
19. USACE, 2010a, United States Army Corps of Engineers (USACE), Hydrologic Modeling System HEC-HMS, Users Manual, Version 3.5, August 2010.
20. USACE, 2010b, United States Army Corps of Engineers (USACE), HEC-RAS River Analysis System, Users Manual, Version 4.1, January, 2010.
21. USGS, 2012. United Stated Geologic Survey. National map viewer, Website:

http://viewer.nationalmap.gov/viewer/, Date Accessed: November 2012.

CEC Unit 1 21 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 24 of 58 ATTACHMENT 1 TABLES CEC Unit 1 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 25 of 58 TABLE 1-1 INVENTORY OF FILES PROVIDED IN RESPONSE TO RAI-1 RAI Question File Name Description Contains a Triangular Irregular Network (TIN)

RAI 1 B topo1.zip and a Digital Elevation Map (DEM) File used to define the topography near Callaway Plant RAI 1 C archydro1.mdb ArcHydro run for Callaway Plant LIP Contains GIS files describing Subbasins and Flowpaths_Catchments.zip Flow Paths RAI 1 D Contains the HEC-HMS files representing HEC-HMS_1-3-13.zip Scenarios 1-5.

TABLE 3-1 DETERMINATION OF PMP RAINFALL DEPTHS Area Duration Ratio of 1-hour PMP Depth (in)

(mi2) 72 hr 10 HMR program printout 40.2 48 hr 10 HMR program printout 38.76 24 hr 10 HMR program printout 34.8 12 hr 10 HMR program printout 33.05 6 hr 10 1/0.662 27.64 (HMR No. 52 Report Figure 23) 1 hr 1 - 18.3 (HMR No. 52 Report Figure 24) 30 min 1 0.756 13.83 (HMR No. 52 Report Figure 38) 15 min 1 0.525 9.61 (HMR No. 52 Report Figure 37) 5 min 1 0.334 6.11 (HMR No. 52 Report Figure 36)

CEC Unit 1 1 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 26 of 58 TABLE 3-2 CUMULATIVE AND INCREMENTAL RAINFALL DEPTHS Time Time Cumulative Incremental PMP (inches (minutes) (hours) PMP (in) PMP (in) per minutes) 5 0.083 6.11 6.11 6.11 15 0.25 9.61 3.50 1.75 30 0.5 13.83 4.23 1.41 60 1 18.30 4.47 0.74 360 6 27.64 9.34 0.16 720 12 33.05 5.41 0.08 1440 24 34.80 1.75 0.01 2880 48 38.76 3.96 0.01 4320 72 40.20 1.44 0.01 TABLE 3-3 HEC-HMS PEAK SIMULATED RUNOFF FOR PMP WITH HIGHEST RAINFALL INTENSITIES FIRST Peak Peak Difference Peak Difference Peak Difference Runoff Runoff Between 6- Runoff Between 6- Runoff Between 6-Subbasin for 6-hr for 12-hr hr and 12 for 48-hr hr and 48 for 72-hr hr and 72 PMP PMP Hour Peak PMP Hour Peak PMP Hour Peak (cfs) (cfs) Runoff (cfs) (cfs) Runoff (cfs) (cfs) Runoff (cfs) 10 1,139 1,139 0 1,139 0 1,139 0 1091 39 39 0 39 0 39 0 1092 48 48 0 48 0 48 0 1093 49 49 0 49 0 49 0 1094 346 346 0 346 0 346 0 1095 100 100 0 100 0 100 0 1098 127 127 0 127 0 127 0 1099 158 158 0 158 0 158 0 1101 23 23 0 23 0 23 0 1102 82 82 0 82 0 82 0 1112 295 295 0 295 0 295 0 1113 287 287 0 287 0 287 0 1114 543 543 0 543 0 543 0 1130 59 59 0 59 0 59 0 1131 77 77 0 77 0 77 0 1132 21 21 0 21 0 21 0 1133 72 72 0 72 0 72 0 1134 37 37 0 37 0 37 0 1135 25 25 0 25 0 25 0 1136 52 52 0 52 0 52 0 CEC Unit 1 2 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 27 of 58 TABLE 3-3 HEC-HMS PEAK SIMULATED RUNOFF FOR PMP WITH HIGHEST RAINFALL INTENSITIES FIRST (CONTINUED)

Peak Peak Difference Peak Difference Peak Difference Runoff Runoff Between 6- Runoff Between 6- Runoff Between 6-Subbasin for 6-hr for 12-hr hr and 12 for 48-hr hr and 48 for 72-hr hr and 72 PMP PMP Hour Peak PMP Hour Peak PMP Hour Peak (cfs) (cfs) Runoff (cfs) (cfs) Runoff (cfs) (cfs) Runoff (cfs) 12 441 441 0 441 0 441 0 13 119 119 0 119 0 119 0 17 236 236 0 236 0 236 0 18 26 26 0 26 0 26 0 19 76 76 0 76 0 76 0 20 332 332 0 332 0 332 0 21 93 93 0 93 0 93 0 22 391 391 0 391 0 391 0 24 24 24 0 24 0 24 0 25 459 459 0 459 0 459 0 26 64 64 0 64 0 64 0 30 91 91 0 91 0 91 0 31 83 83 0 83 0 83 0 33 66 66 0 66 0 66 0 34 24 24 0 24 0 24 0 35 96 96 0 96 0 96 0 37 55 55 0 55 0 55 0 41 143 143 0 143 0 143 0 42 136 136 0 136 0 136 0 43 541 541 0 541 0 541 0 47 69 69 0 69 0 69 0 48 191 191 0 191 0 191 0 49 73 73 0 73 0 73 0 50 28 28 0 28 0 28 0 51 26 26 0 26 0 26 0 52 9 9 0 9 0 9 0 53 46 46 0 46 0 46 0 54 26 26 0 26 0 26 0 55 23 23 0 23 0 23 0 56 113 113 0 113 0 113 0 58 144 144 0 144 0 144 0 Note:

HEC-HMS simulation represents Scenario 5 in Calculation 12-4939 F-02 (RIZZO, 2013a) with a 1-minute time interval, a peaking coefficient, Cp = 0.4 and the VBS opening unblocked.

CEC Unit 1 3 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 28 of 58 TABLE 3-4 HEC-RAS SIMULATED PEAK STAGE USING A PMP WITH HIGHEST RAINFALL INTENSITIES OCCURRING FIRST OR CENTRAL TO THE EVENT Peak Water Level, Peak Water Level, Difference in Subbasin PMP maximum PMP maximum Simulated Peak Intensity early (ft) 1 Intensity Central (ft) 2 Stages (ft) 10 832.59 832.76 0.17 1091 840.32 840.56 0.24 1092 845.68 845.77 0.09 1093 840.32 840.55 0.23 1094 828.02 828.25 0.23 1095 840.35 840.58 0.23 1098 827.32 827.54 0.22 1099 840.29 840.53 0.24 1101 840.32 840.56 0.24 1102 840.31 840.55 0.24 1112 827.07 827.32 0.25 1113 832.37 832.69 0.32 1114 824.07 824.73 0.66 1130 840.35 840.57 0.22 1131 840.32 840.56 0.24 1132 838.54 838.68 0.14 1133 839.76 840.05 0.29 1134 833.90 834.23 0.33 1135 843.81 844.04 0.23 1136 835.55 835.90 0.35 12 838.36 838.82 0.46 13 836.6 836.98 0.38 17 838.35 838.81 0.46 18 838.36 838.82 0.46 19 838.70 838.83 0.13 20 840.83 840.94 0.11 21 832.96 833.10 0.14 22 839.7 839.99 0.29 24 838.94 839.06 0.12 25 842.67 843.01 0.34 26 837.35 837.67 0.32 30 840.32 840.56 0.24 31 839.22 839.31 0.09 33 840.50 840.57 0.07 CEC Unit 1 4 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 29 of 58 TABLE 3-4 HEC-RAS SIMULATED PEAK STAGE USING A PMP WITH HIGHEST RAINFALL INTENSITIES OCCURRING FIRST OR CENTRAL TO THE EVENT (CONTINUED)

Peak Water Level, Peak Water Level, Difference in Subbasin PMP maximum PMP maximum Simulated Peak Intensity early (ft) 1 Intensity Central (ft) 2 Stages (ft) 34 840.32 840.56 0.24 35 835.24 835.54 0.3 37 853.58 853.65 0.07 41 843.81 844.05 0.24 42 831.23 831.88 0.65 43 834.72 835.13 0.41 47 847.42 847.30 -0.12 48 837.91 838.01 0.1 49 838.73 839.03 0.3 50 839.40 839.52 0.12 51 840.05 840.07 0.02 52 838.74 839.04 0.3 53 833.90 834.23 0.33 54 840.35 840.58 0.23 55 840.35 840.57 0.22 56 837.34 837.67 0.33 58 837.35 837.68 0.33 Notes:

1 Peak runoff from HEC-HMS using a 1-minute time interval as used in Calculation 12-4839 F-02 (RIZZO, 2013a) for Scenario 5 with Cp = 0.4 and VBS openings unblocked.

2 Peak runoff from HEC-HMS using a 1-minute time interval for Scenario 5 with Cp = 0.4 and VBS openings unblocked.

CEC Unit 1 5 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 30 of 58 TABLE 4-1 HEC-HMS SIMULATED PEAK RUNOFF USING A 5-MINUTE AND A 1 MINUTE TIME INTERVAL 5-Minute Time Interval 1-Minute Time Interval Difference in Peak Storage Area Peak Runoff (cfs) Peak Runoff (cfs) Runoff (cfs) 10 1,018.83 1,139.06 120.23 1091 31.76 38.86 7.10 1092 39.59 48.45 8.86 1093 40.29 49.30 9.01 1094 355.09 345.95 -9.14 1095 81.49 99.71 18.22 1098 107.33 127.35 20.02 1099 128.92 157.75 28.83 1101 18.95 23.19 4.24 1102 67.43 82.30 14.87 1112 288.16 295.01 6.85 1113 260.23 286.63 26.40 1114 545.13 542.63 -2.50 1130 48.39 59.21 10.82 1131 68.07 77.26 9.19 1132 17.34 21.22 3.88 1133 72.39 72.37 -0.02 1134 30.26 37.03 6.77 1135 20.38 24.94 4.56 1136 45.56 52.03 6.47 12 443.81 441.35 -2.46 13 97.27 119.02 21.75 17 196.24 236.49 40.25 18 21.13 25.85 4.72 19 61.95 75.81 13.86 20 331.77 332.36 0.59 21 76.35 93.43 17.08 22 319.63 391.10 71.47 24 19.51 23.87 4.36 25 406.65 459.33 52.68 26 52.68 64.47 11.79 30 74.48 91.14 16.66 CEC Unit 1 6 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 31 of 58 TABLE 4-1 HEC-HMS SIMULATED PEAK RUNOFF USING A 5-MINUTE AND A 1 MINUTE TIME INTERVAL (CONTINUED) 5-Minute Time Interval 1-Minute Time Interval Difference in Peak Storage Area Peak Runoff (cfs) Peak Runoff (cfs) Runoff (cfs) 31 68.02 83.23 15.21 33 64.54 66.11 1.57 34 19.63 24.02 4.39 35 78.23 95.72 17.49 37 45.01 55.07 10.06 41 148.55 143.30 -5.25 42 135.26 135.75 0.49 43 544.18 541.15 -3.03 47 56.04 68.57 12.53 48 170.75 190.60 19.85 49 59.36 72.63 13.27 50 22.85 27.96 5.11 51 21.19 25.93 4.74 52 6.98 8.54 1.56 53 37.28 45.62 8.34 54 21.45 26.24 4.79 55 18.52 22.66 4.14 56 99.63 112.91 13.28 58 117.75 144.08 26.33 Note:

Simulations represent Scenario 5 of Calculation 12-4939 F-02 (RIZZO, 2013a) with the peaking coefficient, Cp, equal to 0.4 and the VBS openings unblocked.

CEC Unit 1 7 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 32 of 58 TABLE 4-2 HEC-RAS SIMULATED PEAK STAGE USING A 5-MINUTE AND A 1 MINUTE TIME INTERVAL IN HEC-HMS 5-Minute Time 1-Minute Time Difference in Peak Storage Area Interval Interval W.S. Elev (ft)

Peak W.S. Elev (ft) Peak W.S. Elev (ft) 10 832.54 832.59 0.05 1091 840.17 840.32 0.15 1092 845.60 845.68 0.08 1093 840.16 840.32 0.16 1094 828.02 828.02 0.00 1095 840.21 840.35 0.14 1098 827.19 827.32 0.13 1099 840.14 840.29 0.15 1101 840.17 840.32 0.15 1102 840.16 840.31 0.15 1112 826.99 827.07 0.08 1113 832.23 832.37 0.14 1114 823.95 824.07 0.12 1130 840.21 840.35 0.14 1131 840.16 840.32 0.16 1132 838.47 838.54 0.07 1133 839.66 839.76 0.10 1134 833.76 833.90 0.14 1135 843.81 843.81 0.00 1136 835.36 835.55 0.19 12 838.22 838.36 0.14 13 836.48 836.60 0.12 17 838.22 838.35 0.13 18 838.22 838.36 0.14 19 838.66 838.70 0.04 20 840.83 840.83 0.00 21 832.88 832.96 0.08 22 839.58 839.70 0.12 24 838.89 838.94 0.05 25 842.55 842.67 0.12 26 837.18 837.35 0.17 30 840.17 840.32 0.15 31 839.18 839.22 0.04 CEC Unit 1 8 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 33 of 58 TABLE 4-2 HEC-RAS SIMULATED PEAK STAGE USING A 5-MINUTE AND A 1 MINUTE TIME INTERVAL IN HEC-HMS (CONTINUED) 5-Minute Time 1-Minute Time Difference in Peak Storage Area Interval Interval W.S. Elev (ft)

Peak W.S. Elev (ft) Peak W.S. Elev (ft) 33 840.50 840.5 0.00 34 840.17 840.32 0.15 35 835.14 835.24 0.10 37 853.54 853.58 0.04 41 843.81 843.81 0.00 42 831.19 831.23 0.04 43 834.72 834.72 0.00 47 847.88 847.42 -0.46 48 837.90 837.91 0.01 49 838.61 838.73 0.12 50 839.34 839.4 0.06 51 840.03 840.05 0.02 52 838.70 838.74 0.04 53 833.75 833.9 0.15 54 840.21 840.35 0.14 55 840.21 840.35 0.14 56 837.17 837.34 0.17 58 837.19 837.35 0.16 Note:

Simulations represent Scenario 5 of Calculation 12-4939 F-03 (RIZZO, 2013b) with the peaking coefficient, CP, equal to 0.4 and the VBS openings unblocked.

TABLE 6-1 INVENTORY OF FILES PROVIDED IN RESPONSE TO RAI-6 RAI File Name Description Question Contains HEC-GeoRAS files used to create HEC-RAS RAI_6-GIS.zip model geometry including the VBS alignment

RAI 6

HECRAS_Callaway_2-Contains the HEC-RAS files representing Scenarios 1-6.

5-13.zip CEC Unit 1 9 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 34 of 58 TABLE 9-1 LOCATION AND NUMBER OF VBS OPENINGS Number of VBS Total Width of Total number of Openings in the Model SA Connections Various Openings VBS Openings after Merging Nearby (ft)

Openings 823 5 2 16.65 824 2 1 6.66 825 1 1 3.33 826 2 1 6.66 828 2 2 6.66 831 2 2 6.66 834 1 1 3.33 837 2 2 6.66 839 1 1 3.33 865 1 1 3.33 861 2 2 6.66 866 1 1 3.33 TABLE 10-1

SUMMARY

OF MODELING SCENARIO ASSUMPTIONS Transformation S.U.H. Status of VBS Scenario Methodology Parameters2 Openings3 1 None 1 n/a Blocked 2 None 1 n/a Unblocked 3 Snyder Unit Hydrograph Cp = 0.7, Ct =0.4 Unblocked 4 Snyder Unit Hydrograph Cp = 0.5, Ct =0.4 Unblocked 5 Snyder Unit Hydrograph Cp = 0.4, Ct =0.4 Unblocked Notes:

1 Rainfall converted directly to runoff.

2 See Equation 1, RAI Response 5.

3 Accounted for in SA connecting weir profile.

CEC Unit 1 10 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 35 of 58 TABLE 10-2 COMPARISON OF RUNOFF SIMULATED FOR AN SCS UNIT HYDROGRAPH AND A SNYDER UNIT HYDROGRAPH Peak Flow Peak Flow Peak Flow Lag Time Peak Flow Subbasin Snyder - Cp = Snyder - Cp = Snyder - Cp =

(min) SCS (cfs) 0.4 (cfs) 0.5 (cfs) 0.7 (cfs) 10 6.7 2239.4 1569.8 1805.1 2225.8 1091 6.0 73.9 52.4 60.3 73.3 1092 6.0 92.1 65.3 75.2 91.4 1093 6.0 93.7 66.4 76.5 93.0 1094 10.0 706.2 480.7 560.8 696.4 1095 6.0 189.6 134.4 154.8 188.1 1098 6.2 245.4 172.7 198.7 244.3 1099 6.0 299.9 212.6 244.8 297.5 1101 6.0 44.1 31.2 36.0 43.7 1102 6.0 156.7 111.0 127.8 155.5 1112 8.0 594.6 412.5 477.3 589.1 1113 7.0 563.2 394.9 456.1 558.2 1114 8.4 1095.6 757.9 874.8 1087.8 1130 6.0 112.6 79.8 91.9 111.7 1131 6.6 150.6 106.0 121.3 149.9 1132 6.0 40.3 28.6 32.9 40.0 1133 10.9 148.2 100.1 117.2 146.7 1134 6.0 70.4 49.9 57.5 69.8 1135 6.0 47.4 33.6 38.7 47.0 1136 6.6 101.5 71.3 81.6 101.0 12 14.1 893.0 590.4 695.3 878.9 13 6.0 226.3 160.4 184.7 224.5 17 6.1 452.8 319.3 368.1 450.2 18 6.0 49.1 34.8 40.1 48.8 19 6.0 144.1 102.2 117.7 143.0 20 8.3 671.5 464.1 536.2 667.0 21 6.0 177.6 125.9 145.0 176.2 22 6.0 743.5 527.1 607.0 737.6 24 6.0 45.4 32.2 37.1 45.0 25 6.7 897.3 631.3 723.2 890.8 26 6.0 122.6 86.9 100.1 121.6 30 6.0 173.3 122.8 141.5 171.9 31 6.0 158.2 112.2 129.2 157.0 33 7.8 133.8 92.6 107.3 132.6 34 6.0 45.7 32.4 37.3 45.3 35 6.0 182.0 129.0 148.6 180.5 CEC Unit 1 11 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 36 of 58 TABLE 10-2 COMPARISON OF RUNOFF SIMULATED FOR AN SCS UNIT HYDROGRAPH AND A SNYDER UNIT HYDROGRAPH (CONTINUED)

Peak Flow Peak Flow Peak Flow Lag Time Peak Flow Subbasin Snyder - Cp = Snyder - Cp = Snyder - Cp =

(min) SCS (cfs) 0.4 (cfs) 0.5 (cfs) 0.7 (cfs) 37 6.0 104.7 74.2 85.5 103.9 41 9.6 290.9 199.5 231.0 288.8 42 8.3 274.2 189.5 219.2 272.3 43 10.4 1103.5 750.3 872.8 1093.8 47 6.0 130.4 92.4 106.4 129.3 48 6.7 375.1 262.8 302.4 372.7 49 6.0 138.1 97.9 112.7 137.0 50 6.0 53.2 37.7 43.4 52.7 51 6.0 49.3 35.0 40.3 48.9 52 6.0 16.2 11.5 13.3 16.1 53 6.0 86.7 61.5 70.8 86.0 54 6.0 49.9 35.4 40.7 49.5 55 6.0 43.1 30.5 35.2 42.7 56 6.7 220.1 155.0 177.3 218.8 58 6.0 273.9 194.2 223.6 271.8 CEC Unit 1 12 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 37 of 58 TABLE 13-1

SUMMARY

OF SENSITIVITY RUNS (FLOOR ELEV. = 840.50)

Peak Maximum Maximum Sensitivity HEC-HMS Snyder Unit Rainfall HEC-RAS WSL in WSL in or Base Simulation Hydrograph, Intensity regime Subbasin 3 Subbasin 3 Run 1 Time Step Cp Value 2 Position 22 30 Base A 4 Front End 5 minutes Steady State 0.4 839.58 840.17 A-1 Front End 1 minute Steady State 0.4 839.70 840.32 A-2 Central 1 minute Steady State 0.4 839.99 840.56 A-3 Front End 1 minute Transient 0.4 839.47 839.88 A-4 Central 1 minute Transient 0.4 839.74 840.24 Base B 4 Front End 5 minutes Steady State 0.5 839.88 840.50 B-1 Central 1 minute Steady State 0.5 840.12 840.66 B-2 Central 1 minute Transient 0.5 839.78 840.34 B-3 5 Central 1 minute Transient 0.5 839.53 840.34 Base C 4 Front End 5 minutes Steady State 0.7 840.17 840.71 C-1 Central 1 minute Transient 0.7 839.85 840.40 Notes:

1 All sensitivity and base runs were for the unblocked VBS opening condition.

2 Refer to Equation 1, RAI Response 5.

3 Refer to Figure 2-2.

4 Base A, B, and C refer to model runs for the FHRR using Cp = 0.4, 0.5, and 0.7, respectively. A Cp = 0.7 gives peak runoff values that are comparable with the SCS unit hydrograph method for similar time steps and a runoff curve number of 99 (See Table 10-2).

5 This sensitivity run incorporates revised a new stage-storage curve for Subbasin 22 based on revised topography.

CEC Unit 1 13 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 38 of 58 TABLE 15-1 ADDITIONAL NRC REQUIREMENTS (NRC, 2013)

CEC Unit 1 14 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 39 of 58 ATTACHMENT 2 FIGURES CEC Unit 1 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 40 of 58 N

A 0 800 1,600 Feet D Subbasins FIGURE 2-1 DIGITAL IMAGE OF SUBBASINS AND AERIAL PHOTOGRAPH CEC Unit 1 1 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 41 of 58 FIGURE 2-2 SUBBASIN MAP WITH IDENTIFICATION NUMBERS CEC Unit 1 2 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 42 of 58 Local Intense Precipitation Hyetograph Precipitation Depth (inches/5min) 7 6

5 4

3 2

1 0

0 30 60 90 120 150 180 210 240 270 300 330 360 Time (min)

FIGURE 3-1 SIX-HOUR PMP HYETOGRAPH CEC Unit 1 3 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 43 of 58 100 90 80 70 72hr PMP 60 48hr PMP Runoff, cfs 12hr PMP 50 6hr PMP 40 30 20 10 0

0 500 1000 1500 2000 2500 3000 3500 4000 Time, minutes FIGURE 3-2 RUNOFF HYDROGRPAHS FOR SUBASIN #30 FOR THE 6-, 12-, 48-, AND 72-HOUR LIP STORM EVENTS CEC Unit 1 4 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 44 of 58 Local In ntense Precipita P ation Hyyetograp ph 7

Precipitation Depth (inches/5min) 6 5

4 3

2 1

0 0 300 600 900 9 1200 1500 1800 2100 2400 2700 30000 3300 3600 0 3900 4200 min)

Time (m FIGURE 33-3 CENT TRALLY-LOCATED P PMP HYET TOGRAH CEC Unit 1 5 R RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 45 of 58 FIGURE 8-1 HEC-RAS MODEL REACHES CEC Unit 1 6 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 46 of 58

  • VBSopenings Topography, ft

VBS High

  • 992.13 Low 783.709 FIGURE 9-1 (RAI 9A): LOCATION OF VBS OPENINGS CEC Unit 1 7 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 47 of 58 FIGURE 9-2 WEIR PROFILE FOR SA CONNECTION NO. 823 CEC Unit 1 8 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 48 of 58 FIGURE 9-3 WEIR PROFILE FOR SA CONNECTION NO. 824 CEC Unit 1 9 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 49 of 58 FIGURE 9-4 WEIR PROFILE FOR SA CONNECTION NO. 825 CEC Unit 1 10 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 50 of 58 FIGURE 9-5 WEIR PROFILE FOR SA CONNECTION NO. 826 CEC Unit 1 11 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 51 of 58 FIGURE 9-6 WEIR PROFILE FOR SA CONNECTION NO. 828 CEC Unit 1 12 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 52 of 58 FIGURE 9-7 WEIR PROFILE FOR SA CONNECTION NO. 831 CEC Unit 1 13 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 53 of 58

\

FIGURE 9-8 WEIR PROFILE FOR SA CONNECTION NO. 834 CEC Unit 1 14 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 54 of 58 FIGURE 9-9 WEIR PROFILE FOR SA CONNECTION NO. 837 CEC Unit 1 15 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 55 of 58 FIGURE 9-10 WEIR PROFILE FOR SA CONNECTION NO. 839 CEC Unit 1 16 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 56 of 58 FIGURE 9-11 WEIR PROFILE FOR SA CONNECTION NO. 861 CEC Unit 1 17 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 57 of 58 FIGURE 9-12 WEIR PROFILE FOR SA CONNECTION NO. 865 CEC Unit 1 18 RAI Docket No. 50-483, Rev. 0

Enclosure to ULNRC-06081 Page 58 of 58 APPENDIX A ELECTRONIC FILES CEC Unit 1 RAI Docket No. 50-483, Rev. 0

Retrieved from "https://kanterella.com/w/index.php?title=ML14059A233&oldid=2453713"