ML071160227

Staff Technical Evaluation Report, 06-03

ML071160227
Person / Time
Site:	Sequoyah
Issue date:	04/24/2007
From:	Hosung Ahn NRC/NRO/DSER/HEB
To:	Boyce T NRC/NRR/ADRO/DORL/LPLII-2
Hosung Ahn NRR/ECGB/DE 415-1398
Shared Package
ML071160179	List: ML071160190 ML071160227
References
Download: ML071160227 (13)

Text

Staff Technical Evaluation Report For Sequoyah Nuclear Plant (SQN) - Units 1 and 2 - Technical Specifications (TS) Change 06-03 By Hosung Ahn, NRC/NRO/DSER/RHEB (4/24/2007)

1. INTRODUCTION The ultimate heat sink (UHS) is designed to perform a principal safety function of dissipating residual and auxiliary heat after a reactor shutdown or after an accident. The UHS for Sequoyah Nuclear Plant (SQN) units 1 and 2 is the Chickamauga Reservoir in the Tennessee River. The current limiting conditions in the technical specification (TS) for operating the UHS system are that the UHS shall be operable with:

(1) A minimum water level at or above elevation 670 feet mean sea level (ft-msl) datum; (2) An average water temperature of essential raw cooling water (ERCW) supply header of less than or equal to 83 degree Fahrenheit (oF); and (3) When the water level is above 680 ft-msl, the average water temperature at the ERCW supply header may be less than or equal to 84.5 oF.

Recently, the applicant, Tennessee Valley Authority (TVA), proposed a change of the limiting conditions (Reference #1). The proposed change includes the required minimum UHS TS water elevation to 674 ft-msl and the maximum ERCW temperature limit to 87oF. The applicant stated that the proposed changes will minimize the likelihood of a required UHS shutdown as a result of adopting slightly higher river temperatures as a limiting condition during the summer months.

The applicant justified the proposed water level increase based on a hydraulic simulation of reservoir recession rate after a postulated dam failure (Reference #4). Through this application, the applicant reduced the breach width of 400-feet from the original 1000-feet in the Sequoyah Units 1 and 2 Ultimate Final Safety Analysis Report (1988). Because breach width is one of the important parameters in estimating the reservoir recession rate, the staff focused on a review of applicants postulated dam breach scenario and hydraulic analyses. The staff performed a confirmatory analysis to establish a conservative dam breach process and to estimate a corresponding reservoir recession rate in the Chickamauga Reservoir to ensure that sufficient reservoir levels are maintained after a dam failure.

2. TECHNICAL INFORMATION IN THE APPLICATION The applicant requested to change the minimum UHS TS water elevation in the Section 3.7.5.a from 670 ft-msl to 674 ft-msl and to increase the ERCW temperature requirement from 83 oF to 87 oF. The applicant stated that the proposed changes are supported by a combination of design basis re-analysis, bounding analysis, and sensitivity analysis of the ERCW system, the UHS, 1

Enclosure

and supporting systems. The applicant concluded based on the applicants hydraulic analysis that sufficient water surface elevations are maintained even after a postulated failure of the Chickamauga Dam.

They expect that there are no significant hazards associated with the proposed change. The applicant mentioned that no changes are made nor proposed to the capability or capacity of the UHS itself while the applicant continues to satisfy the regulatory requirements. The applicant requests approval of the change of the technical specifications to provide operating leeway and to avoid potential unnecessary UHS related unit shutdowns. The applicant described hydrologic aspects of the impacts of the change on the cooling system as below:

Long-term Containment Cooling In the Sequoyah Nuclear Plant, the heat loads rejected to the UHS under postulated accident conditions are bounding for a normal plant cool down. All of the stored and decay energy is released first to the containment and is ultimately rejected to the UHS for the worst-case accident scenario. Long-term cool down after a postulated accident scenario or a normal cool down with the residual heat removal system will involve heat transfer to the UHS. The long-term containment cool down may be affected by the postulated loss of downstream dam.

The applicant identified that the postulated dam failure will result in a reduction of total flow capacity of the ERCW system of about 7 percent (page E1-11 of Ref. #1). The flow balance test of the ERCW system performed during the design stage of the Sequoyah Power Plants identified that the portion of the ERCW system are balanced to a system configuration with ERCW pumps operated at river elevation of 670 ft-msl, while the remaining ERCW system is balanced to the long-term river level of 639 ft-msl. In general, the cooling system ensures containment integrity following ice meltdown well before river levels stabilized near 639 ft-msl.

The applicant stated that the rate of a long-term heat removal is decreased and the containment temperature is marginally increased, but the temperature increase will not affect the qualified post-accident degradation equivalency calculations and no other parameters are affected by the increased long-term containment temperature. The applicant also stated that the proposed increase in river temperature is considered to have a negligible effect on long-term containment cool down.

UHS Water Level Evaluation Based on the recent ERCW flow balance and flow modeling, the applicant concluded that the component flow balanced at a reservoir elevation of 670 ft-msl are capable of supplying cooling water flow to support both short-term and long-term cooling needs following a loss-of-coolant accident and loss of a downstream dam. Also, a reservoir level lower than 670 ft-msl can still supply the required minimum safety-related water to the plant without loss of net positive suction heads but with less operating margin.

The applicant proposed by the application a minimum UHS TS reservoir level of 674 ft-msl which is conservative at 87 oF to support essential heat loads following the accident events. To meet a short-term containment cooling, the UHS system needs to be maintained for at least 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of reservoir level above 670 ft-msl following a loss of a downstream dam. The applicant claimed 2

that the 4-hour-above-670-foot limiting condition is adequate for compliance with the UHS TS action statement, where the plant would be placed into Hot Standby (Mode 3) and in Cold Shutdown (Mode 5) with the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> because lower river levels can still supply the required minimum safety-related flow rates.

3. Regulatory Requirement and Criteria Section 182a of the Atomic Energy Act requires applicants for nuclear power plant operating licenses to include technical specifications as part of the license. The NRC requirements related to the content of the technical specifications are contained in 10 CFR 50.36. The water temperature and elevation requirements for the UHS are included in the technical specifications in accordance with 10 CFR 50.36 (c) (2), Limiting Conditions for Operation. In 10 CFR 50.59 (c) (1) (I), a licensee is required to submit a license amendment pursuant to 10 CFR 50.90 if a change to the technical specification is required.

10 CFR Part 50 General Design Criterion (GDC) 2, Design Bases for Protection Against Natural Phenomena, requires that structures, systems, and components (SSCs) important to safety shall be designed to withstand the effect of natural phenomena. The SSCs vital to the shutdown capability of the reactor are designed to withstand the maximum probable natural phenomenon expected at the site with a sufficient margin.

GDC 5, Sharing of Structures, Systems, and Components (SCCs), provides the assurance that sharing important to safety SSCs among nuclear power units is prohibited unless it can be shown that such sharing will not significantly impair their ability to perform their safety functions.

GDC 44, Cooling Water, requires a system to transfer heat from SSCs important to safety, to an UHS shall be provided and capable of performing its function under normal and accident conditions.

Regulatory Guide 1.27 provides an acceptable approach for satisfying these criteria. These criteria include recommendations for sufficient cooling ability, integrity during postulated events, function availability and redundancy, and control by the UHS TS. The applicant had evaluated the impacts of the proposed TS changes on the recommended criteria and made a conclusion that these recommended criteria continue to be met. In specific, the cooling capability of the UHS with the proposed increase in temperature has been evaluated and verified to satisfy the recommendations for heat removal considerations.

The applicant stated that the integrity and availability of the UHS system have not been affected by the proposed technical specification changes as the features are not being altered physically.

The applicant stated that the proposed changes to the limiting reservoir elevation levels have been evaluated and verified to continually meet the regulatory requirements for integrity and availability of the UHS. Therefore, the applicant claimed that operation of the Sequoyah Nuclear Plant Units 1 and 2 with the proposed TS changes will not result in a deviation from the recommended criteria in the Regulatory Guide 1.27.

3

4. Staff Technical Evaluation The UHS was designed to perform a principal safety function of dissipating residual and auxiliary heats after a reactor shutdown or after an accident. It was designed consistent with the following four regulatory positions in the Regulatory Guide 1.27:

(1) The UHS should be capable of providing sufficient cooling for at least 30 days.

(2) The UHS should be capable of withstanding the effects of the most severe natural phenomena or events, reasonably probable combinations of less severe phenomena or events, and a single failure of man-made structural features; (3) The UHS should consist of at least two sources of waters unless a single source is large enough, and (4) The technical specifications for the plant should include actions to be taken in the event that conditions threaten partial loss of the capability of the UHS.

The applicant stated that no physical change is made nor proposed to the capability or capacity of the UHS with the proposed TS change, and that the above regulatory positions will not be affected. However, the proposed TS changes affect the operations of the UHS system by affecting the future temperature and the level of the reservoir. The purpose of increasing the UHS temperature limit is to provide operating leeway in order to avoid potential unnecessary UHS related unit shutdowns.

The goal of the staff evaluation here is to determine whether the UHS system with the proposed TS changes can provide enough cooling water to the plant after a postulated downstream dam failure or not. This report includes a staffs evaluation of the applicants technical analyses as well as necessary confirmatory analyses on the postulated dam failure scenario and reservoir recession rate.

Hydrodynamic Modeling The Chickamauga Dam consists with a concrete dam for power generation and two earth dams on both sides of the river. The applicant assumed that the most-likely severe failure scenario of the Chickamauga Dam is a seismic-induced breach of the 3000-feet southern earth embankment. The applicant performed an analysis of the hydrodynamic effects of the postulated dam failure to ensure that sufficient water levels are maintained in the Chickamauga Reservoir to provide a source of enough cooling water to the plant.

The applicant simulated reservoir levels and outflows from the reservoir after the dam failure, and performed sensitivity tests with a range of parameters (e.g., breach width, breach slope, initial water level, upstream inflow) to investigate the margin on the estimates of the reservoir recession rates. The applicant used a computer model, the Simulated Open Channel Hydraulics 4

(SOCH), for simulating the hydrodynamics of the river system with a postulated dam breach scenario. In response to RAI #4, the applicant submitted to the staff a technical documentation for the model as well as the source code and a set of sample input and output.

The SOCH model can simulate a number of complex unsteady flow conditions that commonly occur in the Tennessee River and in cases of a dam breach. It solves unsteady flow equations by a finite difference scheme. The model was set up to simulate the flow in the Chickamauga Reservoir with a postulated dam breach scenario. This model was validated with measured data (Garrison et al., 1969; Ref. #7). Based on the review of the algorithm, documentation, and input and output of the model, the staff concluded that the model is acceptable for simulating Chickamauga Reservoir recessions after dam breach. Thus, the staff review here focused on the validity of model application.

Applicants Postulated Dam Failure Scenario Breach width is the most important parameter in determining the upstream reservoir recession caused by dam failure. The applicant stated that the breach width of 1000-feet used in the Sequoyah Power Plant Units 1 and 2 Ultimate Final Safety Analysis Report (1988) was overly conservative. They pointed out that current industry use and the U.S. Bureau of Reclamation Report are in agreement with assuming a maximum postulated dam breach width at 5 times the dam height. The southern (left) Chickamauga earthen embankment has the following dimensions:

- Length of southern earth dam: about 3000-feet

- Top elevation: 706 ft-msl

- Bottom elevation: 630 ft-msl

- Dam height at the potential breaching point: 76-feet.

Therefore, an estimated breach width is 380-feet. Accordingly, the applicant reduced its assumed breach width from 1000-feet to 400-feet. In addition, the applicant assumed the following conservative dam failure scenario for their hydrodynamic analysis:

• Chickamauga Dam fails during a non-flood event;

• The initial reservoir level at the time of failure is 681 ft-msl which is a median water level in the reservoir;

• An instantaneous dam failure with an assumed breach width occurs; and

• The breach has vertical side slopes extending to the bottom of the dam of 630 ft-msl.

With the above conservative scenario, the applicant simulated the reservoir drawdown after the postulated dam failure. The applicant performed a comprehensive sensitivity analysis by varying breach parameter values to investigate the uncertainties in the estimated recession rate. The result of the sensitivity analysis revealed that an initial water level of the reservoir is very sensitive to the recession rate.

Therefore, staff pointed out in RAI #5 that the applicant should use a conservative initial water level in simulating the recession rate. The applicant responded that conservatism for this submittal was built in by only counting the hours during the recession from elevation 674 ft-msl to 670 ft-msl and that a simulation was added by using an initial level of 675 ft-msl which is exceeded 99.9 percent of the time in actual operations (Attachment B of Ref. #3). The result of 5

the applicants re-simulation showed that the total elapsed time from 674 ft-msl to 670 ft-msl for a breach width of 400-feet is about 4.18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> which satisfies the 4-hour-above-670-foot limiting condition. However, the applicants breach width estimates range from 132-feet to 675-feet, thus the use of 400-feet breach width is not conservative. Therefore, the staff made a confirmatory analysis after determining a conservative initial reservoir level.

Initial Reservoir Level The annual operating guide curves for the Chickamauga Reservoir (in Ref. #2) show that the lowest normal operating zone during the wet period (mid-May to August) is 682.5 ft-msl while that of the dry period (December to next March) is 675 ft-msl. However, the applicant used in their application a median historical reservoir water level of 681 ft as an initial condition in their simulation of the reservoir recession rates.

To determine a reasonable initial reservoir level, staff requested through RAI #6 long-term historical data at the Chickamauga Reservoir. In response to RAI #6, the applicant provided water level and temperature time series. The applicant also confirmed that there was no UHS shutdown experienced during the operation of the Sequoyah Nuclear Plant, implying that there is a leeway in operating the UHS system from the current limiting conditions.

Figure 1 demonstrates that long-term annual minimum water levels have increased consistently due to the increasing of minimum upstream releases with the revised water control policies in the river for the time being. Reservoir levels have not dropped below 675 ft-msl since 2000 even during the dry season (Figure 2). Figure 3 shows that initial water levels greater than 675 ft-msl induces a milder recession rate than that for an initial level of 674 ft-msl. After the steep recession during the first two hours, the recession rates with the initial level above 675 ft-msl are about 1 foot per hour. In order words, the recession rates with initial water levels above 675 ft-msl automatically may meet the 4-hour-above-670-foot limiting condition.

Therefore, the staff used a minimum reservoir level of 675 ft-msl which is reasonable and conservative in estimating both breach width and recession rate. Using this initial water level, the staff estimated breach width and time as below.

Dam Breach Width vs. Recession Time In general, an earth dam breach starts at the toe of the dam, propagates to the top and develops to the bottom, and continues to the sides of dam as a widening process. Because of the widening process, the reservoir storage volume could be an important parameter in predicting the breach width especially for a large reservoir like the Chickamauga Reservoir. Many empirical equations are readily available to predict breach parameters using the dam height, the reservoir volume, or both (Ref. #5). Therefore, the staff recommended that the applicant considers the reservoir volume in predicting the breach width (RAI #1). In response, the applicant provided dam breach estimates using four different equations. The resulting breach widths range from 132-feet to 675-feet, from which the applicant assumed the breach width of 400-feet as an average of the estimated breach widths (Ref. #3).

6

The applicant noted in response to the RAI #2 that the small database of large-dam failures tends to indicate 500-feet as a possible upper bound for breach width (Page 15 of Ref. #5).

However, the staff investigation of the USBR database cited by the Ref. #5 revealed that 10 out of 410 listed dam breach events exceed a breach width of 500-feet. In the same database, the reported maximum breach width is 5800-feet. Therefore, the staff concluded that the breach width of 400-feet at the Chickamauga Dam is not conservative.

Instead, the staff evaluated breach widths and times using the same four equations as the applicant did but an initial reservoir level of 675 ft-msl (Table 1). The reason for estimating breach times is to investigate the margin in the reservoir recession rates. The table also includes elapsed times from 674 ft-msl to 670 ft-msl for the estimated breach widths equations. The elapsed times were computed based on a relationship between breach width and elapsed time given in Figure 4 which was constructed by the applicants reservoir recession rates simulated with the SOCH model.

Table 1. Staff estimates of breach width, breach time, and time elapsed from 674 ft-msl to 670 ft-msl, with an initial reservoir level of 675 ft-msl, initial reservoir storage volume of 392,000 ac-ft, and upstream inflow of 14,000 cfs.

Estimated Estimated Breach Time Elapsed Equation Breach Width Time 674-670 ft-msl (foot) (Hours) (Hours)

Von Thun and Gillette (1990) 297 0.20 4.37 U.S. Bureau of Reclamation 135 0.45 4.70 Federal Energy Reg. Commission 380 1.27 4.21 Froehlich (1995) 645 6.02 3.68 It should be noted that the staffs breach width estimates are nearly identical to those by the applicant. The first three equations in the table use the breach height as an independent variable while the Froehlich equation uses both the breach width and the storage volume as independent variables.

The result shows that the estimated breach widths and times vary noticeably from equation to equation. The breach time by the Froehlich equation is about 30 times longer than the minimum.

The elapsed times of the first three equations meet the 4-hour-above-670-foot limiting condition while that of the Froehlich equation violates the limiting condition. However, the breach time by the Froehlich equation is substantially longer than those of the other three equations, implying that the actual recession time from 674 ft-msl to 670 ft-msl by the Froehlich equation will be delayed substantially if the simulation of the reservoir drawdown considers the estimated breach time instead of assuming an instantaneous breaching. Therefore, the staff concluded that the UHS system with the proposed TS changes meets the 4-hour-above-670-foot limiting condition.

Long-term Recessions The applicant performed a comprehensive sensitivity analysis with the SOCH model to investigate a variability of recession rates with a range of potential breach parameters and varying upstream inflows. They found that the wider breach (W=1000 feet) results in recession times longer than that of shorter breach width (W=300 feet), but the initial (t<12 hours) and final 7

(t>60 hours) recessions of two different breach widths are nearly identical. The applicant confirmed based on the results of the sensitivity tests that the breach parameters are not sensitive to the recession rate especially at the beginning and the ending of the recession.

Using the SOCH model, the applicant developed a family of recession curves for different inflow rates from the Watts Bar Reservoir into the upstream of the Chickamauga Reservoir, from which they developed an outflow rating curve. This new model-generated rating curve would slightly lag the original 1988 prediction recession. The maximum delay is 2 to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, occurring between 24 and 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> after dam failure. The applicant stated that using model-generated curves would predict a slightly lower steady-state elevation after 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br />.

Simulation results by the applicant indicate that after 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> past dam failure, reservoir levels would be maintained in a steady-state mode and the levels are entirely dependent on the river geometry and the inflow from the upstream Watts Bar Dam. The Sequoyah Nuclear Plant Ultimate Final Safety Analysis Report stated that a minimum discharge into the Chickamauga Reservoir is 14,000 cfs. With this inflow volume, the steady-state reservoir level reaches about 641 ft-msl which is marginally higher than the requested long-term UHS level of 639 ft-msl.

Therefore, the UHS system with the proposed TS changes meets the requirement for long-term containment cooling.

Margin in the Estimated Recession Rate In RAI #2, the staff asked whether there are sufficient margins to ensure the provision of at least 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of river level above 670 ft-msl following a loss of the downstream dam. The applicant responded that their postulated breach condition (W=400-feet, initial level of 675 ft-msl) barely meets the 4-hour-above-670-feet limiting condition. The staffs confirmatory analysis shows that the limiting condition is satisfied. Even with the worst case dam breach scenario (by the Froehlich equation) where the breach width exceeds 400-feet, the corresponding breach time is long enough to meet the 4-hour-above-670-foot limiting condition. The margin in the reservoir recession rate is also added by the following two facts:

First, the submerged weir placed in the Chickamauga Reservoir was not considered in the applicants hydrodynamic modeling. The weir will delay the drawdown of the reservoir after dam failure. During the construction of the Sequoyah Nuclear Plant, an underwater rock dam was placed in the main channel below the cooling water intake and upstream of the discharge diffuser pipes to help maintain an available pool of cooler water during the summer time.

According to the plan drawings of the Sequoyah Nuclear Plant, the underwater dam has the following dimensions:

• A maximum height of 19-feet above the streambed

• A top elevation of 654 ft-msl, and

• Natural upstream/downstream side-slopes The dam was constructed of quarry rock placed by a bottom-dump barge. The applicant stated that both the current integrity of the structure and its durability under weir flow conditions are unknown. Although the applicant did not consider the impact of the underwater weir in their evaluation, the weir plays a role in reducing the rate of reservoir drawdown.

Second, the implementation of a series of Water Control Rules in the Tennessee River will increase continually the minimum reservoir levels. In other words, the new rule will reduce the 8

chance of the reservoir levels being below 675 ft-msl and will increase the margin in the estimated recession rate. The applicant stated that they adopted the latest Reservoir Operating Policy in 2004 in response to the changing demands on the reservoir systems in the Tennessee River (Ref. #2). Significant changes in the policy as they impact the Sequoyah Nuclear Plant included extending the summer water level on the Chickamauga Reservoir until November 1 and adopting a tiered minimum flow regime from June through Labor Day at the Chickamauga Dam.

This requires increasing the minimum average weekly flow requirements in early June to August, except in the driest of years when the flow requirement is only 25,000 cfs beginning August 1.

Winter operating levels were also increased on many of the upstream tributary projects, providing more carry-over reservoir storage which can eventually help increase the minimum water levels in the reservoir.

In summary, both the submerged weir and the current water management rule will contribute to delay the reservoir recession after dam failure and thus enhance the UHS operating margin.

Environmental Consideration The applicant stated that the proposed technical specification amendment would change a requirement with respect to installation or use of a facility component located within the restricted area or would change an inspection or surveillance requirement. However, the proposed change does not involve (i) Significant hazards consideration (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the staff does not consider any environmental assessment or impact statement in conjunction with the proposed TS change.

9

Figure 1. Annual minimum headwater levels (ft-msl) in the Chickamauga Dam (from the applicant, Ref. #3).

Figure 2. Seasonal headwater levels and water temperatures from 2000 to 20006 at the Chickamauga Reservoir (from the applicant, Ref #3).

10

Figure 3. Chickamauga Reservoir recession curves simulated by the SOCH model with different initial reservoir levels, using a breach width of 1000-ft, an initial reservoir level of 630 ft-msl, and a Watts Bar release of 14,000 cfs.

Figure 4. Chickamauga Dam breach width versus elapsed time of the reservoir recession level from 674 ft-msl to 670 ft-msl. This plot was re-constructed based on the applicants simulations of recession rates using the SOCH model with an initial reservation level of 675 ft-msl (Ref. #3).

11

5. Conclusion The staff performed a technical review of the hydrologic aspects of the applicants proposal to change the limiting condition in the Technical Specification Section 3.7.5 Ultimate Heat Sink (TVA-SQN-TS-06-03). The review was focused on the postulation of a dam breach scenario and its impacts on the UHS performance with the condition of the proposed TS changes.

As set forth above, the applicant provided sufficient information, through the application and in responses to staffs RAIs, pertaining to the identification and evaluation of the dam breach impacts on the UHS system at the site. The applicant concluded based on their own hydraulic analysis that the UHS system with the proposed TS changes can provide enough cooling water with a postulated seismic-oriented dam failure.

The staff conducted a confirmatory analysis using somewhat different assumptions and approaches. The staff concluded based on the confirmatory analysis that the UHS system with the proposed technical specification changes can still provide the necessary cooling water to the plant after dam failure. The estimated recession time of the Chickamauga Reservoir with the proposed TS change meets the provision of a 4-hour-above-670-foot limiting condition after dam failure. The recession estimate is conservative enough to provide sufficient margins to account for uncertainties.

12

6. References

1) TVA letter to NRC dated July 12, 2006, Sequoyah Nuclear power Plant (SQN) -

Units 1 and 2 - Technical Specification (TS) Change 06-03 Ultimate heat Sing (UHS) Temperature Increase and Elevation Change.

2) TVA Letter to NRC dated July 12, 2006, Sequoyah Nuclear power Plant (SQN) -

Units 1 and 2 - Technical Specification (TS) Change 06-03 Ultimate heat Sing (UHS) Temperature Increase and Elevation Change, Supplemental Information (TAC Nos. MD2621 and MD 2622).

3) TVA Letter to NRC dated January 26, 2007, Sequoyah Nuclear power Plant (SQN) -

Units 1 and 2 - Technical Specification (TS) Change 06-03 Ultimate heat Sing (UHS) Temperature Increase and Elevation Change, Response to Request for Additional Information (TAC Nos. MD2621 and MD 2622).

4) Updated Predictions of Chickamauga Reservoir Recession Resulting from Postulated Failure of the South Embankment at Chickamauga Dam, June 2004, Tennessee Valley Authority - River System Operation and Environment, River Operations and River Scheduling (attached as an appendix of Ref. #1).

5) Bureau of Reclamation, Downstream hazard classification guidelines ACER Tech.

Memorandum No. 11, U.S. Department of Interior, Bureau of Reclamation, Denver, CO, 1988.

6) Wahl, T. L., Uncertainty of Predictions of Embankment Dam Breach Parameters, ASCE Journal of Hydraulic Engineering, Vol. 130, No. 5, May 1, 2004.

7) Garrison, J.M., J.P. Granju, and J.T. Price, Unstead Simulation in Rivers and Reservoirs, Journal of the Hydraulics Division, ASCE, Vol. 95, #HY5, Proceeding Paper 6771, September 1969, pages 1559-1576.

8) Von Thun, J. Lawrence, and David R. Gillette, 1990, Guidance on Breach Parameters, unpublished internal documentation, U.S. Bureau of Reclamation, Denver, Colorado, March 13, 1990, 17 pages.

9) Froehlich, David C., 1995, Peak Outflow from Breached Embankment Dam, Journal of Water Resources and management, vol. 121, no. 1, p90-97.

13