CNL-14-026, Transmittal of Supplemental Clarification Information for the Application to Revise Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis, TAC No. ME8200 (WBN-UFSAR-12-01)

Transmittal of Supplemental Clarification Information for the Application to Revise Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis, TAC No. ME8200 (WBN-UFSAR-12-01)

ML14062A045
Person / Time
Site:	Watts Bar
Issue date:	02/28/2014
From:	James Shea Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNL-14-026, TAC ME8200, WBN-UFSAR-12-01
Download: ML14062A045 (6)

Text

L44 140228 002 Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-14-026 February 28, 2014 10 CFR 50.4 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390

Subject:

Transmittal of Supplemental Clarification Information for the Application to Revise Watts Bar Nuclear Plant Unit 1, Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis, TAC No. ME8200 (WBN-UFSAR-12-01)

Reference:

Application to Revise Watts Bar Nuclear Plant Unit 1 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis, TAC No. ME8200 (WBN-UFSAR-12-01), dated July 19, 2012 (ADAMS Accession No. ML122360173)

By letter dated July 19, 2012 (Reference), Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) to adopt a revised hydrologic analysis for the Watts Bar Nuclear Plant (WBN), Unit 1, Updated Final Safety Analysis Report (UFSAR). The LAR included proposed UFSAR markups to the wind wave runup information associated with the WBN Intake Pumping Station (IPS). This letter transmits updated information based on a functionality evaluation performed as part of the WBN corrective action program. The functionality evaluation conservatively assumed two credible potential pathways that could transfer exterior flood waters to the interior of the IPS versus the one pathway contained in the UFSAR LAR. One potential pathway is through an opening on the western face of the IPS.

The second potential (new) pathway is by the hydraulic head generated from wind-wave runup on the southern face of the IPS.

The enclosure to this letter provides a markup of the proposed revision to UFSAR Section 2.4.3.6, Coincident Wind Wave Activity that was provided in the referenced letter.

The attached supplemental information clarifies the credible potential pathway(s) as represented in the UFSAR. There is no change to the conservative assumption of 741.7 ft for Tennessee River maximum water surface elevation including the effects of coincident wind wave setup and runup.

U.S. Nuclear Regulatory Commission Page 2 February 28, 2014 Consistent with the standards set forth in 10 CFR 50.92(c), TVA has determined that the additional information as provided in this letter does not affect the no significant hazards considerations associated with the proposed amendment previously provided in the Reference letter. TVA has further determined that the proposed amendment still qualifies for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51 .22(c)(9). Additionally, in accordance with 10 CFR 50.91(b)(1) , TVA is sending a copy of this letter and enclosure to the Tennessee Department of Environment and Conservation.

There are no regulatory commitments contained in this letter. Please address any questions regarding this matter to Edward D. Schrull at (423) 751-3850 .

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 27 day of February 2014.

ully,

~

. Shea V ce President, Nuclear Licensing

Enclosure:

Updated UFSAR Markups cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant, Unit 1 Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation

ENCLOSURE Watts Bar Nuclear Plant, Unit 1 Updated UFSAR Markups Please revise/replace UFSAR pages 2.4-29, 2.4-30, and 2.4-31 provided in Attachment 1 of the Reference indicated in this cover letter with the enclosed pages.

The changes to UFSAR Section 2.4.3.6 submitted in the Reference letter are:

1. Page 2.4-29

- Removes critical from the third (LAR proposed new text) paragraph in the section.

2. Page 2.4-30

- Removes critical from the last paragraph (LAR proposed new text) on the page.

3. Page 2.4-31

- Removes critical from the first paragraph (LAR proposed new text) on the page

- Revises the second paragraph (LAR proposed new text) to add the text, and the runup on the critical south face wall is 2.4 ft and reaches elevation 741.7 ft, The additional text clarifies that an assumed second internal flooding pathway exists through the south face wall of the IPS.

WBNP-The third candidate situation considered, failure of Douglas Dam during its PMF was shown in the original analysis to produce a flood crest at the plant site approximately 4.4 feet below the controlling PMF event. Dam safety modifications to Douglas Dam involved raising the height of the dam to prevent overtopping in the PMF and this eliminates failure of Douglas as a candidate situation.

The elevations from the potential controlling PMF events are compared in Table 2.4-7.

2.4.3.6 Coincident Wind Wave Activity Some wind waves are likely when the probable maximum flood crests at Watts Bar Nuclear Plant. The flood would be near its crest for a day beginning about 2 days after cessation of the probable maximum storm (Figure 2.4-572.4-25). The day of occurrence would be in the month of March or possibly the first week in April.

Figure 2.4-982.4-27 shows the main plant general grading plan. The Diesel Generator Buildings to the north and the pumping station to the eastsoutheast of the main building complex must be protected from flooding to assure plant safety. The Diesel Generator Buildings operating floors are at Elevationelevation 742.0 ft which are well above the maximum computed elevation including wind wave runup. The pumping station is shielded from direct wave action on all sides except to the south by either buildings, earth embankments, or the cooling towers. The maximum effective fetch of 1.3 miles occurs from both the southwest and northeast directions (Figure 2.4-67). This allows for the sheltering effect of several hills on the south riverbank which become islands at maximum flood levels.The electrical equipment room of the Intake Pumping Station will flood at elevation 728.0 ft. The Auxiliary and Control Buildings are allowed to flood.

All equipment required to maintain the plant safely during the flood is either designed to operate submerged, is located above the maximum flood level, or is otherwise protected. Those safety-related facilities, systems, and equipment located in the containment structure are protected from flooding by the Shield Building structure with those accesses and penetrations below the maximum flood level designed and constructed as watertight elements.

The maximum effective fetches for the structures are shown on Figure 2.4-28. Effective fetch accounts for the sheltering effect of several hills on the south riverbank which become islands at maximum flood levels. The maximum effective fetch in all cases, except for the west face of the Intake Pumping Station occurs from the northeast or east northeast direction. The maximum effective fetch for the west face of the Intake Pumping Station occurs from the west direction.

The Diesel Generator Building maximum effective fetch is 1.1 miles, and the critical west face of the Intake Pumping Station maximum effective fetch is 1.3 miles. The maximum effective fetch for the Auxiliary, Control, and Shield Buildings is 0.8 miles.

For the Watts Bar UFSARplant site, the two-year extreme wind for the season in which the PMF could occur was adopted to associate with the PMF crest as specified in Regulatory Guide 1.59.

The storm studies on which the PMF determination is based[4] show that the season of maximum rain depth is the month of March. Wind velocity was determined from a statistical analysis of maximum March winds observed at Chattanooga, Tennessee.

2.4-29

WBNP-Records of daily maximum average hourly winds for each direction are available at the Watts Bar site for the period May 23, 1973, through April 30, 1978. This record, however, is too short to use in a statistical analysis to determine the 2two-year extreme wind, as specified in ANSI Standard N170-1976, an appendix to Regulatory Guide 1.59. Further, the necessary 30-minute wind data are not available. To determine applicability of Chattanooga winds at the Watts Bar plant, a Kolmogorov-Smirnov (K-S) statistical test was applied to cumulative frequency distributions of daily maximum hourly winds for each direction at Chattanooga and Watts Bar. The winds compared were those recorded at Chattanooga during the period 1948-74 (the period when the necessary triple-register records were available for analysis) and the Watts Bar record. A concurrent record is not available; however, the K-S test showed that (except for the noncritical east direction) the record of daily maximum hourly velocities at Chattanooga were equal to or greater than that at Watts Bar. From this analysis it was concluded that use of the Chattanooga wind records to define seasonal maximum winds at the Watts Bar site is conservative.

The available data at Chattanooga included 30-minute and hourly winds by seasons and direction for the 27-year period 1948 through 1974. The March 30-minute wind data which was used directly in subsequent wind wave calculations were adjusted to 30 feet by the equation:

1/7 V30 = Vz (30 / Z) where:

V30 = wind speed at 30 feet Vz = wind speed at height Z above the ground The adjusted 30-minute wind data were analyzed for both the southwest and northeast directions.

The winds from the northeast are considerably less than those from the southwest; hence, the southwest direction is controlling. Figure 2.4-66 (historical information)2.4-29 shows the plot of the Chattanooga March maximum 30-minute winds from the critical southwest direction. The 2two-year, 30-minute wind speed is 21 miles per hour determined from a mathematical fit to the Gumbel distribution. This compares with 15 miles per hour determined for the March season from the noncontrolling northeast direction.

Wind wave calculations call for a 28-minute sustained wind. There is, however, no significant difference between a 2-year, 30-minute wind velocity and a 2-year, 28-minute wind velocity.

Thus, the 2-year, 30-minute, 21 mile per hour wind velocity was used to compute wind waves.

Computation of wind waves used the procedures of the Corps Of Engineers.[14] The critical direction for the PMF elevations is from the southwest with an effective fetch of 1.3 miles as shown in Figure 2.4-67. For a 28-minute sustained 21-mile-per-hour wind, 99.6% of the waves approaching the plant would be less than 2.0 feet high, crest to trough, resulting in maximum water elevation of 736.2.Wind speed was adjusted based on the effective fetch length for over water conditions. For the Diesel Generator Building, the adjusted wind speed is 23.8 miles per hour. The Intake Pumping Station maximum adjusted wind speed is 24.2 miles per hour for the critical west face. For the Auxiliary, Control, and Shield Buildings the adjusted wind speed is 23.4 miles per hour.

2.4-30

WBNP-For waves approaching the Diesel Generator Building, the maximum wave height (average height of the maximum 1 percent of waves) would be 1.7 ft high, crest to trough, and the significant wave height (average height of the maximum 33-1/3 percent of waves) would be 1.0 ft high, crest to trough. The corresponding wave period is 2.0 seconds. For the Intake Pumping Station, the maximum wave height would be 2.2 ft and the significant wave height would be 1.3 ft, with a corresponding wave period of 2.3 seconds. For the critical west face, the maximum wave height would be 1.9 ft high, and the significant wave height would be 1.1 ft high. The corresponding wave period is 2.1 seconds. The maximum wave height approaching the Auxiliary, Control, and Shield Buildings would be 1.5 ft high, and the significant wave height would be 0.9 ft high. The corresponding wave period is 1.9 seconds.

Computation of wind setup used the procedures of the Corps Of Engineers[14]. The maximum wind setup is 0.1 ft for all structures. Computation of runup used the procedures of the Corps Of Engineers[14]. At the Diesel Generator Building, corresponding runup on the earth embankment with a 4:1 slope would be 2.0is 2.3 feet, reaching Elevation 736.9 and reaches elevation 741.6 ft, including wind setup. The runup on the southcritical west face wall of the pumping station would be to Elevation 736.9Intake Pumping Station is 2.1 ft and reaches elevation 741.74 ft, and the runup on the critical south face wall is 2.4 ft and reaches elevation 741.7 ft, including wind setup. The configuration of the north face of the Intake Pumping Station, opposite of the intake channel, allows higher runup of 3.4 ft. The remaining south and east faces allows runup of 2.4 ft. However, there are no credible entry points to the structure on the north, south, or east faces. Therefore, the runup on these faces is discounted. The runup on the walls of the Auxiliary, Control, and Shield Buildings is 1.7 ft and reaches elevation 741.0 ft, including wind setup.

Runup does not exceed the design basis flood level for any of the structures. Additionally, runup at the Diesel Generator Building is maintained on the slopes approaching the structure and is below all access points to the building. Runup has no consequence at the Shield Building because all accesses and penetrations below runup are designed and constructed as watertight elements.

Wind wave setup is not a problem since the wind direction is opposite to the flow of the river.

The static effect of wind waves was accounted for by taking the static water pressure from the maximum height of the runup. The dynamic effects of wind waves were accounted for as follows:

The dynamic effect of nonbreaking waves on the walls of safety-related structures was investigated using the RainflowSainflou method[15]. Concrete and reinforcing stresses were found to be within allowable limits.

The dynamic effect of breaking waves on the walls of safety-related structures was investigated using a method developed by D. D. Gaillard and D. A. Molitar[16]. The concrete and reinforcing stresses were found to be less than the allowable stresses.

The dynamic effect of broken waves on the walls of safety-related structures was investigated using the method proposed by the U.S. Army Coastal Engineering Research Center.[15] Concrete and reinforcing stresses were found to be within allowable limits.

2.4-31