Text

Application to Revise License Condition 2.C(4) PAD4TCD
	ML15365A595
Person / Time
Site:	Watts Bar
Issue date:	12/31/2015
From:	James Shea; Tennessee Valley Authority
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	CNL-15-239
	Download: ML15365A595 (31)
	v • d • e

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-15-239 December 31, 2015 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391

SUBJECT:

WATTS BAR NUCLEAR PLANT UNIT 2 - APPLICATION TO REVISE LICENSE CONDITION 2.C(4) PAD4TCD

Reference:

NRC Letter to TVA, Issuance of Facility Operation License No. NPF-96, Watts Bar Nuclear Plant Unit 2, dated October 22, 2015 [ML15251A587]

In accordance with the provisions of Title 10 of the Code of Federal Regulations (CFR)

§50.90, Application for amendment of license, construction permit, or early site permit, Tennessee Valley Authority (TVA) is submitting a request for an amendment to Facility Operating License No. NFP-96 for the Watts Bar Nuclear Plant (WBN) Unit 2. The proposed change would amend license condition 2.C(4) to permit the use of the Fuel Rod Performance and Design 4 Thermal Conductivity Degradation (PAD4TCD) computer program for the second cycle of plant operation. provides a description and technical evaluation of the proposed change, a regulatory evaluation, and a discussion of environmental considerations. Attachment 1 to Enclosure 1 provides the proposed revised license condition 2.C(4).

TVA requests approval of the proposed License Amendment by April 12, 2016, to permit core design for the next operating cycle for WBN Unit 2. The License Amendment will be implemented within 14 days of approval.

TVA has determined that there are no significant hazards considerations associated with the proposed change and that the change qualifies for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9).

U.S. Nuclear Regulatory Commission CNL-15-239 Page 2 December 31, 2015

The WBN Plant Operations Review Committee and the TVA Nuclear Safety Review Board have reviewed this proposed change and determined that operation of WBN in accordance with the proposed change will not endanger the health and safety of the public. Additionally, in accordance with 10 CFR 50.91(b)(1), TVA is sending a copy of this letter and the enclosures to the Tennessee Department of Environment and Conservation.

There are no new regulatory commitments in this submittal. Please address any questions regarding this request to Gordon Arent at 423-365-2004.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 31st day of December 2015.

Respectfully, Digitally signed by J. W. Shea J. W. Shea DN: cn=J. W. Shea, o=Tennessee Valley Authority, ou=Nuclear Licensing, email=jwshea@tva.gov, c=US Date: 2015.12.31 10:15:50 -05'00' J. W. Shea Vice President, Nuclear Licensing

Enclosure:

Evaluation of Proposed Change cc (Enclosure):

U.S. Nuclear Regulatory Commission, Region II Administrator NRC Senior Resident Inspector, Watts Bar Nuclear Plant NRC Project Manager, Watts Bar Nuclear Plant Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation

ENCLOSURE EVALUATION OF PROPOSED CHANGE

SUBJECT:

WATTS BAR NUCLEAR PLANT UNIT 2-APPLICATION TO REVISE LICENSE CONDITION 2.C(4) RELATED TO USE OF PAD4TCD 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION

3.0 TECHNICAL EVALUATION

4.0 REGULATORY EVALUATION

5.0 ENVIRONMENTAL CONSIDERATION

6.0 REFERENCES

ATTACHMENT 1 - Figures ATTACHMENT 2-WBN Unit 2 Proposed License Condition 2.C(4)

Note that the Figures contained in Attachment 1 are from Reference 6 of this Enclosure.

Reference 6 included an affidavit for the Proprietary portions, none of which are included herein, and also included the following Copyright Notice.

COPYRIGHT NOTICE The reports transmitted herewith each bear a Westinghouse copyright notice. The NRC is pennitted to make the number of copies of the infonnation contained in these reports which are necessary for its internal use in connection with generic and plant-specific reviews and approvals as well as the issuance, denial , amendment, transfer, renewal, modification, suspension, revocation, or violation of a license, permit, order, or regulation subject to the requirements of I 0 CFR 2.390 regarding restrictions on public disclosure to the extent such infonnation has been identified as proprietary by Westinghouse, copyright protection notwithstanding. With respect to the non-proprietary versions of these reports, the NRC is permitted to make the number of copies beyond those necessary for its internal use which are necessary in order to have one copy available for public viewing in the appropriate docket files in the public document room in Washington, DC and in local public document rooms as may be required by NRC regulations if the number of copies submitted is insufficient for this purpose. Copies made by the NRC must include the copyright notice in all instances and the proprietary notice ifthe original was identified as proprietary.

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ENCLOSURE EVALUATION OF PROPOSED CHANGE 1.0

SUMMARY

DESCRIPTION Pursuant to Title 10 of the Code of Federal Regulations (CFR) §50.90, Tennessee Valley Authority (TVA) is submitting a request for a change to Facility Operating License No. NPF-96 for Watts Bar Nuclear Plant (WBN) Unit 2. The proposed change will revise License Condition 2.C(4) to permit the use of the Fuel Rod Performance and Design 4 Thermal Conductivity Degradation (PAD4TCD) computer code for the second operating cycle.

The proposed change is required to allow start-up and operation of WBN Unit 2 after the first refueling outage. Approval of the license amendment request is required by April 12, 2016, to support Cycle 2 core design and the refueling outage scheduled for September 2016.

2.0 DETAILED DESCRIPTION Proposed Change Watts Bar Nuclear Plant, Unit 2 Operating License, License Condition 2.C(4) states that PAD4TCD may be used to establish core operating limits for Cycle 1 only. PAD4TCD may not be used to establish core operating limits for subsequent reload cycles. The proposed change would read as follows: PAD4TCD may be used to establish core operating limits for Cycles 1 and 2 only. PAD4TCD may not be used to establish core operating limits for subsequent reload cycles.

The change is required because there is not an approved alternative to PAD4TCD.

Without this change, WBN Unit 2 could not return to power operation after the first refueling outage for an undetermined period of time.

3.0 TECHNICAL EVALUATION

3.1 Thermal Conductivity Degradation Nuclear Regulatory Commission (NRC) Information Notice (IN) 2009-23 [Reference 1]

describes how fuel performance codes may over-predict fuel rod thermal conductivity at higher burn-ups based on new experimental data. Information Notice IN 2011-21

[Reference 2] notified licensees that one licensee had performed analyses to quantify the potential effects of thermal conductivity degradation (TCD) when using the Fuel Rod Performance and Design (PAD) code in conjunction with the Westinghouse Electric Corporation (Westinghouse) Automated Statistical Treatment of Uncertainty Method (ASTRUM) Evaluation Model [Reference 5] that resulted in a change in peak clad temperature (PCT) that was greater than 50o F. A change in PCT of greater than 50o F is considered a significant change in 10 CFR 50.46(a)(3)(i). The operating experience indicates that the realistic emergency core cooling evaluation models developed by Westinghouse, which rely on the PAD code for fuel thermal mechanical performance data, are susceptible to errors of similar magnitude to the plant-specific results described above.

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ENCLOSURE EVALUATION OF PROPOSED CHANGE 3.2 WBN Unit 2 and TCD Watts Bar Nuclear Plant Unit 2 submitted Final Safety Analysis Report (FSAR)

Amendment 97 on January 15, 2010 [Reference 3] providing an Emergency Core Cooling System (ECCS) evaluation methodology using ASTRUM for evaluating large break Loss-of-Coolant Accidents (LOCAs) to establish compliance with 10 CFR 50.46.

The NRC approved Westinghouse Best-Estimate Loss-of-Coolant Accident (BELOCA)

ASTRUM methodology [Reference 4] is based on the PAD 4.0 fuel performance code

[Reference 5]. PAD 4.0 was licensed without explicitly considering fuel TCD with increased burnup. Explicit modeling of TCD in the fuel performance code leads directly to increased fuel temperatures (pellet radial average temperature) as well as other fuel performance related effects beyond beginning-of-life. Because PAD provides input to the large-break LOCA analysis, this will tend to increase the stored energy at the beginning of the simulated large-break LOCA event. This in turn leads to an increase in PCT if there is no provision to credit off-setting effects.

The WBN Unit 2 PCT without explicit consideration of TCD was calculated to be 1552oF, the Maximum Local Oxidation (MLO) was calculated to be 1.04% and the Core-Wide Oxidation (CWO) was calculated to be 0.0% with the licensed Westinghouse BELOCA methodology (Amendment 97 FSAR Table 15.4-18b)[Reference 3]. The analysis demonstrated margin to the regulatory limits of:

PCT 2200°F MLO 17%

CWO 1%

WBN Unit 2 had a large margin to the 10 CFR 50.46 PCT limit of 2200oF and other criteria; thus, by inspection, TCD would not result in WBN Unit 2 evaluation model results approaching the regulatory limits. The NRC reviewed the WBN Unit 2 fuel design in NUREG-0847, Supplemental Safety Evaluation Report (SSER) 23, Related to the Operation of Watts Bar Nuclear Unit 2 that discussed TCD. The SSER concluded that the NRC staff needed additional information from TVA to demonstrate that PAD 4.0 can conservatively calculate the fuel temperature and other impacted variables, such as stored energy, given the lack of a fuel thermal conductivity degradation model. This issue became SSER Open Item 61.

On TVAs request, Westinghouse addressed the TCD issue and SSER Open Item 61 for WBN Unit 2 for issuance of the operating license by performing a series of analyses that explicitly addressed TCD. These analyses were described in detail in the, August 6, 2013, TVA submittal to the NRC [Reference 6]. Section 15.4, Condition IV Limiting Events, of the WBN Unit 2 FSAR was revised to incorporate the information provided in Reference 6. Amendment 110 of the WBN Unit 2 FSAR that incorporated the results of the Westinghouse TCD evaluation and was submitted to the NRC on August 14, 2013 [Reference 7].

Fuel performance data that accounts for fuel TCD was used as input to the updated WBN Unit 2 BELOCA analysis discussed herein and summarizes the information provided in the non-proprietary Enclosure 3 of Reference 6. The new PAD fuel performance data was generated with an updated PAD model that includes explicit E1-3

ENCLOSURE EVALUATION OF PROPOSED CHANGE modeling of TCD. Therefore, the BELOCA analysis was updated to consider the fuel TCD effects cited in NRC Information Notice 2011-21 [Reference 2].

3.2.1 Input Parameters, Assumptions and Acceptance Criteria:

No updates to design inputs and plant operating ranges to gain large-break LOCA margin were utilized in this updated analysis to show compliance with the 10 CFR 50.46 acceptance criteria while maintaining a margin of safety to the prescribed limits. The acceptance criteria and results of the updated BELOCA analysis considering TCD effects are discussed in Section 4.0. The base input assumptions are provided in Tables 15.4-14, 15, 16, 19, and 23, and Figure 15.456 of the FSAR [References 3 and 7], with the limited exception of core peaking factors as noted below.

In order to mitigate the impact of the increasing effect of pellet TCD with burnup, the large-break LOCA evaluation of second Cycle fuel utilized reduced peaking factors from those shown in FSAR Table 15.4-19 [References 6 and 7]. The reduced peaking factors are limited to the following application:

Burndown credit for the hot rod and hot assembly is taken for higher burnup fuel in the second and third cycle of operation. The WBN Unit 2 peaking factor values utilized in this updated analysis are shown in Table 1. Note that the beginning-to-middle of life values are retained at their original [Reference 6] values.

3.2.2 Description on Analysis and Evaluations The purpose of the updated analysis was to consider fuel performance inputs that explicitly model TCD to show compliance with the 10 CFR 50.46 acceptance criteria while maintaining a margin of safety to the prescribed limits. The updated BELOCA analysis considering the effects of TCD has been provided in FSAR Section 15.4.1.1 [References 6 and 7].

The updated analysis also credited peaking factor burndown to evaluate higher burnup fuel in its second and third cycle of irradiation. Evaluation of fuel in its second and third cycle of irradiation is beyond the first cycle considered in the approved ASTRUM Evaluation Model (EM), but was considered in the updated analysis when explicitly modeling TCD to demonstrate that conformance to the acceptance criteria is met for the second/third cycle fuel. Physically, accounting for TCD leads to an increase in fuel temperature as the fuel is burned, while accounting for peaking factor burndown leads to a reduction in fuel temperature as the fuel is burned. The compensating nature of these phenomena is considered in the updated analysis in order to appropriately capture the effect of TCD in the updated WBN Unit 2 BELOCA analysis.

The analysis was updated by re-running all 124 cases from the original ASTRUM analysis (FSAR Section 15.4.1.1 [References 3 and 6]) in both the first cycle and the second cycle. Therefore, the same non-parametric order statistics singular statement of a 95th percentile at the 95-percent confidence joint probability for PCT, MLO and CWO of an ASTRUM re-analysis is ensured for the WBN Unit 2 updated analysis.

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ENCLOSURE EVALUATION OF PROPOSED CHANGE The WBN Unit 2 PCT-limiting transient is a double-ended cold leg guillotine break when considering fuel TCD and the peaking factor burndown provided in Table 1. Table 2 summarizes the results of the updated BELOCA analysis considering the effects of TCD.

Figures 1 through 15 provide a variety of transient responses for the limiting HOTSPOT PCT transient [second Cycle, run073, non-integral fuel burnable absorber (IFBA)] and are generally self explanatory in nature. Figures 2-15 are from the associated WCOBRA/TRAC response. Figure 1 multi-plots the following: HOTSPOT Clad Temperature at the limiting PCT elevation (observe the peak at 1766°F)

WCOBRA/TRAC PCT. This PCT represents the highest clad temperature at any elevation.

These Figures are equivalent to FSAR Amendment 110 and later amendments Figures 15.4-41 through 15.4-55 [References 6 and 7].

The updated FSAR Amendment 110 TCD analysis compared to the FSAR Amendment 97 analysis as well as the IFBA and non-IFBA PCT results for both WBN Unit 2 cycle 1 and cycle 2 are given in Table 3.

3.2.3 10 CFR 50.46 Requirements It must be demonstrated that there is a high level of probability that the limits set forth in 10 CFR 50.46 are met. The demonstration that these limits are met is as follows:

(b)(1) The limiting PCT corresponds to a bounding estimate of the 95th percentile PCT at the 95-percent confidence level. Since the resulting PCT for the limiting case is 1766°F, the updated analysis confirms that 10 CFR 50.46 acceptance criterion (b)(1),

i.e., Peak Clad Temperature less than 2200°F, is demonstrated. The result is shown in Table 2.

(b)(2) The maximum local cladding oxidation corresponds to a bounding estimate of the 95th percentile MLO at the 95-percent confidence level. Since the resulting transient MLO for the limiting case is 1.99%, the updated analysis confirms that 10 CFR 50.46 acceptance criterion (b)(2), i.e., Maximum Local Oxidation of the cladding less than 17percent, is demonstrated. The result is shown in Table 2.

(b)(3) The limiting core-wide oxidation corresponds to a bounding estimate of the 95th percentile CWO at the 95-percent confidence level. The limiting Hot Assembly Rod (HAR) total power census includes many lower power assemblies. The CWO value can be conservatively chosen as that calculated for the limiting HAR, 0.08%. A detailed CWO calculation is not needed due to the margin in the conservatively obtained result.

Therefore, the updated analysis confirms that 10 CFR 50.46 acceptance criterion (b)(3),

i.e., Core-Wide Oxidation less than 1 percent, is demonstrated. The result is shown in Table 2.

(b)(4) 10 CFR 50.46 acceptance criterion (b)(4) requires that the calculated changes in core geometry are such that the core remains amenable to cooling. This criterion has historically been satisfied by adherence to criteria (b)(1) and (b)(2), and by assuring that fuel deformation due to combined LOCA and seismic loads is specifically addressed. It has been demonstrated that the PCT and maximum cladding oxidation limits remain in effect for BE LOCA applications. The approved methodology [Reference 4] specifies E1-5

ENCLOSURE EVALUATION OF PROPOSED CHANGE that effects of LOCA and seismic loads on core geometry do not need to be considered unless grid crushing extends beyond the 44 assemblies on the core periphery. This situation is not calculated to occur for WBN Unit 2 per FSAR 15.4.1.1.6 [Reference 3]

prior to TCD considerations, and this conclusion is not affected by the modeling of fuel TCD. Therefore, acceptance criterion (b)(4) remains satisfied.

(b)(5) 10 CFR 50.46 acceptance criterion (b)(5) requires that long-term core cooling be provided following the successful initial operation of the ECCS. Long-term cooling is dependent on the demonstration of continued delivery of cooling water to the core. The actions, automatic or manual, that are currently in place at these plants to maintain long-term cooling remain unchanged due to the modeling of fuel TCD, as follows:

The primary impact of TCD in the fuel potentially important to Long Term Cooling (LTC) is an increase in initial fuel pellet temperature. This in turn leads to a higher amount of stored energy at the initiation of the LOCA event. Initial stored energy is not important to LTC evaluations as these evaluations only consider decay heat removal during the sump recirculation phase of ECCS operation. The increased stored energy in the fuel due to higher fuel pellet temperature is a short-term effect that does not persist into the LTC phase of ECCS performance evaluations; therefore, the heat source remains limited to decay heat for LTC evaluations. Consequential impacts of higher fuel pellet temperature such as higher fuel rod internal pressure also have no impact on LTC evaluations as fuel cladding temperatures are maintained well below the threshold for cladding rupture such that cladding burst and blockage does not occur during LTC. Based on the above, it is shown that no additional LTC analysis is required to assess TCD for WBN Unit 2.

3.2.4 Results Summary An update to the analysis was performed considering fuel performance inputs that explicitly model TCD and the inherently associated peaking factors burndown credit for second cycle analysis only (Table 1), including IFBA fuel product to show compliance with the current 10 CFR 50.46 acceptance criteria while maintaining a margin of safety to the prescribed limits. For both the first cycle study and the second cycle study, the ASTRUM EM [Reference 4] required 124 runs were executed using the same random seed. In this way, the integrity of the TCD analysis is maintained and the difference between the new 95/95 estimate herein and the previous pre-TCD estimate FSAR

[References 3 and 7] Section 15.4.1.1 is the singular effect of TCD. Based on the results from the updated BELOCA analysis (see Table 2), it is concluded that WBN Unit 2 continues to maintain a margin of safety to the limits prescribed by 10 CFR 50.46.

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ENCLOSURE EVALUATION OF PROPOSED CHANGE 3.2.5 Additional Information:

For additional information on treatment of burnup and fuel in the second and the third cycle of irradiation, please refer to Section 11-2-2 of the ASTRUM Topical [Reference 4]

for more information.

Table 1 Watts Bar Unit 2 Best-Estimate Large-Break LOCA Updated Analysis Considering the Effects of Thermal Conductivity Degradation - Summary of Peaking Factor Burndown Utilized Hot Rod Burnup FdH FQ Transient FQ Steady-State (MWD/MTU) (with uncertainties) (with uncertainties) (without uncertainties) 0 1.65 (1) 2.5 (1) 2.00 (1) 30000 1.65 (1) 2.5 (1) 2.00 (1) 60000 1.525 2.25 1.800 62000 1.525 2.25 1.8000 Note 1 Same Value as FSAR Table 15.419 (Note FQ SS is titled SS depletion therein)

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ENCLOSURE EVALUATION OF PROPOSED CHANGE Table 2 Watts Bar Unit 2 Best-Estimate Large-Break LOCA Updated Analysis Considering the Effects of Thermal Conductivity Degradation - Comparison of Results to Current 10 CFR 50.46(b) Acceptance Criteria Result Acceptance Criterion o o 95/95 Peak Clad Temperature 1766 F <2200 F 95/95 Transient Maximum Local Oxidation 1.99% <17%

95/95 Core Wide Oxidation 0.08% <1%

Coolable Geometry Criterion Met Remains Coolable Long-Term Cooling Maintained - See Long Term Cooling TCD assessment in Section 3.2.3 b(5)

Table 3 Peak Clad Temperature Rank Run # Non-IFBA Non-IFBS Run # IFBA IFBA HOTSPOT Hot Rod HOTSPOT Hot Rod o o PCT ( F) Burnup PCT ( F) Burnup (MWD/MTU) (MWD/MTU)

FSAR Amendment 97 No TCD 1 18 1552 FSAR Amendment 110 - Explicit Treatment of TCD st 1 Cycle 1 100 1580 14940 100 1579 14940 nd 2 Cycle 1 73 1766 46909 73 1763 46909 2 100 1646 46759 104 1646 52673 3 104 1630 52673 100 1645 46759 4 42 1609 57001 118 1637 37365 5 118 1596 37365 42 1607 57001 Tables 1, 2, and 3 are Westinghouse Non-Proprietary Class 3 and are taken from NP-Attachment to WBT-D-4396 E1-8

ENCLOSURE EVALUATION OF PROPOSED CHANGE 3.2.6 Conclusions On May 22, 2014, TVA provided detailed information on the WBN Unit 2 fuel as well as specific computer code input data the NRC requested [Reference 8] to allow the staff to perform a confirmatory calculation using the FRAPCON-3.4 fuel performance computer.

The results of the NRC review of the analyses described above and the confirmatory analyses performed by the NRC were documented in Watts Bar Nuclear Unit 2 SSER 27. The NRC Staffs review concluded:

Based upon (1) comparison of the PAD4TCD model predictions against Halden high burnup fuel temperature measurements and (2) good agreement of the temperature dependent and exposure dependent coefficients between PAD4TCD and FRAPCON3.4 thermal conductivity models, the NRC staff has previously found the PAD4TCD thermal conductivity model acceptable during the review of the Turkey Point Units 3 and 4 Extended Power Uprate (EPU) (ADAMS Accession No. ML11293A365).

Using the information supplied in the May 22, 2014, letter, the NRC staff performed a confirmatory analysis similar to that performed in the Turkey Point Units 3 and 4 EPU, which demonstrated that there is good agreement between PAD4TCD and FRAPCON3.5 for the fuel design planned for WBN Unit 2. Based upon the previous review of PAD4TCD done for the Turkey Point 3 and 4 EPU and the confirmatory analysis performed by the NRC staff on the Watts BAr fuel, the NRC staff finds that this open item has been satisfied and considers Open Item 61 to be closed.

The TVA re-analysis was performed considering fuel performance inputs that explicitly model TCD and the inherently associated peaking factors burndown credit for the second cycle. The results of this analysis remain consistent with the conclusions reached by the NRC Staff in SSER 27.

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements and Criteria The proposed change License Condition 2.C(4) does not reduce or change the Watts Bar Nuclear Plant (WBN) Unit 2s level of compliance with the following applicable regulations and requirements:

10 CFR 50.46, Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors, requires that emergency core cooling systems (ECCS) be designed such that analyses show that acceptance criteria such as peak clad temperature, cladding oxidation, hydrogen generation, maintenance of a coolable core geometry, and long-term cooling are met for a range of loss-of-coolant accidents (LOCAs), including the most severe LOCA.

10 CFR 50, Appendix K, ECCS Evaluation Models, provides both high level criteria that must be considered in an ECCS Evaluation Model, or may be used specifically in an Appendix K ECCS Evaluation Model for determining that 10 CFR 50.46 acceptance criteria are met. Appendix K requires, among other considerations, that the initial stored energy in the fuel must be appropriately accounted for.

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ENCLOSURE EVALUATION OF PROPOSED CHANGE 4.2 Precedent The NRC issued a License Amendment to Florida Power and Light Company on June 15, 2012 permitting the use of PAD 4.0 TCD for Turkey Point Units 3 and 4 subject to certain conditions until the NRC approves a revised generic version of PAD that accounts for Thermal Conductivity Degradation (TCD). (ML11293A365) 4.3 Significant Hazards Consideration The Tennessee Valley Authority (TVA) proposes to amend the Unit 2 Facility Operating License No. NFP-96 for the Watts Bar Nuclear Plant (WBN) by changing License Condition 2.C(4) to allow second cycle plant operation using the Fuel Rod Performance and Design 4 Thermal Conductivity Degradation (PAD4TCD) computer code.

TVA has concluded that the change License Condition 2.C(4) does not involve a significant hazards consideration. TVAs conclusion is based on its evaluation in accordance with 10 CFR 50.91(a)(1) of the three standards set forth in 10 CFR 50.92, Issuance of amendment, as discussed below:

1. Does the proposed amendment involve a significant increase in the probability or consequence of an accident previously evaluated?

Response: No.

The Emergency Core Cooling System (ECCS) response to a large break LossofCoolant Accident (LOCA) as described in the WBN Unit 2 Final Safety Analysis Report (FSAR) Chapter 15 incorporated an explicit evaluation of the effects of Thermal Conductivity Degradation (TCD). The FSAR evaluation considered fuel burn-up values that represent multi-cycle cores where the effects of TCD would be more evident. These analyses showed that the calculated peak clad temperature was 1776oF which provides a large margin to the regulatory limit specified in 10 CFR 50.46 of 2200oF.

The change to License Condition 2.C(4) does not change the safety analysis or any plant feature or design. Thus it is concluded that a significant increase in the consequences of an accident previously evaluated will not occur as a result of the proposed change.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Does the proposed amendment create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No.

The proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated. The proposed change to license condition 2.C(4) does not change or modify the plant design, introduce any new modes E1-10

ENCLOSURE EVALUATION OF PROPOSED CHANGE of plant operation, change or modify the design of the ECCS, or change or modify the accident analyses presented in the WBN Unit 2 FSAR.

Therefore, the proposed change does not create the possibility of a new or different kind of accident from any previously evaluated.

3. Does the proposed amendment involve a significant reduction in a margin of safety?

Response: No.

The safety analyses for WBN Unit 2 described in the FSAR have explicitly accounted for the potential effects of TCD where applicable. The results of these analyses have established that WBN Unit 2 can operate safely and in the unlikely event that a design basis event occurs, there are large margins to the regulatory limits explicitly accounting for TCD. This proposed change to License Condition 2.C(4) does not change these analyses or conclusions. Thus, the proposed change does not result in a significant reduction in the margin of safety.

4.4 Conclusions TVA evaluated the proposed revision to WBN Unit 2 License Condition 2.C(4) to allow the continued use of the PAD4TCD code for the second operating cycle. The evaluation determined that the ECCS evaluation analyses performed to show compliance with 10 CFR 50.46 explicitly accounted for the effect of TCD for the second operating cycle.

The WBN analyses accounting for TCD have large amounts of margin compared to the regulatory limits defined in 10 CFR 50.46. Confirmatory analyses performed by the Nuclear Regulatory Commission and comparisons of PAD4TCD results to Halden test measurements establish that the PAD4TCD thermal conductivity model is acceptable.

The evaluation establishes that the proposed change does not constitute a substantial safety hazard. The proposed change prevents an otherwise unnecessary shutdown of the WBN Unit 2.

5.0 ENVIRONMENTAL CONSIDERATION

The proposed amendment revises WBN Unit 2 Operating License, License Condition 2.C(4). The proposed amendment meets the eligibility criterion for a categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

6.0 REFERENCES

1. NRC Information Notice 2009-23, Nuclear Fuel Thermal Conductivity Degradation, dated October 8, 2009 [ADAMS Accession Number ML091550527]

2. NRC Information Notice 2011-21, Realistic Emergency Core Cooling System Evaluation Model Effects Resulting from Nuclear Fuel Thermal Conductivity Degradation, December 13, 2011. [ADAMS Accession Number ML113430785]

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ENCLOSURE EVALUATION OF PROPOSED CHANGE

3. TVA Letter to NRC, Watts Bar Nuclear Plant, Unit 2, Final Safety Analysis Report, Amendment 97, dated January 15, 2010 [ADAMS Accession No. ML100191421]

4. Westinghouse Report WCAP-16009-P-A, Realistic Large-Break LOCA Evaluation Methodology Using the Automated Statistical Treatment Of Uncertainty Method (ASTRUM), January 2005. (Westinghouse Proprietary Class 2)

5. Westinghouse Report WCAP-15063-P-A, Revision 1 with Errata, Westinghouse Improved Performance Analysis and Design Model (PAD 4.0), July 2000.

(Westinghouse Proprietary Class 2)

6. TVA Letter to NRC, Watts Bar Nuclear Plant Unit 2 - Fuel Thermal Conductivity Degradation, Response to Supplemental Safety Evaluation Report Open Item 61, dated August 6, 2013 [ADAMs Accession No. ML13225A024] including WBT-D-1373, WEC to TVA ASTRUM FSAR Package.

7. TVA Letter to NRC, Watts Bar Nuclear Plant (WBN) - Unit 2 - Final Safety Analysis Report (FSAR), Amendment 110, dated August 14, 2013 [ADAMS Accession No. ML13254A310].

8. TVA Letter to NRC, Watts Bar Nuclear Plant Unit 2 - Fuel Thermal Conductivity Degradation, Response to Supplemental Safety Evaluation Report Open Item 61, dated May 22, 2014 [ADAMS Accession No. ML14143A252]

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ENCLOSURE EVALUATION OF PROPOSED CHANGE ATTACHMENT 1 Figures

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 12 of 26 Figure 1 Watts Bar Unit 2 Limiting PCT Case (2nd Cycle, Run073, non-IFBA) HOTSPOT Clad Temperature at the Limiting Elevation and WC/T PCT 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 13 of 26 Time After Break (S)

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 14 of 26 Figure 3 Watts Bar Unit 2 Limiting PCT Case Pressurizer Pressure 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 15 of 26 Figure 4 Watts Bar Unit 2 Limiting PCT Case Broken and Intact Loop Pump Void Fractions 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 16 of 26 Figure 5 Watts Bar Unit 2 Limiting PCT Case Core Vapor Flow at the Top of the Core for a Core Average Channel 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 17 of 26 Figure 6 Watts Bar Unit 2 Limiting PCT Case Core Vapor Flow at the Top of the Core for the Hot Assembly Channel 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 18 of 26 Figure 7 Watts Bar Unit 2 Limiting PCT Case Lower Plenum Collapsed Liquid Level 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 19 of 26 Figure 8 Watts Bar Unit 2 Limiting PCT Case Intact Loop Accumulator Flow 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 20 of 26 Figure 9 Watts Bar Unit 2 Limiting PCT Case Intact Loop Safety Injection Flow 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 21 of 26 Figure 10 Watts Bar Unit 2 Limiting PCT Case Core Average Channel Collapsed Liquid Level 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 22 of 26 Figure 11 Watts Bar Unit 2 Limiting PCT Case Loop 2 Downcomer Collapsed Liquid Level 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 25 of 26 Figure 14 Watts Bar Unit 2 Limiting PCT Case Liquid and Saturation Temperature at Bottom of Downcomer Channel 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 NP-Attachment to WBT-D-4396 Page 26 of 26 Figure 15 Watts Bar Unit 2 Limiting PCT Case Peak Cladding Temperature for all 5 Rods 2013 Westinghouse Electric Company LLC All Rights Reserved

ENCLOSURE EVALUATION OF PROPOSED CHANGE ATTACHMENT 2 Revised License Condition PAD4TCD may be used to establish core operating limits for Cycles 1 and 2 only.

PAD4TCD may not be used to establish core operating limits for subsequent reload cycles.