ML071210604

(WBN) Unit 1 - Technical Specification Change 07-01, Revision of Number of Tritium Producing Burnable Absorber Rods (TPBARS) in the Reactor Core

ML071210604
Person / Time
Site:	Watts Bar
Issue date:	04/25/2007
From:	James Smith Tennessee Valley Authority
To:	Document Control Desk, NRC/NRR/ADRO
References
TVA-WBN-TS-07-01
Download: ML071210604 (37)

Text

T04 070425 811 April 25, 2007 TVA-WBN-TS-07-01 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555 Gentlemen:

In the Matter of ) Docket No. 50-390 Tennessee Valley Authority )

WATTS BAR NUCLEAR PLANT (WBN) UNIT 1 - TECHNICAL SPECIFICATION CHANGE 07-01, REVISION OF NUMBER OF TRITIUM PRODUCING BURNABLE ABSORBER RODS (TPBARS) IN THE REACTOR CORE Pursuant to 10 CFR 50.90, TVA is submitting a request for a TS change (TVA-WBN-TS-07-01) to Operating License NPF-90 for WBN Unit 1. The proposed TS change revises Technical Specification Surveillance Requirement 3.5.1.4, Accumulators and 3.5.4.3, RWST to remove the note stating that the number of TPBARs is limited to no more than 240 based on TVA to NRC letter dated August 18, 2003. This change will also revise TS 4.2.1, Fuel Assemblies to revise the maximum number of TPBARs that can be irradiated in the WBN reactor core to 400.

Additionally, in accordance with 10 CFR 50.91(b)(1), TVA is sending a copy of this letter and attachments to the Tennessee State Department of Public Health.

U.S. Nuclear Regulatory Commission Page 2 April 25, 2007 to this letter provides the description and evaluation of the proposed change, including the analytical results demonstrating that the number of TPBARs can be increased without adverse impact to public health and safety and plant operations. This enclosure includes TVAs determination that the proposed change does not involve a significant hazards consideration which qualifies this change for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9). contains copies of the appropriate TS pages marked-up to show the proposed change. contains copies of the appropriate TS Bases pages for information only marked-up to show the proposed change.

This request has been applied to the pages previously approved by NRC in Amendment 48 on September 23, 2002. Amendment 48 was implemented when 240 TPBARs were loaded into the WBN reactor core at the beginning of WBN Cycle 6 (October 2003).

TVA has subsequently irradiated 240 TPBARs in Cycle 7 and Cycle 8 (current cycle).

TVA is planning to increase the number of TPBARs in the WBN core in Cycle 9 (February 2008); therefore, we are requesting approval of this amendment request by December 31, 2007.

Certain aspects of the TPBAR design are classified; therefore, it may be helpful for NRC staff to visit the PNNL offices in Richland, Washington to engage in classified discussions with TVA and PNNL staff in order to fully understand the changes being requested in this amendment request. TVA would be pleased to arrange such a meeting at NRCs convenience.

There are no regulatory commitments associated with this submittal.

U.S. Nuclear Regulatory Commission Page 3 April 25, 2007 If you have any questions about this change, please contact me at (423) 365-1824.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on this 25th day of April 2007.

Sincerely, Signed by Brian J. Thomas for J. D. Smith Manager, Site Licensing and Industry Affairs (Acting)

Enclosures

1. TVA Evaluation and Proposed Change

2. Proposed Technical Specification Changes (mark-up)

3. Proposed Technical Specification Bases Changes (mark-up) cc: See page 4

U.S. Nuclear Regulatory Commission Page 4 April 25, 2007 Enclosures cc (Enclosures):

NRC Resident Inspector Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381 Mr. Brendan T. Moroney, Project Manager U.S. Nuclear Regulatory Commission MS 08G9a One White Flint North 11555 Rockville Pike Rockville, Maryland 20852-2738 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. Lawrence E. Nanny, Director Division of Radiological Health 3rd Floor L & C Annex 401 Church Street Nashville, Tennessee 37243

U.S. Nuclear Regulatory Commission Page 5 April 25, 2007 JDS:RAS Enclosures cc (Enclosures):

A. S. Bhatnagar, LP 6A-C R. H. Bryan, BR 4X-C J. E. Hinman, ADM 1B-WBN A. M. Hinson, EQB 2A-WBN M. J. Lorek, MOB 2R-WBN M. T. McFadden, ADM 1Q-WBN NSRB Support, LP 5M-C (including Advisors)

J. E. Semelsberger, EQB 2W-WBN M. D. Skaggs, ADM 1V-WBN P. D. Swafford, LP 6A-C E. J. Vigluicci, WT 6A-K B. A. Wetzel, BR 4X-C K. W. Whittenburg, SP2B-C Sequoyah Licensing Files, OPS 4C-SQN EDMS, WT 3B-K M:\SUBMIT\WBN TS 07 REVISION TO NUMBER OF TPBARS.DOC

ENCLOSURE 1 TENNESSEE VALLEY AUTHORITY WATTS BARS BAR NUCLEAR PLANT (WBN) UNIT 1 TVA EVALUATION OF PROPOSED CHANGE

1. DESCRIPTION TVA requests to amend Operating License NPF-90 for Watts Bar Nuclear Plant (WBN) Unit 1. The proposed Technical Specification (TS) change will revise WBN Unit 1 TS Surveillance Requirements (SRs) 3.5.1.4, Accumulators, and 3.5.4.3, Refueling Water Storage Tank (RWST), to remove the note stating that the number of TPBARs is limited to no more than 240 based on TVA to NRC Letter dated August 18, 2003. This change will also revise TS 4.2.1 Fuel Assemblies to revise the maximum number of TPBARs that can be irradiated to 400.

2. PROPOSED CHANGE This amendment request will revise SRs 3.5.1.4, Accumulators, and 3.5.4.3, RWST, to remove the note which limits the number of TPBARs in the reactor core to 240. This change will also revise TS 4.2.1, Fuel Assemblies to revise the maximum number of TPBARs that can be irradiated in the WBN reactor core from 240 to 400. TVA is planning to irradiate 368 TPBARs in the WBN reactor core during Cycle-9. While the exact number of TPBARs to be irradiated in WBN Cycle-9 is 368, this amendment requests increasing the limit on TPBARs that can be irradiated to 400. The analysis to support the irradiation of 400 TPBARs is provided with this amendment request.

In addition, supporting changes to each corresponding bases pages are being made as indicated by the page mark-ups in Enclosure 3. A discussion of TPBARs is included on bases page B 3.5-26.

This proposed change has been applied to the issued pages previously approved by NRC on September 23, 2002, in WBN Amendment 40 and the pages approved by NRC on October 8, 2003 in WBN Amendment 48. Amendment 40 was not scheduled for implementation until TPBARs were loaded into the WBN reactor (which occurred with Cycle 6 as authorized by Amendment 48). Amendment 40 addressed the changes needed for the production of tritium and included boron changes for the cold leg accumulators (CLAs) and RWST. Amendment E1-1

48 established the boron limit for 240 TPBARs in the core and also limited the number of TPBARs to 240, based on issues related to credit for control rod insertion and boron concentrations following a Large Break Loss of Coolant Accident (LBLOCA). Please refer to the specific TS pages markups provided in Enclosure 2.

In summary, the actual number of TPBARs to be irradiated in Cycle 9 will be 368. Approval of this amendment request will authorize the irradiation of up to (and including) 400 TPBARs.

3. BACKGROUND The U.S. Department of Energy (DOE) has chosen TVAs Watts Bar Unit 1 and Sequoyah Nuclear Plants (Units 1 and 2) to produce tritium for the replenishment of the National Security Stockpile by irradiating TPBARs installed in the reload cores at each refueling outage. The number of TPBARs required to be irradiated is to be identified by the DOE. Based on these numbers, TVA, along with its fuel vendors, will determine the number of TPBARs to be installed and irradiated at each site.

4. Technical Analysis Watts Bar Unit 1 Cycles 6, 7, and 8 each employed 240 TPBARs in the reactor core design. The U.S. DOE has requested TVA to produce higher levels of tritium in future cycles of Watts Bar Unit 1. Consequently, this license amendment request proposes raising the maximum number of TPBARs from 240 to 400 TPBARs. Currently, the planned TPBAR inventory for Watts Bar Unit 1 Cycle 9 is 368 TPBARs.

Cycle 9 is expected to begin operation in February of 2008.

In the past three cycles, the number of TPBARs in Watts Bar Unit 1 was limited to 240 in part by concerns related to post-LOCA subcriticality. The maximum allowable number of TPBARs is currently included in the bases for the Refueling Water Storage Tank (RWST) and Accumulator Technical Specifications. These Technical Specifications relate to post-LOCA subcriticality margin since the boron concentrations of these Emergency Core Cooling System (ECCS) water sources are important in determining the boron concentration of the water in the containment sump. The Design Features Technical Specification also includes the maximum TPBAR inventory. The number of TPBARs used in the E1-2

core design is reported in the Core Operating Limits Report (COLR) each reload cycle.

As will be discussed below, post-LOCA subcriticality is a function of the detailed core design and key assumptions like the RWST and CLA boron concentrations. As an attribute of the core design, the number of TPBARs plays a role in determining post-LOCA subcriticality margin, but the magnitude of the subcriticality margin is not directly determined by the number of TPBARs. Two core designs can have the same number of TPBARs but very different post-LOCA subcriticality margins.

Post-LOCA Subcriticality Margin Post-LOCA subcriticality margin, which is evaluated each cycle as part of the reload safety evaluation process, is determined by the core excess reactivity at cold conditions and by the sump boron concentration.

The core excess reactivity, i.e., the reactivity controlled by the soluble boron in the moderator, is a function of several core design attributes, specifically, the cycle energy, the fuel design, the inventory of discrete and integral burnable absorbers, and the coolant conditions.

Cores are designed such that the excess reactivity at normal operating conditions is controlled with soluble boron levels that permit limits on moderator temperature coefficient to be met. In Watts Bar Unit 1, hot full power (HFP) critical boron concentrations are generally less than approximately 1250 ppm near beginning of life. Core reactivity at post-LOCA conditions increases relative to normal operation conditions due to several factors: (1) the decrease in fuel temperatures from full power to zero power (reduced negative Doppler feedback), (2) increased neutron moderation due to larger moderator densities (reduced negative moderator feedback), (3) axial neutron flux redistribution (flux shape shifts toward the top of the core where the fuel is more reactive), and (4) the assumption of no xenon or reduced xenon levels. These factors combine to make the post-LOCA condition significantly more reactive than normal operation conditions. Consequently, the cold critical boron concentrations at post-LOCA conditions are larger than the typical values at hot conditions. As part of the safety evaluation for each reload core design, analyses are performed to ensure that the cold critical boron E1-3

concentration is less than the post-LOCA sump boron, thus ensuring subcriticality.

The sump boron concentration calculation assumes the minimum RWST, CLA, and containment ice boron concentrations permitted by the plant Technical Specifications. The sump boron calculation also assumes that the core is at peak xenon prior to the event. This has the effect of minimizing the reactor coolant system (RCS) boron concentration which, in turn, conservatively reduces the sump boron concentration. The sump boron concentration is maintained as a key safety parameter in the reload safety evaluation process and is specified as a function of RCS boron concentration.

Core designers can improve the post-LOCA subcriticality margin of the core by adjusting the inventory of burnable absorbers. All burnable absorbers, including TPBARs, increase the subcriticality margin since they reduce core reactivity. Typically, large inventories of integral fuel burnable absorbers (IFBA) are employed in 18-month cycle core designs to reduce core reactivity so that key safety parameter limits, including post-LOCA subcriticality, can be met. The key assumptions of the post-LOCA subcriticality methodology will be discussed in more detail below. One key assumption for TPBARs is that TPBARs loaded into the core interior are conservatively assumed to fail for cold leg break LOCAs, resulting in loss of some of the Li-6 absorber material. Thus, only a portion of the Li-6 in the TPBARs is credited in the subcriticality analysis.

Method of Analysis The post-LOCA subcriticality analysis methodology employed is described below:

The subcriticality analysis is performed using versions of the ANC and PHOENIX-P computer codes that have TPBAR modeling capability. These are described in Section 2.4.3.1 of Reference 1. PHOENIX-P is a lattice code used to generate fuel cross sections for ANC, which is the three-dimensional core simulator. The subcriticality calculation at cold, post-LOCA conditions is performed using ANC.

As described above, the sump boron concentration is calculated assuming minimum RWST, CLA, and containment ice E1-4

boron concentrations. These minimum concentrations are specified in the plant Technical Specifications. Also, the RCS boron concentration is minimized through the assumption of peak xenon as the accident pre-condition. ANC is used to calculate the HFP, peak xenon critical boron concentration at the most reactive time in life. The sump boron, which is specified as a function of the peak xenon RCS boron, can then be determined.

ANC is also used to calculate the cold critical boron concentration at post-LOCA conditions. The most reactive temperature in the range of 50 degrees F to 212 degrees F is evaluated. The moderator is assumed to be sub-cooled, and no credit is taken for the negative reactivity effect of voids. The fuel temperature is assumed to be equal to the moderator temperature, so that no credit is taken for decay heat and Doppler feedback. The resulting cold critical boron concentration is compared to the sump boron concentration. If the sump boron concentration is larger than the cold critical boron concentration, then the core is subcritical.

To address the potential for TPBAR failure, the post-LOCA subcriticality evaluation must consider two scenarios: (1) the hot leg break scenario, and (2) the cold leg break scenario.

Furthermore, two types of cold leg break scenarios are examined: (a) long term subcriticality, and (b) subcriticality at the time of hot leg switchover. In the hot leg break scenario, TPBAR failure is not expected due to the low temperatures of the fuel and TPBARs. Therefore, the assumptions for evaluating this scenario are as follows:

a) no TPBAR failures, b) no xenon in the cold critical boron calculation, c) no control rod insertion, d) cold conditions, e) a pre-condition of peak xenon to minimize the RCS boron concentration, and f) most reactive time in life.

In the cold leg break scenario, TPBAR failure is conservatively assumed to occur for all interior TPBARs (i.e., TPBARs not loaded on the core periphery). While control rod insertion is expected for cold leg breaks, the E1-5

negative reactivity worth of control rods is not credited.

The key assumptions for the long-term subcriticality evaluation, therefore, are as follows:

a) TPBAR failure for interior TPBARs with 50 percent Li-6 leaching and loss of 12 inches of LiAlO2 pellets, b) no xenon in the cold critical boron calculation, c) no control rod insertion, d) cold conditions, e) a pre-condition of peak xenon to minimize the RCS boron concentration, and f) most reactive time in life.

This scenario is the same as the hot leg break scenario except for the assumption of TPBAR failure. Because TPBAR failure is assumed, this scenario is more limiting than the hot leg break scenario.

For cold leg break LOCAs, the potential exists for boron dilution of the sump prior to hot leg switchover. For Watts Bar Unit 1, hot leg switchover (HLSO) occurs at 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> into the transient. At this time, switchover to hot leg recirculation is performed to prevent the boron concentration in the core from building up to the precipitation level. Prior to HLSO, unborated steam from the core condenses in the containment potentially reducing the boron concentration in the sump. This reduced boron concentration is assumed in the subcriticality evaluation at HLSO. Because of the potential for dilution of the sump boron, the cold leg break subcriticality assessment at hot leg switchover is the most limiting scenario. The key assumptions for the subcriticality evaluation at HLSO, therefore, are as follows:

a) TPBAR failure for interior TPBARs with 50 percent Li-6 leaching and loss of 12 inches of LiAlO2 pellets, b) a conservative xenon credit, c) no control rod insertion, d) cold conditions, e) a pre-condition of peak xenon to minimize the RCS boron concentration, f) most reactive time in life, and g) sump boron at the time of hot leg switchover (includes sump dilution effects).

For this case, the TPBAR failure assumptions are very conservative since leaching of the TPBARs is not E1-6

instantaneous. The expected leaching rate is 3 percent per day; therefore, less than 1 percent of the lithium would have leached at the time of HLSO (3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />).

Post-LOCA subcriticality evaluations for Watts Bar Unit 1 core designs with up to 400 TPBARs will employ the above methodology. If subcriticality cannot be demonstrated, then the first option is to modify the core design.

Results To evaluate the effect of increasing the maximum TPBAR inventory from 240 TPBARs to 400 TPBARs, the post-LOCA subcriticality calculations performed for the past three cycles were reviewed. Cycles 6, 7, and 8 each had 240 TPBARs. The effect on post-LOCA subcriticality margin of adding additional TPBARs, up to the maximum of 400, is estimated in Table 1 below.

The second column of Table 1 gives the ANC cold critical boron concentration without TPBAR failures, while the third column gives the slightly larger cold critical boron concentration assuming TPBAR failures. The difference between these two values is effectively the boron worth of the Li-6 lost due to TPBAR failure. This difference can be divided by the number of TPBARs (240) to give a sensitivity factor that can be used to estimate the reduction in subcriticality margin with an increase in the TPBAR inventory. This sensitivity factor is given in the fourth column. The calculated subcriticality margins for Cycle 6, 7, and 8 are given in column 5. Column 6 gives the estimated margin for each cycle for an inventory of 400 TPBARs. This estimate assumes that the excess reactivity of the core with 400 TPBARs is comparable to the excess reactivity of the original core design. As the table shows, it is expected that each of these designs could have accommodated 400 TPBARs. The expected reduction in subcriticality margin is on the order of 16-22 ppm. As discussed above, core design options are available that can increase subcriticality margin, e.g., through increasing the core inventory of integral fuel burnable absorber rods.

Table 1 provides estimated values of the post-LOCA subcriticality margin for the Cycle 6, 7, and 8 Watts Bar Unit 1 core designs assuming that each had 400 TPBARs. To augment these estimates, an explicit analysis was performed for a core design with 400 TPBARs. The core design is a E1-7

modification of the Cycle 8 core design. In this modified design, 8 feed assemblies with a U-235 enrichment of 4.1 w/o and 104 IFBA fuel rods were replaced with 8 feed assemblies with an enrichment of 4.4 w/o, 80 IFBA fuel rods, and 20 TPBARs each. Thus, the additional 160 TPBARs in these feed assemblies brought the total TPBAR inventory to 400 TPBARs for this modified Cycle 8 design.

Table 1 Estimated Effect of Additional TPBARs on Post-LOCA Subcriticality Margin Core Cold Cold Sensitivity Calculated Expected Design Critical Critical Factor for Minimum Minimum Boron (ppm) Boron (ppm) Lost Subcriticality Subcriticality at BOL, no at BOL, no Li-6 Margin for 240 Margin for 400 Xenon, no Xenon, with (ppm/TPBAR) TPBARs TPBARs TPBAR TPBAR (ppm) (ppm) failure failure Cycle 6 1909 1943 0.14 66 44 Cycle 7 1854 1878 0.10 126 110 Cycle 8 1828 1858 0.13 131 110 Post-LOCA subcriticality calculations were then performed for the modified Cycle 8 design for each of the post-LOCA scenarios described above and for cycle burnups up to 8000 MWD/MTU. Post-LOCA subcriticality margin is limiting early in the cycle, so that cycle burnups beyond 8000 MWD/MTU are clearly non-limiting.

As discussed above, the post-LOCA sump boron concentration is a function of the RCS boron concentration, since the RCS is assumed to mix with the RWST, CLA, and containment ice fluid volumes in the sump. To determine a conservative sump boron concentration, the RCS boron is minimized by assuming HFP, peak xenon as the accident pre-condition.

ANC is used to calculate the pre-condition boron concentrations at the peak xenon condition at several different burnup steps. The resulting values can then be used to determine the sump boron concentrations.

Cold critical boron concentrations are then calculated assuming no xenon. The coolant conditions are atmospheric pressure and the most reactive temperature between 50 degrees F and 212 degrees F (typically, higher coolant temperatures are very slightly more limiting). For the HLSO subcriticality assessment, a conservative xenon credit is taken since HLSO occurs 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> into the transient, at E1-8

which time a significant xenon inventory would remain in the core. For a HLSO time of 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, the conservative xenon credit assumed is 210 ppm. While the exact level of xenon present in the core depends on the reactor design, core design, pre-trip history, time-in-life, and specific HLSO time, generic minimum xenon credit values were determined for various HLSO times. It should be noted that the minimum xenon credit values conservatively assume a reactor trip and a 15 hour1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> power ramp to full power prior to the LOCA. If one were to assume a pre-trip power history consistent with the assumptions that maximize sump dilution (i.e., most reactive time-in-life, continuous full power operation), xenon credit would be much higher.

The subcriticality margin is calculated by subtracting the calculated critical boron concentration from the sump boron concentration. Tables 2, 3, and 4 give the subcriticality assessments for the hot leg break scenario, the cold leg break long-term assessment, and the cold leg break assessment at HLSO. These assessments employ the key assumptions discussed above for each scenario. The results in Table 5 give the subcriticality margin for the HLSO assessment but without TPBAR failure. Comparison of the Table 4 and 5 results provides an estimate of the margin loss due to TPBAR failure.

Table 2 Post-LOCA Subcriticality Margin for a Hot Leg Break (all boron concentrations in ppm)

Pre-condition Burnup Boron Concentration Sump No Xenon, Cold Subcriticality (MWD/MTU) (HFP, Peak Xenon) Boron Critical Boron Margin 150 932 2058 1813 245 1000 910 2055 1796 259 2000 901 2054 1788 266 3000 874 2050 1770 280 4000 826 2044 1741 303 6000 693 2026 1660 366 8000 529 2005 1557 448 E1-9

Table 3 Post-LOCA Subcriticality for a Cold Leg Break:

Long Term Assessment (all boron concentrations in ppm)

Pre-condition Burnup Boron Concentration Sump No Xenon, Cold Subcriticality (MWD/MTU) (HFP, Peak Xenon) Boron Critical Boron Margin 150 932 2058 1865 193 1000 910 2055 1846 209 2000 901 2054 1836 218 3000 874 2050 1817 233 4000 826 2044 1788 256 6000 693 2026 1707 319 8000 529 2005 1604 401 Table 4 Post-LOCA Subcriticality for a Cold Leg Break:

HLSO Assessment (all boron concentrations in ppm)

No Xenon, Cold Pre-condition Cold Critical Burnup Boron Concentration Sump Critical Xenon Boron with Subcriticality MWD/MTU) (HFP, Peak Xenon) Boron Boron Credit Xenon Credit Margin 150 932 1771 1865 210 1655 116 1000 910 1766 1846 210 1636 130 2000 901 1764 1836 210 1626 138 3000 874 1759 1817 210 1607 152 4000 826 1748 1788 210 1578 170 6000 693 1721 1707 210 1497 224 8000 529 1686 1604 210 1394 292 E1-10

Table 5 Post-LOCA Subcriticality for a Cold Leg Break: HLSO Assessment assuming No TPBAR Failure (all boron concentrations in ppm)

No Xenon, Cold Pre-condition Cold Critical Burnup Boron Concentration Sump Critical Xenon Boron with Subcriticality MWD/MTU) (HFP, Peak Xenon) Boron Boron Credit Xenon Credit Margin 150 932 1771 1813 210 1603 168 1000 910 1766 1796 210 1586 180 2000 901 1764 1788 210 1578 186 3000 874 1759 1770 210 1560 199 4000 826 1748 1741 210 1531 217 6000 693 1721 1660 210 1450 271 8000 529 1686 1557 210 1347 339 As the tables show, BOL (150 MWD/MTU) is the most limiting time in life for each scenario. Also, as expected, the HLSO assessment is the most limiting scenario with a minimum margin of 116 ppm at BOL. This is in good agreement with the estimated value of 110 ppm in Table 1.

The modified Cycle 8 core has slightly less excess reactivity than the excess reactivity assumed in Table 1 (1813 ppm critical boron vs. 1828 ppm critical boron at cold conditions, 150 MWD/MTU for the modified Cycle 8 core and the actual Cycle 8 core, respectively). This accounts for the slightly greater margin in the explicit calculations.

The subcriticality margin values in Tables 4 and 5 show that, at 150 MWD/MTU, the worth of the Li-6 lost due to TPBAR failure is 52 ppm (168 ppm - 116 ppm). This is equivalent to 0.13 ppm per TPBAR, which is consistent with the value assumed in Table 1 for Cycle 8. This supports the reasonableness of the Table 1 estimates for Cycles 6 and 7.

The results of this section show that adequate subcriticality margin can be demonstrated for a core design with 400 TPBARs. The methods used here will be employed for each future Watts Bar Unit 1 core design to assess the cycle specific post-LOCA subcriticality margin.

E1-11

Conclusion The requested increase in maximum TPBAR inventory from 240 TPBARs to 400 TPBARs will have at most a modest effect on post-LOCA subcriticality margin. An explicit calculation for a core design with 400 TPBARs demonstrated adequate subcriticality margin (116 ppm). Core design options are available to ensure post-LOCA subcriticality with increases in the TPBAR inventory. In the event that subcriticality for a core design under consideration cannot be demonstrated using the methodology described above, then the core design will be modified to maintain subcriticality margin. Post-LOCA subcriticality will continue to be evaluated for each core design as part of the cycle specific comprehensive reload safety evaluation process.

Tritium Permeation

Background

Tritium producing burnable absorber rods (TPBARs) are designed to control reactivity, similar to discrete burnable absorbers, with the additional function to produce and retain tritium. This is accomplished by using lithium-6 as an absorber material in place of boron-10 and incorporating in the TPBAR a getter to capture the tritium.

The TPBARs are designed to be compatible with Westinghouse 17X17 fuel assemblies. Evaluations performed previously have confirmed that the TPBAR nuclear, thermal, and mechanical characteristics are comparable and compatible with those of conventional burnable absorber rods (References 1-4).

Functional criteria established prior to the irradiation of 32 TPBARs in lead test assemblies (LTA) during WBN Cycle 2 stated that the TPBARs would not release (permeate) more than 6.7 curies of tritium per TPBAR per year to the WBN RCS. Monitoring of the RCS during operation and post irradiation examinations performed on a sample of the LTA TPBARs confirmed this criterion was met. Based on the LTA results, when preparing the Tritium Production Core Topical Report, which provided the technical justification for Amendment No 40, it was agreed that the design could support a reduction in the postulated tritium permeation from the TPBARs and the limit was revised to 1 Ci/TPBAR/year. This same criterion was applied to the 240 E1-12

production TPBARs irradiated in WBN Cycle 6 (September 2003 to February 2005). However, in recognition of statistical uncertainties, the criterion was stated as no more than 1,000 Ci/1,000 TPBARs/year.

When taking measurements of RCS tritium levels, it is not possible to differentiate between tritium from TPBARs and tritium from other core components and RCS sources, therefore the tritium attributed to TPBARs is determined by subtracting the expected tritium value established by measurements taken in cycles without TPBARs from the total tritium measured in the RCS with TPBARs. There are significant uncertainties in both the measurements and the determination of the amount of tritium generated from non-TPBAR sources. This results in a significant uncertainty in the amount of tritium attributable to TPBARs.

The RCS was sampled for tritium activity throughout Cycle

6. Late in Cycle 6 operation, it was noted from RCS samples that the release criterion of 1 Ci/TPBAR/year was being exceeded (however, the releases were still well below regulatory and technical specification limits on tritium release, with only 240 TPBARs in the core).

Actions were initiated immediately by TVA and DOE to understand the cause of the greater than expected permeation and, in a March 22, 2005 letter to NRC, TVA committed to irradiate no more than 240 TPBARs in any operating cycle until corrective actions were taken. The March 22nd letter also stated that instead of applying a permeation limit on a per TPBAR basis (because of the uncertainty addressed above), the metric to be applied beginning with Cycle 7, would be the limit established in WBN operating license amendment number 40 of 2,304 Ci/year to the RCS attributable to TPBARs. As noted below, the releases from both Cycle 6 and Cycle 7, on a calendar year basis were well below this limit. This same metric will be applied to the 400 TPBAR limit being requested in this amendment for Cycle 9, as well as all future cycles.

Based on the fact that the TPBARs scheduled for irradiation in WBN Cycle 7 were of the same design as those of Cycle 6, performance was expected to be similar to that of Cycle 6.

Thus with the new limit on tritium attributed to TPBARs, 240 TPBARs were also irradiated in Cycle 7. Daily monitoring of the RCS for tritium and tracking of water feed and bleed, boron and lithium injections, etc. was E1-13

performed during Cycle 7 to increase the understanding of TPBAR tritium permeation and tritium due to other core components. The tritium permeation from TPBARs in Cycle 7 closely tracked that of Cycle 6 (Figure 1).

Figure 1 Cumulative TPBAR Tritium Release to RCS in Cycle 6 and Cycle 7 as a function of time in effective Full Power Days Calculations indicated that the actual Cycle 6 release was 2.4 +/- 1.0 Ci/TPBAR/year. Taking the upper bound on the uncertainty, the release was 3.4 Ci/TPBAR/year. The actual release from Cycle 7 TPBARs was calculated to be 2.7+/-1.0 Ci/TPBAR/year or an upper bound of 3.7 Ci/TPBAR/year. The difference in the results is within the statistical uncertainty associated with the measurements. With these releases and 240 TPBARs in each cycle, the tritium release on a calendar year basis for both Cycle 6 and Cycle 7 was well below regulatory limits and the limit of 2,304 Ci/year attributable to TPBARs.

WBN Cycle 8 is currently in operation with 240 TPBARs of the same design as Cycles 6 and 7 and at this time in the cycle (operation began in December 2006) there is nothing to indicate that the TPBAR performance will be any different than the two previous cycles. RCS tritium is E1-14

being monitored on a regular basis to identify any anomalous behavior.

Increasing the number of TPBARs in the core to 400 can be accommodated without exceeding the limit of 2,304 Ci/year attributable to TPBARs even if the design changes addressed below are not effective and the tritium permeation from Cycle 9 TPBARs is at the same level as from Cycles 6, 7, and 8. However, as discussed below, it is expected that the performance will be improved by the changes to be included in the Cycle 9 TPBAR design.

Post Irradiation Examination Following the refueling outage at the end of Cycle 6, six TPBARs were sent from WBN to Idaho National Laboratory and PNNL (3 to each location) for post irradiation examination (PIE) to understand why the permeation was greater than expected. Based on the PIE of Cycle 6 TPBARs and a comparison with the LTA PIE results, it was determined that there were tritium permeation pathways that had not been properly accounted for in the production TPBAR design, which included some design changes from the LTA TPBARs.

Based on reviews of the permeation mechanisms by PNNL and independent reviews by staff at Sandia National Laboratory, design changes have been proposed to reduce the tritium permeation. These design changes have been reviewed by TVA and are proposed to be incorporated in TPBARs scheduled for irradiation in WBN Cycle 9 beginning in March 2008. A brief discussion of the proposed design changes and their impact on the TBPAR ability to perform its function is provided below.

TPBAR Design Changes for Cycle 9 The Production multi-pencil TPBAR design (Figure 2) is being refined to a full-length getter (FLG) design. The FLG design, known as the Mark 9.2 TPBAR (Figure 3),

incorporates internal and external component design enhancements. Design enhancements to the internal components include a full-length getter, an Upper spacer assembly (cruciform spacer), Standard and Variable Pellet Stacks (changes to inner liner length and pellet length),

Pellet length reduction, Lower spacer assembly (cruciform spacer), and adding a lower getter disk (similar to LTA).

Changes to the external components include the bottom end E1-15

plug (solid plug with no bore out, shorter insert length),

top end plug (hex, bore hole reduction, shorter body length, and shorter insert length), and cladding length (length increase).

Figure 2 Production multi-pencil TPBAR design Figure 3 Mark 9.2 TPBAR E1-16

Full-length getter (FLG)

TPBARs used in the previous cycles, beginning with the LTA, consisted of packets of lithium aluminate pellets stacked on a zirconium liner, surrounded by a nickel-plated zirconium (NPZ) getter tube. The getter tube is coined on the top and bottom ends to capture the pellets and liner. This assembly is referred to as a pencil. Each pencil is approximately 12 inches long and the pencils are stacked in the stainless steel cladding to achieve the desired absorber column length (approximately 11 feet).

Top and bottom NPZ spacers are used to properly locate the pellet stack in the cladding and a spring clip is inserted at the top of the top spacer to maintain the components in the proper location during shipping and handling. Top and bottom end plugs are welded to the cladding to complete the pressure boundary. The internal surface of the cladding is coated with a permeation resistant aluminized barrier.

In the FLG TPBAR design, a single getter tube runs the full-length of the TPBAR and surrounds the pellet column in one continuous length as compared to 11 individual getters that are required in the multi-pencil design (11 pencil assemblies). In addition, the getter surrounds the plenum and lower spacers (see discussions, upper cruciform spacer and lower cruciform spacer). The design-function of the getter to provide pellet retention and tritium absorption does not change in the FLG. Because there are no pencil gaps, the FLG represents an enhancement in regard to tritium retention performance. Thus, there are no adverse effects to the approved TPBAR design and there is no other permeation path as a result of the FLG. Because there are no gaps between the pellets comparable to the gaps between the pencils, the FLG design provides a design enhancement that reduces power peaking in adjacent fuel rods (See discussion below, TPBAR Axial Power Peaking).

Elimination of Bore Hole in Bottom End Plug The design of the bottom end plug remains the same as in the Production multi-pencil TPBAR design with minor changes made to the insert length and it is now a solid piece with no bore hole. The bore hole on the insert has been removed to accommodate the placement of the getter disk (see getter disk discussion below), elimination of the bore hole also reduces the surface area of un-coated stainless steel. The E1-17

lower getter disk was effective in the LTA TPBARs, but was removed in the Production TPBAR design. There are no adverse affects to the approved TPBAR design as the design function of the bottom end plug to provide a containment boundary has not changed, but also provides a design enhancement that improves TPBAR tritium retention performance by providing less uncoated surface area, which mitigates the migration of tritium out the bottom end plug.

The end plug refinements have been analyzed to verify that they will not result in violation of the design basis assumptions and requirements for the weld area. The weld joint configuration has been burst tested to verify that the end plug weld joint will satisfy the design basis requirements.

Top End Plug The design of the top end plug remains the same as in the Production multi-pencil TPBAR design, with minor changes made to the body length, insert length, and bore hole dimensions. Changes to the top end plug length allows for a cladding length change (see discussion below).

Additionally a hex pattern has been placed on the body to facilitate removal from the hold down assembly base plate.

There are no adverse affects to the approved TPBAR design as the design function of the top end plug to provide a containment boundary has not changed. The end plug refinements have been analyzed to verify that they will not result in violation of the design basis assumptions and requirements for the weld area. The weld joint configuration has been burst tested to verify that the end plug weld joint will satisfy the design basis requirements.

Upper Cruciform Spacer A cruciform shaped spacer has replaced the plenum spacer tube used in the multi-pencil design. The cruciform rests on top of the pellet stack and slightly extends above the full-length getter to allow placement of the spring clip.

The design function and arrangement of the cruciform spacer is such that the cruciform spacer reduces tritiated water not reduced to molecular tritium within the pellet stacks, further enhancing tritium capture. This is expected to be an improvement over the previous design. There are no adverse affects to the approved TPBAR design as the changes do not adversely impact the function of the plenum spacer, but rather improves the performance to capture any tritium E1-18

that migrates up the annulus of the pellet stacks to the ends of the TPBAR.

Lower Cruciform Spacer The lower cruciform spacer assembly has replaced the thick-walled spacer used in the multi-pencil design. The lower cruciform spacer is surrounded by the FLG, which sits on the getter disk. The design function and arrangement of the cruciform spacer is such that the cruciform spacer reduces tritiated water not reduced to molecular tritium within the pellet stacks, enhancing tritium capture. This is expected to be an improvement over the previous design.

There are no adverse affects to the approved TPBAR design as the changes do not adversely impact the function of the lower spacer, but rather improves the performance to capture any tritium that migrates down the annulus of the pellet stacks to the ends of the TPBAR.

Getter Disk The getter disk (previous irradiation experience provided in the LTA), sits outside and below the FLG and on top of the bottom end plug. The getter disk is sized to fit within the ID of the cladding such that the FLG rests on top of the getter disk. The bottom end plug insert end has been modified (no bore hole) for placement of the getter disk. The getter disk is a design enhancement that does not adversely affect tritium retention performance, but is intended to improve the capture of any tritium that migrates down the annulus of the pellet stacks past the lower cruciform spacer to the bottom end of the TPBAR. The use of getter disks in the TPBAR has been addressed in the Tritium Production Core (TPC) Topical Report. There are no adverse affects to the approved TPBAR design Shorter Pellets The pellets remain the same as in the multi-pencil design, except for a reduction in the acceptable length of a pellet (change from nominal 2-inch pellets to nominal 1-inch pellets). There is no change to the overall absorber column length. The design function of the pellets for tritium production is not changed. The shorter pellets enhance tritium capture and improve overall performance.

Therefore, the nominal 1-inch pellets will not change TPBAR performance during LBLOCA burst conditions. The Mark 9.2 E1-19

FLG TPBAR configuration with nominal 1-inch pellets has been LBLOCA burst tested and the results are within acceptable limits. The pellet length change has no adverse effects on the approved TPBAR design.

One of the findings from the Cycle 6 PIE was that high tritium concentration in the surrounding getter occurred at pellet-pellet interfaces. This higher concentration could increase the tritium pressure against the cladding and increase tritium permeation. The shorter pellets will allow the tritium that escapes at the pellet-pellet interfaces to be captured over a larger portion of the getter, thus mitigating the peaking in tritium concentration at these locations. Shorter (optimum) length pellets are being evaluated for use in future cycles.

Cladding Length The trimmed cladding length has been increased by about 100 mils to accommodate the top end plug body length change.

The overall finished length of the TPBAR will not change.

Design refinements to the cladding to end plug preparation details were incorporated due to the insert length change on the end plugs. There is no impact from this change on the active absorber length or placement of the active absorber relative to the core centerline. The full range of the allowable active absorber length is still present to provide flexibility for the core-reload safety analysis.

There are no adverse affects to the TPBAR Approved Design as the design function of the cladding to provide a containment boundary has not changed, the active absorber is still centered on the core centerline, and the finished length of the TPBAR has not changed.

Zirconium Content The components used in the Cycle 9 design TPBAR results in a slight increase in the amount of zirconium in the core.

The increased zirconium content has a negligible impact on hydrogen generation during accident conditions. Zirconium content is within current analysis for hydrogen generation as addressed in Reference 1. Therefore, there are no adverse effects to the Approved TPBAR Design.

E1-20

TPBAR Axial Power Peaking The use of the full-length-getter design eliminates the need for variable-length pencils and different TPBAR types (A, B, & C) as used in the multi-pencil design to minimize the impact of power peaking in adjacent fuel rods resulting from axial gaps between pencil assemblies. The pellet column in the full-length-getter TPBAR design is essentially continuous, and there is no power peaking penalty from axial gaps in the absorber column. In comparison, the multi-pencil TPBAR design as a result of the pencil configuration can create gaps between the pellets. These gaps in the pellets cause local axial power spikes in the nearby fuel pins. Analyses performed by PNNL for the full-length getter show that the maximum pellet-to-pellet gap is significantly smaller than gaps experienced in the multi-pencil design (Production TPBAR). As the gap is significantly smaller than gaps experienced in the multi-pencil design, the full-length getter power peaking is negligible. There is no credible mode that would tend to generate large pellet-to-pellet gaps for the full-length getter. Thus, the full-length getter design has no adverse impacts on the design functional requirement for axial power peaking.

Conclusion Based on the PIE and review of the mechanisms associated with tritium transport within the TPBAR, several design changes have been made to the TPBARs to be inserted in WBN Cycle 9. These design changes have been selected to address issues identified in the PIE as discussed above.

It is concluded that the design changes will mitigate the features that caused the tritium permeation in Cycle 6 to exceed the functional criterion associated with the production TPBAR design. These changes will not result in a reduction in the TPBAR ability to perform its safety related function to absorb neutrons as part of the core reactivity control system. The proposed changes are expected to decrease the tritium permeation and achieve the improvements needed to reduce the tritium permeation to the previously stated goal of less than one curie per TPBAR per year. However, increasing the number of TPBARs in the core to 400 can be accommodated without exceeding the limit of 2,304 CI/year attributable to TPBARs even if the design changes are not effective and the tritium permeation from Cycle 9 TPBARs is at the same level as from Cycles 6, 7, E1-21

and 8. The effectiveness of the changes will be determined through the monitoring of RCS tritium levels throughout Cycle 9 operation.

6. REGULATORY SAFETY ANALYSIS 6.1. No Significant Hazards Consideration The proposed TS change will revise Watts Bar Nuclear Plant (WBN) Unit 1 Technical Specification (TS) Surveillance Requirements (SRs) 3.5.1.4, Accumulators, 3.5.4.3, Refueling Water Storage Tank (RWST), and 4.2.1, Fuel Assemblies to modify the maximum number of tritium producing burnable absorber rods (TPBARs) in the core.

This proposed change will allow the flexibility to increase the number of TPBARs in the core. Whether or not a significant hazards consideration is involved with the proposed amendment was determined by focusing on 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 consequences of an accident previously evaluated?

Response: No.

The proposed change modifies the maximum number of TPBARs in the core. The required boron concentration for the cold leg accumulators (CLAs) and RWST remains unchanged.

The current boron concentration has been demonstrated to maintain the required accident mitigation safety function for the CLAs and RWST with the higher number of TPBARs and this will be verified for each core that contains TPBARs as part of the normal reload analysis. The CLAs and RWST safety function is to mitigate accidents that require the injection of borated water to cool the core and to control reactivity. These functions are not potential sources for accident generation and the modification of the number of TPBARs will not increase the potential for an accident. Therefore, the possibility of an accident is not increased by the proposed changes. The current boron concentration levels are supported by the proposed number of TPBARs in the core. Since the current boron concentration levels will continue to maintain the safety function of the CLAs and RWST in the same manner as currently approved, the E1-22

consequences of an accident are not increased by the proposed changes.

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 only modifies the maximum number of TPBARs in the core. The boron concentrations for accident mitigation functions of the CLAs and RWST remain unchanged. These functions do not have a potential to generate accidents as they only serve to perform mitigation functions associated with an accident. The proposed modification will maintain the mitigation function in an identical manner as currently approved.

There are no plant equipment or operational changes associated with the proposed revision. Therefore, since the CLA and RWST functions are not altered and the plant will continue to operate without change, the possibility of a new or different kind of an accident is not created.

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

Response: No.

This change proposes a change to the maximum number of TPBARs in the core. The boron concentration requirements that support the accident mitigation functions of the CLAs and RWST remain unchanged. The proposed change does not alter any plant equipment or components and does not alter any setpoints utilized for the actuation of accident mitigation system or control functions. The proposed number of TPBARs, in conjunction with the current boron concentration values, has been demonstrated to provide an adequate level of reactivity control for accident mitigation and this will be verified for each core that contains TPBARs as part of the normal reload analysis. Therefore, the proposed change will not involve a significant reduction in a margin of safety.

6.2. Applicable Regulatory Requirements/Criteria The CLA and RWST functions are described in the Updated Final Safety Analysis Report (UFSAR) Sections 6.2.2, 6.3, E1-23

9.1, 15.2.4 and 15.4.3, respectively. For these sections, the principal review performed by NRC is documented in the Safety Evaluation Report (SER), NUREG-0847, dated June 1982. The assessment of these functions is documented in the following sections of the SER:

6.2.2, Containment Heat Removal Systems 6.3, Emergency Core Cooling System 9.1, Fuel Storage Facility 15.2.4, Reactivity and Power Distribution Anomalies 15.4, Radiological Consequences of Accidents Subsequent to the above review, by application dated August 20, 2001, TVA requested a license amendment to revise the WBN TS to address the irradiation of TPBARs for the DOE. Part of that amendment requested that both the CLA and RWST boron concentrations be raised to accommodate the irradiation of a maximum of 2,304 TPBARs during a single cycle. NRC approved and issued a Safety Evaluation (SE) for amendment 40 on September 23, 2002.

NRCs review of those boron concentration changes is documented in SE Section 3.2, Evaluation of Technical Specification Changes. The change proposed by this amendment has been calculated by Westinghouse using a similar methodology as was used during the initial plant licensing and subsequent tritium amendments proposed changes to determine CLA and RWST boron concentrations.

The proposed amendment will increase the limit on the number of TPBARs that can be irradiated in the WBN core to 400, which is bounded by the analyses supporting the 2,304 limit imposed with Amendment Number 40. The CLA and RWST boron concentration requirements existing in SRs 3.5.1.4, Accumulators, and 3.5.4.3, Refueling Water Storage Tank (RWST), for 240 TPBARs also provides adequate protection for the number of 400 TPBARs.

The existing boron concentrations for 240 TPBARs will also prevent a recriticality event with 400 TPBARs during postulated accidents and will not adversely affect compliance with the requirements for emergency core cooling systems in 10 CFR 50.46 or Appendix K of 10 CFR 50.

In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health E1-24

and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

7. ENVIRONMENTAL CONSIDERATION The proposed change does not involve (i) a 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 proposed amendment meets the eligibility criteria for 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 proposed amendment.

8. REFERENCES

1. NDP-00-0344, Rev. 1, Revision 1, Implementation and Utilization of Tritium Producing Burnable Absorber Rods (TPBARS in Watts Bar Unit 1, Westinghouse Electric Company, July 2001. (This document was Enclosure 4 of TVAs letter to NRC dated August 20, 2001, Watts Bar Nuclear Plant (WBN) - Unit 1 - Revision of Boron Concentration Limits, Reactor Core Limitations for Tritium Production Cores (TPCs) - Technical Specification (TS) Change No. TVA-WBN-TS-00-015.)

2. NRCs letter to TVA dated September 23, 2002, Watts Bar Nuclear Plant, Unit 1 - Issuance of Amendment to Irradiate up to 2304 Tritium-Producing Burnable Absorber Rods in the Reactor Core (TAC No. MB1884). and related NRC Safety Evaluation Report for Amendment 40.

3. TVAs letter to NRC dated May 30, 2003, Watts Bar Nuclear Plant (WBN) Unit 1 - Technical Specification Change 03-02, Revision of Boron Requirements for Cold Leg Accumulators and Refueling Water Storage Tank

4. NRCs letter to TVA dated October 3, 2003, Watts Bar Nuclear Plant, Unit 1 - Issuance of Amendment Regarding Revision of Boron Requirements for Cold Leg Accumulators E1-25

and Refueling Water Storage Tank (TAC. No. MB9480) and related NRC Safety Evaluation Report for Amendment 48.

5. TVAs letter to NRC April 27, 2004, Watts Bar Nuclear Plant (WBN) Unit 1 - Tritium Production Program - Program Enhancements.

6. TVAs letter to NRC dated March 22, 2005, Watts Bar Nuclear Plant (WBN) Unit 1Tritium Production Program Unit 1 Cycle 6 Operating Experience E1-26

ENCLOSURE 2 TVA-WBN-TS-07-01 REVISION TO NUMBER OF TRITIUM PRODUCING BURNABLE ADSORBER RODS (TPBARS) IN THE REACTOR CORE PROPOSED TECHNICAL SPECIFICATION PAGE MARKUPS AFFECTED TS PAGES TS 3.5-2 TS 3.5-10 TS 4.0-2 E2-1

Accumulators 3.5.1 SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.5.1.1 Verify each accumulator isolation valve is fully open. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> SR 3.5.1.2 Verify borated water volume in each accumulator is 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> t 7630 gallons and d 8000 gallons.

SR 3.5.1.3 Verify nitrogen cover pressure in each accumulator is 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> t 610 psig and d 660 psig SR 3.5.1.4 -------------------------------NOTE-------------------------------- 31 days The number of TPBARs in the reactor core is contained in the Core Operating Limits Report AND (COLR) for each operating cycle. *The number of TPBARs is limited to no more than 240 based on TVA -------NOTE -----------

Delete to NRC letter dated August 18, 2003. Only required to be

---

performed for affected accumulators.

Verify boron concentration in each accumulator is as Once within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> provided below depending on the number of tritium after each solution producing burnable absorber rods (TPBARs) installed volume increase of t in the reactor core for this operating cycle.: 75 gallons, that is not the result of addition from the refueling Number of TPBARs Boron Concentration Ranges water storage tank.

0-240* t 3000 ppm and d 3300 ppm (continued)

Replace with:

0 - 400 Watts Bar-Unit 1 3.52 Amendment 7, 21, 40,48

RWST 3.5.4 SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.5.4.1 ----------------NOTE----------------------

Only required to be performed when ambient air temperature is < 60°F or > 105°F.

Verify RWST borated water temperature is 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 60°F and 105°F.

SR 3.5.4.2 Verify RWST borated water volume is 7 days 370,000 gallons.

SR 3.5.4.3 ------------------NOTE---------------------

The number of TPBARs in the reactor core is contained in the Core Operating Limits Report (COLR) for each operating cycle.

• The number of TPBARS is limited to no more than 240 based on TVA to NRC Letter dated Delete August 18, 2003.

Verify boron concentration in the RWST is 7 days as provided below depending on the number of tritium producing burnable absorber rods (TPBARs) installed in the reactor core for this operating cycle:

Number of TPBARS Boron Concentration Ranges 0-240* 3100 ppm and 3300 ppm Replace with:

0 - 400 Watts Bar-Unit 1 3.5-10 Amendment 7, 40, 48

Design Features 4.0 4.0 DESIGN FEATURES 4.1 Site 4.1.1 Site and Exclusion Area Boundaries The site and exclusion area boundaries shall be as shown in Figure 4.1-1.

4.1.2 Low Population Zone (LPZ)

The LPZ shall be as shown in Figure 4.1-2 (within the 3-mile circle).

4.2 Reactor Core 4.2.1 Fuel Assemblies The reactor shall contain 193 fuel assemblies. Each assembly shall consist of a matrix of Zircalloy or Zirlo fuel rods with an initial composition of natural or slightly enriched uranium dioxide (UO2) as fuel material. Limited substitutions of zirconium alloy or stainless steel filler rods for fuel rods, in accordance with approved applications of fuel rod configurations, may be used. Fuel assemblies shall be limited to those fuel designs that have been analyzed with applicable NRC staff approved codes and methods and shown by tests or analyses to comply with all fuel safety design bases. A limited number of lead test assemblies that have not completed representative testing may be placed in nonlimiting core regions. For Unit 1, Watts Bar is authorized to place a maximum of 240 Tritium Producing Burnable Absorber Rods into the reactor in an operating cycle.

Replace with:

4.2.2 Control Rod Assemblies 400 The reactor core shall contain 57 control rod assemblies. The control material shall be boron carbide with silver indium cadmium tips as approved by the NRC.

(continued)

Watts Bar Unit 1 4.0-1 Amendment 8, 40, 48

ENCLOSURE 3 TVA-WBN-TS-07-01 REVISION TO NUMBER OF TRITIUM PRODUCING BURNABLE ADSORBER RODS (TPBARS) IN THE REACTOR CORE PROPOSED TECHNICAL SPECIFICATION BASES PAGE MARKUPS (INFORMATION ONLY)

AFFECTED TS PAGES TS B 3.5-26 E3-1

RWST B 3.5.4 BASES APPLICABLE required volume is a small fraction of the available volume.

SAFETY ANALYSES The deliverable volume limit is set by the LOCA and (continued) containment analyses. For the RWST, the deliverable volume is different from the total volume contained since, due to the design of the tank, more water can be contained than can be delivered. The minimum boron concentration is an explicit assumption in the main steam line break (MSLB) analysis to ensure the required shutdown capability. The maximum boron concentration is an explicit assumption in the inadvertent ECCS actuation analysis, although it is typically a nonlimiting event and the results are very insensitive to boron concentrations. The maximum temperature ensures that the amount of cooling provided from the RWST during the heatup phase of a feedline break is consistent with safety analysis assumptions; the minimum is an assumption in both the MSLB and inadvertent ECCS actuation analyses, although the inadvertent ECCS actuation event is typically nonlimiting.

The MSLB analysis has considered a delay associated with the interlock between the VCT and RWST isolation valves, and the results show that the departure from nucleate boiling design basis is met. The delay has been established as 27 seconds, with offsite power available, or 37 seconds without offsite power.

Technical Specification Surveillance Requirements 3.5.1.4, Replace with: Accumulators, and 3.5.4.3, RWST, match boron concentrations to the number of tritium producing burnable 400 absorbers rods (TPBARs) installed in the reactor core.

Watts Bar is authorized to place a maximum of 240 TPBARs into the reactor in an operating cycle. Generally, TPBARs act as burnable absorber rods normally found in similar reactor core designs. However, unlike burnable absorber rods which lose their poison effects over the life of the cycle, some residual effect remains in the TPBARs at the end of the cycle. When larger amounts of excess neutron poisons (as in the case with larger loads of TPBARs) are added to a core, there is competition for neutrons from all the poison and the negative worth of each poison (including the reactor coolant system (RCS) boron) decreases. The positive reactivity insertion due to the negative moderator coefficient that occurs during the cooldown from hot full power to cold conditions following a loss of coolant accident (LOCA) must be overcome by RCS boron. Because the RCS boron is worth less, it takes a higher concentration to maintain subcriticality.

For a large break LOCA Analysis, the minimum water volume limit of 370,000 gallons and the minimum boron concentration limit is used to compute the post LOCA sump boron concentration necessary to assure subcriticality. This (continued)

Watts Bar-Unit 1 B 3.5-26 Revision 13, 61 Amendment 7, 40, 48