ML073520546
| ML073520546 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 01/18/2008 |
| From: | Moroney B NRC/NRR/ADRO/DORL/LPLII-2 |
| To: | Campbell W Tennessee Valley Authority |
| Moroney B, NRR/DORL, 415-3974 | |
| Shared Package | |
| ML073530482 | List: |
| References | |
| TAC MD5430 | |
| Download: ML073520546 (16) | |
Text
January 18, 2008 Mr. William R. Campbell, Jr.
Chief Nuclear Officer and Executive Vice President Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801
SUBJECT:
WATTS BAR NUCLEAR PLANT, UNIT 1 - ISSUANCE OF AMENDMENT REGARDING THE MAXIMUM NUMBER OF TRITIUM PRODUCING BURNABLE ASSEMBLY RODS IN THE REACTOR CORE (TAC NO. MD5430)
Dear Mr. Campbell:
The Commission has issued the enclosed Amendment No. 67 to Facility Operating License No. NPF-90 for Watts Bar Nuclear Plant, Unit 1 (WBN-1). This amendment is in response to your application dated April 25, 2007, as supplemented by letter dated August 22, 2007.
The amendment revises Technical Specification Surveillance Requirement 3.5.1.4, AAccumulators,@ and 3.5.4.3, ARefueling Water Storage Tanks,@ to remove the note limiting the number of tritium producing burnable absorber rods (TPBARs) to no more than 240. This change will also revise TS 4.2.1, AFuel Assemblies,@ to revise the maximum number of TPBARs that can be irradiated in the WBN-1 reactor core to 400.
A copy of the safety evaluation is also enclosed. Notice of issuance will be included in the Commission's biweekly Federal Register notice.
Sincerely,
/RA/
Brendan T. Moroney, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-390
Enclosures:
- 1. Amendment No. 67 to NPF-90
- 2. Safety Evaluation cc w/enclosures: See next page
ML073520546 Package No.: ML073530482 TS No.:ML080220378 NRR-058 OFFICE LPL2-2/PM LPL2-2/LA CVIB/BC SNPB/BC ITSB/BC OGC LPL2-2/BC NAME BMoroney RSola MMitchell AMendiola TKobetz NLO TBoyce By memo dtd By memo dtd EWilliams DATE 12/20/07 12/19/07 10/29/07 12/04/07 01/03/08 01/09/08 01/18//08 William R. Campbell, Jr.
Tennessee Valley Authority WATTS BAR NUCLEAR PLANT cc:
Mr. Gordon P. Arent Ms. Beth A. Wetzel, Manager New Generation Licensing Manager Corporate Nuclear Licensing and Tennessee Valley Authority Industry Affairs 5A Lookout Place Tennessee Valley Authority 1101 Market Street 4X Blue Ridge Chattanooga, TN 37402-2801 1101 Market Street Chattanooga, TN 37402-2801 Mr. Ashok S. Bhatnagar Senior Vice President Mr. Masoud Bajestani, Vice President Nuclear Generation Development Watts Bar Unit 2 and Construction Watts Bar Nuclear Plant Tennessee Valley Authority Tennessee Valley Authority 6A Lookout Place P.O. Box 2000, EQB 1B 1101 Market Street Spring City, TN 37381 Chattanooga, TN 37402-2801 Mr. Michael K. Brandon, Manager Mr. James R. Douet Licensing and Industry Affairs Vice President Watts Bar Nuclear Plant Nuclear Support Tennessee Valley Authority Tennessee Valley Authority P.O. Box 2000 3R Lookout Place Spring City, TN 37381 1101 Market Street Chattanooga, TN 37402-2801 Mr. Michael J. Lorek, Plant Manager Watts Bar Nuclear Plant Mr. H. Rick Rogers Tennessee Valley Authority Vice President P.O. Box 2000 Nuclear Engineering & Technical Services Spring City, TN 37381 Tennessee Valley Authority 3R Lookout Place Senior Resident Inspector 1101 Market Street Watts Bar Nuclear Plant Chattanooga, TN 37402-2801 U.S. Nuclear Regulatory Commission 1260 Nuclear Plant Road Mr. Michael D. Skaggs, Site Vice President Spring City, TN 37381 Watts Bar Nuclear Plant Tennessee Valley Authority County Executive P.O. Box 2000 375 Church Street Spring City, TN 37381 Suite 215 Dayton, TN 37321 General Counsel Tennessee Valley Authority County Mayor 6A West Tower P. O. Box 156 400 West Summit Hill Drive Decatur, TN 37322 Knoxville, TN 37902 Mr. Lawrence E. Nanney, Director Mr. John C. Fornicola, Manager Division of Radiological Health Nuclear Assurance Dept. of Environment & Conservation Tennessee Valley Authority Third Floor, L and C Annex 3R Lookout Place 401 Church Street 1101 Market Street Nashville, TN 37243-1532 Chattanooga, TN 37402-2801 Mr. Larry E. Nicholson, General Manager Performance Improvement Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801
TENNESSEE VALLEY AUTHORITY DOCKET NO. 50-390 WATTS BAR NUCLEAR PLANT, UNIT 1 AMENDMENT TO FACILITY OPERATING LICENSE Amendment No. 67 License No. NPF-90
- 1. The Nuclear Regulatory Commission (the Commission) has found that:
A. The application for amendment by the Tennessee Valley Authority (the licensee) dated April 25, 2007, as supplemented by letter dated August 22, 2007, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commission's rules and regulations set forth in Title 10 Code of Federal Regulations (10 CFR) Chapter I; B. The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C. There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commission's regulations; D. The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E. The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commission's regulations and all applicable requirements have been satisfied.
Enclosure 1
- 2. Accordingly, the license is amended by changes to the Technical Specifications as indicated in the attachment to this license amendment, and paragraph 2.C.(2) of Facility Operating License No. NPF-90 is hereby amended to read as follows:
(2) Technical Specifications and Environmental Protection Plan The Technical Specifications contained in Appendices A and B, as revised through Amendment No. 67, and the Environmental Protection Plan contained in Appendix B, both of which are attached hereto, are hereby incorporated into this license. TVA shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan.
- 3. This license amendment is effective as of the date of its issuance, and shall be implemented no later than 45 days from the date of its issuance.
FOR THE NUCLEAR REGULATORY COMMISSION
/RA/
Thomas H. Boyce, Branch Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
Attachment:
Changes to License No. NPF-90 and the Technical Specifications Date of Issuance: January 18, 2008
ATTACHMENT TO LICENSE AMENDMENT NO. 67 FACILITY OPERATING LICENSE NO. NPF-90 DOCKET NO. 50-390 Replace page 3 of Operating License No. NPF-90 with the attached page 3.
Replace the following pages of the Appendix A Technical Specifications with the attached revised pages. The revised pages are identified by amendment number and contain marginal lines indicating the area of change.
REMOVE INSERT 3.5-2 3.5-2 3.5-10 3.5-10 4.0-1 4.0-1
(4) TVA, pursuant to the Act and 10 CFR Parts 30, 40 and 70, to receive, possess, and use in amounts as required, any byproduct, source or special nuclear material without restriction to chemical or physical form, for sample analysis, instrument calibration, or other activity associated with radioactive apparatus or components; and (5) TVA, pursuant to the Act and 10 CFR Parts 30, 40 and 70, to possess, but not separate, such byproduct and special nuclear materials as may be produced by the operation of the facility.
C. This license shall be deemed to contain and is subject to the conditions specified in the Commission's regulations set forth in 10 CFR Chapter I and is subject to all applicable provisions of the Act and to the rules, regulations, and orders of the Commission now or hereafter in effect, and is subject to the additional conditions specified or incorporated below.
(1) Maximum Power Level TVA is authorized to operate the facility at reactor core power levels not in excess of 3459 megawatts thermal.
(2) Technical Specifications and Environmental Protection Plan The Technical Specifications contained in Appendix A, as revised through Amendment No. 67, and the Environmental Protection Plan contained in Appendix B, both of which are attached hereto, are hereby incorporated into this license. TVA shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan.
(3) Safety Parameter Display System (SPDS) (Section 18.2 of SER Supplements 5 and 15)
Prior to startup following the first refueling outage, TVA shall accomplish the necessary activities, provide acceptable responses, and implement all proposed corrective actions related to having the Watts Bar Unit 1 SPDS operational.
(4) Vehicle Bomb Control Program (Section 13.6.9 of SSER 20)
During the period of the exemption granted in paragraph 2.D.(3) of this license, in implementing the power ascension phase of the approved initial test program, TVA shall not exceed 50% power until the requirements of 10 CFR 73.55(c)(7) and (8) are fully implemented. TVA shall submit a letter under oath or affirmation when the requirements of 73.55(c)(7) and (8) have been fully implemented.
Amendment No.
SAFETY EVALUATION OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO REACTOR VESSEL INTEGRITY FOR THE REVISION OF THE NUMBER OF TRITIUM PRODUCING BURNABLE ABSORBER RODS IN THE REACTOR CORE WATTS BAR NUCLEAR PLANT, UNIT 1 DOCKET NO. 50-390
1.0 INTRODUCTION
By letter dated April 25, 2007 (Reference 1), as supplemented by letter dated August 22, 2007 (Reference 2), the Tennessee Valley Authority (TVA, licensee) submitted a request for changes to the Technical Specifications (TSs) for Watts Bar Nuclear Plant, Unit 1 (WBN-1). Notice of this amendment was given in the Federal Register on June 5, 2007 (72 FR 31105). The August 22, 2007, letter provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
The proposed amendment revises the WBN-1 TSs 3.5.1.4, AAccumulators,@ 3.5.4.3, @Refueling Water Storage Tank (RWST),@ and 4.2.1 AFuel Assemblies,@ to increase the maximum number of tritium producing burnable absorber rods (TPBARs) that can be irradiated from 240 to 400.
Although TVA is planning to irradiate only 368 TPBARs in the WBN-1 reactor core during Cycle 9, the proposed change increases the limit on TPBARs that can be irradiated to 400, and the licensee has provided an analysis to support the irradiation of up to 400 TPBARs.
2.0 BACKGROUND
The U.S. Department of Energy (DOE) has chosen TVA=s WBN-1 to produce tritium for the replenishment of the National Security Stockpile by irradiating TPBARs installed in the core.
The number of TPBARs required to be irradiated is to be identified by DOE. Based on these numbers, TVA, along with its fuel vendors, will determine the number of TPBARs to be installed and irradiated.
On September 15, 1997, the U. S. Nuclear Regulatory Commission (NRC) issued Amendment No. 8 to the WBN-1 Operating License, which authorized the irradiation of 32 Lead Test Assembly TPBARs in the WBN-1 core during operating Cycle 2.
Amendment No. 40 to the WBN-1 Operating License was issued September 23, 2002, and authorized the insertion of up to 2,304 TPBARs in the WBN-1 core. Amendment No. 40 addressed the changes needed for the production of tritium and included boron changes for the cold leg accumulators (CLAs) and RWST. The amendment stated that the number of TPBARs to be inserted in the WBN-1 core would be determined for each cycle, but would be less than or equal to 2,304.
Amendment No. 48 was issued on October 8, 2003, and authorized the irradiation of 240 TPBARs in the WBN-1 core during operating Cycle 6. Based on issues related to credit for control rod insertion during a cold leg loss-of-coolant-accident (LOCA) and sump boron, TVA noted that the number of TPBARs to be irradiated would be limited to 240 instead of the previously approved limit of 2,304.
Because the tritium permeation from TPBARs was found to be greater than expected in Cycle 6, TVA stated in a March 22, 2005, letter to NRC that the number of TPBARs irradiated in WBN-1 would remain at 240 until the permeation issue was understood and resolved, thus only 240 TPBARs were irradiated in operating Cycles 6, 7 and 8.
The DOE has requested TVA to produce higher levels of tritium in future cycles of WBN-1.
Consequently, the licensee proposes raising the maximum number of TPBARs from 240 to 400.
On the basis of post-irradiation examinations performed on the Cycle 6 TPBARs, Pacific Northwest National Laboratory (PNNL), designer of the TPBARs, has proposed changes to the TPBAR design to correct the permeation issue. TPBARs with these design changes are proposed to be irradiated in the WBN-1 core during operating Cycle 9, beginning in the spring of 2008.
TVA uses Westinghouse to perform reload safety evaluations for each reload core design to ensure that safety limits will continue to be met. The analyses performed include post-LOCA subcriticality analyses to demonstrate that subcriticality is maintained in the event of a LOCA.
Post-LOCA subcriticality margin is a function of overall core design, not simply the number of TPBARs. TVA requested that the limit on number of TPBARs be increased from 240 to 400, with the understanding that WBN-1 Cycle 9 will be analyzed using the same post-LOCA subcriticality methodology and assumptions used in Cycles 6 through 8. The core will be designed to ensure that subcriticality is maintained when the current methodology is employed.
3.0 REGULATORY EVALUATION
Title 10 of the Code of Federal Regulations (10 CFR), Section 50.46, AAcceptance criteria for emergency core cooling systems for light-water nuclear power reactors,@ and 10 CFR Part 50, Appendix K, AECCS Evaluation Models,@ specify the requirements for the design and analysis of emergency core cooling systems (ECCS). These regulations ensure adequate core cooling following a LOCA such that specified acceptance criteria are satisfied. The specified acceptance criteria include peak clad temperature, total cladding oxidation, total hydrogen generation, maintaining a coolable core geometry and ensuring adequate long-term core cooling. The applicable acceptance criterion for this license amendment is the long-term core cooling criterion. This criterion requires that the core temperature be maintained at an acceptably low value and that decay heat be removed for the extended period of time required by the long-lived radioactive nuclides remaining in the core.
The post-LOCA long-term core cooling analysis for WBN-1 requires that the core remain subcritical considering that all boration sources are injected and mixed in the containment sump.
These boration sources include the CLAs, the RWST, and the melted ice from the ice condenser containment. The minimum boron requirement for the CLAs ensures that the reactor core will remain subcritical during the post-LOCA recirculation phase by ensuring there is
sufficient boron concentration in the containment sump following a LOCA. The minimum boron requirement for the RWST ensures that sufficient negative reactivity is injected into the core to counteract any positive increase in reactivity caused by reactor coolant system (RCS) cooldown.
Appendices G and H to 10 CFR Part 50, and 10 CFR 50.61, "Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock (PTS)," provide the requirements for determining the effects of neutron irradiation on the integrity of the reactor vessel. Appendix H to 10 CFR Part 50 specifies material surveillance program requirements to monitor changes in the fracture toughness properties of the reactor vessel that occur as a result of exposure of these materials to neutron irradiation. Appendix G to 10 CFR Part 50 requires that reactor vessel beltline materials have Charpy upper shelf energy (USE) values in the transverse direction for the base metal and along the weld for the weld material of no less than 75 ft-lb (102 J) initially, and must maintain Charpy USE values throughout the life of the vessel of no less than 50 ft-lb (68 J). However, in accordance with 10 CFR Part 50, Appendix G, paragraph IV.A.1.a., Charpy USE values below these criteria may be acceptable if it is demonstrated, in a manner approved by the Director, NRC Office of Nuclear Reactor Regulation, that the lower values of Charpy USE will provide margins of safety against fracture equivalent to those required by Appendix G of Section XI of the American Society of Mechanical Engineers Code. Regulatory Guide 1.99, Revision 2, Radiation Embrittlement of Reactor Vessel Materials, provides an expanded discussion regarding the calculation of Charpy USE values. 10 CFR 50.61 establishes a PTS screening criteria that define a limiting level of neutron embrittlement beyond which plant operation cannot continue without further plant-specific evaluation.
The provisions of 10 CFR 50.36, Technical Specifications, which implements section 182a of the Atomic Energy Act, include requirements for determining the contents of TSs. These shall include surveillance requirements (SRs) relating to test, calibration, or inspection to assure that the necessary quality of systems and components is maintained, that facility operation will be within safety limits, and that the limiting conditions for operation (LCO) will be met.
4.0 TECHNICAL EVALUATION
4.1 Technical Specifications Changes The licensee proposes to revise SR 3.5.1.4 for the Accumulators by deleting the statement,
- The number of TPBARS is limited to no more than 240 based on TVA to NRC letter dated August 18, 2003, and by revising the number of TPBARs in the table from 0-240* to 0-400.
The same changes are proposed for SR 3.5.4.3 for the RWST. Finally, in the Design Features section of the TSs, TS 4.2.1, Fuel Assemblies, is revised to state that WBN-1 is authorized to place a maximum of 400 TPBARs into the reactor.
The purpose of the SRs is to assure that the LCOs for operability of the RWST and accumulators will be maintained by periodically verifying that their boron concentrations are within the designated ranges required by the analyses supporting the number of TPBARs in the core. This has not changed and the LCOs remain in effect. The table in the LCO has been revised to reflect the new TPBAR limit. However, since the supporting analysis has been revised, the reference to the August 18, 2003, letter is no longer valid. In this letter, which was a response to an NRC staff request for additional information associated with Amendment
No. 48, TVA limited the number of TPBARs to 240 and indicated that additional analyses and/or revised boron concentrations would be required to support future increases in this number.
The current proposed amendment provides the revised information. Thus, the reference to the August 18, 2003, letter can be deleted.
The change to TS 4.2.1 updates the fuel assembly design information to reflect the increased number of TPBARs authorized.
Based on the above discussion, the NRC staff concludes that the proposed revisions to the TSs are consistent with the requirements of 10 CFR 50.36 and accurately incorporate the design change to the number of TPBARs, which is evaluated in the following sections of this safety evaluation, and are, therefore, acceptable.
The licensee also provided, for information, the proposed change to the applicable TS Bases.
The proposed change should be incorporated in accordance with the licensees TS Bases Control Program.
4.2 Post-LOCA Subcriticality Margin In the past 3 cycles, the number of TPBARs in WBN-1 was limited to 240 due, in part, to concerns related to post-LOCA subcriticality. The maximum allowable number of TPBARs is currently included in the RWST and Accumulator TSs. These TSs are related to post-LOCA subcriticality margins since the boron concentrations of ECCS water sources are important in determining the boron concentration of the water in the containment sump. The Design Features section of the TSs also includes the maximum TPBAR inventory.
Post-LOCA subcriticality analysis is a function of the detailed core design and key assumptions like the RWST and CLA boron concentrations. Depending on the core design, the number of TPBARs plays a role in determining post-LOCA subcriticality margin. However, the magnitude of the subcriticality margin is not directly determined by the number of TPBARs; that is, two different core designs can have the same number of TPBARs, but very different post-LOCA subcriticality margins.
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 designs attributes - specifically, the cycle energy, the fuel design, the inventory of discrete and integral burnable absorbers, and the coolant conditions. The licensee analyzed post-LOCA subcritically conditions under normal and abnormal conditions to ensure subcriticality margin does exist and will continue to exist throughout the cycle.
The subcriticality analysis was performed using the latest versions of the ANC and PHOENIX-P computer codes combination that have TPBAR modeling capability. These have been approved for use by the NRC and are described in Section 2.4.3.1 of Reference 3.
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 stated above, the sump boron concentration is calculated assuming minimum RWST, CLA, and containment ice condenser boron concentrations. These minimum concentrations are specified in the plant TSs. Also, the RCS boron concentration is minimized through the assumption of peak xenon as the accident precondition. ANC is then used to calculate the HFP, peak xenon critical boron concentration at the most reactive time in life. The boron in the sump is determined based on a specified function of the peak xenon RCS boron.
The licensee reviewed the hot-leg break scenario and determined that TPBAR failure is not expected due to the low temperatures of the fuel of the TPBARs. The detail supporting this conclusion is provided in Reference 1.
The licensee also used ANC 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 licensee conducted post-LOCA subcriticality calculations assuming two scenarios: (1) hot leg break and (2) cold leg break. In addition, the licensee considered two types of cold leg break scenarios: (a) long term subcriticality and (b) subcriticality at the time of hot leg switch-over (HLSO). The details of these calculations are presented in Reference 1.
The licensee also considered cold leg breaks. For cold leg break LOCAs, the potential exists for boron dilution of the sump prior to HLSO. For WBN-1, 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, switch-over 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 HLSO is the most limiting scenario. The key assumptions for the subcriticality evaluation at HLSO are presented in Reference 1.
4.2.1 Results of the Analysis To evaluate the effect of increasing the maximum TPBAR inventory from 240 to 400, the licensee reviewed the post-LOCA subcriticality margin calculations that were performed for the past three cycles. The effect on post-LOCA subcriticality margin calculation of adding additional TPBARs, up to the maximum of 400 TPBARs, is provided in Table 1 of Reference 1. The analysis shows that the past three cycles could have accommodated the additional TPBARs with only a slight reduction in the subcriticality margin.
As stated in the licensees submittal, the core designer has options available that can increase subcriticality margin of the core through increasing the core inventory of integral fuel burnable absorber rods. As such, an explicit analysis was performed for a core design with 400 TPBARs for the upcoming Cycle 9.
The Cycle 9 core design is a modification of the Cycle 8 core design. This implies that the licensee had performed post-LOCA subcriticality calculations for each of the post-LOCA scenarios for cycle burnups up to 8000 megawatt days per metric ton of uranium (MWD/MTU).
Post-LOCA subcriticality margin is limiting early in the cycle, so that cycle burnups beyond 8000 MWD/MTU are clearly non-limiting.
ANC is used to calculate the precondition 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 were also calculated assuming no xenon. The coolant conditions are atmospheric pressure and the most reactive temperature between 50 degrees Fahrenheit (°F) and 212 °F. For the HLSO subcriticality assessment, a conservative xenon credit is utilized, 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 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 parts per million (ppm). A detailed description supporting the assumption used in this calculation is contained in the Aresults@ section of the Reference 1. The licensee stated that the minimum xenon credit values conservatively assume a reactor trip and a 15-hour power ramp to full power prior to the LOCA. If pre-trip power history is 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, 4, and 5 of Reference 1 provide the results of the post-LOCA subcriticality analysis for hot and cold leg breaks.
As the tables show, beginning of life (BOL) (150 MWD/MTU) is the most limiting time in life for each scenario. Also, the licensee pointed out that the HLSO assessment is the most limiting scenario with a minimum margin of 116 ppm at BOL.
A review of the tables indicates that 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 BOL cold conditions for the modified Cycle 8 core and the actual Cycle 8 core, respectively).
Also, 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 B 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 staff concurs with the licensees results, as presented in Reference 1, that adequate subcriticality margin has been demonstrated for a core design with 400 TPBARs. Additionally, the methods described in this submittal are adequate to assess the cycle-specific post-LOCA subcriticality margin for future WBN-1 core designs.
4.3 Reactor Vessel Integrity The neutron fluence is the main parameter used to characterize the extent of embrittlement expected in the reactor vessel material. The proposed increase in the number of TPBARs from 240 to 400 is well below the 2,304 TPBARs approved in the staff's safety evaluation dated September 23, 2002. Therefore, the projected neutron fluence still remains valid, and the reactor vessel pressure-temperature limit curves and material reference temperature (RTPTS) values evaluated for the end of license neutron fluence using the PTS screening criteria remain valid for the end of life conditions.
As stated in the staff's safety evaluation dated September 23, 2002, WBN-1 license condition C.(5) requiring TVA to perform fracture toughness (J-R curve) testing on specimens removed from surveillance capsules W and X is sufficient to ensure that the WBN-1 reactor vessel complies with the Charpy USE requirements of Appendix G to 10 CFR Part 50 through the end of its license. It should be noted that this license condition was initially included because the staff conditioned its acceptance of the TVA's equivalent margins analysis in the NRC's Supplement No. 14 to NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Units 1 and 2," dated December 1994.
The NRC staff finds that the increase in the number of TPBARs from 240 to 400 at WBN-1 does not change the analysis related to the reactor vessel integrity and that the requirements of the staffs safety evaluation dated September 23, 2002, related to the reactor vessel integrity analysis remain valid.
4.4 Structural Changes As previously noted, PNNL, the designer of the TPBARs, proposed changes to the TPBAR design to correct the permeation issue, and TPBARs with these design changes are proposed to be irradiated in the WBN-1 core starting with operating Cycle 9. The changes are primarily related to the design of internal components.
In its safety evaluation for Amendment No. 40 to the WBN-1 Operating License, which authorized the insertion of up to 2,304 TPBARs in the WBN-1 core, the NRC staff did not perform a detailed structural evaluation. Rather, it based its acceptance of the structural design on review of the DOE/TVA Interagency Agreement, which provides a means for imposing TVA requirements for safety-related components directly on DOEs TPBAR suppliers. This insures that TPBAR design, procurement and fabrication will be performed in accordance with a quality assurance (QA) program that complies with 10 CFR Part 50, Appendix B and NRC Regulatory Guide 1.28, Quality Assurance Program Requirements (Design and Construction).
In its August 22, 2007, response to a staff request for additional information, the licensee stated that the controls used in the design, fabrication and procurement of the redesigned TPBARs and TPBAR components are the same as those used in the original design.
Therefore, the NRC staff concludes that the changes to the structural design of the TPBARs will be made in accordance with applicable NRC regulatory procurement and QA requirements, and are acceptable.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, an official of the Tennessee Bureau of Radiological Health was notified of the proposed issuance of the amendment. The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20, and changes surveillance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (72 FR 31105). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health 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 Commission's regulations, and (3) the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public. Therefore, on the basis of the above review and justification, the staff concludes that the requests proposed in TVAs April 25, 2007 submittal are acceptable.
8.0 REFERENCES
Technical Specification Change 07-01, Revision of Number of Tritium Producing Burnable Absorber Rods (TPBARS) in the Reactor Core, dated April 25, 2007.
Technical Specification Change 07-01, Revision of Number of Tritium Producing Burnable Absorber Rods (TPBARS) in the Reactor Core - Response to Telecon Questions, dated August 22, 2007.
- 3. NDP-00-0344, Rev. 1, Revision 1, AImplementation 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 TVA=s letter to NRC, dated August 20, 2001, AWatts 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.@)
Principle Contributors: Anthony Attard John Honcharik Brendan Moroney Date: January 18, 2008