ML082940170

Request for Additional Information - Watts Bar Emergency Core Cooling System Boron Requirements

ML082940170
Person / Time
Site:	Watts Bar
Issue date:	10/28/2008
From:	Lamb J G Watts Bar Special Projects Branch
To:	Campbell W R Tennessee Valley Authority
Lamb John G./NRR/DORL, 415-3100
References
TAC MD9396
Download: ML082940170 (7)

Text

October 28, 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 - REQUEST FOR ADDITIONAL INFORMATION - WATTS BAR EMERGENCY CORE COOLING SYSTEM BORON REQUIREMENTS (TAC NO. MD9396)

Dear Mr. Campbell:

By letter dated August 1, 2008, Tennessee Valley Authority (TVA) proposed a license amendment to change the Watts Bar Nuclear Plant, Unit 1 (WBN-1), Technical Specifications (TSs). The proposed request is to revise the boron requirements for cold leg accumulators and refueling water storage tank.

The staff has reviewed the information provided by TVA and has determined that additional information is required to complete its evaluation of the proposed license amendment. The specific questions are detailed in the enclosed request for additional information (RAI). We have had several discussions with your staff regarding these RAIs. Based on discussions with your staff, we understand that you plan to respond to the enclosed RAIs within 45 days of the date of this letter.

The staff expects and requires your timely and complete responses so as to complete its review consistent with our performance goals.

If you have any questions regarding this issue, please feel free to contact me at (301) 415-3100.

Sincerely,

/RA/

John G. Lamb, Senior Project Manager Watts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Docket No. 50-390

Enclosure:

RAI

cc w/enclosure: See next page 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 - REQUEST FOR ADDITIONAL INFORMATION - WATTS BAR EMERGENCY CORE COOLING SYSTEM BORON REQUIREMENTS (TAC NO. MD9396)

Dear Mr. Campbell:

By letter dated August 1, 2008, Tennessee Valley Authority (TVA) proposed a license amendment to change the Watts Bar Nuclear Plant, Unit 1 (WBN-1), Technical Specifications (TSs). The proposed request is to revise the boron requirements for cold leg accumulators and refueling water storage tank.

The staff has reviewed the information provided by TVA and has determined that additional information is required to complete its evaluation of the proposed license amendment. The specific questions are detailed in the enclosed request for additional information (RAI). We have had several discussions with your staff regarding these RAIs. Based on discussions with your staff, we understand that you plan to respond to the enclosed RAIs within 45 days of the date of this letter.

The staff expects and requires your timely and complete responses so as to complete its review consistent with our performance goals.

If you have any questions regarding this issue, please feel free to contact me at (301) 415-3100.

Sincerely,

/RA/

John G. Lamb, Senior Project Manager Watts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Docket No. 50-390

Enclosure:

RAI cc w/enclosures: See next page DISTRIBUTION:

PUBLIC RidsNrrPMJLamb B. Parks, NRR RidsNrrDorlDpr LP-WB R/F RidsNrrLABClayton RidsOgcRp RidRgn2MailCenter RidsNrrDorlLpwb RidsNrrDssSrxb RidsAcrsAcnwMailCenter ADAMS Accession Number: ML082940170 OFFICE LP-WBB/PM LP-WB/LA SRXB/BC LP-WB/BC NAME JLamb BClayton GCranston LRaghavan DATE 10/ 21 /08 10/ 21 /08 10/ 21 /08 10/ 28 /08 OFFICIAL RECORD COPY William R. Campbell, Jr. Tennessee Valley Authority WATTS BAR NUCLEAR PLANT

cc:

Mr. Gordon P. Arent New Generation Licensing Manager Tennessee Valley Authority 5A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

Mr. Ashok S. Bhatnagar Senior Vice President Nuclear Generation Development and Construction Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

Vice President Nuclear Support Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

Mr. Michael J. Lorek Vice President Nuclear Engineering & Technical Services Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

General Counsel Tennessee Valley Authority 6A West Tower 400 West Summit Hill Drive Knoxville, TN 37902

Mr. John C. Fornicola, Manager Nuclear Assurance Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

Mr. Larry E. Nicholson, General Manager Performance Improvement Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

Mr. Michael D. Skaggs Site Vice President Watts Bar Nuclear Plant Tennessee Valley Authority P. O. Box 2000 Spring City, TN 37381 Mr. Michael A. Purcell Senior Licensing Manager Nuclear Power Group Tennessee Valley Authority 4K Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

Ms. Beth A. Wetzel, Manager Corporate Nuclear Licensing and Industry Affairs Tennessee Valley Authority 4K Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

Mr. Masoud Bajestani, Vice President Watts Bar Unit 2 Watts Bar Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Spring City, TN 37381

Mr. Michael K. Brandon, Manager Licensing and Industry Affairs Watts Bar Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Spring City, TN 37381

Mr. Gregory A. Boerschig, Plant Manager Watts Bar Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Spring City, TN 37381

Senior Resident Inspector Watts Bar Nuclear Plant U.S. Nuclear Regulatory Commission 1260 Nuclear Plant Road Spring City, TN 37381

County Executive 375 Church Street

Suite 215 Dayton, TN 37321

County Mayor P. O. Box 156 Decatur, TN 37322

Mr. Lawrence E. Nanney, Director Division of Radiological Health Dept. of Environment & Conservation Third Floor, L and C Annex 401 Church Street Nashville, TN 37243-1532 Enclosure REQUEST FOR ADDITIONAL INFORMATION REGARDING TECHNICAL SPECIFICATIONS REVISIONS EMERGENCY CORE COOLING SYSTEM BORIC ACID CONCENTRATION REQUIREMENTS WATTS BAR NUCLEAR PLANT, UNIT 1 TENNESSEE VALLEY AUTHORITY DOCKET NO. 50-390 By letter dated August 1, 2008 (ADAMS Accession No. ML082180091), the Tennessee Valley Authority (TVA), the licensee for Watts Bar Nuclear Plant (WBN) Unit 1, submitted a request to revise the WBN Unit 1 Technical Specifications (TSs) to change the boron requirements for cold leg accumulators and refueling water storage tank (RWST). The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing this request, and has determined that additional information is necessary for the staff to complete its review, as discussed below.

Question 1. Inclusion Of Emergency Core Cooling System (ECCS) Boron Requirements In the Core Operating Limits Report (COLR)

NRC Generic Letter (GL) 88-16, "Removal of Cycle-Specific Parameter Limits from Technical Specifications (TSs)" provides a means by which licensees may avoid cycle-specific revisions to the TSs by modifying the TSs to note that cycle-specific parameters shall be maintained in a COLR, which is provided to the NRC for information on a cycle-specific basis. To implement the GL 88-16 guidance, licensees are required to maintain, in their TSs, references to NRC-approved methodologies that are used to determine the parameter operating limits. If the methodology is plant-specific, a reference to the NRC safety evaluation (SE) approving the use of the methodology is alternatively required.

TVA proposes to implement the guidance contained in GL 88-16 to provide discreet levels of ECCS boron concentration requirements. Each level would be specified in the applicable Surveillance Requirement, and the specific level determined for the cycle would be specified in the COLR. To support this request, the licensee has proposed a COLR reference to Westinghouse document WCAP-16932-P, Revision 1, as approved by the NRC staff's SE.

However, WCAP-16932-P describes the technical adequacy of an assumption crediting control rod insertion for certain postulated post-loss-of-coolant accident (LOCA) scenarios, in which trip reactivity is required for post-LOCA subcriticality. Hence, this proposed reference appears inappropriate, because it does not contain the methodology used to determine the cycle-specific ECCS boron concentration requirement.

Additionally, the NRC staff believes that a strong contingent of the cycle-to-cycle variability in required ECCS boron concentration is the inventory of Tritium Producing Burnable Absorber Rods (TPBARs) in the core. This belief is supported by, among other things, the fact that a previously approved request submitted by TVA provided discreet levels of boron concentrations based solely on the TPBAR inventory.

In light of these considerations, please provide the following additional information:

Revise your proposed TS reference so that it accurately reflects a methodology document describing explicitly how the boron concentration level published in the COLR will be determined.

Explain what additional cycle-specific design considerations warrant your proposed boron concentration requirements' inclusion in the COLR as opposed to in the TSs. Why is this proposal inconsistent with your previous TS requirement?

Question 2. Analytic Basis for ECCS Boron Concentration Requirements.

As required by Title 10 of the Code of Federal Regulations, Section 50.46, each pressurized light water nuclear power reactor must be provided with an ECCS that must be designed so that its calculated cooling performance following postulated LOCAs conforms to, among others, a requirement for long-term cooling. After any calculated successful initial operation of the ECCS, the calculated core temperature shall be maintained at an acceptably low value and decay heat shall be removed for the extended period of time required by the long-lived radioactivity remaining in the core.

As a part of this requirement, Westinghouse-evaluated ECCS designs are typically required to assist in maintaining a subcritical core configuration. As such, the ECCS is designed to contain sufficient boron to compensate for positive reactivity effects that could be associated with a postulated LOCA, for instance, reductions in average coolant temperature.

Please justify the technical adequacy of your proposed ECCS boron concentration requirements:

You state, "the negative worth of each absorber, including the reactor coolant system (RCS) boron worth, decreases" (page E1-4 of submittal letter). Explain how your analysis accounts for the phenomena that contribute to the reduction of the boron worth.

Confirm that your analytic codes and methods are capable of accounting for the neutronic effects of boron concentration levels as high as 3800 parts per million (ppm).

Question 3. Critical Boron Requirements for a High Burnable Absorber Loading

The NRC staff's initial review of the fuel system design required to support the requested TPBAR loading is documented in numerous letters and submittals between TVA and the NRC staff. The NRC staff's review was governed, in part, by the guidance contained in Section 4.2 of the Standard Review Plan (SRP 4.2). SRP 4.2 directs the NRC staff to review areas concerning reactivity control requirements and provisions. As such, the licensee submitted a description of changes in critical boron requirements to support operation with the requested number of TPBARs (Westinghouse Report NDP-00-0344, submitted to NRC on August 20, 2001). These boron requirements increased over those required for previous Watts Bar Cycle designs (see page 2-20 of NDP-00-0344).

While the NRC staff does not intend to repeat its review of the original request to operate a tritium production core, certain assumptions regarding the initial boric acid concentration could affect the required performance of the ECCS, immediate post-LOCA) subcriticality, and the outcome of the long-term core cooling calculation.

Please explain how the core design computer codes determine the critical boron concentration for cycle reloads.

The NRC staff reviewed Licensing Topical Report WCAP-11596-P-A describing the qualification of the PHOENIX-P/ANC code system. Most of the presented validation for critical boron concentration extended to slightly higher than 1000 ppm, with increased scatter at higher boron concentrations.

Does the current validation data set for the applicable version of PHOENIX/ANC include critical boron concentration measurements that extend to 2000 ppm or beyond?

Do available core-follow statistics include reactors operating with heavy loadings of neutronic absorbers with low atomic numbers?

How does this compare to critical boron concentrations predicted for current core designs at similar Westinghouse 4-loop Pressurized-Water Reactors (PWRs)?

How is the core critical boron concentration incorporated into the post-LOCA long-term core cooling analysis?

Question 4. Nuclear Safety Advisory Letter 07-7

The NRC staff is aware that Westinghouse has recently issued a Nuclear Safety Advisory Letter

concerning the capability of a PWR core to remain subcritical in the early stages following a large break LOCA based on the contribution of negative reactivity from core voiding during the blowdown, existing RCS boron concentration, and cold leg accumulator boron concentration.

Confirm whether the proposed boron concentration levels account for the potential effects identified in that Nuclear Safety Advisory Letter.

Question 5. Selection of Pipe Breaks for Post-LOCA Subcriticality

For the scenarios used to evaluate post-LOCA subcriticality, a cold leg accumulator line break and a pressurizer surge line break are assumed. The post-LOCA subcriticality analyses do not appear to account for reactor coolant pipe breaks. Please explain.

Question 6. Staff Confirmatory Calculation of Post-LOCA Long-Term Core Cooling

Due to the high ECCS boric acid concentration requirements, the NRC staff intends to perform confirmatory analysis r egarding the long term core cooling capability.

1. Please provide the following information for the WBN Unit 1 Nuclear Steam Supply System (NSSS): a. Volume of the lower plenum, core and upper plenum below the bottom elevation of the hot leg, each identified separately. Also, provide heights of these regions.

b. Loop friction and geometry pressure losses from the core exit through the steam generators to the inlet nozzle of the reactor vessel. Also, provide the locked rotor Reactor Coolant Pump (RCP) k-factor. Please provide the mass flow rates, flow areas, k-factors, and coolant temperatures for the pressure losses provided (upper plenum, hot legs, Steam Generators (SGs), suction legs, RCPs, and discharge legs). Please include the reduced SG flow areas due to plugged tubes. Please also provide the loss from each of the intact cold legs through the annulus to a single broken cold leg.

c. Capacity and boron concentration of the RWST.

d. Capacity of the condensate storage tank.

e. Boric acid concentration vs. time for the limiting large break.

f. Flushing flow rate at the time of switch to simultaneous injection.

g. High Pressure Safety Injection runout flow rate.

2. What is the sump temperature vs. time following recirculation and how does this impact precipitation? Is the boric acid concentration in the vessel below the precipitation limit based on the minimum sump temperature at the time the switch to simultaneous injection is performed? Please explain.

3. Please provide the following elevation data:

a. bottom elevation of the suction leg horizontal leg piping

b. top elevation of the cold leg at the RCP discharge

c. top elevation of the core (also, height of core)

d. bottom elevation of the downcomer Question 7. Boric Acid Concentration Calculation of Post-LOCA Long-Term Core Cooling

The NRC staff is aware that a boric acid concentration calculation has been performed that more closely aligns to the NRC staff's current expectations and acceptance criteria regarding the precipitability of boric acid in the long-term phase following a LOCA. Please provide a summary of this calculation.