ML041350165
| ML041350165 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/12/2004 |
| From: | Abney T Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-98-005 | |
| Download: ML041350165 (21) | |
Text
May 12, 2004 10 CFR 50.55a(a)(3)(i)
U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:
In the Matter of ) Docket No. 50-259 Tennessee Valley Authority )
BROWNS FERRY NUCLEAR PLANT (BFN) - UNIT 1 - AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) SECTION XI AND AUGMENTED INSPECTIONS - REQUEST FOR RELIEF, 1-ISI-19, REGARDING REACTOR PRESSURE VESSEL (RPV) CIRCUMFERENTIAL SHELL WELDS In accordance with 10 CFR 50.55a(a)(3)(i), TVA is requesting permanent relief from inservice inspection requirements of 10 CFR 50.55a(g) for the volumetric examination of the BFN Unit 1 reactor pressure vessel circumferential welds. This relief is for the remaining term of operation under the existing license. The alternative in TVAs request for relief provides an acceptable level of quality and safety and is consistent with the guidance and criteria described in NRC Generic Letter (GL) 98-05, Boiling Water Reactor Licensees Use of the BWRVIP-05 Report to Request Relief from Augmented Examination Requirements on Reactor Pressure Vessel Circumferential Shell Welds.
NRC issued GL 98-05 on November 10, 1998, which stated that licensees of BWRs may request permanent relief from the inservice inspection requirements of 10 CFR 50.55a(g) for the volumetric examination of circumferential reactor pressure vessel shell welds by demonstrating that: (1) at the expiration of the operating license, the circumferential welds will continue to satisfy the limiting conditional failure probability for circumferential welds in the NRC staffs safety evaluation (SER) of the BWRVIP-05 Report dated July 28, 1998, and (2) licensee has implemented operator training and established procedures that limit the frequency
U.S. Nuclear Regulatory Commission Page 2 May 12, 2004 of cold over-pressure events to the amount specified in the staffs July 28, 1998, SER. The enclosed request for relief demonstrates that TVA meets the guidance in GL 98-05 for permanent relief from the inservice inspection requirements of 10 CFR 50.55a(g) for the volumetric examination of the BFN Unit 1 RPV circumferential welds.
TVA requests approval of this request for relief by October 30, 2004, to support BFN Unit 1 restart activities.
This request for relief is consistent with those submitted to NRC for BFN Unit 3 by TVA letters dated June 25, 1999, and October 22, 1999, and for BFN Unit 2 by letter dated March 24, 2000. NRC letters to TVA dated November 18, 1999, and August 14, 2000 approved these relief requests for BFN Unit 3 and BFN Unit 2, respectively.
There are no new commitments contained in this letter. If you have any questions, please telephone me at (256) 729-2636.
Sincerely, Original signed by:
T. E. Abney Manager of Licensing and Industry Affairs Enclosure cc: See Page 3
U.S. Nuclear Regulatory Commission Page 3 May 12, 2004 Enclosure cc: (Enclosure):
(Via NRC Electronic Distribution)
U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-3415 Mr. Stephen J. Cahill, Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Senior Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, AL 35611-6970 Kahtan N. Jabbour, Senior Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)
One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739
U.S. Nuclear Regulatory Commission Page 4 May 12, 2004 MJB:BAB Enclosure cc (Enclosure):
M. J. Burzynski, BR 4X-C R. G. Jones, NAB 1A-BFN J. E. Maddox, LP 6A-C R. F. Marks, PAB 1C-BFN D. C. Olcsvary, LP 6A-C J. R. Rupert, NAB 1A-BFN K. W. Singer, LP 6A-C M. D. Skaggs, POB 2C-BFN J. Valente, NAB 1E-BFN E. J. Vigluicci, ET 11A-K NSRB Support, LP 5M-C EDMS-K S:lic/submit/subs/BFN U1 Circ Weld.doc
E-1 ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 1 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME)
SECTION XI, INSERVICE (ISI) AND AUGMENTED INSPECTION PROGRAM (FIRST TEN YEAR INSPECTION INTERVAL)
REQUEST FOR RELIEF 1-ISI-19 (SEE ATTACHED)
E-2 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 1 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME)
SECTION XI, INSERVICE (ISI) AND AUGMENTED INSPECTION PROGRAM (FIRST TEN YEAR INSPECTION INTERVAL)
REQUEST FOR RELIEF 1-ISI-19 Executive Summary:
TVA is requesting permanent relief from the inservice inspection requirements for volumetric examination of reactor pressure vessel (RPV) circumferential shell welds.
This request applies to the remaining term of operation under the existing license.
This request for relief will eliminate examination of the BFN Unit 1 RPV circumferential shell welds and is consistent with the guidance provided in NRC Generic Letter (GL) 98-05, Boiling Water Reactor Licensees Use Of The BWRVIP-05 Report To Request Relief From Augmented Examination Requirements On Reactor Pressure Vessel Circumferential Shell Welds dated November 10, 1998.
The intent of the 1992 10 CFR 50.55a rule change was to require licensees to perform an expanded RPV shell weld examination as specified in the 1989 Edition of the ASME Section XI Code, on an expedited basis.
Expedited in this context effectively means during the inspection interval that the rule was approved or the first period of the next inspection interval. The final rule change was published in the Federal Register on August 6, 1992.
The examination schedule for the RPV axially oriented welds shall continue as required by the ASME Section XI Code.
TVA is scheduled to perform the RPV shell weld examinations required by the ASME
E-3 Section XI Code on BFN Unit 1 prior to restart of the unit and in accordance with the requirements of ASME Section XI for the remaining term of the existing license due to expire on December 20, 2013.
The BWRVIP-05 Report and the associated NRC SER supports exclusion of the examinations of the RPV circumferential shell welds provided certain limiting conditions regarding end of license vessel embrittlement and cold over-pressurization events are satisfied. TVA has satisfied the limiting conditions specified in GL 98-05 for BFN Unit 1.
Further, BFN Unit 1 has been shut down and in an extended outage since 1985. Due to this extended shutdown, the BFN Unit 1 reactor vessel total neutron fluence at the end of the current operating license (December 20, 2013) will be much less than the 32 Effective Full Power Years (EFPY) of operation. Further, since TVA intends to submit license amendment requests to allow operation at approximately 120% of the current licensed power level (Extended Power Uprate), and to allow operation in an extended operational domain (Maximum Extended Load Line Limit Analysis Plus),
the end of license fluence value used below also reflects operation at these higher power levels. Accordingly, there is substantial conservatism in the evaluation supporting this request.
This request for relief is consistent with those submitted to NRC for BFN Unit 3 by TVA letters dated June 25, 1999, and October 22, 1999, and for BFN Unit 2 by letter dated March 24, 2000. NRC letters to TVA dated November 18, 1999, and August 14, 2000 approved these relief requests for BFN Unit 3 and BFN Unit 2, respectively.
Therefore, in accordance with the guidance provided in GL 98-05 and pursuant to 10 CFR 50.55a(a)(3)(i), TVA requests that relief be granted from performing the
E-4 volumetric examinations of the BFN Unit 1 RPV circumferential shell welds.
Unit:
One (1)
System:
Components:
Table 1 lists the BFN Unit 1 RPV circumferential welds for which TVA is requesting permanent relief from volumetric examination. The proposed relief is for the remaining term of operation under the existing license which expires December 20, 2013.
TABLE 1 Weld Description Category and Exam Method Table IWB-2500-1 Item Number Vessel Shell to Shell Weld No.C-4-5 B-A, Volumetric B1.11 Vessel Shell to Shell Weld No. C-3-4 B-A, Volumetric B1.11 Vessel Shell to Shell Weld No. C-2-3 B-A, Volumetric B1.11 Vessel Shell to Shell Weld No. C-1-2 (Located in Belt-line Region)
B-A, Volumetric B1.11 Vessel Shell to Bottom Head Weld No. C-BH-1 B-A, Volumetric B1.11 ASME Code Class:
ASME Code Class 1 Section XI Edition:
1995 Edition, 1996 addenda Code Table:
E-5 Examination Category:
B-A (Pressure Retaining Welds in Reactor Vessel)
Examination Item Number:
B1.11 (Circumferential Shell Welds)
Code Requirement From Which Relief Is Requested:
The inservice inspection requirements for the volumetric examination of RPV circumferential welds, ASME Section XI, Table IWB-2500-1, Examination Category B-A, Item B1.11, Circumferential Shell Welds, and the (expedited) augmented examination requirements of 10 CFR 50.55a(g)(6)(ii)(A) for vessel circumferential welds.
List Of Items Associated With The Relief Request:
See Table 1 Basis for Relief:
The basis for this request for relief is outlined in the NRCs July 28, 1998 Safety Evaluation (BWRVIP-05 Report SER) for the BWRVIP-05 Report (Electric Power Research Institute Report No. TR-105697) and the guidance outlined in GL 98-05. These documents provide the basis for the elimination of examinations of the BWR RPV circumferential shell welds. The BWRVIP-05 Report SER concluded that the probability of failure of the BWR RPV circumferential shell welds is orders of magnitude lower than that of the axial shell welds. In addition, the NRC conducted an independent risk-informed assessment of the analysis contained in the BWRVIP-05 Report SER. The NRC assessment and GL 98-05 concluded that the inspection of BWR RPV circumferential shell welds does not measurably affect the probability of failure. The industry examination results identified in the BWRVIP-05 report indicate that the
E-6 necessity for performance of the circumferential shell weld volumetric examinations is not warranted based upon the low probability of failure of these welds.
TVA has addressed the two criteria listed in the Permitted Action section of Generic Letter 98-05: (1) the Unit 1 RPV is bounded by the applicable limiting conditional failure probability identified in the NRC Staffs July 28, 1998 Safety Evaluation of the BWRVIP-05 report, and (2) licensees have implemented operator training and established procedures that limit the frequency of cold over-pressure events to the amount specified in the BWRVIP-05 SER. These criteria are addressed below.
Conditional Failure Probability The conditional failure probability of the BFN Unit 1 RPV beltline weld is bounded by the limiting Babcock & Wilcox (B&W) circumferential weld identified in Table 2.6-4 of the NRC Staffs Safety Evaluation of the BWRVIP-05 report (BWRVIP-05 SER).
The BFN Unit 1 RPV was manufactured by B&W.
The NRC Staffs review of the BWRVIP-05 Report included an independent assessment of the failure probability for BWR reactor vessels, based on manufacturer. As part of that assessment, the NRC Staff calculated conditional failure probabilities for the circumferential welds (probability of failure assuming occurrence of a cold overpressure event).
Those conditional failure probabilities were based on limiting weld assumptions for each manufacturer. TVA has evaluated the BFN Unit 1 beltline girth weld against these limiting assumptions and has determined that it is bounded by the assumptions used in the NRC assessment.
E-7 The NRC evaluation used an end of license 1/4 T fluence of 0.095 x 1019 n/cm2 for B&W reactor vessels. TVA has calculated an end of license 1/4 T fluence, of 0.0799 x 1019 n/cm2 for the BFN Unit 1 beltline weld (Weld C-1-2), using a methodology consistent with the guidance contained in NRC Regulatory Guide 1.190, and using very conservative assumptions. Specifically, the BFN Unit 1 fluence assumes 32 EFPY of operation, 120% of original licensed thermal power (Extended Power Uprate conditions), and operation in an expanded operating domain (Maximum Load Line Limit Analysis Plus). Assuming operation at Extended Power Uprate conditions and in the expanded operating domain ensures that this evaluation bounds anticipated BFN Unit 1 license amendments. Further, BFN has been shut down since 1985 and is expected to accumulate less than 14 EFPY by the end of its current license. This combination of inputs results in an extremely conservative evaluation relative to the development of the end of license Mean Nil Ductility Transition Temperature (RTNDT). Even given these conservative assumptions, the BFN Unit 1 beltline girth weld fluence is less than that listed in Table 2.6-4 of the BWRVIP-05 SER for B&W reactor vessels.
Based on the BFN Unit 1 Weld C-1-2 chemistries, the chemistry factor is less than that assumed in the NRC assessment for the B&W circumferential weld. The result of these assumptions and properties is that the calculated BFN Unit 1 end of license Mean RTNDT is less than that used in the NRC assessment; therefore, the conditional failure probability of the BFN Unit 1 reactor vessel circumferential welds are bounded by the results obtained in the NRC assessment. A comparison of the data used in the BFN Unit 1 calculation and the NRC Staff assessment is provided in Table 2 below.
E-8 TABLE 2 PARAMETER BFN UNIT 1 Weld C-1-2 LIMITING B&W RPV Fluence (1019 n/cm2) 0.0799 0.095 Initial RTNDT 200F 200F Chemistry Factor 184 196.7 Cu (Wt %)
0.27%
0.31%
Ni (Wt %)
0.60%
0.59%
[Initial RTNDT
+ RTNDT]
89.90F 99.80F Operator Training and Procedures The NRC staff stated in GL 98-05 that beyond design-basis events occurring during plant shutdown could lead to cold over-pressure events that could challenge vessel integrity. Although unlikely, the industry concluded that condensate and control rod drive pumps could cause conditions that could lead to cold over-pressure events that could challenge vessel integrity. For a BWR to experience such an event, the plant would require several operator errors.
The NRC staffs assessment described several types of events that could be
E-9 precursors to BWR RPV cold over-pressure transients. These were identified as precursors because no cold over-pressure event has occurred at a U.S. BWR. The staff assessment identified one actual cold over-pressure event that occurred during shutdown at a non-U.S. BWR. This event apparently included several operator errors that resulted in a maximum RPV pressure of 1150 psi with a temperature range of 79oF to 88oF. The operating procedures for BFN Unit 1 are sufficient to prevent a cold over-pressure event from occurring during activities such as the system leak test performed at the conclusion of each refueling outage.
Thus, the challenge to the BFN Unit 1 RPV from a non-design basis cold over-pressure transient is unlikely. The following discussion will provide further information to support TVAs conclusion.
BFN Operation procedures and administrative control processes are in place to minimize the potential for occurrence of RPV cold over-pressurization events. These processes include plant operating procedures, plant evolution planning and scheduling, administrative controls, and operator training.
Since cold over-pressurization events are most likely to occur during normal cold shutdown conditions, BFN operating procedures are written to require that RPV water level, pressure, and temperature are established and maintained in well controlled bands. Plant Unit Operators frequently monitor these parameters for abnormalities and indications of unwanted transients. Also, any plant evolution which requires changes in these critical parameters is performed under the oversight of the Shift Manager who is also notified immediately of any abnormalities in the indications. Therefore, any deviation of these parameters from the
E-10 established bands are promptly identified and corrected.
In addition to these procedures, unit conditions for on-going activities which potentially can affect the maintenance of acceptable operating conditions and available contingency systems and plans are discussed by unit operations personnel at the time of shift turnover. These administrative controls and procedures provide assurance that activities which could adversely affect RPV water level, temperature, and pressure are precluded.
Nuclear Experience reviews and industry operating histories have shown that inadequate work-control processes and procedures could precipitate a cold over-pressurization event. For BFN, outage work is controlled through planning and scheduling activities performed by the Outage Management and Work Control Team.
Unit and system work activities are carefully reviewed and coordinated to avoid conditions which could adversely affect the units RPV water level, temperature, and pressure. Plant activities are routinely coordinated through the use of a plan-of-the-day (POD) which contains a list of activities to be performed and frequently contains cautionary notes on the activities.
These PODs are reviewed and discussed with station management and copies are maintained in appropriate locations.
Changes to work schedules are approved through the Operations Department Management and the Shift Manager. In addition, during outages, work on unit systems and components is coordinated through work control centers which provide an additional level of unit operations oversight.
In the main control room, the Shift Manager is required to maintain cognizance of any activity which could potentially
E-11 affect reactivity, reactor water level, or decay heat removal. Unit Operators are required to provide positive control of reactor water level, temperature, and pressure within the specified bands, promptly report when operation outside the required bands occurs, and notify the Shift Manager of any restoration corrective measures being taken. As part of the outage work control process, special procedures such as hydrostatic testing require pre-job briefings conducted with operations personnel for any activity which could potentially affect critical plant parameters. The pre-job briefing includes all cognizant individuals involved in the work activities. Expected plant system and component responses and contingency actions to mitigate unexpected conditions are also discussed.
When the plant is in cold shutdown, plant procedures require that the RPV head vent valves be opened after the reactor has been cooled to less than 212oF.
Administrative and plant operations control procedures for this evolution and for controlling reactor water level, temperature, and pressure are an integral part of operator initial and re-qualification training. Responses to abnormal water level and RPV conditions are also part of the operators training.
In addition, unit-specific brittle-fracture operating pressure-temperature limit curves and procedures have been developed to provide the appropriate guidance for compliance with the operating limits and the associated Technical Specification requirements.
Review of High Pressure Injection Sources RPV water injection sources during cold shutdown conditions include three systems.
During normal cold shutdown, RPV water level and pressure are controlled through
E-12 the Control Rod Drive (CRD) and the Reactor Water Cleanup (RWCU) Systems.
RPV conditions are controlled through a feed and bleed process using these two systems. The RPV and its piping system are not placed in solid water conditions and after the plant is cooled below 212oF, the head vent valves are opened. If either one of the RWCU or CRD Systems fail, the Unit Operator would adjust the other system to maintain the proper water level and pressure. In addition, BFN also has water level instrumentation with set-points for high and low water levels that alarm to alert operators that a level transient is in progress and action is required. During these plant activities the CRD System typically injects water at a rate of less than 60 gallons per minute (gpm). Injection rates at this level allow the operator sufficient time to compensate for unanticipated level and pressure changes. Therefore, the probability of an occurrence of a high-pressure/low temperature event from these two systems, which places RPV conditions outside the pressure-temperature curve limits, is low.
In addition to the RWCU and CRD Systems, the Standby Liquid Control (SLC) System is another high-pressure source to the RPV.
For BFN, SLC System operation occurs only if the system is manually initiated by operator action in accordance with emergency operating procedures. Thus, SLC operation will not occur during cold shutdown operations except under stringently controlled test conditions.
In the event of an inadvertent injection, the SLC injection rate (approximately 50 gpm) is sufficiently low to allow operators to intervene and control the reactor pressure.
During cold shutdown periods following refueling, the RPV is pressure tested in accordance with the applicable ASME
E-13 Section XI Code requirements. BFN hydrostatic tests of the RPV and the reactor coolant system are designated as complex and infrequently performed tests.
For these types of tests BFN requires a detailed pre-job briefing with all individuals participating in the test.
RPV and reactor coolant system pressure testing is a carefully controlled plant evolution which receives special Operations management oversight and utilizes procedural controls to ensure that the test does not precipitate a transient outside the specified safety limits. These tests are also performed after the RPV and system are heated to the proper system inservice pressure test temperatures prior to increasing the system pressure. During these tests the RPV pressure, water level, and temperature are controlled through the CRD and RWCU Systems using the feed and bleed process. Increases (or decreases) in system pressure are limited to 50 pounds per square inch (psi) per minute. For example, if any RWCU valve fails, then the CRD pump is tripped and the RPV is depressurized. This practice minimizes the probability of exceeding the specified Technical Specification pressure-temperature limits during the system pressure test.
During plant startup following a cold shutdown, the High Pressure Coolant Injection (HPCI) and the Reactor Core Isolation Cooling (RCIC) pumps provide a possible means to over-pressurize the RPV. However, for BFN, these systems have high pressure steam-driven pumps which have automatic isolation instrumentation allowable values of 100 psig and 50 psig respectively; and will not function when the plant is in cold shutdown.
Based upon the above evaluation the likelihood of a cold over-pressure transient event placing the Unit 1 RPV
E-14 in non-design conditions is very low.
Therefore, the probability of an occurrence of a cold over-pressure transient is considered to be less than or equal to the probability used in the analysis described in the NRC independent evaluation performed in the assessment of the BWRVIP-05 Report.
Alternative Examination:
As an alternative, TVA proposes to perform only the Unit 1 RPV longitudinal shell weld examinations for the remaining term of the existing license.
Justification For The Granting Of Relief:
Based upon the previous stated technical justifications, performance of the examination of the Unit 1 RPV circumferential shell welds in accordance with the ASME Code requirements, is not warranted. This position is supported by actual industry inspection experience, industry initiatives, and their supporting calculations. Further, the additional costs and personnel exposure that would be incurred without any apparent increase in safety does not warrant the performance of the examinations. These factors provide reasonable assurance of the continued structural integrity of the BFN Unit 1 RPV. Therefore, pursuant to 10 CFR 50.55a (a)(3)(i), TVA requests that permanent relief, to the end of the current operating license (December 20, 2013) be granted from the inservice inspection and the augmented inspection requirements of 10 CFR 50.55a(g)(6)(ii)(A), for volumetric examination of reactor pressure vessel circumferential shell welds, ASME Section XI, Table IWB-2500-1, Examination Category B-A, Item B1.11, Circumferential Shell Welds as permitted by GL 98-05.
Further, in accordance with the guidance specified in the NRC SER, Section 4.0
E-15 for the BWRVIP-05 Report, TVA intends to examine the RPV circumferential shell welds should axial weld examinations reveal an active mechanistic mode of degradation. The scope and schedule of these examinations would be submitted to NRC for approval.
This request for relief is consistent with those submitted to NRC for BFN Unit 3 by TVA letters dated June 25, 1999, and October 22, 1999, and for BFN Unit 2 by letter dated March 24, 2000. NRC letters to TVA dated November 18, 1999, and August 14, 2000 approved these relief requests for BFN Unit 3 and BFN Unit 2, respectively.
Implementation Schedule:
This Request for Relief will be implemented during the First Ten Year ISI Inspection Interval for Browns Ferry Unit 1 and continue in effect for the remaining term of operation under the existing license.
Attachment:
Brown Ferry Unit 1 RPV shell weld location schematic drawing.
1-ISI-19 Attachment