ML18038B113
| ML18038B113 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 01/23/1995 |
| From: | Salas P TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9502010039 | |
| Download: ML18038B113 (19) | |
Text
PRIORITY
'ACCELERATED RIDS PROCESSING) j.
REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION NBR:9502010039 DOC.DATE: 95/01/23 NOTARIZED: NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION SALAS,P. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Requests discretionary enforcement from requirements of TS LCO 3.9.B.3 in order to perform repairs & maintenance necessary to return DG C to operations.
DISTRIBUTION CODE: D030D COPIES RECEIVED:LTR i ENCL Q SIZE: /
TITLE: TVA Facilities Routine Correspondence NOTES RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-4 1 1 PD2-4-PD 1 1 WILLIAMS,J. 1 1 INTERNAL: ACRS 6 FILE CENTE~O 1 1 NRR/DSSA 1 1 OGC/HDS3 1 0 RES/DE/SSEB/SES 1 1 EXTERNAL: NOAC 1 1 NRC PDR 1 1 NOTE TO ALL"RIDS" RECIPIENTS:
PLEASE HELP US TO REDUCE iVASTE! CONTACTTHE DOCUMENTCONTROL DESK, ROOM PI -37 (EXT. 504-2083 ) TO ELIlNIINATE YOUR NAXIE FROM DISTRIBUTION LISTS I'OR DOC!.;MENTS YOU DON"I'EED!
TOTAL NUMBER OF COPIES REQUIRED: LTTR 15 ENCL 14
Tennessee Valley Authority, Post Office Box 2000, Oecatur, Alabama 35609 January 23, 1995 10 CFR 2, Appendix C U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:
In the Matter of ) Docket No. 50-260 Tennessee Valley Authority )
BROWNS FERRY NUCLEAR PLANT (BFN) - REQUEST FOR DISCRETIONARY ENFORCEMENT FROM COMPLIANCE WITH THE REQUIREMENTS OF TECHNICAL SPECIFICATION (TS) LIMITING CONDITION FOR OPERATION (LCO) 3 ' 'E 3 This letter requests Discretionary Enforcement from the requirements of TS LCO 3.9.B.3 in order to perform the repairs and maintenance necessary to return Diesel Generator C to operations. The current LCO 3.9.B.3 permits continued reactor power operation for seven days with one of the Units 1 and 2 diesel generators inoperable, provided that certain other equipment and offsite power sources are operable.
On January 16, 1995, at 8:05 pm Central Standard Time (CST),
during the performance of normal surveillance testing, Diesel Generator C experienced a failure of its turbocharger. In accordance with TS Surveillance Requirement 4.9.B.3, the remaining Units 1 and 2 diesel generators were demonstrated to be operable and power availability for the associated boards is being verified every eight hours. The repairs and maintenance necessary to return Diesel Generator C to operations, including receipt of parts and generator realignment, are expected to take a maximum of ten days to complete. With Diesel Generator C inoperable and the Discretionary Enforcement not in place, TS 3.9.B.3 would require an orderly shutdown be initiated on January 23, 1995, at 8:05 pm CST and BFN Unit 2 placed in a cold shutdown condition within the next twenty four hours.
'tt502010039 'st50123 Ogo PDR 4DOCK 05000260 p PDR t
U.S. Nuclear Regulatory Commission Page 2 January 23, 1995 TVA considers the potential risk associated with the required shutdown to be greater than the risk associated with the proposed Enforcement Discretion. Therefore, TVA requests Discretionary Enforcement from the, requirements of BFN Unit 2 TS LCO 3.9.'B.3 for a period of seventy two hours until January 26, 1995, at 8:05 pm CST.
The enclosure to this letter provides: (1) the TS that would be violated; (2) circumstances of the- diesel generator inoperability, including root cause, the need for prompt action, a description of why the situation could not have been avoided, and relevant historical events; (3) the safety basis for the request that enforcement discretion be exercised, including an evaluation of the safety significance and potential consequences of the proposed course of action; (4) the basis for the conclusion that the request will not be of potential detriment to the public health and safety and that a significant hazard consideration is not involved; (5) the basis for the conclusion that this request will not involve adverse environmental consequences; and (6) a discussion of compensatory actions.
The BFN Plant Operations Review Committee has reviewed this proposed Enforcement Discretion and has determined that operation of BFN Unit 2 in accordance with the proposed Enforcement Discretion will not endanger the health and safety of the public and does not involve a significant hazards consideration. There are no commitments contained in this letter. If you have any questions, please contact me at (205) 729-2636.
S' y, alas Manager of Site Licensing Enclosure cc: see page 3
U.S. Nuclear Regulatory Commission Page 3 January 23, 1995 cc (Enclosure):
Mr. Mark S. Lesser, Section Chief U.S. Nuclear Regulatory Commission Region 101 II Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35611 Mr. J. F. Williams, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Regional Administrator U.S. Nuclear Regulatory Commission Region 101 II Marietta St. NW, Suite 2900 Atlanta, Georgia 30323
ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 2 REQUEST FOR DZSCRETIONARY ENFORCEMENT FROM COMPLIANCE WITH THE REQUIREMENTS OF TECHNZCAL SPECZFICATION (TS)
LIMITING CONDITION FOR OPERATION (LCO) 3 GAB 3i OPERATZON WITH INOPERABLE EQUIPMENT I'ECHNICAL SPECIFICATION THAT WOULD BE VIOLATED BFN Unit 2 LCO 3.9.B.3 states:
When one of the units 1 and 2 diesel generator is INOPERABLE, continued REACTOR POWER OPERATION is permissible during the succeeding 7 days, provided that 2 offsite power sources are available as specified in 3.9.A.1.c and all of the CS, RHR (LPCI and containment cooling) systems, and the remaining three units 1 and 2 diesel generators are OPERABLE. If this requirement cannot be met, an orderly shutdown shall be initiated and the reactor shall be in the COLD SHUTDOWN CONDITION within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
II'IRCUMSTANCES OF THE DIESEL GENERATOR INOPERABILITY On January 16, 1995, at 8:05 pm CST, Diesel Generator C experienced a failure of its turbocharger during the performance of normal surveillance testing. This failure requires an inspection of the diesel generator, the removal and replacement of the turbocharger and associated gearing, the re-alignment of the diesel generator, and performance of the required post-maintenance testing.
The failure of the Diesel Generator C turbocharger was an unforeseen occurrence. Assessment of the extent of damage, identification of the required replacement parts, and consultations with the diesel generator vendor were started as soon as practical. The repairs and maintenance necessary to return Diesel Generator C to operations, including receipt of parts and generator realignment, are expected to take a maximum of ten days (240 hours0.00278 days <br />0.0667 hours <br />3.968254e-4 weeks <br />9.132e-5 months <br />) to complete.
An action plan has been established to determine the root cause of the turbocharger failure. Preliminary indications are that the turbocharger failed during diesel unloading. A failure during unloading would not have
prevented the diesel generator from loading and performing its intended safety function prior to the failure. This failure is self-evident upon unloading of the diesel generator.
Historically, a mechanical failure of the 3A diesel generator turbocharger occurred on August 25, 1992, also during diesel unloading. The damaged turbocharger was removed and sent to the vendor for disassembly and inspection. The vendor determined that the cause of the failure was planetary bearing failure, which caused a loss of concentricity in the gear train. The loss of concentricity within the gear train resulted in an improper meshing of the associated turbocharger gears and a failure of gear teeth. The root cause of the bearing failure was not possible to determine, but similar failures have occurred at other utilities due to improper lubrication. However, during disassembly of the turbocharger, lubricating oil was evident on all bearing surfaces and all drilled oil passages appeared clear.
The turbochargers for all eight BFN diesel generators were replaced in 1986. TVA began recording and trending diesel generator data in mid-1987 in response to Generic Letter 84-15< and Regulatory Guide 1.108< >. TVA has reviewed the operating history for the diesel generators since mid-1987 and the approximate number of starts for each diesel is shown below.
NRC letter to All Licensees of Operating Reactors, Applicants for an Operating License, and Holders of Construction Permits, dated July 2, 1984, Proposed Staff Actions to Improve and Maintain Diesel Generator Reliability (Generic Letter 84-15)
Regulatory Guide 1.108, Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants E-2
NUMBER OF STARTS DIESEL GENERATOR AS OF DECEMBER 1994 175 169 157 D 164 3A 167 3B 155 3C 154 3D . 159 TOTAL 1300 The turbocharger for Diesel Generator 3A failed in August 1992 after 116 starts. The turbocharger for Diesel Generator C failed after 157 starts. Four of the other diesels have more than 157 starts. Therefore, TVA considers it unlikely that the root cause of the diesel generator turbocharger failure is strictly age related.
The two failures in over 1,300 starts< > demonstrates the overall reliability of the turbochargers in use at BFN.
However, as the investigation of the root cause of the failure of Diesel Generator C continues, generic implications will be investigated and addressed in accordance with the BFN Corrective Action Program and the requirements of 10 CFR 21, Reporting of Defects and Noncompliances.
III. SAFETY BASIS Diesel Generator supplies emergency power to the C
following major safety related loads power and a if a loss of offsite design basis accident occur simultaneously:
~ Residual Heat Removal (RHR) Pump 2B Note that the number of starts during the period between when the diesel generator turbochargers were replaced (1986) and the when trending was started (mid-1987) are not counted in the total number of starts noted above.
E-3
~ Core Spray Pump 2B
~ RHR Service Water Pump B2 and Emergency Equipment Cooling Water (EECW) Pump B3 BFN is analyzed for a seven day allowed outage time (AOT),
during which no other single failure is assumed to occur in conjunction with a Design Basis Accident (DBA). This requested Enforcement Discretion would extend the AOT for an additional three days. During the AOT, standby auxiliary power for this equipment would not be available from its normal diesel generator. The three remaining RHR and Core Spray pumps will still be supplied from both the normal offsite power and standby power will be available from their normal diesel generators, For a long term loss of offsite power, if it is required.
Diesel Generator 3C could be manually aligned through the existing board tie breakers to supply power to this equipment, if needed.
Normal station power is from the unit station service transformers connected between the generator breaker and main transformer of each unit. Auxiliary power is available through the two common station service transformers, which are fed from two 161-kV lines supplying the 161-kV switchyard, one line each from the Athens and Trinity substations. Historically, this has proven a very reliable source of power. Table 3.1.1-,1 of the BFN Individual Plant Examination (IPE) reflected this low annual loss of offsite power initiating event frequency (3.52 x 10 ). Thus, the probability of a loss of offsite power occurring during the seventy two hours the Enforcement Discretion would be in effect is extremely low (2.89 x 10 ).
As described in Section 8.5.3 of the BFN Updated Final Safety Analysis Report, the standby AC supply and distribution system for Units 1 and 2 'consists of four diesel generators, four 4.16-kV shutdown boards, four 480-V shutdown boards and other supporting equipment. The standby AC supply and distribution system for Unit 3 is separate from that of Units 1 and 2. The Unit 3 system consists of four diesel generators (3A, 3B, 3C, and 3D),
four 4.16-kV shutdown boards, two 480-V shutdown boards and other supporting equipment. The Unit 3 diesels are required to support common equipment (Standby Gas Treatment System, Control Room Emergency Ventilation, RHR Service Water, and EECW). The attached figure shows the arrangement of the overall auxiliary power system.
There are three possible 4-kV supplies to each of the Unit 1/2 shutdown boards following a loss of offsite power.
The first alternate is from the other shutdown bus. The E-4
second alternate is from the diesel generator and the third alternate is to manually align the Unit 3 diesel generator via a Unit 3 shutdown board. Thus, with the Diesel Generator C inoperable, there are still three sources of 4-kV-power to the associated Unit 1/2 shutdown board. These options provide flexibility in the availability of power supplies to the 4-kV shutdown boards.
Each Unit 1/2 diesel generator normally supplies one division or train of the Engineered Safeguards System (ESS) and is assigned primarily to one 4-kV shutdown board. These diesel generators are highly reliable and have a high availability. Additionally, the probability of a loss of offsite power occurring on one unit concurrent with a design basis accident is extremely low.
TVA is currently replacing the 250-V DC shutdown board control power supply (SDBCPS) batteries. The replacement of the battery associated with Shutdown Board A is currently in progress. The loads that are normally supplied by Shutdown Board A are being suppli'ed by Battery Board 2. The associated LCO was entered on January 3, 1995. Work is proceeding on schedule and TVA currently anticipates exiting the LCO on February 5, 1995.
The replacement. is needed because the batteries are approaching the end of their service life and the additional capacity provided by the new batteries will be needed to support future multi-unit operation. TS 3.9.B.8 would normally permit a five day allowed outage time if one of the batteries and/or associated battery board that supplies shutdown board control power is inoperable.
Since approximately forty five days is needed to replace and test the batteries, an allowed outage time of forty five days was granted in TS Amendment No. 228, dated December 7, 1994.
In TVA's May 11, 1994 letter, TVA committed to implement compensatory measures while performing the modifications during operation. Specifically, the following compensatory measures are in effect while the 250-V DC .
SDBCPS Battery A modification is in progress:
No planned maintenance activities are scheduled or will be performed on any of the safety-related 250-V DC power supplies that could affect their operation.
There are no ongoing maintenance activities which could render critical safety equipment (such as diesel generators or emergency core cooling system pumps) out of service. Special authorization from the Plant E-5
Manager is required to perform these activities. TVA has developed a listthis of critical safety limitation.
equipment within the scope of Unplanned corrective maintenance is not being performed on critical safety equipment, unless necessary to restore operability. Unplanned corrective maintenance to restore equipment operability receives the highest priority.
Testing on the 250-V power supplies and critical safety equipment is-being scheduled around the control power supply modification outage period.
Pre-job briefings, to ensure that individuals are familiar with the scope of the special modifications activities, knowledgeable of their responsibilities, and aware of the hazards involved, was conducted prior to beginning modifications on the power supply.
Modification work is being performed in accordance with approved procedures and work instructions. Special training and procedures have been provided to operations personnel describing the actions to be taken if a 250-V DC power supply failure occurs while supplying shutdown board control power loads.
it is If a 250-V plant DC power supply malfunctions while is supplying shutdown board control power, the normal it plant loads can be transferred to the alternate power supply. However, control power will be lost to the affected shutdown board. Therefore, a temporary power supply cable has been staged and made available, so that control. power can be restored to the shutdown board.
These compensatory measures provide controls above and beyond those required by the Technical Specifications.
These measures provide additional assurance that BFN Unit 2 will be operated in a safe manner for the duration of the 250-V DC battery modification activity.
In order to quantify the risk to plant safety of having Diesel Generator C in an inoperable condition and the battery associated with Shutdown Board A being replaced, TVA used a probabilistic risk assessment (PRA) model E-6
I derived from the BFN Unit 2 IPE< >, designated BFNQUICK.
The truncation limits in this model were altered slightly to shorten the computation time. The BFNQUICK model was shown to give a reactor core damage frequency for normal Unit 2 operation comparable to that in the IPE. The base case for BFNQUICK shows an annual core damage frequency of 4.6 x 10 ~ for normal Unit 2 operation. The failure rates of various components in the normal and auxiliary power-supply systems were also taken from the IPE.
TVA calculated the change in core damage frequency between: (1) normal Unit 2 operation, and (2) Diesel Generator C inoperable and the modification to the battery associated with Shutdown Board A in progress. The result is an increase of 2.21 x 10 7 per day (approximately one-half percent). This increase in risk over the 72-hour time period of the Enforcement Discretion (6.63 x 10 or approximately one and a half percent) is negligible.
There is also negligible risk to BFN Units 1 and 3 during the Enforcement Discretion period since they are defueled and in a shutdown condition.
IV NO SIGNIFXCANT HAZARDS CONSIDERATXON TVA has concluded that operation of BFN Unit 2 during the period of Discretionary Enforcement does not involve a significant hazards consideration. This conclusion is based on the following considerations:
A. The ro osed Enforcement Discretion does not involve a si nificant increase in the robabilit or conse uences of an accident reviousl evaluated.
The proposed Enforcement Discretion extends the allowable time for plant operation with an inoperable diesel generator. Diesel generator operation is not a precursor to any design basis accident or transient analyzed in the Browns Ferry Updated Final Safety Analysis Report. Therefore, this Enforcement Discretion does not increase the probability of any previously evaluated accident.
BFN is analyzed for a seven day allowed outage time (AOT), during which no other single failure is assumed to occur in conjunction with a Design Basis (4) The BFN Unit 2 IPE was submitted by TVA on September 1, 1992. The NRC's review was issued on September 28, 1994, and concluded that the IPE met the intent of Generic Letter 88-20.
E-7
Accident (DBA). This requested Enforcement Discretion would extend the AOT for an additional three days. During'the AOT, standby auxiliary power for this equipment would not be available from its normal diesel generator. The three remaining RHR and Core Spray pumps will still be supplied from both the normal offsite power and standby power will be available from their normal diesel generators, is required. For a long term loss of offsite power, if it Diesel Generator 3C could be manually aligned through the existing board tie breakers to supply power to this equipment, not result in a if needed.
loss of the This configuration does ability to mitigate the consequences of a design basis accident. Therefore, this Enforcement Discretion does not significantly increase the consequences of any previously evaluated accident.
B. The ro osed Enforcement Discretion does not create the ossibilit of a new or different kind of accident from an accident reviousl evaluated.
The proposed Enforcement Discretion extends the acceptable time for plant operation with an inoperable diesel generator; it does not involve modification to plant equipment. No new failure a
modes are introduced. There is no effect on the function of any plant system and no new system interactions are introduced by this Enforcement.
Discretion. Therefore, the proposed Enforcement, Discretion does not create the possibility of a new or different kind of accident from any accident previously evaluated.
C. The ro osed Enforcement Discretion does not involve a si nificant reduction in a mar in of safet The proposed Enforcement Discretion extends the acceptable time for plant operation with an inoperable diesel generator. The redundant offsite circuits and the remaining diesel generators will ensure sufficient power for the safety related equipment required to mitigate the consequences of a Design Basis Accident on Unit 2. TVA has used a probabilistic risk assessment (PRA) model to quantify the risk to plant safety of having Diesel Generator C in an inoperable condition and the battery associated with Shutdown Board A being replaced. The change in core damage frequency between normal Unit 2 operation and operation with Diesel Generator C inoperable and the modification to the battery associated 7 with Shutdown Board A in progress is 2.21 x 10 per day E-8
(approximately one-half percent). This increase in risk (6.63 x 10 7 or approximately one and a half percent) is negligible over the 72-hour time period of the Enforcement Discretion. There is also negligible risk to BFN Units 1 and 3 during the Enforcement Discretion period since they are defueled and in a shutdown condition., Therefore, the proposed Enforcement Discretion does not involve a significant reduction in a margin of safety.
V ENVIRONMENTAL CONSIDERATIONS The proposed Enforcement Discretion has been reviewed against the criteria of 10 CFR 51.22 for environmental considerations. The proposed Enforcement Discretion does not involve a significant hazards consideration, nor increase the types and amounts of effluents that may be released offsite, nor significantly increase individual or cumulative occupational radiation exposures. Therefore, the proposed Enforcement Discretion meets the criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Accordingly, pursuant to 10 CFR 51.22 (b), no environmental impact statement or environmental assessment need be prepared.
VI ~ COMPENSATORY ACTIONS TVA has reviewed the available means of compensating for the inoperability of Diesel Generator C during the period of this Enforcement Discretion. Based on the considerations discussed below, TVA does not consider any additional compensatory actions to be required.
In order to ensure a highly reliable power source remains with Diesel Generator C inoperable, TVA will continue to demonstrate the availability of the required offsite circuits on a frequent basis. Demonstration of the availability of the associated boards every eight hours is required by TS Surveillance Requirement 4.9.B.3. Eight hours is considered an acceptable timeframe to ensure the reliability of this power source because of the number of remaining AC sources and the low probability of a Design Basis Accident coupled with a loss of offsite power occurring during this time.
For this situation (one diesel generator inoperable), TVA has also reviewed the issue of the operability of:
- 1. The remaining Units 1 and 2 diesel generators.
E-9
2 ~ During a long term loss of offsite power, Diesel Generator 3C, which can be manually cross-connected to supply the shutdown board normally supplied by Diesel Generator C.
'. The Unit 3 diesel generators, which are relied upon to supply emergency power to Standby Gas Treatment System Train C, Control Room Emergency Ventilation System Train B, RHR Service Water, and EECW.
These diesel generators have recently been demonstrated to be operable:
Diesel Generator A January .16, 1995 Diesel Generator B January 16, 1995 Diesel Generator D January 16, 1995 Diesel Generator 3A January 14, 1995 Diesel Generator 3B January 10, 1995 Diesel Generator 3C December 26, 1994 Diesel Generator 3D December 27, 1994 These tests are considered acceptable to demonstrate the operability of the remaining diesel generators.
Therefore, based on the demonstration of the required voltage for the associate boards every eight hours and the demonstrated operability of the remaining diesel generators, TVA does not consider any, additional compensatory actions to be required.
E-10
1 ~ ~ ~
~ I 8
1 ~ ' ~ ~ '
I e