ML20077E053
| ML20077E053 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 12/07/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20077E050 | List: |
| References | |
| NUDOCS 9412120077 | |
| Download: ML20077E053 (8) | |
Text
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UNITED STATES E
NUCLEAR REGULATORY COMMISSION f
WASHINGTON, D.C. 20W54001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0. 'MR TO FACILITY OPERATING LICENSE NO. DPR-52 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT UNIT 2 DOCKET'NO. 50-260
1.0 INTRODUCTION
By letter dated May 11, 1994, the Tennessee Valley Authority (the licensee) requested an amendment to the technical specifications (TS) for the Browns Ferry Nuclear Plant (BFN) Unit 2.
This request proposes a temporary extension of the allowed outage time (A0T) given in TS 3.9.B.8 for 250 V de shutdown board control power supply (250 V dc SDBCPS) batteries. The licensee proposes to extend the A0T while it replaces these batteries and associated hardware that supply 250 V dc. control power to the BFN Unit 1 and 2 shutdown boards.,
The replacement is needed because the batteries are approaching the end of their service life, and additional capacity will be needed to support multi
_1 unit operation.
The licensee determined that approximately 45 days will be required to perform the modifications and conduct necessary testing for each power supply.
TS 3.9.B.8 permits an A0T of 5 days if one of the batteries and/or associated battery-board that supplies shutdown board control power is found to *t inoperable.
The temporary A0T extension applies only to the power supply' being modifled.
The existing 5-day A0T will remain in effect for the existing power supplies prior to the modification, and to the modified power supplies after their return to service.
The licensee plans to begin these modifications'in early 1995, and has requested that the extended A0T be in effect from January 1 to December 31, 1995.
2.0 EVALUATION 2.1 Proposed Temporary Changes to the TS The licensee proposed to change the BFN Unit 2 TS Section 3.9.B.8 temporarily for a period of 1 year from January 1, 1995, to December 31, 1995. At present, the TS Section 3.9.B.8 reads as follows:
From and after the date that one of the 250-V shutdown board batteries and/or its associated battery board is found to be INOPERABLE for any reason, continued REACTOR POWER OPERATION is permissible during the succeeding five days in accordance with j
3.9.B.7.
fNCLOSURE 2 l
i 9412120077 941207 PDR ADOCK 05000260 P
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i The licensee proposed to change the TS Section 3.9.8.8.as follows:
From and after the date that one of the 250-V shutdown board batteries and/or its associated battery board is found to be inoperable for any reason, continued REACTOR POWER OPERATION is permissible during the succeeding five days in accordance with l
3.9.B.7 except as noted in 3.9.B.8.a,b, and c below:
a.
For the purpose of shutdown board battery and component replacement only, REACTOR POWER OPERATION is permissible for the succeeding forty-five (45) days providing.
1.
Only one of the shutdown board batteries and associated components is being replaced at a time.
2.
All components normally supplied from the shutdown board battery which is being replaced are fed from its alternate source.
3.
Units 1 and 3 are defueled.
b.
NRC notification for 3.9.B.7 is not required for shutdown board battery and component replacement, c.
Resumption of REACTOR POWER OPERATION is permissible following a shutdown while shutdown board battery and component replacements are in progress.
i NOTE: The provisions of specification 3.9.B.8 will apply from i
January 1, 1995, to December 31, 1995, while modifications are l
being performed on the shutdown board batteries and/or their i
associated battery boards.
i The licensee also proposes to add a reference to the temporary A0T extension to TS 3.9.A.4.
2.2 Discussion The licensee stated that the extension of the A0T is required to allow performance of the control power system upgrade at power.
Four 250 V dc control power supplies (A, B, C, and D) provide control power to Units 1 and 2, 480 V and 4160 V shutdown boards and anticipated transient without scram (ATWS) loads. The existing batteries are approaching the end of their qualified service life, and will soon need to be replaced.
The first battery's qualified service life expires in November 1996.
The licensee has designed a new 250 V dc SDBCPS system to handle the new loads added since previous three-unit operation. Modifications to install new components are needed to support the return to service of BFN Unit 3, which is expected in late 1995 or early 1996.
The primary new load to be added is the i
4 ATWS mitigation system for Units 1 and 3.
Other miscellaneous loads will also be added.
The existing power supplies are of lead-calcium grid construction (C&D type 3DCV-9) with a 1-minute rating of 148 amperes and an 8-hour discharge rating of 100 ampere-hours at a terminal voltage of 210 V at 77"F.
The C&D type KCR-ll batteries were selected as the most practical replacement battery considering multi-unit operation load requirements, available riargin, and economics.
The new batteries will have a 1-minute rating of 500 amperes and an 8-hour discharge rating of 410 ampere-hours at a terminal voltage of 210 V at 77*F.
Each shutdown board is supplied 250 V de control power from a normal source (250 V dc control power supply) or from an alternate safety-related source (250 V unit de power supply).
The ATWS loads also have redundant control power supplies from 250 V dc control power system.
To ensure that a reliable source of control power is available to the shutdown boards while the modifications are in progress, control power for the affected shutdown boards will be provided by their alternate power supply.
The licensee has determined that the alternate power supply has adequate capacity to supply loads under normal and accident conditions.
Calculations were performed to shcw that normal and accident electrical loading on alternate sorrce is acceptable. All cables used for the alternate feeds have been evaluatec for ampacity, voltage drop, short-circuit, and protection considerations, and determined to be acceptable.
The power supply configuration during the modification period is essentially the same as currently exists when a 250 V dc SDBCPS is out of service within the 5-day A0T period.
Due to an increase in the size and weight of the new batteries, new seismic Class 1, three-tier battery racks will be fabricated and installed.
Larger capacity battery chargers will also be installed.
The existing battery chargers have a capacity of 20 amperes.
With BFN Units 2 and 3 operating, the chargers will need to have a capacity of at least 22 amperes.
The new charger has a capacity of 50 amperes.
Furthermore, the existing 250 V dc control power supply distribution panels are rcted at 100 amperes and are too small to accommodate load growth and hence will be replaced by new 300 ampere, 250 V dc panels.
The existing ground fault detectors for the 250 V dc control power supplies will be replaced by new detectors that are located on the new distribution panels. Also, the power supplies to these ground fault detectors will be upgraded.
The electrical cables and circuits associated with the 250 V de control power supplies (e.g., battery charger circuit breakers and i
input and output power cables) will be replaced.
The replaced cables will be installed in conduits and are seismically qualified.
The licensee reviewed the maintenance activities associated with the system batteries and found several recent battery malfunctions.
The licensee stated it believes that the installation of new components will increase system reliability.
The licensee stated that the existing batteries require annual maintenance as they approach the end of their qualified life.
Installing new batteries will reduce the maintenance requirements since the new batteries will require
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. i biennial maintenance.
Furthermore, the annual maintenance' requires that the i
batteries be removed from service, reducing their availability.
Therefore,
. increasing the maintenance period will improve the system's overall availability.
The licensee stated that the modifications to the BFN Unit 1 and 2 control power supplies will be performed in series on one power supply at a time. The modifications to the first control power supply are scheduled to begin in early January 1995. The remaining power supply modifications will follow promptly while minimizing the impact on the plant. The licensee estimates that the modifications work and testing on each power supply will require approximately 45 days to complete. The licensee estimates that a 2-week period in between each modification period is'needed to prepare for the work and conduct maintenance and testing of other equipment.
This 2-week period extends the time needed to perform modifications on each power supply to
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approximately 2 months each, so approximately 8 months is required to perform the four power supply modifications.
The licensee's schedule included an additional 4 months for contingency purposes to ensure that unforeseen circumstances can be handled without additional impact on NRC and TVA.
Therefore, the temporary TS change is needed for a period of 1 year.
The licensee committed to implement compensatory measures while performing the modifications during operation. These compensatory measures include developing a special procedure to address actions for dealing with transients
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or accidents, restricting the testing and maintenance that can be performed while modifications are in progress, and providing alternative means of supplying control power. The following compensatory measures will be in ofect during the time that 250 V dc SDBCPS modifications are in progress:
j No planned maintenance on any of the safety-related 250 V dc power
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supplies that could affect their operation will be scheduled.
Planned maintenance will be limited to those periods between control power supply modification outages.
There will be no planned maintenance which could render critical safety
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equipment (such as diesel generators or emergency core cooling system pumps) out of service unless authorized by the Flant Manager. The licensee will develop a list of critical safety equipment within the scope of this limitation.
Unplanned corrective maintenance will not be performed on critical safety equipment unless necessary to restore operability.
This unplanned maintenance will receive the highest priority.
j Testing on the 250 V power supplies and critical safety equipment will
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be scheduled around control power supply modification outage periods where possible.
Pre-job briefings to ensure that individuals are familiar with the scope
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of the special modifications activities, knowledgeable of their responsibilities, and aware of the hazards involved, will be conducted prior to beginning modifications on each power supply.
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' Modification work.will be performed in accordance with approved i
procedures and work instructions. Special training and procedures will be provided to operations personnel describing the actions to be taken if a 250 V dc power supply failure occurs while it is supplying shutdown board control power loads.
If a 250 V plant de power supply malfunctions.while it is supplying shutdown board control power, the normal plant loads can be transferred to their alternate power supplies. However, control power will be lost to the affected shutdown boards. Therefore, a temporary power supply ~
cable will be staged and made available so that control power can. be restored to the shutdown boards.
These compensatory measures provide controls above and beyond those required by the Technical Specifications. These measures provide additional assurance that the facility will be operated in a safe manner for the duration of the 250 V de SDBCPS modification activities.
Since the plant configuration during the proposed modification period is very similar to that existing during the current A0T period, the change in risk to the facility is dominated by the change in the A0T period from 5 to 45 days.
The licensee evaluated the potential increase of the reactor core damage frequency of using the five alternate shutdown board control power supply
.i systems during the proposed modification periods. Note that one of these modifications, BFN Unit 3 250 V dc SDBCPS 3EB, is permissible under the existing TS because BFN Unit 3 is defueled. No TS change is required to permit the licensee to upgrade this system. The proposed TS change is relevant only to the modifications to the BFN Unit 1 and 2 250 V dc SDBCPS, designated "A,"
"B," "C,"
and "D."
For the estimation of the core damage frequencies, the licensee used a probibalistic risk assessment (PRA) model derived from the BFN Unit 2 Individual Plant Examination (IPE), designated BFNQUICK.
The truncation limits in this model were' altered slightly to shorten the computation time.
i The altered model was.shown to give a reactor core damage frequency comparable to that in the IPE for normal alignment of the shutdown board control power supply systems. The failure rates of various components.in the power supply systems were also taken from the IPE.
The BFN Unit 2 IPE was submitted by the licensee on September 1, 1992.. In re'sponse to staff requests on August 4, 1993 and November 19, 1993, the licensee provided additional information on September 21, 1993 and December 28, 1993.
This information was reviewed by the NRC staff and its contractors.
Results of this review were issued on September 28, 1994.
In this review, the staff concluded that the IPE met the intent of Generic Letter 88-20 with no unresolved issues except that the licensee needs to further examine the benefit of certain containment performance improvements.
These exceptions are not relevant to the proposed TS amendment.
The licensee used the BFNQUICK model to estimate the reactor core damage frequencies for the five SDBCPS systems, assuming that the normal batteries i
A were unavailable and the alternate batteries were used. The event trees were modified to reflect this assumption.
The estimated increase in the core damage frequency of using the alternate power systems over the normal alignment during a given modification ranges from 0.4 to 1.1 percent for the four cases affected by the proposed TS. The licensee provided no uncertainty analysis of the computation.
The staff has determined that the methodology used in the licensee's assessment is appropriate, the assumptions made are reasonable, and the supporting data are relevant.
The staff concludes that the licensee's analysis is capable of determining whether the proposed modification would significantly affect the overe:1 core damage risk.
The staff has determined that the licensee's assessment of the proposed battery modification activities during BFN Unit 2 power operations is valid, and the estimated overall potential increase in risk from relying upon the alternate power systems is negligibly small.
The licensee's proposed activity also constitutes negligible risk to BFN Units 1 and 3 while they are shutdown and defueled during the planned modifications. Although the licensee provided no uncertainty analysis, the staff believes that the computed risk increase is within the uncertainty of the model calculations, based on the staff's knowledge of the PRA used in the IPE, and the staff's general knowledge of PRA methods and results.
The staff determined that there is diversity in the electrical distribution system at the Browns Ferry Nuclear Plant.
This system was designed to support simultaneous power operation of three units.
Since only BFN Unit 2 will be operating during the planned modification, there will be a large excess of electrical capacity and capability available.
The licensee has proposed that NRC notification per TS 3.9.B.7 not be required for the SDBCPS modificnions. The resident inspector staff and other NRC personnel routinely closely monitor the licensee's modification activities.
Therefore, deleting NRC notification requirements for these modifications is not expected to inhibit the agency's ability to monitor and evaluate the licensee's activities.
Other requirements outside the scope of the modification activities are unaffected. Therefore, this proposed change is acceptable.
The licensee has proposed to permit the reactor to resume power operations if there is a shutdown during a modification period.
The staff concludes that restarting the reactor does not represent a risk materially different from any risk associated with power operations prior to any shutdown. Other requirements outside the scope of the modification activities are unaffected.
Therefore, this proposed change is acceptable.
The licensee has proposed to add a reference in TS 3.9.A.4 to the temporary allowed outage time extension.
This reference is consistent with other requirements as discussed above, and is acceptable.
. 2.3 Summary Based on its review, the staff agrees with the licensee that extending the 250 V dc SDBCPS A0T to 45 days will not adversely impact the health and safety of the public. The planned modifications will increase the capacity and reliability of the 250 V dc shutdova board control power supply system, which the staff believes is a net safety benefit. The proposed temporary amendment would allow the power supplies to be replaced without requiring a' lengthy extension to a future Unit 2 refueling outage, or a costly modification to temporarily fulfill the 250 V dc SDBCPS functions during the modification period.
The staff feels that the following considerations justify performance of the modifications while Unit 2 is operating:
BFN Units 1 and 3 will be defueled during the modification.
This results in a reduced electrical load on the batteries and excess capacity being available. The BFN electrical distribution system is designed to support operation of three units simultaneously.
Since only BFN Unit 2 will be operating for the duration of the A0T extension, there is a large excess of electrical capacity available during the modification period.
All safety systems will have power available and will remain operable during the proposed modifications.
Appropriate configuration controls will be implemented by the licensee to ensure the continued availability of critical systems, and their prompt return to service if they are taken out of service for unplanned corrective maintenance.
The licensee will implement other compensatory measures during the modifications periods, including training and materials which will improve the ability of facility personnel to recognize and mitigate the effects of a postulated control power supply f ailure.
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Only one shutdown board control power supply will be removed from service at a time.
There is no change in the TS requirements associated with the control power systems which are not in the process of being i
modified.
At no time during a modification period will any of the three plant power supplies be removed from service for planned maintenance.
Therefore, 250 V de control power will be provided through qualified, alternate safety related power supplies for the duration of the modification period.
Performing the proposed 250 V de system modification will increase system reliability and is required for multi-unit operation due to an increase in loads.
The staff believes this modification represents a net safety benefit to future facility operations as the existing control power supplies are replaced with more reliable and capable systems.
The licensee's PSA is acceptable justification demonstrating there is an insignificant increase in risk associated with the proposed amendment.
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The removal of NRC-reporting requirements and restart restrictions does not significantly affect the agency's ability to monitor licensee activities or significantly increase risk' to the facility.
Based on these factors, the licensee's proposed TS to increase the allowed outage time, remove reporting requirements, and remove restart restrictions.
during the power supply modification are acceptable. The staff graats these amendments for a period of one year from January 1, 1995, to December 31, 1995.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Alabama State official was notified of the proposed issuance of the amendment. The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part'20 and changes the surveillance requirements. The NRC staff has determined that the amendments involve 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 i
occupational radiation exposure.
The Commission has previously~ issued a l
proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (59 FR 42347). Accordingly, the amendments meet the eligibility criteria for i
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.
5.0 CONCLUSION
1 The Commission has concluded, based upon 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, and (2) such activities will be conducted in compliance with the Commission's-regulations, and (3) issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: Amar Pal, James Wing, and Joseph Williams Dated: December 7, 1994
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