ML19320D087
| ML19320D087 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 06/26/1980 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| IEB-79-27, NUDOCS 8007180523 | |
| Download: ML19320D087 (8) | |
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TENNESSEE VALLEY AUTHORITY
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CHATTANOOG A. TENNESSEE 374ol,R C R {',1.
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i A8 58 June 26, 1980 Mr. James P. O'Reilly, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Region II - Suite 3100 101 Marietta Street Atlanta, Georgia 30303
Dear Mr. O'Reilly:
OFFICE OF INSPECTION AND ENFORCEMENT BULLETIN 79 RII:JP0 50-259, -260, -296 - BROWNS FERRY NUCLEAR PLANT UNITS 1, 2, AND 3 Enclosed is our response to IE Bulletin 79-27, transmitted by your letter to H. G. Parris dated November 30, 1979, for the Browns Ferry Nuclear Plant. This also responds to the Confirmatory Orders for Browns Ferry transmitted by letter from Victor Stello, Jr., to H. G. Parris dated April 4, 1980. The enclosure provides the information requested in Attachment A to the Confirmatory Orders.
Very truly yours, TENNESSEE VALLEY AUTHORITY lM l L. M. Mills,' Manager Nuclear Regulation and Safety Subscribed and sworn to before methisd(s day of OM 1980, i
C4h Pfothry Public 6
My Commission Expires k.
[Nf Enclosure cc:
See page 2 300718eN OFFICIAL COPY An C@at Opportunity Employer i
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1 2-Mr. James P. O'Reilly June 26, 1980 cc (Enclosure):
Director of Reactor Operations Inspections Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, DC 20555 Mr. Victor Stello, Jr., Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, DC 20555 i
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ENCLOSURE i
RESPONSE TO IE BULLETIN 79-27 AND ATTACHMENT A TO CONFIRMATORY ORDERS BROWNS FERRY NUCLEAR PLMG (DOCKET NOS. 50-259, -260, -296)
ITEM 1 Review the class lE and non-class 1E buses supplying power to safety and non-safety-related instrumentation and control systems which could affect the ability to achtsve a cold shutdown condition using existing procedures or procedures developed under item 2 below. For each bus:
a) identify and review the alarm and/or indication provided in the control room to alert the cperator to the loss of power to the bus.
b) identify the instrueent and control system loads connseted to the bus and evaluate the effects of loss of power to these loads including the ability to achieve a cold shutdown condition.
c) describe any proposed derign modifications resulting from these reviews and evaluations, and your proposed schedule for implementing those modifications.
. RESPONSE We have identified and reviewed all class 1E and nonclass lE buses which supply power to safety-and nonsafety-related instrumentation and control systems that are required to achieve cold shutdown.
Item la - As a part of this review, we examined in detail the alarm and/or indication provided in the control room which alerts the operatoc of the loss of power to the bus. No deficiencies were discovered as a result of this review.
Item lb - We have performed an analysis of each bus identified in item la and have evaluated the effects of a sustained loss of power to the instrument and control system loads supplied by each bus required to achieve cold shutdown.
As a result of this analysis, a deficiency was discovered in the reactor feedwater system. The analysis performed on 250-V de battery board No. 1
. 4 (battery boards 2 and 3 are similar) revealed that the feedwater pump speed control circuits and the 250-V de feedwater pump turbine trip circuits are supplied from the same battery board.
This deficiency was reported to NRC on June 2,1980, and Licensee Event Report (LER) No.
BFR0 50-259/8044 was submitted. A detailed analysis of this deficiency appears in Appendix A.
No deficiencies were discovered during the reviews of the other buses identified in item la.
The method used in performing the bus failure analysis is described in detail in Appendix B.
Item 1c - Descriptions of the proposed design modifications and the schedules for implementation developed as a result of the reviews and analyses undertaken for items la and Ib are discussed in Appendix A.
ITEM 2 Prepare emergency procedures or review existing ones that will be used by control room operators, including procedures required to achieve e cold shutdown condition, upon loss of power to each class lE and non-class lE bus supplying power to safety and non-safety-related instrument and control systems. The emergency procedures should include:
a)
C..e diagnostics / alarms / indicators / symptom resulting from the the eview and evaluation conducted per item 1 above, b) the use of alternate indication and/or control circuits which may be powered from other non-class lE or class lE instrumentation and control buses.
c) methods for restoring power to the bus.
Describe any proposed design modification or administrative controls to be implemented resulting from these procedures, and your proposed r
schedule for implementing the changes.
RESPONSE
l We have prepared appropriate emergency procedures to include the information requested in items 2a, 2b,-and 2c.
There are no design changes or modifi-
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l cations to be implemented as a result of the preparation and review of these emergency procedures. The only administrative controls to be implemented are described in detail in Appendix A.
ITEM 3 i
Re-review IE Circular No. 79-02, Failure of 120 Volt Vital AC Power Supplies, dated January 11, 1979, to include both class lE and non-class 1E safety-related power supply inverters.
Based on a review of operating experience and your re-review of IE Circular No. 79-02, describe any proposed design modific '..'ons or administrative controls to be implemented as a result of the re-review.
RESPONSE
We have reviewod IE Circular 79-02, " Failure of 120-V Vital AC Power Supplies," dated January 11, 1979, and we have concluded that it does not apply to Browns Ferry. As a result of this review, no design modifi-4 cations or administrative controls are required.
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APPENDIX A IE Bulletin 79-27 The following contains a detailed analysis of the reactor feedwater pump / main turbine control circuitry supplied from 250-V de battery board No. 1 (battery boards 2 and 3 are similar). The analysis that follows assumes a total sustained loss of voltage to the 250-V battery board bus.
Reactor Feedwater System All main control room and automatic trip functions, test circuitry, and associated alarms are lost for the feedwater pump turbines (FWPT). This includes the FWPT trip on high level in the reactor vessel. The only available methods of tripping the feedwater pumps are by either closing their steam supply valves, closing the main steam isolation valves (MSIV's), tripping the feedwater pump locally, closing the feedwater pump suction valves, or tripping the condensate booster pumps.
Power to transfer to the manual speed control mode of the feedwater pumps is lost. Therefore, if the feedwater system is in automatic control when the power loss occurs, manual control cannot be used.
If the feedwater control system (FWCS) is operating in channel B, the FWPT speed will be automatically controlled between 3,000-5,000 r/ min.
If the FWCS is operating in channel A, the FWPT's will go to their high-speed setting of 5,000 r/ min.
Fbin Turbine Control System All main turbine trip functions are lost except trip functions for high vibration, backup overspeed, loss of both turbine speed feedback channels and local manual trip. This includes the turbine trip resulting from high water level in the moisture separators.
Analysis of this bus failure is highly dependent upon the mode of operation of the FWCS, With the FWCS in channel A, feedwater flow to the reactor vessel increas'es rapidly as the FWPT's go to their high-speed setting of 5,000 r/ min. Should a scram occur with the FWPT trip system disabled, the FWPT's will not receive a high reactor water level trip signal. The reactor vessel will overfill unless the operator responds quickly using one of the alternate methods of tripping the FUPT's discussed previously.
With the FWCS in channel B, the speed of the FWPT's will not be able to be decreased below 3,000 r/ min.
Even with only one feedwater pump operating at 3,000 r/ min, the reactor vessel will overfill should a Scram occur.
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.o-Should the operator be unable to trip the FWPT's before overfilling the vessel, automatic actuations of the main steam relief valves (MSRV) will depressurize the reactor vessel.
Depressurization of the reactor vessel in this manner will entail the entrapment of water in the discharge flow of the MSRV in those cases where the MSIV's and/or turbine bypass valves are closed.
The results of activating the MSRV with water in the main steam line are currently being evaluated and discussed within the BWR owner's group and NRC.
Testing these valves under these operating conditions is being considered.
The interim-and long-term modifications necessary to provide a solution to this problem are discussed below.
Interim Solution An immediate solution was sought to separate the feedwater pump speed control circuitry and the FWpT trip circuitry.
By changir.g the power supplies of LM-46-6 (Steam-Feedwater-Rx Level Differential Amplifier GE #6-104) and LM-46-6A (comparator module GE #6-104A) from battery board No. 1 to the unit-preferred bus, the desired separation of the speed control and trip circuitry was obtained.
This solution provided a fix for operation in channel B of the FWCS only. Administrative controls were implemented to provide for operation of the FWCS in channel A.
An independent operator is to be stationed in front of transfer switch XS-3-53 when the FWCS ic being operated in channel A.
Transfer switch XS-3-53 provides for selection of the controlling channel. for the feed-water system. Should failure of battery board Mo. 1 occur with the FWCS in channel A, the operator will manually place XS-3-53 in the channel B position. Under these conditions, the plant will only operate in channel A when maintenance is to be performed or instruments are to be calibrated in channel B.
Single element control of the FUCS has not been affected by this interim solution. This solution was implemented on June 4,1980, using the Plant Operating Review Committee's approved temporary alteration procedures.
Long-Term Modification TVA is presently investigating a long-term solution to this problem.
The solution will involve upgrading the existing feedwater pump turbine and main turbine trip circuitry. We will notify your office, at a later date, of the solution and a schedule for its implementation.
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APPENDlX B IE Bulletin 79-27 Bus Failure Analysis Method 1.
Shutdown logic diagrams were generated to identify the alternate combinations of systems which are required to achieve cold shutdown.
2.
Safety function diagrams were generated to identify those components which are required or which could affect the function of the systems required to achieve cold shutdown.
3.
The instrument and control bus boundaries were identified for analysis purposes.
4.
The loads on the identified buses were compared with the L. stems identified on the shutdown logic diagram.
Those loads which could be clearly identified as having no effect on the function of the systems required to achieve cold shutdown were eliminated from any further analysis.
5.
Those loads which appeared to have a potential for affecting the shutdown systems were traced to the component level (valve, pump, switch, instrument, annunciator, indicating light, etc.); and the effect of loss of power to that component was determined.
6.
The component information was then analyzed with the ese of the
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safety function diagrams in order to determine which systems were inoperable and the effect their failure would have on plant operation.
i 7.
The results of the analysis undertaken in paragraph 6 were used, in conjunction with the normal plant shutdown sequence generated on j
the shutdown logic diagram, to determine whether cold shutdown ould be achieved. Alternate sequences to achieve cold shutdown ware identified and evaluated.
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