ML19290G038
| ML19290G038 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Summer |
| Issue date: | 11/03/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML093450149 | List:
|
| References | |
| FOIA-80-515, FOIA-80-555 NUDOCS 8011130047 | |
| Download: ML19290G038 (17) | |
Text
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SAFETY EVALUATION REPORT 9,
VIRGIL C. SUMMER NUCLEAR STATION IMPLEMENTATIONS OF RECOMMENCATIONS FOR AUXILIARY FEEDWATER SYSTEMS n r::vction and 3ackaround
~ne -'. rte Mil e 's Ind Uni: 2 (7MI-2) accident and subsicuent invas:';a:icns Inc studies higniigh ad the i cor ance of the auxiitary eec-ata-ijstam (AF'S)
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. : r AFW system failure due to common causes, single point vulnerabilities, and human error.
In accordance with the requirements of Item II.E.1.1 of NUREG-0660, "NRC Action Plan Developed as a Result of the TMI-2 Accident," we have included the following results of the V. C. Summer AFW system review in this SER:
1.
We have applied the generic results and recommendations from the above described reviews for operating plants to the V. C. Summer AFWS.
2.
We are reviewing the detailed Summer AFWS reliability evaluation submitted by the applicant. Our conclusion will Je contained in a suppicment to this SER.
3.
We have reviewed the applicant's deterministic comparison of the V. C.
Summer AFWS against Standard Review Plan (SRP) Section 10.4.9 and Branch Technical Position (BTP) ASB 10-1, and find that the AFWS design is in compliance. Environmental qualification of the AFWS is being reviewed by the Equipment Qualification Branch as a separate item, and will be reported in a separata safety evaluation at a later date.
4.
We have reviewed the applicant's response to our request in Enclosure 2 af our letter dated March 10, 1980, regarding the design basis for AFWS flow requirements. The applicant provided this information in a letter dated August 15, 1980. We conclude that the applicant's design basis for AFWS flow requirements is acceptable.
. We conclude that the implementation of the folicwing recommendations identified from the above reviews have improved the reliability of the V. C. Summer AFW system.
II.
Imolementation of Our Recommendations A.
Short Term Recommendations 1.
Recommendation GS-1 "The licensee should propose modifications to the Technical Specifications to limit the time that one AF.i system pump and its associated flow train and essential instrumentation can be inoperable. The outage time limit and subsequent action time should be as required in current Technical Specifications; i.e., 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, resoectively."
In response, the applicant indicated n a letter dated August 15, 1980, that the proposed V. C. Summer Technical Specification, section 3.7.1.2 applies. This specification limits the plant operation with one AFW train out of service to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and the subsequent action time to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. We conclude that this Technical Specification is in com-pliance with our recommendation and is, therefore, acceptable.
2.
Recommendation GS-2 "The licensee shoul. lock open single valves or multiple valves in series in the AFW system cump suction piping and lock open other single valves or multiple valves in series that could interrupt all AFW flow. Monthly inspections should be performed to verify that these valves are locked and in the open position. These inspections should be proposed for incorporation into the surveillance requirements of the plant Technical Specifications. See Recommendation GL-2 for the longer-term resolution of this concern."
_4 In a letter dated August 15, 1980, the applicant responded to this recommendation by stating that the primary AFW system water passes through a single normally locked open valve in the connon suction piping to the AFW pumps. This valve is provided with a limit switch which is alarmed in the control,oom when it is not in the full open position.
In addition, the applicant will incorporate periodic inspections into the surveillance requirements of the Technical Specifications to verify the valve position. In accordance with our requirement we will assure that these inspections be performed mon thly. The applicant has also connitted to remove the hand wheel from this valve to provide further protection against its inadver-tent closure. Based upon the above commitments, we conclude that the applicant's response is acceptable, pending formal documentation of the commitnents.
3.
Recommendation GS-3 "The licensee has stated that it throttles AFW system flow to avoid water hammer. The licensee should reexamine the practice of throttling AFW system flow to avoid water hammer.
The licensee should verify that the AFW system will supply on demand sufficient initial flow to the necessary steam generators to assure adequate decay heat removal following loss of main feedwater flow and a reactor trip from 100% power. In cases where this reevaluation results in an increase in initial AFW system flow, the licensee should provide sufficient informaticn to demonstrate that the required initial AFW system flow will not result in plant damage due to water hammer."
In response, the applicant indicated in a letter dated August 15, 1980, that throttling of the APdS to avoid water hammer will not be utilized.
Based on the applicant's response, we conclude that Recomendation 15-3 is not applicable to V. C. Summer.
Recomendation GS-4
" Emergency procedures for transferring to alter-
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nate sources of APA supply should be available to the plant operators.
These procedures should include criteria to inform the operator when, and in wnat order, the transfer to alternate water sources should take place. The following cases should be covered by the procedures:
- 1) The case in which the primary water supply is not initially available. The pmcedures for this case should include any operator actions reouired to protect the AF4 system oumos against self-damage before water flow is initiated.
- 2) The case in which the primary water supply is being depleted. The procedures for this case should provide for transfer to the alter-nate water sources prior to draining of the primary water supply."
In response to this reconnendation, the acplicant indicated in a letter dated August 15, 1980, that plant procedures provide criteria for transfer to the alternate water source for both the case where crimary water supply is not initially available and the case where the primary water supply is being depleted. 'de conclude that the applicant's response is acceptable pending verification of the plant procedures by the Office of Inscection and Enforcement.
5.
Recomendation GS-5 "The as-built plant should be capable of providing the required AF4 flow for at least two hours from one AF4 pump train, independent of any alternating current power source.
If manual AFW system initiation or flow control is required following a complete loss of alternating current power, emergency procedures should be established for manually initiating and controlling the system under these conditions.
Sirce the water for cooling of the lube oil for the turbine-driven pump bearings may be dependent on alternating current power, design or proce-dural changes shall be made to eliminate this dependency as soon as practicable. Until this is 'done, the em rgency procedures should pro-vide for an individual to be stationed at the turbine-driven pump in the event of the loss of all alternating current pcwer to monitor pump bearing and/or lube oil temperatures. If necessary, this operator would operate the turbine-driven pump in a manual on-off mode until alter-nating current power is restored. Adequate lighting powered by direct current power sources and communications at local stations should also be provided if manua. initiation and control of the AFW system is needed.
(See Recommendation GL-3 for the longer-term resolution of this concern.)"
In response to this recomendation, the applicant indicated in a letter dated August 15, 1980, that the turbine-driven pump is capable of aeing automatically initiated and operated independent of any AC power source for at least two hours. Essential controls, valve operators and other supporting systems associated with the turbine-driven AP4 pump train are independent of AC power. This indeoendence extends to the lube oil cooler which receives cooling water from the pump discharge (recircu-lation line). We have reviewed the applicant's response and conclude that the provisions available in the existing AF4S at 't.
C. Summer meet the requirements outlined in this reconTnendation and are, there-fare, acceptable.
6.
Recorrendation GS-6 "The licensee should confirm flow path availability of an AFW system flow train that has been out of service to perform periodic testing or maintenance as folicws:
- Procedures should be implemented to require an operator to determine that the AFW system valves are properly aligned and a second operator to independently verify that the valves are properly aligned.
- The licensee should propose Technical Specifications to assure that prior to plant startup folicwing an extended cold shutdown, a flow test would be performed to verify the normal flow path from the primary AFW system water source to the steam generators.
The flow test should be conducted with AFW system valves in their nomal alignment."
In a letter dated August 15, 1980, the applicant responded to this recommendation, stating that South Carolina Electric and Gas Company procedures require that the AFW system flow path be verified after it has been out of service for periodic testing or maintenance.
The applicant has further comitted in a telephone conversation with the Staff to include initial detennination and second (independent) operator verification of proper valve alignment in plant procedures as required by the first part of this recommendation. 'de conclude that the first part of this recomendation is satisfied pending formal documentation of this commitment, and pending verification of the plant procedures by the Office of Inspection and Enforcement.
In addition, we note that the AFAS is used to supply #aedwater to the steam generators during normal plant startup, shutdown, and layup operations. Therefore, the availability of an AF4 flow path from the primary water source (condensate storage tank) to the steam generators is automatically verified for that flow path during normal plant startup.
'de, therefore, conclude that the second part of this recom-mendation is satisfied.
7.
Recommendation GS-7 "The licensee should verify that the automatic start AF4 system signals and associated circuitry are safety grade.
If this cannot be verified, the AF4 system automatic initiation system should be modified in the short-tenn to meet the functional require-ments listed below. For the longer tenn, the automatic initiation signals and circuits should be upgraded to meet safety-grade require-ments as indicated in Recommendation GL-5.
(1) The design should provide for th; automatic initiation of the auxiliary feedwater s. cem flow.
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(2) The automatic initiation signals and circuits should be designed so that a single failure will not result in the ioss of auxiliary feedwater system function.
(3) Testability of the initiation signals and circuits shall be a feature of the design.
(4) The initiation signals and circuits should be powered from the emergency buses.
(5) Manual capability to initiate the auxiliary fee &ater system from the control rocm should be retained and should be implemented so that a single failure in the manual circuits will not result in the loss of system function.
(6) The alternating current motor-driven pumps and valves in the auxiliary feedwater system should be included in the automatic actuation (simultaneous and/or sequential) of the loads to the emergency buses.
(7) The automatic initiation signals and circuits shall be designed so that their failure will not result in the loss of manual capability to initiate the AP4 system from the control mom."
In response to this recorrendation, the anglicant stated in a letter dated August 15, 1980, that the V. C. Summer AF4 system is designed so that automatic initiation signals and circuits are redundant and meet safety-grade requirements. The Instrumentation and Control Systems Branch will review this response and provide a safety evaluation at a later date.
8.
Recommendation GS V. C. Sumer's present design provides for auto-matic initiation of AF'4 system flow. Recor:Tnendation GS-7 verifies automatic initiation of this system. Therefore, we conclude that this recomendation is not applicable to V. C. Sumer.
B.
Additional Short Term Recarrendations 1.
Recommendation "The licensee should provide redundant level indication and low level alarms in the control room for the AF4 system primary water supply, to allow the operator to anticipate the need to make up water or transfer to an alternate water supply and prevent a icw pumo suction pressure condition from occurring.
The low level alann set-point should allow at least 20 minutes for operator action, assuming that the largest capacity AP4 pump is operating."
In response, the applicant indicated in a letter dated August 15, 1980, that redundant level indication and low level alarms for the conden-sate storage tank are present in the control room. Each level indica-tion system is powered from a separate battery-backed bus with one channel recorded. The low level alann setpoint allcws at least 20 minutes for operator action, assuming that the largest capacity AP4 system pump is operating. 'de have reviewed the applicant's response to this recommendation and conclude that it is acceptable.
2.
Recommendation (This recomendation has been revised from the original recommendation in NUREG-0611)_
"The licensee should perfom a 48-hour endurance test on all AFW system pumps, if such a test or continuous period of operation has not been accomplished to date. Following the 48-hour pump run, the pumps 'should be shut down and cooled down and then restarted and run for one hour. Test acceptance criteria should include demonstrating that the pumps remain within design limits with respect to bearing / bearing oil temperatures and vibration and that pump room ambient conditions (temperature, humidity) do not exceed environmental qualification limits for safety-related equipment in the rcom."
In a letter dated August 15, 1980, the applicant committed to perform a 72-hour endurance test on all AP4 pumps during startup testing. As noted above, this recommendation has been revised from the original recorrendation in the March 10, 1980 letter to require a 48-hour endurance test an all AFW systen pumps. The applicant has been advised to revise its commitment in this regard. In addition, the applicant should pro-vide a copy of test results including:
(1) a brief description of the test method and instrumentation used, (2) a plot of bearino and bearing oil temoerature vs. time for each pump demonstrating that the temperature design limits were not exceeded, (3) a plot of pump room ambient tempera-ture and humidity vs. time to demonstrate that the pump room ambient conditions do not exceed environmental qualification limits for safety-related equipment in the room, and (4) a statement confirming that the pumo vibration limits were not exceeded. Assuming that the applicant modifies its comitment as discussed aoove, we conclude that the response to this recomendation is acceptable. However, we request that the Office of Inspection and Enforcement verify the acceptabili ty of the AP4 pump test results. If the results are not acceptable, we will require modifications and provide a safety evaluation regarding the tests and modifications.
3.
Recommendation "The licensee should implement the following require-ments as specified by Item 2.1.7.b on page A-32 of NUREG-0578:
' Safety-grade indication of auxiliary feedwater flow to each steam generator shall be provided in the control room. The auxilii.ry feedwater flow instrument channels shall be powered from the emergency buses consistent with satisfying the emer-gency power diversity requirements for the auxiliary feedwater system set forth in Auxiliary Systems Branch Technical Position 10-1 of the Standard Review Plan, Section 10.4.9.'"
In a letter dated August 15, 1980, the applicant responded to this recommendation by stating that the AP4 system design includes safety-grade, redundant indication of AF4 flow to each steam generator in the control room. The AFJ flow instrument channels are pcwered frcm the emergency buses. The Enstrumentation and Control Systems 3 ranch will review this response and will provide a safety evaluation at a later date.
4.
Recommendation
" Licensees with plants which require local manual realignment of valves to conduct periodic tests on one AF4 system train, and there is only one remaining AF4 train available for operation should propose Technical Specifications to provide that a dedicated individual who is in communication with the control room be stationed at the manual valves. Upon instruction from the control room, this operator would realign the valves in the AF4 system train from the test mode to their operational alignment."
In response to this recommendation, the applicant by letter dated August 15, 1980, indicated that the V. C. Sc=ce plant does not require the realignment of local manual valves to conduct periodic tests on one AF4 system. The AF4 control valves may be operated from the control room to isolate the AF'd pumps for periodic testing.
In addi-tion, there are three AF4 trains available. 'de conclude that this recommendation is not applicable to V. C. Sumer.
C.
Long Tern Recommendations 1.
Recommendation GL-1 "For plants with a manual starting AF4 system, the licensee should install a system to automatically initiate the AF4 system flow. This system and associated automatic initiation signals should be designed and installed to meet safety-grade requirements. Manual AF4 system start and control capability should be retained with manual start serving as backup to automatic AP4 system initiation."
Because the applicant's response to Recomendation GS-7 stated that the V. C. Summer AF4S design already includes automatic start, Recommenda-tion GL-1 is not applicable to V. C. Summer.
2.
Recommendation GL-2
" Licensees with plant der;gns in which all (primary and alternate) water supplies to the AFW systems pass through valves in a single flow path should install redundant parallel flow paths (piping and valves).
Licensees with plants in which the primary AF4 system water supply passes through valves in a single flow path, but the alternate AFW system water supplies connect to the AFW system pump suction pipinn dcwnstream of the above valve (s), should install redundant valves parallel to the above valve (s) or provide automatic opening of the valve (s) from the alternate water supply upon low pump ruction pressure.
The licensee shocid propose Technical Specifications to incorporate appropriate periodic inspections to verify the valve positions."
In response to this recommendation, the applicant indicated, in a letter dated August 15, 1980, that the AF4 system alternate water supply (service water system) connects to the A.il system pump suction ciping c
downstream of the single nomally locked-open nive in a single flow path f rom t.'e primary water source. Automatic opening of the motor operated valves from the alternate water supply uoan low pump suction pressure will be omvf ded. However, the applicant at a subsequent meeting expressed concern that this automatic opening of valves to the alternate source may not occur in time to prevent AFJ pumn damage should the common suction valve be inadvertently left closed. We require that the appli-cant test this plant feature to assure that Dump damage will not result prior to affecting the transfer. We request that the resident NRC inspector be notified of the test prior to its perfomance inorder that he may witness it. We will report resolution of this item in a suppie-ment to this SER.
3.
Recomendation GL-3 "At least one AF4 system pump and its associated flow path and essential instrumentation should automatically initiate APJ system ficw and be capable of being operated independently of any AC pcwer source for at least two hours. Conversion of DC power to AC power is acceptable."
In response to this recommendation, the applicant indicated in a letter dated August 15, 1980, that the turbine-driven auxiliary feedwater pump and its associated ficw path and essential instrumentation automatically initiate AFW system flow and is capable of being operated independent of any AC power source for at least two hours. We have reviewed this response, and confirm that the turbine-driven APd pump train is available to supply emergency feedwater independent of onsite or offsite AC power supplies. Based on our review, we conclude that the applicant's response is acceptable.
4 Recomendation GL-4
" Licensees having plants with unprotected normal AF4 system water supplies should evaluate the design of their AF4 systems to determine if automatic pmtection of the pumps is necessary folicwing a seismic event or a tornado. The time available before pump damage,
. the alarms and indications available to the control room operator, and the time necessary for assessing the problem and taking action should be considered in determing whether operator action can be relied on to prevent pump damage. Consideration should be given to providing pump p-otection by means such as automatic switchover of the pump suctions to the alternate safety-grade source of water, automatic pump trips on low suction pressure, or upgrading the normal source of water to meet seismic Category I and tornado protection requirements."
As indicated in a letter dated August 15, 1980, the applicant will pro-vide automatic switchover of AF4 pump suction supply to the alternate source (service water) on low suction pressure as would result upon failure of the primary water source (condensate storage tank) due to tornado missiles.
'de note that the primary water supoly to the V. C. Summer AFW system pumps, the condensate storage tank, is designed to satisfy seismic Category I requirements but is not protected against the effects of tornado missiles. However, its loss as a result of tornado missiles does not affect AF4 system function since the tornado-missile protected alternate source (service water system) serves as a sufficient backup supply of emergency feedwater. As noted under Racomendation GL-2, we require that the applicant test the automatic suction supply trans-fer feature to assure that AP4 pump damage will not result prior to affecting the switchover. We will report resolution of this item in a supplerient to this SER.
5.
Recomendation GL-5 "The licensee should upgrade the APA system auto-matic initiation signals and circuits to meet safety-grade recuirements.'
. In response to this recennendation, the licensee indicated in a letter dated August 15, 1980, that the present AF4 systen automatic initiation signals and circuits are safety grade. The Instrumentation and Control Systems Branch will review the applicant's design in detail and provide a safety evaluation at a later date.