ML19270H670
| ML19270H670 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 12/28/1979 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19270H671 | List: |
| References | |
| TAC-12428, TAC-12429, NUDOCS 8001020525 | |
| Download: ML19270H670 (15) | |
Text
.
NSR2 NORTHERN STATES POWER COMPANY MIN N E A PO Li s. MIN N E SOTA 55409 December 28, 1979 Director of Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, D.C.
20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Auxiliary Feedwater System Information Lessons Learned Recommendations 2.1.7a and b References (1) Letter, L. O. Mayer (NSP) to Director of Nuclear Reactor Regulation (NRC), dated November 20, 1979 (2) Letter, L. O. Mayer (NSP) to Director of Nuclear Reactor Regulation (NRC), dated November 21, 1979 During recent conversations with the NRC Project Manager, additional information was requested in regard to the auxiliary feedwater system to confirm that the Prairie Island system does meet Lessons Lcarned Recommendations 2.1.7.a and 2.1.7.b.
Enclosure (1) contains the requested information on (1) AFW System automatic initiation and (2) AFW System Flow Indication to the Steam Generators.
Transmitted herewith are 40 copies of this cover letter and enclosure (1).
Also included are three (3) sets of pertinent electrical, flow, and logic diagrams [ Enclosure (2)]. Due to the size and volume of these diagrams, the three sets are being transmitted at the request of Mr. Grotenhuis of your staff.
This information, in conjunction with that provided on November 20 and 21, 1979 [ References (1) and (2)], addresses all items on Lessons Learned 2.1.7a and b.
Should you need additional information to continue your evaluation, please contact this office.
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L. O. Mayer, P.
16g2 003 Manager of Nuclear Support Services cc: James G. Keppler G. Charnoff Attachments O
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Enclosure (1) to NSP letter to NRC dated Decemb er 28, 1979 b
INFORMATION REQUIRED FOR STAFF EVALUATION OF LICENSEE RESPONSE OF LESS'lNS LEARNED RECOMMENDATIONS 2.1.7a and b.
2.1.7a AFW System Automatic Initiation CRITERIA:
1.
The design shall provide for the automatic initiation of the auxiliary feedwater system.
RESPONSE
The following signals AUTOMATICALLY start the pump motor and open the steam admission volve to the turbine criven pump, of the af fected unit:
1.
Low-Low water level in either steam generator 2.
Trip of both main feedwater pumps 3.
Safety Injection 4.
Under voltage on both 4.16 KV normal buses (turbine driven pump only)
O Instrumentation installed for the initation of the Engineered Safety Features (ESF) systems provides actuation by redundant logic and coincidence networks similar t; those used for Reactor Protection circuits. Each coincident network actuates a device that operates the associatec engineerec safety features equipment, motor starters and valve operators.
The channels are designed to combine redundant sensors, independent channel circuitry, and coincident trip and/or actuation logic so that a safe and reliable system exists in which a single failure sill not defeat the intended channel function.
The action initiating sensors, bistables and logic are shown in the figures included in the detailed Engineered Safety Features Instrumentation Description in FSAR Section 7.5.2.
The Engineered Safety Features Instrumentation System automatically actuates the Auxiliary Feedwater System.
The Auxiliary Feedwater System logic and wiring schematics, for Unit 1 and sinilar to Fag Unit 2, are included for informational purposes.
1672 004
_1-
CRlTERIA:
2.
The automatic initiation signals and circuits shall be designed so that a single failure will not result in the loss of auxiliary feedwater system function.
RESPONSE: The Engineered Safety Features actuation circuits are designed in accordance with the principle and philosophy of WCAP-7486, "An Evaluation of Anticipated Operational Transients in Westinghouse Pressurized Water Reactors".
This report presents a detailed failure analysis of the Reactor Protection System.
In additicn, the FSAR page 7.2-4 states:
Protection Systems Redundancy and Independence Criterion: Redundancy and independence designed into protection systems shall be sufficient to j eg assure that no single failure or removal p
from service of any component or channel of such a system will result in loss of the protec-tion function. The redundancy provided shall include, as a minimum, two channels of protection for each protection function to be served. (GDC 20)
The Protection System consists of two discrete protions of circuitry: an analog portion consisting of two to four redundant channels which monitor various plant parameters in systems such as the Reactor Coolant System, Neutron Flux System, Pressurizer System, Steam System, containment,res-sure, etc.; and a digital portion consisting of two redu dant logic channels (trains) which receive inputs from the analog protection channels and performs the needed logic to initiate reactor trips, engineered safety features, etc.
Each digital channel is capable of actuating a separate and independent rag trip breaker in the case of the reactor protection system or the appropriate equipment required in the case of the Engineered 1672 005 Safeguards System. The intent is that "any single f ailure within the Protection System shall not prevent proper protection system operation when required".
The channelized concept is applied to both the analog and logic portions of the system.
Separation of redundant analog channels begins at the process sensors and is maintained in the field wiring, containment vessel penetrations and analog protection racks, terminating at the redundant groups of protection logic racks.
In certain applications, it is considered advantageous to employ control signals derived from individual protection channels through isolation amplifiers contained in the protection channel. In these cases, analog signals derived from protection channels for non-protective functions are f8hg obtained through isolation amplifiers located in the analog protection racks.
(By definition, non-protective functions include those signals used for control, remote process indication, computer monitoring, etc.)
The isolation amplifiers are designed such that a short circuit, open circuit, or the application of 118 VAC or 140 VDC on the isolated output portion of the circuit (i.e., non-protective side of the circuit) will not upset the input (protection) side of the circuit. Since the signals obtained through is' lation amplifiers are never returned to the protection o
racks, any postulated failure in the control system will not affect the protection channel.
CRITERIA:
3.
Testability of the initiating signals and circuits shall be a feature of the design.
RESPONSE: The design provides for controlled access to all trip
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settings, module calibration adjustments, test points, and signal injection points. The FSAR Section 7.2.2.
" System Design", deta.ls the testing provisions:
1672 006 Process Analog Protection Channel Testing Provisions are made, for process variables, to manually.
place the output of the bistable in a tripped condition for "at power" testing.
The basic arrangement of elements comprising a representa-tive analog protection channel is shwon in Figure 7.2-5 attached. These elements include a sensor or transmitter, power supply, bistable, bistable trip switch and proving lamp, test-operate switch, test annunciator, test signal injection jack, and test points. A portion of the logic system is also included to illustrate the overlap between the typical analog channel and the corresponding logic circuits.
The analog system symbols are given in Figure
- 7. 2-9, attached. Each process protection rack includes a ph test panel containing those switches, test jacks and relat-ed equipment needed to test the channels contained in the rack.
Testing of process analog protection channels requires that the bistable output relays of the channel under test be placed in the tripped mode prior to proceeding with the analog channel tests.
Thus, for the channel under test, the relay elements in the two-out-of-f our coincident matrices will be in the tripped mode during
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the entire test of that channel.
It is observed that the remaining channels of the two-out-of-three or the two-out-of-four protective functions meet the single failure criterion when a channel is bypassed or tripped.
Placing the bistable trip switch in the tripped mode de-energizes (trips) the bistable output relays and connects a proving lamp to the bistable output circuit.
This permits the Fag electrical operation of the bistable to be observed and the bistable set point relative to the channel analog signal to be verified. Upon completion of test of the analog channel,
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1672 007
the bistable strip switches are manually reset to their operate mode.
Process Analog channel test is accomplished by simulating a process measurement signal, varying the simulated signal over its signal span and checking the correlation of bis-table set points, channel readouts and other loop elements with precision protable read-out equipment. See Figure 7.2-5.
Test jacks are provided in the test panel for injec-tion of the simulated process signal into each process analog protection channel.
Test points are provided in the channel to facilitate an independent means for precision measurement and correlation of the test signal.
Logic Channel testing is similarly described in FSAR Section 7.2.2.
CRITERIA:
4.
The initiating signals and circuits shall be powered from the emergency buses.
RESPONSE
As shown in Figure 1 attached, buses numbered 15, 16, 25 and 26 provide power for the Engineered Safety Features and have emergency supplies available from the two diesel generators.
These two diesel units serve as a standby for Engineered Safety Feature buses serving both units. Figure 2 completes the power distribution diagram including the instr ment buses.
CRITERIA:
5.
Manual capability to initiate the auxiliary feedwater system from the control room shall be retained and shall be implemented so that a single failure in the manual circuits will not result in the loss of system function.
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1672 008
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ANALOG SYSTEM SYMBOLS v'
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- Alarm Buf
- Buffer f
- Special ~ unction (such as a pressure compensation unit or lead / log compensativ.-)
FC
- Flow controller (off-on unless output signal is shown)
FI
- Flow Indicator FT
- Flow Transmitter
!Il LRT
- High Level Reactor Trip Hi PRT
- High Pressure Reactor Trip I/I
- Isolation Current Repeater ISOL
- Isolation (other than I/I)
- Level controller (of f-on unless output signal is shown)
- Level Indicator L/L
- Lead / Lag i,-Low: LOL - Low Level to LRT
- Low Level Reactor Trip Le PRI
- Low Pressure Reactor Trip V
L
- Programmed Reference Level ef LT
- Level Transmitter NC
- Nuclear Flux Controller NE
- Nuclear Flux Detector NI
- Nuclear Flux Indicator NM
- Nuclear Flux Signal Modifier NQ
- Nuclear Power Supply PC
- Pressure Controller (of f-on unless output signal is shown)
- Pressure Indicator PM
- Pressure Signal Madifier P
- Programmed Reference Pressure g
PS
- Power Supply PI
- Pressure Indicator PT
- Pressure Transmitter QM
- Nuclear Flux Signal Modifier ANALOG SYSTEM SIGNALS Figure 7.2-9
, 1672 012
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- Resistance to Current Connector RTD
- Resistence Temperature Device S
- Control channel transfer switch (used to maintain auto channel during test of the protection channel)
- Safety Injection T
- Built-In Test Point TC
- Temperature Controller TE
- Temperature Element TI
- Temperature Indicator TJ
- Test Signal Insertion Jack TM
- Temperature Signal Modifier TP
- Test Point dU,L
- Out of core upper or lower ion chamber flux signals ANALOG SYSTEM SIGNALS Figure
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RESPONSE: According to FSAR Section 7.2 page 7.2-8, means are provided for manual initiation of the protaction system action. Failure in the automatic system does not prevent the manual actuation of protection functions.
The electrical schematics enclosed, NF-40008-24 and NF-40006-59, illus tra te the independent starting circuits of all the Auxiliary Feedwater Pumps, such that no single failure will prevent more than one pump from starting. Reference FSAR Section 6.6.2 page 6.6-3.
CRITERIA:
6.
The a-c motor-driven pumps and valves in the axuiliary feedwater system shall be included in the automatic actuation (simultaneous and/or sequential) of the loads onto the emergency buses.
RESPONSE
Using NF-40019-1A attached, the load rejection and restoration for busses 15 and 16 and the Auxiliary Feedwater System is shoun. The electrical schematics NF-40008 sheet 67, 24, 130 and NF-40006 sheet 59 represent typical Auxiliary Feedwater System safeguards bus power supplies.
CRITERLA:
7.
The automatic initiating signals and circuits shall be designed so that their failure will not result in the loss of manual capability to initiate the AFWS from the control room.
RESPONSE
Refer to the Response to Criteria No. 5 above.
2.1.7b AFW System Flow Indication to the S team Generators CF.1TERIA:
1.
Single Failure Auxiliary Feedwater flow indication by itself does not satisfy
RESPONSE
the single failure criterion, however. each flow channel b
is backed up by a steam generator level channel.
1672 014
CRITERIA:
2.
Testability RESPONSE: A typical Auxiliary Feedwater flow channel is shown in Figure 3.
Each device is fully calibrated, from the process input, on an established Preventive Maintenance program.
CRITERIA:
3.
Power Supply
RESPONSE
Refer to Figures 1 and 2 of the previous section.
Power supply for this indication is from Instrument Bus IV.
Each inverter is continuously supplied power from one of the saftguards 480 volt AC buses and from one of the 125 volt DC emergency batteries.
CRITERIA:
4.
Indication Accuracy RESPONSE: Typical channel accuracy, using the square root of the sum of the squares method is j; 2.3% which is significantly better than the suggested accuracy of j; 10%.
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41228-0:
TYPICAL CHANNEL (AFW to 12 Stm Gen F)
FIGURE 3 1672 016 SET 3 Enclosure (2) to NSP Letter, dated December 28, 1979 Drawing No Type of Diagram Description NE-40006-QQ Sheet 59 Electrical 12 AFW Pump NE-40008-BQ Sheet 67 Electrical Loop A Main Steam Supply Valve to TD AFW Pump and 11/12 AFW to SG Isolation Valve 5652D20 Sheet 8 Logic Safeguards Actuation Signals NE-40008 Sheet 24 Electrical 11 TD AFW Pump efain Steam Supply Valve NF-40312-2F Logic Auxiliary Feedwater System - Unit 1 NE-40008-BQ Sheet 130 Electrical Loop B Main Steam Supply Valve to 11 TD AFW Pump and 11/12 AFW to 1B SG Isolation Valve NE-40312-lJ Logic Auxiliary Feedwater System - Unit 1 NE-40019-1A Logic Busses 15 and 16 Load Rejection - Restoring Unit 1 ll3E347 Sheet 18 Electrical Reactor Protection System 113E347 Sheet 10 Electrical Reactor Protection System ll3E347 Sheet 12 Electrical Reactor Protection System 113E347 Sheet 4 Electrical Reactor Protection System ll3E347 Sheet 19 Electrical Reactor Protection System NF-40295-9D Logic External Wiring Diagram 14 Misc Systems Relay Rack Instruments NE-40012 Sheet 4 Electrical AFW to 11 and 12 SG Flow NF-39316-lK Flow AFW Piping Units 1 and 2 N
NF-39222 N
Flow Feedwater System Unit 1 NF-39223 CD Flow Feedwater System Unit 2 N