ML20209F887
| ML20209F887 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 04/23/1987 |
| From: | Fay C WISCONSIN ELECTRIC POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| CON-NRC-87-033, CON-NRC-87-33 VPNPD-87-124, NUDOCS 8704300413 | |
| Download: ML20209F887 (9) | |
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iMsconsm Electnc ma coww 231 W. MICHIGAN, P.O. BOX 2046, MILWAUKEE, WI 53201 (414)221-2345 VPNPD-87-124 NRC-87-033 April 23, 1987
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U. S. NUCLEAR REGULATORY COMMISSION Document Control Desk Washington, D. C.
20555 Gentlemen:
DOCKETS 50-266 AND 50-301 ATWS MITIGATING SYSTEM ACTUATION CIRCUITRY (AMSAC)
FINAL DESIGN AND IMPLEMENTATION SCHEDULE POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 On September 23, 1986, we received a letter from Mr. T. G.
Colburn of your staff transmitting the staff's Safety Evaluation Report (SER) on the Westinghouse Owners Group (WOG)
Topical Report WCAP-10858, "AMSAC Generic Design Package."
Our letter of October 10, 1986 provided a tentative schedule for implementation of the AMSAC at Point Beach Nuclear Plant (PBNP) and stated that Wisconsin Electric would submit a description of the final AMSAC desian by April 30, 1987.
The purpose of this letter is to provide the final AMSAC design description and to confirm the implementation schedule for Point Beach.
Attached is a design description of the AMSAC to be installed at PBNP.
The design is based upon the conceptual design presented in Section 5.0 of WCAP-10858, " Functional y
Requirements, ATWS Mitigation System Actuation Circuitry (Logic 3: AMSAC Actuation on Main Feedwater Pump Trip or Main Feedwater Valve Closure)."
Note that this design is different from the tentative design referred to in our September 30, 1985 letter to you (Logic 1, Steam Generator Level).
The' design was re-evaluated based upon consideration of our existing plant equipment.
The attachment also addresses how our design meets
/I the fourteen plant-specific points identified in your,SER.
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Please note that there is one exception to the SER that we are requesting.
Our design does not include provisions for automatic. isolation of the steam generator sample valves upon initiation of the AMSAC.
Relief is requested from this requirement, based on the small size of these lines (one 3/8 inch line per generator) and the consequene~ limited flow that could occur through these lines.
The schedule for implementation remains the s6me as stited in our October 10, 1986 submittal and is based in 'part upon the NRC staff's review'of our plant-specific design.
Following final staff approval of our PBNP-specific design, implementation will occur during the first scheduled outage for each unit after a twelve-month period for procurement of materials.
We feel that this approach will help ensure that the AMSAC design to be implemented at Point Beach will adequately meet the requirements of 10 CFR 50.62.
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If you have any questions regarding this matter, please contact us.
Very truly yours, l/h'j C. W. ' Fay Vice President
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Nuclear Power Attachment
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Copies to NRC Region Administrator, Region III NRC Resident Inspector j
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j ATTACHMENT ANTICIPATED TRANSIENTS WITHOUT SCRAM I/
MITIGATING SYSTEM ACTUATION CIRCUITRY
6 System Description
b The Anticipated Transients Without Scram Mitigating System Actuation Circuitry (AMSAC) proposed for the Point Beach Nuclear Plant (PBNP) will be mechanized so that closure of both main feedwater regulating valves or opening of both main feedwater pump motor breakers will trip the turbine and start all auxbli>ary feedwater (AFW) pumps.
The current design of the auxiliary feedwater pump start circuitry causes the steam generator blowdown isolation valves to trip closed whenever any AFW pump is started.
AMSAC will be automatically enabled above approximately 40% turbine power and will be automatically defeated below approximately 40% turbine power following a nominal sixty second time delay.
After.the input logic is made up there is a nominal 30 second time delay before output actuation.
This time delay should allow the reactor trip system to actuate first.
On each of the two main feedwater regulating valves (CV466 and CV476) switches will be mounted to provide redundant switch contacts that close when the valves are closed.
These contacts are referred,to as1 type,bc contacts.
These switch contacts will be connected in a circuit such that if one out of two contacts associatediwith valve Cv466 closes and one out of two contacts associated with valve CV476 close AMSAC will be initiated.
This configuration w5s chosen because no single failure of a switch contact will prevents actuation from occurring when both valves are closed, nor will a single switch contact failure cause actuation to occur when both valves are not closed.
The main feedwater regulating valves were chosen because their closure wi.11 result in a completct loss of feedwater flow at power.
The main feedwater regulating valve bypass valves, CV480 and CV481, are normally closed when at power levels greater than 20 to 30%,
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therefore these valves were not included in the AMSAC.
The main feedwater pump discharge valves, MOV 2189 and MOV 2190 are motor s operated valves which are open at power.
These valves are interlocked with the main feedwater pump breakers, and can only automatically close if the pump breakers open.
Since main feedwater pump breaker trip actuates AMSAC, these valves will not be included in the AMSAC.
PBNP does not have fast acting feedwater isolation valves, other than check valves, in the i dteam generator feedwater lines.
.je undant, physically independent normally closed contacts on the main feedwater pump motor breakers will be connected in a circuit such that if one out of two contacts associated with the A main feedwater pump breaker closes and one out of two contacts associated with the B main feedwater pump breaker closes AMSAC _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
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I will be initiated.
When both pump breakers are opened no single failure of a switch contact can prevent AMSAC initiation.
When both pump breakers are closed no single failure of a switch contact can cause spurious AMSAC actuation.
A pressure transmitter connected to turbine first stage pressure will be used as a signal source to measure turbine power.
A bistable connected to the transmitter output will actuate at approximately 40% power.
When the bistable is actuated a time-delay-on-dropout relay will be immediately energized and the AMSAC enabled.
On decreasing power level the time delay relay will keep AMSAC enabled for approximately 60 seconds after the power level has decreased to below 40%.
This circuit, known as the C-20 permissive, will be used as the automatic ENABLE / DISABLE circuit for AMSAC.
The AMSAC output relays will be latching type, Westinghouse MG-6 or equivalent.
Separate Train A and Train B output relays will be used for the actuation of the associated train of the auxiliary feedwater system, including both shared electric motor driven pumps P38A and P38B, the unit specific steam turbine driven pumps 1-P29 or 2-P29, and tripping of the turbine.
A preliminary circuit diagram of the proposed AMSAC is provided at the end of this attachment.
The proposed AMSAC meets each of the fourteen plant specific points identified in the NRC Safety Evaluation Report on WCAP-10858 as discussed below:
Diversity The pressure transmitter and bistable used to provide the C-20 permissive within AMSAC will be diverse from those used to provide the permissives used in the reactor trip system.
Latching relays and time delay relays will be used in AMSAC but are not used in the reactor trip system.
Latching relays and time delay relays are used in.the engineered safety features actuation system (safeguards) so AMSAC will be diverse in this regard from the reactor trip system but not from the safeguards system.
Relays other than latching or time delay will be selected to be diverse from those used in the reactor trip system.
Other hardware such as switches, lichts, wire and annunciators will not be selected to be diverse from those used in or with the reactor trip system.
-Logic Power Supplies The power supply for AMSAC will be a 120 Vac single phase instrument bus derived from a diesel generator powered bus.
The designator for this diesel bus is 1B03 for Unit 1 and 2B04 for Unit 2.
A Sola isolating and regulating transformer or equivalent will be used to supply the 120 volt single phase from the 480 volt 3 phase bus.
The diesel generators supply rated voltage to these buses within ten seconds after a loss of l
offsite power.
This power is diverse from the 125 Vdc battery power and 120-Vac inverter power used in the reactor trip system.
Safety Related Interface The AMSAC safety related interface is with the auxiliary feedwater pump starting circuits.
This interface is via the latching relays which will be Westinghouse type MG-6 or equivalent.
These relays will be procured, installed, and maintained in accordance with the PBNP nuclear quality assurance program.
There is no direct interface between AMSAC and the reactor trip system.
Quality Assurance The requirements of Generic Letter #85-06 will be met, as follows:
The modification requests used to develop, approve, and install AMSAC will be identified as QA scope.
This will assure the same design control and drawing control as would be followed in a safety related modification.
The components used in AMSAC will be divided into QA and non-QA categories.
The components in the QA category are the output relays that interface with the Auxiliary Feedwater System and the wire used for that connection.
The QA components will be handled in accordance with the PBNP nuclear quality assurance program.
Manufacturers of the QA components will be required to have an acceptable QA program and the quality of the QA material will be documented via vendor Certificates of Compliance and Test Reports as appropriate.
Other relays, switches, lights and annunciators will be designated as non-QA.
Handling of the non-QA equipment will be consistent with PBNP practices for non-safety-related equipment.
Maintenance Bypasses A key operated bypass switch will be provided on the local AMSAC test panel.
This switch will be used to bypass the AMSAC for either test purposes or maintenance purposes.
A second bypass switch may be installed in the Control Room.
An annunciator located in the Control Room, labeled AMSAC BYPASSED or similar, l
will be activated whenever the bypass switch or switches are put into the BYPASS position.
t Operating Bypasses The AMSAC logic includes an automatic enable signal which is derived from first stage turbine pressure.
This signal is called C-20 in the Westinghouse WCAP and NRC letter.
This enable signal will be set at approximately 40% power.
On decreasing power the enable signal will be retained for a nominal 60 seconds after power decreases below 40%.
A control room light labeled "AMSAC IN SERVICE" or similar will be illuminated whenever this enable signal is present, provided the system is not bypassed.
Means for Bypassing A permanently installed AMSAC bypass switch will be provided on the test panel.
A second switch may be provided as a design option in the Control Room.
This switch or switches can be used for either maintenance or testing purposes.
No lifting of leads, removal of fuses, or blocking of relays will be necessary to perform periodic testing of AMSAC.
Placing the bypass switch in the BYPASS position activates an annunicator located in the Control Room.
Manual Initiation There will not be a manual initiation button or switch for AMSAC other than a local test switch.
The control room operator can manually trip the turbine from the control room by pressing one pushbutton switch.
The control room operator can start any of the auxiliary feedwater pumps from the control room by use of pump start switches and valve operating switches.
Electrical Independence from Existing Reactor Protection System The inputs to AMSAC are separate from and independent of the reactor protection system.
No sensors are common to the reactor trip system and AMSAC.
Therefore, no isolators are required between the reactor protection system and AMSAC.
Physical Separation from Existing Reactor Protection System The AMSAC will be mounted in a cabinet different than the cabinets containing the reactor trip system.
There are no incoming signals from the reactor trip system so the separa: 'on criteria for the existing reactor trip system are not compromised.
Environmental Qualification The AMSAC, except for field contacts, will be located in a mild environment area.
It will be designed to function with some reasonable variations in temperature and power supply voltage but the detailed limits have not been determined.
Consistent i
with 10 CFR 50.49 no special testing is planned.
The temperature and power supply limitations of the hardware used will be taken from manufacturers data or specification sheets.
In order to minimze the power supply voltage variations, an existing Sola regulating transformer or equivalent will be used to supply power to AMSAC.
Testability at Power Portions of AMSAC will be testable at power when the system is placed in bypass.
Testing of the complete AMSAC will be
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performed when the plant is shutdown.
Actuation of AMSAC will be annunciated in the control room in a manner consistent with plant design and a human factors standards document being written for the PBNP control room design review.
The switch contacts'on the feedwater regulating valves, switch contacts on the feedwater pump motor breakers and the output latching relays are the portions of AMSAC that cannot be tested at power.
The-bistables, time delay relays and other relays are testable at
-power.
Continuity of the latching coils of the output relays can be measured at power.
No periodic program for testing AMSAC at' power has been established, however, and we believe none is necessary because of the reliability of the components used in the proposed AMSAC.
Completion of Mitigative Action The AMSAC ouput relays will be a latching type relay.
Once set, the relay will remain in the set position even if the set voltage is removed.
Deliberate operator action will be required to reset these relays.
Once actuated, the turbine trip circuit will maintain the turbine tripped even though the initiating signal is no longer present.
Operator action is required to relatch the turbine after the trip signal is cleared.
Once started, the auxiliary feedwater pumps continue to run even though the initiating signal is no longer present.
Operator action is required to secure the auxiliary feedwater pumps once started by an automatic start signal.
Technical Specifications Presently there are no plans to include AMSAC in the technical specifications.
It is our understanding that the issue of technical specifications for AMSAC will be addressed by the Westinghouse Owners Group.
Two unique features of the proposed AMSAC design are discussed below:
Sample Isolation Valves The proposed AMSAC design does not provide for closure of the steam generator sample line isolation valves.
Closure of these valves upon AMSAC actuation is recommended by the NRC Safety Evaulation of WCAP-10858, AMSAC Generic Design Package.
At the Point Beach Nuclear Plant the sample lines consist of one 3/8 inch diameter line per steam geneartor.
Due to component limitations and the small size of the sample line, sample flow is limited to less than one gpm per steam generator.
It is, therefore, not necessary to provide automatic closure of the sample line isolation valves on actuation of AMSAC.
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Anticipatory Turbine Trip The Point Beach Nuclear Plant presently has design features that perform a portion of the AMSAC function.
Circuitry is in place 1
per the original plant design to trip the turbine and start.the motor driven' auxiliary feedwater pumps whenever both main.
feedwater pump motor breakers open.
There is presently no time delay or power based enable'in this circuit.
It is classified as an anticipatory trip and no credit is taken for its action in i.
the safety analysis.
This existing circuit will-be reworked and incorporated into the proposed AMSAC to provide the required enable and time delay.
Presently, a circuit is provided that starts the steam driven auxiliary feedwater pump whenever an undervoltage condition exists cx1 the buses that power the main feedwater pumps, after a three to fifteen second time. delay.
Startup of.any auxiliary feedwater pump isolates steam generator blowdown.
These l
circuits will not be modified as part of the proposed AMSAC.
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- 2) LCCAL PANEL TO Bt f(2)c15a NPD Au m C
S A.G.S. FILE NO 1007
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