ML17305B634
| ML17305B634 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 07/04/1991 |
| From: | Catherine Thompson Office of Nuclear Reactor Regulation |
| To: | Conway W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| References | |
| TAC-59124, TAC-62798, TAC-67168, NUDOCS 9107110195 | |
| Download: ML17305B634 (8) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 JUL 0 4 1991 Docket Nos.
50-528, 50-529, and 50-530 Mr. William F.
Conway Executive Vice President Arizona Public Service Company P. 0.
Box 53999 Phoenix, Arizona 85072-3999
Dear Mr. Conway:
SUBJECT:
REVIEW OF PALO VERDE DIVERSE AUXILIARY FEEDWATER ACTUATION SYSTEM DESIGN CLARIFICATION (TAC NOS. 59124,
- 62798, AND 67168)
By letter dated December 21, 1990, Arizona Public Service (APS)
Company provided a number of clarifications which identified some changes to the diverse auxiliary feedwater actuation system (DAFAS) design from the conceptual design which was approved by NRC on October 18, 1990.
A conference call was held on March 19, 1991, between the NRC staff and APS to discuss these clarifications.
The following are the DAFAS design changes and the staff 's comments:
(1)
APS Clarification:
The purpose of the DAFAS block when an Auxiliary Feedwater Actuation Signal (AFAS) is present is to prevent the anticipated transient without scram (ATWS) anticipated operational occurence (A00) system from interfering with the "smart" AFAS design-basis event (DBE) rupture identification logic already present in the Palo Verde design.
Staff Comment:
In the conceptual
- design, the DAFAS actuation will be blocked by the Main Steam Isolation System (MSIS) signal to prevent additional mass/energy feeding into the containment through ruptured steam generator.
At Palo Verde design, this feature is implemented through
" smart" AFAS logic.
The staff finds this clarification acceptable.
(2)
APS Clarification:
The final DAFAS design will provide features that provide alarms to indicate system status to the operator s, but does not provide direct data points to the plant computer.
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,William F.
Conway Staff Comment:
It is the staff 's understanding that the Palo Verde plant computer system picks up signals from the plant annunciator cabinet.
This modification will not affect the capability to provide the DAFAS status to the operators.
Therefore, this modification is acceptable.
(3)
APS Clarification:
The instrument sensor field bus power sour ce for the DAFAS steam generator level transmitters is integrated with the sensor loop current to voltage converters.
It is understood these were excluded from the diversity requirements, since they are technically part of the sensors, which are excluded from the diversity requirements of the ATWS Rule.
The current to voltage sensor field bus power source is considered the "sensor output," and is, therefore, also excluded from the diversity requirements of the AVOWS Rule.
The instrument channel components which process signals to the DAFAS and separately to the reactor protection system (RPS
) from this point are separate and diverse.
The DAFAS interface with the auxiliary feedwater (AFW) system will be through an initiation relay which will not be used in the RPS.
This relay will be of a different manufacturer than that of the AFAS initiation relays.
Staff Comment:
It is the staff 's understanding that the DAFAS steam generator level signals are from the existing RPS narrow range steam generator level signals located in the class IE process cabinets.
Each existing level signal is measured by a Foxboro level transmitter and then processed by a current to voltage converter.
The converter and the transmitter are in the integrated
- loop, and both components use the same power source.
Each DAFAS input signal is interfaced and isolated by a fiber optic transmitter module.
Each of the 16 level signals is transmitted to the DAFAS cabinets on separate fiber optic cables.
The level signals are received by fiber optic receiver modules at the DAFAS cabinet where they are converted to an analog voltage signal and provide input to each of the DAFAS programmable logic controllers (PLC).
Each DAFAS cabinet contain two PLCs.
Each PLC will initiate an actuation signal.
The actuation signal is generated at the PLC which is separate and diverse from the RPS actuation circuitry.
The DAFAS interface with the AFW system is through an initiation relay which is made by a different manufacturer than the existing AFAS initiation relays.
The staff finds that the level of diversity described in the above clarification is acceptable.
1
. William F.
Conway (4)
APS Clarification: The DAFAS conceptual design submitted to the NRC by APS letter, dated July 31 1990 (161-03369),
included the use of uninterruptible power supply UPS) power sources.
The final DAFAS design includes a power source to the DAFAS and power supplies within the DAFAS similar to those used in the Diver se Scram System (DSS).
The vital instrument buses will provide power to the safety-related DAFAS cabinets.
Power supplies from a different manufacturer than the existing RPS will be used in the DAFAS.
Staff Comment:
In NRC letter dated October 18, 1990, the staff concluded that the DSS design is sufficient to comply with the electrical independence requirements of 10 CFR 50.62.
The above clarification stated that the DAFAS power source arrangement wi 11 be similar to the DSS design.
The staff finds the above clarification acceptable.
(5)
APS Clarification:
The human factors review referred to in this section is included as part of the normal design change process used at APS.
A stand-alone human factors review, specifically for ATWS systems, is not required or planned.
Staff Comment:
The APS design change process includes a walkdown review at the main control room control board.
This is in keeping with the licensee s
control room design review process.
The staff finds the above clarification acceptable.
Based on the information provided by APS and the discussion on March 19, 1991, the NRC staff concludes that the clarifications provided in its December 21,
- 1990, letter are acceptable.
These clarifications do not change the overall conclusion in the staff's safety evaluation dated October 18, 1990, which stated that the DAFAS proposal for implementation at the Palo Verde Nuclear Generating Station, Units 1, 2, and 3, conforms to the requirements of 10 CFR 50.62, and is, therefore, acceptable.
Sincerely, ORIGINAL'IGNED 8Y Catherine M. Thompson, Project Manager Project Directorate V
Division of Reactor Projects III/IV/V Office of Nuclear Reactor Regulation cc:
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