ML20237H219

Informs of Revs to 861024 Schedule for Implementation of ATWS Mitigating Sys Actuation Circuitry & plant-specific Design.Delay of Completion Date Until Nov 1989 Cycle 14 Startup Requested.Delay Justification & Related Info Encl

ML20237H219
Person / Time
Site:	Prairie Island
Issue date:	08/28/1987
From:	Musolf D NORTHERN STATES POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
NUDOCS 8709030174
Download: ML20237H219 (8)

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q Northern States Power Company 414 Nicollet Mall ,

Minneapoks Minnesota 55401 l Telephone (612) 330 5500 l

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l August 28, 1987 10 CFR 50.62 l U S Nuclear Regulatory Commission Attn: Document Control Desk; Washington, DC' 20555' PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Revisions to Schedule for Implementation of AMSAC and to the Plant Specific AMSAC Design In our letter dated October 24, 1986, we provided a schedule for the installation of the ATWS mitigation system actuation circuitry (AMSAC) at Prairie Island. AMSAC was expected to be installed on both units prior to the startup of Cycle 13. The startup of Cycle 13 was scheduled for September 1988 for Unit 1 and March 1989 for Unit 2.

This schedule was established prior to completion cf the preliminary plant specific AMSAC design, which was submitted for NRC review by letter dated February 26, 1987. As a recult of additional engineering work on the AMSAC design and its implementation, we have found the proposed completion date for Unit 1 to be impractical and request that the Unit 1 AMSAC completion date be delayed until prior to the startup of Cycle 14 (presently scheduled for November of 1989). The details of our justification for this schedule delay are discussed in Attachment I to this letter.

The preliminary plant specific AMSAC design provided in our February 26, 1987 letter discussed the relationship between the planned upgrade of the Prairie Island feedwater control system and the AMSAC installation.

Further engineering performed on the feedwater control upgrade and the AMSAC installation has resulted in revisions to the original plant specific AMSAC design. Revised sections from the original AMSAC Conceptual Design Report for Prairie Island and the Response to Plant Specific Questions are attached (Attachments II and III).

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I U S Nuclear Regulatory Commission i August 28, 1987 Northem States Power Company -

Page 2 Please contact us if you have any questions related to the information we 1 have provided. ]

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Dal d Muso f.. l Manager - Nuclear Support Services  !

DMM/EFE/efe c: Regional Administrator-III, NRC NRR Project Manager, NRC Resident Inspector, NRC G Charnoff Attachments l

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ATTACHMENT I JUSTIFICATION FOR DELAY OF PRAIRIE ISIAND UNIT 1 AMSAC SYSTEM As discussed in the AMSAC preliminary conceptual design report submitted by our letter dated February 26, 1987, Prairie Island is upgrading the Unit 1 and 2 feedwater control systems. The new feedwater controls will be a microprocessor based system utilizing a design developed as part of the Westinghouse Owners Group trip reduction prograia. Because the Prairie Island AMSAC system will be dependent on the feedwater control system for input signals, the design and ins es11ation of the AMSAC system has to be integrated with the design and installation of the upgraded feedwater control system.

Because of this inter-dependence, we believe it is important to complete the engineering and review of the Unit 1 feedwater control upgrade prior to the final engineering of the AMSAC system and to install AMSAC at the same time as the feedwater control upgrade or subsequent to the installation of the feedwater control upgrade. However, the feedwater i

control upgrade engineering schedule does not allow adequate time to complete the final AMSAC design engineering by the beginning of Unit 1 j Cycle 13 (original AMSAC completion date for Unit 1) and thus will not ]

support the original AMSAC installation schedule for Unit 1. l l

Prairie Island is installing a new plant process monitoring computer, and has begun the process of transferring the functions from its Westinghouse l P250 computer to the new computer system. The physical removal of the j P250 computer is scheduled for July-August 1988, which corresponds to the j present schedule for installation of the Unit 1 AMSAC system. The Unit 1 l AMSAC system is to be installed in the same area were the P250 is located, and there is concern that the removal of the P250 at the same time as the installation of the Unit 1 AMSAC system may lead to complications and possible delays in the installation of AMSAC which could in turn extend the refueling outage.

Additionally, the control room control panel upgrade project will require work on the control panel annunciator cabinets in the area surrounding the P250 computer during the next four refueling outages. These modifications when combined with the P250 removal effort will further complicate installation of the Unit 1 AMSAC system during the August 1988 refueling outage.

For the reasons discussed above, we believe that the installation of the Unit 1 Amsac system prior to the start of Cycle 13 is impractical and that the proposed schedule delay would enhance the installation of both the AMSAC system and the feedwater control upgrade on Prairie Island Unit 1.

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L ATTACHMENT II AMSAC PRELIMINARY CONCEPTUAL DESIGN REPORT FOR PRAIRIE ISLAND REVISION 1

, Power Sources - The AMSAC system electronics will be powered from dual multinest

-power supplies rack-mounted in the base of each AMSAC cabinet. .Both power supplies are capable of providing all power requirements for the rack-mounted equipment. The two rack-mounted power supplies receive instrument AC from independent computer uninterruptible power supplies (UPS's). The sama instrument AC sources will be used for the AMSAC systems of both Prairie Island units. These are nonsafeguards sources, totally diverse from the reactor protection and control system. Each computer UPS is powered from an AC bus which has a nonsafeguard diesel-generator as an alternate source. Each UPS has its own battery. This results in a power supply system for the AMSAC electronics which is redundant and diverse from the sources used in the reactor protection and control system.

The Turbine Impulse pressure transmitters to be used for AMSAC are PT-485 and PT-486. This design requires the use of reactor protection system uninterruptible instrument AC sources for the transmitter and existing isolation amplifier power supplies for the impulse pressure signals. Transmitter PT-485 is powered from i Instrument AC Bus 2. The isolation amplifier, which would provide an impulse pressure signal to the feedwater rack from PT-485, is powered from Instrument AC Bus 1. PT-486, and its isolation amplifier providing the signal to the feedwater rack, are powered from Instrument AC Bus 3.

Although feedwater flow transmitters are presently used in the reactor protection system Prairie Island intends to upgrade its feedwater control system and reactor protection system in approximately the same time frame in which AMSAC is installed. At the time of this upgrade, the transmitter power supply circuits will be changed from the existing power supply to the feedwater cabinet power supplies. The transmitters will be powered from dual auctioneered power supplies in the feedwater rack. Thus loss of either power source will not effect the power to the transmitters. The feedwater instrumentation located in the protec-tion racks will be removed. The existing cable from the transmitter to the protection racks will be abandoned and new cable will be pulled from the transmitters directly to the feedwater rack. Thus feedwater will become a non-protection system.

In summary, Impulse Pressure signals will be input to the upgraded feedwater control system from Reactor Protection system isolation amplifiers. Feedwater Flow transmitters will be powered by, and will feed their signals directly to the feedwater control system. These input signals will be isolated by the control system and output signals for each of the input signals will be provided to the AMSAC system.

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I The feedwater flow transmitters and feedwater control circuits to be used for j AMSAC.will be powered as follows:

TRANSMITTER LOOP AS POWER SUPPLY FT-466 A Auctioneered Instrument Bus 1 and 3 FT-467 A Auctioneered Instrument Bus 1 and 3 FT-476 B Auctioneered Instrument Bus 1 and 3 FT-477 B Auctioneered Instrument Bus 1 and 3 Analog Inputs - The AMSAC system recexves analog inputs for Turbine Impulse Pressure and Feedwater Flow. For the f ailure of the instrument AC bus serving either the transmitter power supply or the signal isolation acplifier, the i signal to AMSAC would drop below the nominal live zero level and would be detectable as a signal failure.

The Turbine Impulse Pressure signals are from existing safety-related/IE  ;

transmitters, which are used for reactor protection and control. Each  !

transmitter, with its power supply, forms a current loop providing an input signal to bistables and signal isolation amplifiers. (See attached sketch of typical analog signal system). The transmitters are PT-485 and PT-486. The signal isolation amplifiers are Foxboro type M/66-BC. This equipment is used ,

throughout the reactor protection and control system to isolate protection j functions from potential failures in the control systems.

The turbine 1st stage pressure channels PT-485 and PT-486 will be input to the digital feedwater controller on individual Analog Input Cards, where the analog ,

signal is converted to a digital value and stored in engineering units. The l turbine 1st stage pressure values are then output to AMSAC on individual Analog ,

Output Cards. These outputs are isolated from the AMSAC system. [

The present Feedwater Flow Transmitter's are designed as follows: The Feedwater l '

Flow transmitters (two per feedwater loop) are presently used in the reactor protection and control system as part of the low steam generator level /(Feedwater (

Flow & Steam Flow) reactor trip. An isolated signal from these transmitters is (

used in Feedwater Flow Control. In each case sn additional isolation amplifier 1 provides an isolated signal to a computer input. This will be changed as follows: l The feedwater transmitters will be powered from Dual Auctioneered power supplies. l This is the same power which powers the existing feedwater rack.

The Transmitter power is supplied by the Analog Input Card. Each of the feedwater flow transmitters will be powered by an individual Card, where the analog signal is converted to a digital value and stored in engineering units.

The feedwater flow values are then output to AMSAC on individual Analog Output j Cards.

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4 ATTACHMENT III RESPONSE TO PLANT SPECIFIC QUESTIONS CONTAINED IN NRC i SAFETY EVALUATION OF WCAP-10858 REVISION I 1.) DIVERSITY The proposed AMSAC system is diverse from the reactor protection and control system to the extent practicable. The AMSAC power sources are totally diverse from the protection system Instrunent AC power supplies.

The AMSAC control eltetronics are significantly more current in design and operating principles than those used in the reactor protection and control system. The turbine impulse analog signals are isolated within the reactor l protection and control instrument racks (existing isolation corresponding to another function the signals provided). The feedwater flow signals are removed from the protection racks and the analog signals are isolated in i, the FW rack by the upgraded control system. They are isolated again with i isolation circuits of diverse design within the Foxboro SPEC 200 instrument i racks. The outputs to plant systems are in the form of relay contacts to be wired into existing system circuitry to provide the redundant actuation.

3.) SAFETY-RELATED INTERFACE The existing reactor protection system will be unaffected by the AMSAC installation. The ana.1og signals used in reactor protection are icelated from the signals leaving the existing instrument racks, going to the Feedwater System. The use of these isolators is discussed in WCAP-7685 l

" Isolation Amplifier" (June 1971), and in the Prairie Island USAR (page 7.4.-4). The analog signals are re-isolated at the AMSAC racks.

The system interface for actuation is accomplished by use of energize-to-actuate relay logic. The IE AMSAC actuation relays will be wired into the device actuation circuits for Auxiliary Feedwater initiation Turbine trip, Steam Generator Blowdown isolation, and Sample isolation.

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