ML20082D619

Forwards Response to NRC 831031 Request for Addl Info Re Analog Reactor Protection Sys Instrumentation Being Installed at Facility

ML20082D619
Person / Time
Site:	Browns Ferry
Issue date:	11/17/1983
From:	Mills L TENNESSEE VALLEY AUTHORITY
To:	Harold Denton Office of Nuclear Reactor Regulation
References
NUDOCS 8311220485
Download: ML20082D619 (9)

Text

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TENNESSEE VALLEY AUTHORITY CH ATTANOOG A. TENNESSEE 374o5 400 Chestnut Street Tower II November 17, 1983 Mr. Harold R. Denton, Director Office of Nuclear Reactoi Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Denton:

In the Matter of the

)

Docket No. 50-259 Tennessee Valley Authority

)

By lotter from D. B. Vassallo to H. G. Parris dated October 31, 1983, we received the third request for additional information regarding the analog Reactor Protection System instrumentation being installed on the Browns Ferry Nuclear Plant unit 1.

Enclosed is our response to that request. These responses were discussed with R. J. Clark, J. L. Mauck, and M. Virgilio of your staff on November 8, 1983 Ne trust that the enclosed responses fully satisfy your staff's concerns.

If not please get in touch with us immediately through the Browns Ferry Project Manager. The technical specifications are needed by December 3, 1983 to support a startup of December 9, 1983 Very truly yours, TENNESSEE VALLEY AUTHORITY r

L. M. Mills, Manager Nuclear Licensing Subscribed a sworn t efore me t is

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0311220485 831117 PDR ADOCK 05000259 P

PDR An Equal Opportunity Employer

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P Mr. Harold R. Denton November 17, 1983 cc (Enclosures):

-0.S.' Nuclear Regulatory Commission

' Region II 4

ATTN: l James P. O'Reilly, Regional Administrator b

101~Marietta Street, NW, Suite 2900 Atlanta,. Georgia 30303

.Mr. R. J. Clark Browns Ferry Project Manager U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, Maryland 20814 s

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1

,e ENCLOSUREE

-RESPONSE TO LETTER,FROM D. B.'VASESALLO TO H. G. PARRIS LDATED 0CTOBER 31, 1983

. ANALOG TRIP SYSTEM BROWNS FERRY-NUCLEAR PLANT UNIT 1

1 LNRC QUESTION'

The Rosemount instruction manual-(4471-1 Revision.A)' states that the analog' trip. units (ATUs) operate within Electromagnetic Interference (EMI)1 conditions that'are-normally expected in a' power plant control room environment, provided that shielded wires are used for all

-signals connections and the auxiliary analog output. Provide a discussion of the shielding-techniques implemented for this-modification and ' clarify tl e apparent discrepancy between the wiring diagrams:and the plant interconnection diagram regarding the shield

' terminal designation.

RESPONSE

Twisted pair cable with.100-percent foil shield was used between the transmitters and the master trip units.- The shields'are connected to the plant grounding system in the analog trip' unit (ATU) cabinets. The cabinets themselves are connected to the plant grounding system and provide additional shielding for the components-they house.

The cable between'the transmitters and the cabinets is routed in conduit separate

- from all other. plant. circuits.

Aux'iliary analog outputs are not used.

. The plant-interconnection drawing (Figure 1) shows routing of the cable

-shielding..

NOTE: :This figure supercedes the interconnection. drawing included in 3

TVA's 0ctober-20,'1983 submittal.

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" 2.

NRC QUESTION The submittal regarding the analog trip system (ATS) states that the consequences of the loss of the MG-set power source is the same as it was before the transmitter trip unit installation, and the loss of a single trip unit cabinet power supply does not disable the trip unit because it is backed up with a redundant power supply.

Provide a dethiled discussion regarding the power supply design (MG-set to the ATUS) and the various failure modes, (e.g., open circuits, hot shorts, overvoltage, undervoltage, overfrequency, and underfrequency) that could occur and the resulting consequences. In addition, discuss the condition resulting from the loss of a fuse (e.g., FU-99-A1) or a cooling fan (e.g., FAN-99-A1).

RESPONSE

The power for the reactor protection system (RPS) is supplied by two independent motor-generator (MG) sets. Figure 2 shows the RPS power supply single line for one train. Each MG set has relay protection to ensure that its output voltages do not exceed 132-V ac cr decrease below 108-V ac, and that its output frequency does not decrease below 57 Hz.

Each MG set supplies 120-V ac single phase power to two channels in the same train for both RPS channel logic and the RPS ATUs. The RPS logic is wired for fail-safe operation; i.e., they go to the trip state on loss of power. The ATUs are interfaced to the existing RPS logic by interposing relays. The interposing relays are wired for fail-safe operation. Loss of one MG set results in loss of power to two channels of RPS logic and to two ATU cabinets. This results in a half scram since both the RPS logic relays and the interposing relays go to the trip condition.

Loss of one 120-V ao input power fuse (FU-99-A1, etc.) results in the loss of power to one ATU cabinet. Since the interposing relays are mounted in the ATU cabinets and are powered from the 24-V power supplies which are fed by the 120-V ac power, loss of power deenergizes the interposing relays and produces a half scram.

The Rosemount transmitters being used in the analog trip system (ATS) require a minimum of 13.5 V at the transmitter terminals to operate properly. Considering the transmitter operating voltage and allowing for load and wire resistances at full transmitter output (20 ma), the minimum required power supply voltage is 20.2 V.

The minimum rated output voltage of the power supplies at full load current and 60 Hz is 24 V.

The power supplies' output voltages do not change-significantly with input voltage variations in the range stated above. The output voltage does vary linearly with input frequency, with a change of 1.3 percent for each 1 percent change in frequency. Assume the worst case of a 5-percent (3 Hz) decrease in frequency before the MG set protective rclays would trip the MG sets, the power supply voltage would drop to about 22.5 V.

This still provides substantial margin to the minimum required transmitter voltage.

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'3.

NRC QUESTION

' Provide verification that the length of the cable runs associated-with the ATU transmitter installation does not exceed the design

. requirements provided in Table 3, " Voltages _Available For Transmitter Operation" of the Rosemount Instruction Manual.

RESPONSE l Each cable length is less than 500 feet. The effects of cable length are

-discussed in quesion 2..

-4..

NRC QUESTION The Rosemount Instruction Manual contains a warning regarding operating at low ATU power supply voltages because if certain conditions exist, a low-supply voltage at the-transmitter may cause it-_to operate improperly and a desired trip may not occur.

Therefore, the staff is concerned that an undervoltage condition -

icould exist that would incapacitate the trip functions of all the effected ATUs.. To alleviate this concern, design details regarding protection against undervoltage. conditions'(e.g., electrical protection assemblies).needs to bo provided.

RESPONSE' Conditions which could result'in undervoltages have been addressed in.

question 2.-

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'4 5.

NRC QUESTION

^

Your response to a previous question regarding increased technical specification surveillance requirements (letter dated September 21, 1983, from D. B. Vassallo to H. G. Parris) is unacceptable. Under-the current technical specification the reactor protection system instrument ~ setpoints are to be verified only at 18-month intervals during the channel calibration for most channels. Although the staff has not per'?ormed a detailed review of the methodology used to establish the taip setpoints for the Browns-Ferry facility, the setpoint methodology used for the General Electric supplied systems would include a more frequent setpoint verification and adjt+tment.

The staff has concluded that a more frequent setpoint verification is warranted since the addition of the analog trip system instruments to the RPS has introduced new components (e.g., power supplies, operational amplifiers, buffers, comparators) that will

-have an effect on determining setpoints (e.g., uncertainties, drift, response times). In addition as noted in the staff review of NEDO-21617-A (letter dated June 27, 1978 from O. D. Parr to General-Electric Company), the advantage of an ATS modification with respect to regulatory requirements is in the area of improved testing procedures _and capabilities.

Therefore, for each reactor protection syster. instrument channel where the ATS has been added, provide technical specification

. modifications where the method and frequency for determining the trip unit setpoints and resetting the setpoints is consistent with the assumptions of the setpoint methodology used for the General Electric' supplied ATS systems.

RESPONSE

The method and frequency for determining the trip unit setpoints are consistent with the assumptions.of the Browns Ferry-established setpoint methodology. As described in our [[letter::05000260/LER-1983-056-03, /03L-0:on 830920,while Performing SI 4.2.B-57, Discovered That RHR Pump 2C Cooler Fan Would Not Operate. Caused by GE CR124CO28 Overload Relay Tripping.Overload Relay Replaced|October 20, 1983 letter]] from L. M.

Mills to H. lR. Denton we will verify the unit 1 ATS setpoints on a monthly basis during the functional tests in addition to the prcsently required loop calibration every 18 months.

1

. 6.

NRC QUESTION Section 2.0 of'your October 20 submittal states that because each channel is located in iss own cabinet, and the external wiring is separated, the separations of the RPS channels are maintained ard the requirements of Regulatory Guide 1.75 (ac it applies to Browns Ferry) are met. The staff recognizes that it is not possible for the licensee to make all retrofit modifications meet the requirements of regulatory guides that are not applicable to their plant design. However, the staff has concluded that when a retrofit modification can be completed and present regulatory requirements met, a significant improvement in safety margin can be obtained.

Therefore, provide a description of the wiring modifications completed-and which of these modifications do not meet Regulatory Guide 1.75. -In addition, justifications (e.g., physical limitations, cost) should be provided for the exceptions taken to this Regulatory Guide. The above description should include a discussion of the wiring modifications associated with the ATS power supplies..

RESPONSE

The wiring for each transmitter is run in flex conduit from the transmitters to a junction box and then to an ATU cabinet in the auxiliary instrument room in rigid metallic conduit. The power supply cables for the ATU cabinets are run in conduit from the RPS logic panels.

The output signal cables frca the ATUs are rcuted in conduit from the ATU cabinets to the RPS logie panels-The cables for each channel are routed in separate conduits. The annunciator cables are run in conduit from-the ATU cabinets to overhead nondivisional medium voltage cable trays and then to the main control room in conduit.

The nondivisional; annunciator system wiring is routed with the ATS wiring

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inside the ATU cabinets but is electrically isolated by normal relay coil contact isolation.

The wiring for the ATS conforms to the requirements of Regulatory Guide 1.75 except for the internal panel wiring of the annunciator circuitry.

The design of.the equipment mounted in the cabinets prevents maintaining complete physical separation between the annunicator wiring and the class 1E wiring. This does not pose a problem because-the annunicator circuitry is a low energy circuit. The annunicators interrogate contacts in the ATS with a 140-V de algnal that is currently limited to a maximum of 1 mA by the annunciator input resistance.

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