ML20082T142

Forwards Info on Proposed Mod to Reactor Trip Sys in Response to Generic Ltr 83-28, Required Actions Based on Generic Implications of Salem ATWS Events

ML20082T142
Person / Time
Site:	Davis Besse
Issue date:	12/09/1983
From:	Crouse R TOLEDO EDISON CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
1012, GL-83-28, TAC-53170, NUDOCS 8312150175
Download: ML20082T142 (14)

Text

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i TOLEDO EDISON Docket No. 50-346 (',1$cm m.,

, License No. NPF-3 ."isi ese szai Se' rial No. 1012 December 9, 1983 Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz Operating Reactor Branch No. 4

• Division of Operating Reactors United States Nuclear Regulatory Commission -

Washington, D.C. 20555

Dear Mr. Stolz:

This is in response to Mr. D. G. Eisenhut's letter dated July 8, 1983 (Log No. 1322) concerning Required Actions Based on Generic Implications of Salem ATWS Event (Generic Letter 83-28), Item 4.3. Attached is Toledo Edison's report on proposed modification of the reactor trip system for Davis-Besse Nuclear Power Station Unit No. 1 (DB-1).

, The attached report outlines the proposed modifications that will be

( implemented at DB-1 for the automatic actuation of Reactor Trip Breaker

! Shunt Trip Attachment. Attachment 1 of the report contains the requested information as identified in Enclosure 1 of your letter dated September 22, 1983 (Log No. 1378). That letter transmitted a " Safety Evaluation l

Report Generic Modifications of Reactor Trip Breakers for B&W Plants to Provide Automatic Actuation of Shunt Trip Attachments" for Arkansas Nuclear One, Unit No. 1. Toledo Edison endorses the generic aspect of l

ANO-1 design approved in the SER as it relates to the Davis-Desse Unit No. 1.

Very truly yours, f = ~

RPC: GAB:MAK:lah attachments -

cc: DB-1 NRC Resident Inspector f

8312150175 831200 /7 PDR ADOCK 05000346 9 P PDR O

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THE TOLEDO EDISDN COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO OH!O 43652 l

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REACTOR TRIP BREAKER

SHUNT TRIP CIRCUIT MODIFICATION DAVIS-BESSE UNIT NO. 1 BACKGROUND The NRC generic letter 83-28, dated July 8,1983, requested actions based on generic implication of Salem ATWS events. Item 4.3 of the letter required that B&W and Westinghouse reactors be modified by providing automatic actuation of the breaker shunt trip attachments. Also, the shunt trip attachment stated to be safety related (Class 1E). A report describing the modification was requested in response to item 4.3.

NRC letter dated September 22, 1983 issued a safety evaluation review (SER) on a proposal submitted by Arkansas Power and Light Company (AP&L) for the Arkansas Nuclear One (ANO) Unit No. 1. The modifications proposed were for both the AC and DC reactor trip breakers. The SER concluded that the generic aspect of the proposed modification design were acceptable,

• however, additional information, as indicated in Enclosure 1 of the SER, were to be submitted for individual power plants to conclude the review of this matter.

PURPOSE This report is to endorse the applicable features of AP&L generic design for. application to Toledo Edison Company's (TED). Davis-desse Nuclear Power Station (DBNPS) Unit No. 1. The differences of the TED and AP&L designs have been described with supporting information and subsequent conclusions

-provided for TED s proposal. Finally, in Attachment I, additional infor-i mation concerning items of Enclosure 1 are provided to conclude this matter on a plant specific Lasis.

DIFFERENCES BETVEEN TED & AP&L PROPOSED MODIFICATIONS (Attachments III, IV & V)

Basically, the TED proposed modification design (TED's design) for all the four AC trip breakers is the same as the AP&L design for AC breakers. The differences, however, are described as follows:

UV SENSOR

( (Attachments IV & V) l' TED design includes an undervoltage (UV) sensor of the same model as in

( AP&L's design, i.e., ITE-27-H, but a different type, i.e., 211B instead of f 211R .- The basic difference being operation of the output relay in each type. The output relay of the type 211B is normally energized when the 1

control power is og and undergoes a contact position change upon loss of control power the same way as the loss of input signal. A normally closed contact of this sensor has been used in TED's design. The output relay of

211R type UV sensor is normally deenergized irrespective of the control

! power status and picks up only on loss or degradation of input signal .

below the set limits. This was confirmed by the vendor while discussing the information in reference to NRC Information Notice No. 82-50 in which operation of the 211B type UV sensor under a loss of control power i

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'.f condition, was reported as a cause of concern. Also confirmed by the vendor was the fact that internal circuitry of the 211R relay is such that 8

, it provides the same terminal block orientation on.the drawing as the 211B type, i.e., the output relay is assumed as energized normally and a ,

normally close contact to provide the undervoltage closure.

The type 211B UV sensor used in the TED's design requires 120 VAC instead of 125 VDC as the control power. Schematically shown, the sensor is connected right across.the breaker undervoltage release (UVD) which receives 120 VAC from the vital bus through the reactor protection system

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(RPS), anticipatory reactor trip system (ARTS) and manual reactor trip switch. Also, the connection to the input terminals of the sensor are

.. omitted. As evident, this design eliminates the need of a separate class 1E DC control power for the operation of the UV sensor.

t POWER SUPPLY (Attachment III)

Control power for the shunt trip circuits of two of the breakers (A & B) originates in two different.125 VDC non-1E distribution panels which in turn, are powered from two redundant 125 VDC 1E distribution panels. The non-IE panels are installed to Seismic Category I. (S/I) requirements. The

-isolation between the 1E and non-1E panel is a fuse installed in the IE panel on .the feeder to non-1E panel. _Each IE panel, the non-1E panel fed

-from this 1E panel, and the raceways carrying the control power between

.these are all. located inside a redundant seismic room and therefore are ,

. ' separated from the equipment and raceways of the other redundant channel.

' - All the conduits carrying the control power. cables are installed on the r seismic supports with the exception of conduit indicated as 'Z' on Attach-

! ment III which is'a short run. (approx. 30 ft.).

LControl power for the other two AC breakers (C & D) is non-1E 120 VAC l

derived from secondary windings of two 480/120 volt control transfcrmers,

!- primary of which are connected to the incoming 480 VAC.to the reactor trip l breakers as shown in attachment III. The control transformer for breaker i C is located in breaker A. Both breaker C and A and the raceways carrying

(' the control power between these breakers are located inside a redundant l

seismic room and the conduit carrying the control power cable between the two breakers is seismically supported. The control transformer for breaker D is located within the breaker itself, and the breaker is located  ;

within a seismic structure. However the 480 volt feed to the primsry of control transformer is from the breaker B and the conduits carrying the feeder cable,-indicated as_'Y', is not installed S/I.

I SHUNT TRIP ATTACHMEN'S

, (Attachments IV & V) f JThe non-1E source interruption device (SID) is installed in two of the j~ breakers (A & B). The SID was seismic tested as part of a circuit breaker similar-.to those installed at DBNPS Unit No. 1. No physical damage to SID was reported after the test completion. Similarly, the non-1E shunt trip coil of the breaker was tested with no damage reported.

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The DC shunt trip coils in the other two of the breakers (C & D) will be replaced with similar.AC coils which operate on a voltage range of 95 to.

125. The DBNPS Unit No. I distribution voltage analysis indicates that under normal bus line-up the 480 volt bus will not degrade to the extent

- to cause 95 volts on the shunt trip coil.

The isolation of non-1E shunt trip circuits from the IE undervoltage

- circuits is achieved through the coil to contact isolation of' tne quali-fled UV sensor.

The shunt trip coils are not provided with any unnecessary fuse protection as 'in AP&L design and, therefore, no reliability problem exists.

INDICATING LIGHT (Attachments IV & V)

To facilitate the breaker. shunt trip circuit testing independently and.

indicate. status of the DC control power to the shunt trip circuit, a blue .

-light is provided. The blue is TED's standard color for the standby status indication. Also, no indicating light is provided in the under-voltage circuit since.a loss of power will result in a breaker trip and 6 indication which will be sufficient for both normal operation and testing.

CONCLUSION Based on the above described facts to support the differences of the TED's design from AP&L's design, TED concludes as follows: ,

1. The use of type 211B UV sensor adds more reliability to the class 1E undervoltage circuits as no separate control power to operate the sensor is required.

2. Although the shunt trip circuits are non-1E, their existence will not

' interfere with the IE undervoltage circuits during a SSE. This has been proved by the seismic tests conducted on a similar breaker unit.

3. The non-1E. control power to the shunt trip circuits of breaker A and B'are as reliable as the 1E power supplies since the non-1E power is derived from the IE power source located within the same seismic room and all_the associated raceways carrying the control power cables are-installed as S/I with the exception as noted.

4.- The non-1E control power supply to the shunt trip circuit of breaker' C is equally reliable to a 1E power supply since the control trans-former supplying this power is located within the seismically quali-fled breaker A and is type tested as part of the breaker. Also, both the breaker A and C and the raceway carrying control power between these are located within the same seismic room and all the associated raceways carrying tne control power cables are installed as-S/I.

A loss of primary voltage of the control transformer wil'1 occur simultaneous to a loss of power to control rod drive motor and, therefore, does not pose a reliability concern.

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5. The non-1E control power supply to shunt trip circuit of breaker D is '

equally reliable to a 1E power supply, with the exceptions as noted, since the control transformer supplying this power is located within the breaker itself.and has been type tested during the breaker seismic qualification. Also, a loss of power to control transformer primary will not be a reliability concern as indicated in (4) above.

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A*lTAC10:ENT 1 RESPONSE TO ENCLOSURE 1 0F SER TO AP&L DESIGN-

, DATED SEPTEMBER 22.-1983 ,

ITEM _1 A statement confirming that the UV sensor (high speed undervoltage relay) Model ITE-27H-211R, is environmentally and seismically qualified for its service conditions.

RESPONSE: As confirmed by_the vendor, the UV sensor Model ITE-27-211B used in TED's design has been identically qualified to Model ITE-27-211R for all the standard requirements listed below:

IEEE 323-1974 Environmental Qualifications

IEEE 501 Seismic Qualifications

. IEEE 313 Dielectric Test (line-to-line and line-to-ground)

IEEE-472 Surge Withstand Test We believe that this sensor will meet the applicable SSE level

-requirements at DBNPS Unit No. 1. .

Since all the four reactor trip breakers at DBNPS Unit No. I are located in non-harsh environment, the environmental qualification of the sensors is not applicable, however, the sensors will be purchased i

to' meet all the above listed standards.

ITEM 2 A statement confirming that all other additional components involved in the shunt trip circuita are environmentally and seismically qualified for their service conditions.

l. RESPONSE: The other additional components involved are: the test switch, power alarm relay, indicating light, AC shunt trip coils and cables.

None of these components are required to be environmentally qualified for the reason mentioned in the response to Item 1.

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The test switch and the power alarm relay however, will be purchased as items qualified to IEEE-323-1974 and IEEE-344-1971 (1975 ~

for power alarm relay).

The indicating light is not a qualified item, however, as part of ,

our facility modification, we will assure that this item will not interfere with the safety related circuits and components during an SSE.

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J ATTACHMENT I The AC shunt coils are of similar physical characteristics as the existing DC shunt coils seismically tested as part of the breaker with no mechanical damage.

All additional cables will be qualified to IEEE 383.

l ITEM 3 .,

l 1A statement confirming that the shunt trip attachment is or will be environmentally and seismically qualified for its service conditions. i RESPONSE: The existing shunt trip attachments in all four breakers including the source ihterruption device installed inside two of the breakers, have been type tested for SSE level applicable to DBNPS Unit No. 1. Upon test completion, no physical damage was reported.. ,

The shunt trip coils in two of the breakers will be replaced with ,

physically similar coils therefore a requalification is not applicable.

ITEM 4 i

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Identify the classification (safety related or not) and separation

.(train or channel identification) for the reactor trip shunt and UV trip circuits, power supplies, and any interface isolation devices.

RESPONSE: The undervoltage trip circuits in all four breakers are safety related and each circuit is powered from a safety grade power supply.

The shunt trip circuits are non-safety related and each circuit is powered from a non-safety related power supply details of which are given in this report elsewhere.

The isolation.of safety related undervoltage circuits and non-safety.

related shunt trip circuits is achieved through the coil to contact isolation of a qualified undervoltage sensor.

ITEM 5 4

If the wiring to the UV sensor involves different separation groups (train or channel), identify the minimum separation (distance) between wiring of the different groups. Provide an analysis of the consequences of short circuits between wiring in different separation groups to confirm that the consequences do not adversely impact redundant safety related systems.

RESPONSE: Wiring to UV sensor does not involve different class IE power trains and therefore do not adversly impact redundant~ safety related systems.

Wiring to UV sensor does involve a non-1E source. Since the distance between the IE and non-1E wiring at the sensor terminals is a few inches, the analyses for the possibility of short circuits between the two groups of. wiring are provided as follows.

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ATTACHMENT I 1 .

1. Breakers with 125V DC non-1E control power (A & B):

At DBNPS Unit No. 1, DC control power is suppli'ed by a 3 wire system with the common ungrounded. Therefore, a short circuit between the two groups of wiring involving one leg from each circuit will not result in jeopardizing the function of safety related undervoltage trip circuit. . ,

2. Breakers with 120 VAC non-1E control power (C & D):

A short circuit between the two groups of wiring involving one leg from each circuit will have no effect on the UV or shunt trip circuits since the non-IE control power is derived from the isolated secondary winding of a dedicated control transformer for each breaker.

ITEM 6' Provide an outline of the test procedures to independently verify the operability of the shunt and UV trip circuits and components.

Identify the sequence of action to be performed. Address your. intent regarding periodic surveillance to confirm the operability of the power failure alarms.

RESPONSE: Attachment No. II provides the test outline for verifying -

operability of the undervoltage and shunt trips and other components.

ITEM 7 Provide a draft of any proposed technical specification changes as a result of this modification.

RESPONSE: There is no technical specification change required as a result of this modification.

ITEM 8 Provide the electrical schematics for the shunt and UV trip circuits.

RESPONSE: Electrical schematic for the shunt and undervoltage trip circuits have been provided in Attachment IV and V.

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ATTACHMENT II TEST OUTLINE

1.0 OBJECTIVE

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The purpose of this outline is to list the sequence of operation required to independently verify the operability of the UV and shunt trip circuits of the four reactor trip breakers A, B, C & D. It is being assumed that Anticipatory Reactor Trip System (ARTS) will be in normal functional state at the time of this testing.

2.0 PROCEDURE

(Refer to Attachments IV & V) 2.1 Testing of UV trip circuit and the power alarm relay (typical for all four breakers). .

2.1.1 Verify that the breaker under test is in closed position and the control power to the shunt trip circuit of the breaker is on (blue light on the breaker is lit). Also verify that Reactor Protection System (RPS) is energized.

2.1.2 Turn the key operated test switch to "UV Test" position and hold.

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2.1.3 Observe that the blue indicating light is not lit and an alarm is received in the Control Room indicating a loss of shunt trip circuit control power.

2.1.4 At the Reactor Trip Module of the RPS place the Reactor Trip Module Reactor Protection channel switches "A" and "B" in the "Sim Trip" position. This will actuate the relay Contacts A and B in the undervoltage trip circuit of the breaker associated with the RPS channel actuated.

2.1.5 Verify that the breaker has tripped.

2.2 Testing of the shunt trip circuit (typical for all four breakers).

2.2.1 Verify that the breaker under test is in closed position and the control power to the shunt trip circuit is available (blue indicating light is lit).

2.2.2 Turn the key operated test switch to " shunt trip" position, the breaker will trip momentarily.-

3.0 ACCEPTANCE CRITERIA:

Each Reactor Trip Breaker trips on UV and shunt trip tests.

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