NRC-91-0128, Forwards Response to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.'

Forwards Response to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.'

ML20085K973
Person / Time
Site:	Fermi
Issue date:	10/25/1991
From:	Orser W DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-91-0128, CON-NRC-91-128, REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR GL-91-06, GL-91-6, NUDOCS 9111010167
Download: ML20085K973 (9)

Text

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oct ober 25, 1991 NRC-91-0128 U. S. Nuclear Regulatory Ccetmission Attn Document Control Desk Washingt on, D. C. 20555

References:

1) Fermi 2 NRC Docket No. 50-341 NRC License No. NPF-43

2) NRC Generic Let ter 91-06, " Resolution of Generic Issue A-30; Adequacy of Safety-Related DC Power Supplies Pursaant to 10CFR50.54(f)," dated April 29, 1991

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Subject:

Response t o Generic _ Le t ter 91-06 The purpose of this let ter is to provide Detroit Edison's response t o

'NRC Ceneric Letter 91-06 (Reference 2) .

Det roit Edison has reviewed Generic Let ter 91-06 and t he at tachment to thin-letter r"ovides our response to each specific NRC question in the form of- e- complet ed GL 91-06 Enclosure 1. Also, as sper.ified by

. question numbera 5 and 9, if the answer to any part of a question is "no", ' additional information has been provided t o justify the answer. -

If you have any questions, please contact Mr. Girija S. Shukla at (313) 586-4270.

Since rely, Vh Enclosure cc: A. B. Davis R. W. DeFayet t e

l. J. F. Stang i S. Stasek

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9111010167 91102'5 gd tl PDR -ADOCK 05000341 "I g

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UStJRC october 25, 1991 flRC-91-0128 I. WILLI AM S. OPSER. do hereby af firm that the foregoing e.tatements are bat.ed on facts and circumst ances which are t rue and accurat e t o the beat of my knowledge and belief. -

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• WIILIAM S. ORSER 3enior Vice President on this & day of ..

bM __. 1991 before me personally appeared William S. Orcer, being fi rst duly sworn and says that he executed the foregoing as his f ree act and deed. ..

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4 ENCLOSURE 1

-10 CFR 50.54(f) REQUEST - GENERIC ISSUE (GI) A-30 " ADEQUACY OF SAFETY-RELATED DC POWER SUPPLIES"

_Bac_kground

-The specific area of concern of GI A-30 " Adequacy of Safety-Related DC Power

-Supplies" is the-adequacy of the safety-related de power in operating nuclear power plants, particularly with regard to m:.1tiple vid common cause failures.

Risk analysis and past plant experience support conclusions that failure of the de power supplies could represent a significant contribution to the unreliability of shutdown cooling. A_nalysis indicates that inadequate maintenance and serveillance and failure to detect battery unavailability are the prime contributors to failure of the de power systems.

During the development of plans to resolve GI A-30, it was observed that several previously issued regulatory notices (IENs) bulletins (IEBs)and

' letters (GLs) submitted to licensees include recome,ndations similar to those that have been identified to resolve G1 A-30. More specifically, it has been determined that recommendations contained in notifications IEN 85-74, "Sthtion Battery Problems", IEB 79-27, " Loss of Non-Class IE Instrumentation and Control Power System Bus during Operation," and separate actions being taken to resolve GI 49, " Interlocks and LCOs for Class IE Tie Breakers

• include the elements necessary to resolve GI A-30.

It is therefore concluded that licensees that have implemented these reco F4tions and actions will have resolved GI A-30.

The response to the questien follow is necessary to provide the staff with information to determim a. ~aer any further action is required for your facility.

Questions The following .information is to be provided for each unit at each site:

1. Unit Fermi 2

2. a.. The number of independent redundant divisions of Class 1E or safety-related de power for this plant.is -- two _. (Includeany

-separate Class IE or safety-related de, such as any de dedicated to the diesel generators.)

b. The number of functional safety-related divisions of de power necessary to attain safe shutdown for this unit is one .

3.- Does. the control room at this unit have the following separate, independently annunciated alarms and indications-for each division of de power?

a. alarms

1. Battery -disconnect or circuit breaker open? _ No

2. Battery charger disconnect or circuit breaker open (both input ac and output dc)? nn

'r

y

3. de system ground? __No

4. de bus undervoltage? __Yes

5. de bus overvoltage? ,, _ Y e s

6. Battery charger failure? No

7. Battery discharge? _ No

b. Indications

1. Battery float charge current? No

2. Battery circuit output current? _N o

3. Battery discharge? No

4. Bus voltage? No

c. Does the unit ha.e written procedures for response to the above alarms and indications? yes

4. Does this unit have indication of bypassed and inoperable status of circuit breakers or other devices tilat can be used to disconnect the

' battery and battery charger from its de bus and the battery charger from its ac power source during maintenance or testing? .121, by u s e o f administrative controls.

5. If the answer to any part of question 3 or 4 is no, then provide information justifying the existing design features of the facility's safety-related de systems. ~*See note below.

6. (1) Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one de division to be unavailable? Yes and (2) do plant procedures prohibit uaintenance or testing on redundant de divisions at the same time?

Yes If .he facility Technical Specifications havc provisions equivalent to those found in the Westinghouse and Combustion Engineering Standard Technical Specifications for maintenance and surveillance, then question 7 may be skipped and a statement to that effect may be inserted here.

7. Are maintenance, surveillance and test procedures regarding station batteries conducted routinely at this plant? Specifically:

a. At least once per 7 days are the following verified to be within acceptable limits:

1. Pilot cell electrolyte level? Yes l

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l y ,

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2. Specific gravity or charging current? yns (pilot cell, per NUREG/CR-5414).

3. Float voltage? y n e, (Pilot cell, per NUREG/CP-5414).

4. Total bus voltage on float charge? yns

5. Physical condition of all cells? yes

b. At least once per 92 days, or within 7 days af ter a battery discharge, overcharge, or if the pilot cell readings are outside the 7-day surveillance requircments are the following verified to be within acceptable limits:

1. Electrolyte level of each cell? yns

2. The average specific gravity of all cells? yns

3. The specific gravity of each cell? _ynt 4 The average electrolyte temperature of a representative number of cells? le s

5. The float voltage of each cell? yes

6. Visually inspect or measure resistance of terminals and connectors (including the connectors at the de bus)?

Yes - except for connectors at the dc bus,

c. At least every 18 months are the following verified:

1. Low resistance of each connection (by test)? ,les

2. Physical condition of the battery? yes ,_,,

3. Battery charger capability to deliver rated empere output to the de bus? yes 4 The capability of the battery to deliver its design duty cycle to the dc bus? yne

5. Each individual cell voltage is within acceptable limits during the service test? vne

d. At least every 60 months, is capacity of each battery verified by performance of a discharge test? yne

e. At least annually, is the battery capacity verified by performance discharge test, if the battery shows signs of degradation or has reached 85% of the expected service life? nn i

l

l Enclosure 1

8. Does this plant have operational features such that following loss of one 3dfety-related dC power supply or bus:

a. Capability is maintained for ensuring continued and adequate reactor cooling? Yes

b. Reactor coolant system integrity and isolation capability are maintali Yes

c. Operating procedures, instrumentation (including indicators and annunciators), and control functions are adequate to initiate systems as required to maintain adequate core cooling? Yes

" 9. If the answer to any part of question 6, 7 or 8 is no, then provide your basis for not performing the maliitenance, surveillance and test procedures described and/or the bases for not including the operational features cited. *See note below.

• Note: For questions involving supporting type infonnation (question numbers 5 and 9) instead of developing and supplying the information in response to this letter, you may com:it to further evaluate the need for such provisions during the performance of your individual plant examination for severe accident vulnerabilities (IPE). If you select this option, you are required to:

'(1) So state in response to these questions, and (2) Comit to explicitly address questions 5 and 9 in your IPE submittal per the guidelines outlined in NUREG-1335 (Section 2.1.6 Subitem 7),

" Individual Plant Examination: Submittal Guidance."

1

Enclosure to NEC-91-0128 Page 1 Ad_dstional Information_Regarding Response to NRC Generic _ Letter 91-06 The Detroit Edison response t o each question of the Generic Lettet is provided in the at tached complet al Enclosure 1 of GL 91-06. Al s t , as specified by Question Numbers 5 and 9, if the answer t o any question is "no", addit ional information is provided below t o justi fy the enswer.

o guention 3.a.1, Basis for "no"_ _as Regot3se:

At Fe rtai 2, the bat tery can be disconnec t ed f rom the DC bus by opening of main feeder fuses and/or fuse links between the bat tery and (i) Motor Cont rol Center (MCC) and (ii) the main dist ribution cabinet s.

The monitoring of these fuses and/or links is accomplished as follovs:

(i) Opening of fuses to MCC is sensed immediately by activat ion of MCC position power alarm relays. Opening of fuses would de-energize the relays which would annunciate the cont rol room alarms for Div. I RCIC valves motor overload / loss of power and Div. II HPCI valves mot or overload / loss of power supply. Therefore, an indirect control room elaria exists for the condition of the battery being disconnect ed from MCC.

(ii) Opening of fuses or fuse link to main distribution cabinets would disconnect the bat t ery from the char ger and the charger would carry the loads. This would result

--in the battery voltage decreasing from float charge voltage of 133 VDC to a battery full charge voltage of appr oximat ely 125 VDC. This low volt age of 125 VDC would be det ected during the performance of the weekly battery surveillance which verifies that t he tot t e ry volt age is

> 13 0 VD C. Once low volt age is dett:t ed, cor rective action would take place. Det roit Edison considers this an accept able alt erna tive t o a a f t ery disconnect ed alarm.

However, opening of these 400 amp fuses or fuse link is very unlikely as the maximum normal current through the fuses is only 115 amps, which is 1.15 times t he r a t ed c urr en t output of the cha r ge rs.

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Enclosure to NRC-91-0128 Page 2 o Question 3.a.2, Basis for "no"_as_Respon_s,e Accept able alt ernatives to these alarcis exist at Fermi 2. Input

-ac breaker open would be det ected directly by existing control room alarm for loss of ac power at the charger, while the output de breaker open would be det ec t ed indirectly via the de bus low volt age alarms, o guestion 3.a.3, Basis _for "no" Response:

Fermi 2 safety relat ed batteries ate ungrour.ded and requite two grounds t o be in a f ault condition. Therefore, an alarm is not provided in the control room. Inst ead, a local ground det ect or i c locat ed by t he ba t t e ry cha rge rs. This detector is monitored once a day by an operator performing his daily rounds. Once a ground is detected, corrective action would t ake place. . Detroit Edison considers this an acceptable alternative to a control room ala rm ,

o Question 3.a.6, Basis for "no" Response:

An acceptable alternative to above alarm exist at Fe rmi 2.

Charger failure vould be noted as a low voltage on the DC bus.

.This is detected by the low voltage alarms (see response to Question 3.a.2) .

o guestion_3.a.7, Basis for "no" Response:

For a battery to discharge would require the DC bus loads to exceed the battery charger output current limit of 115 amps.

This discharge would be det ect ed once a day when the plant operator performs his daily rounds and records the charger output current. Any value above 25 amps would be secorded as unsatisf actory resulting in corrective action. Also, if t he bat tery is discharged, it would be det ected during the performance of weekly tattery inspections where it would be noted as a low pilot cell- specific gravity, which is an indication that I a bactery is discharged (less than 100% oof rating). Detroit l Edison considers that these instections ate an acceptabF al t e rma t ive t o a ba t t e ry d is cha r ge ala rm .

o guestion_3.b.1, 2. 3 _ Basis for "no" Ren,ponse:

T1ue need for cont rol room indication of it ema 3.b.1, 2. and 3 l reflects a . concern regarding the battery capacity.

Battery capacity is a coneerri:when the battery la discharging

- during a loss of bat t ery cha 7er event. A los s of a bat t e ry charge r would result in an undervoltage (1128.5 VDC) alarm being recnived in the control room. Operat or inves tigation will reveal

4 Enclosure to tJRC-91-0128 Page

• the loss of the bat tery charger and cor rective actionn would take place. The tiecd t o know remaining capacity la not evident, nince ef for to will be made t o rectore charger support as soon as possible. Additionally, a hat tt ty capacity monit or (ampere-hour a:onitor) will be of lit tle value for indication of remaining capacity in a bat tery. Bat t ety capaci t y in depetider t on other var iables which can not be nionit or ed on-line t o deter mine bat t e ry remaining capacity. Variables ar e bat t ery age, discharge rate and temperature. Ther ef or e, Det roit Edican considers that it in acceptable not t o have a bat t ery capaci t y raonit or .

o Question 3.b.4,, Basin for_,"no" Response:

Fermi 2 han a bus vol tmet er locat ed locally near the let t erica which is considered an accept able alt ernative. This along wit h t he high and low volt age cont rol r oom alarms would meet the needn of monit oring buo volt age. Also the plant operator records the bus voltage during his daily roundo and action it taken for voltage above 138 VDC or below 132.5 VDC.

o Question 7.b.6,_ Additional t Informatlon:

In responce t o question 7 b.6 t he connect ors at the DC bus are not inspec t ed at the f requency indica t ed. These connections are int erpret ed t o emon the t ermination f rom the let tery to the MCC r.nd main dist ribution cebinets. These teircinations at MCC and dist ribut ion cabinet a a re not inspect ed as these t erniinat ions once made are not disturbed. Also, acid is nct present at t ermination point s (as could be on bat tery post s) which could cause oxidation and high resist ance. The re f or e , it i t. felt that inspectica is r.ot necessa ry at thece *.rrminations at the indicated f requency of once every 92 days. An inapection frequency of once every 36 mont hs is determined to be sufficient. PM events will be established for visual inupection of cable terminations at MCC and main dictribution cabinets for any corrosion or abnormalities, o Question 7.e, Banis for ,"no" Responce:

At Fermi 2 bt eries that have degraded or reached 85% of t heir expect ed li fe are t est al at leas t once per 18 montha vs.

at.n u al l y . The 18 sont h period is based on the Technical Specifications and is reflective of Fermi 2 refuel cycle durution which is considered accept able.

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