ML20011E398

Responds to NRC 891117 Ltr Re Violations Noted in Insp Repts 50-456/89-26 & 50-457/89-26 on 890917-1003.Corrective Actions:Acceptable Alternative to Existing Tech Spec Re Use of Dc cross-tie Breakers Will Be Developed

ML20011E398
Person / Time
Site:	Braidwood
Issue date:	12/18/1989
From:	Kovach T COMMONWEALTH EDISON CO.
To:	Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
0423T, 423T, NUDOCS 9002130354
Download: ML20011E398 (14)

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Addrees Reply to: Post Omce B 67'~ l A- Chicago,lihnoes 60690 0767 j i

.V December 18, 1989  !

Mr. A.B. Davis Regional Administrator US Nuclear Regulatory Commission

~ Region III 799 Roosevelt Road ]

Glen Ellyn, 11 60137 j 1

Subject:

Braidwood Station Units 1 & 2 Response to Inspection Report Nos. '

50-456/89026 & 50-457/89026 '

NRC Docket Nos. 50-456 and 50-457 References (a) W.D. Shafer letter to Cordell Reed dated November 17, 1989 Dear Mr. Davis t .

Reference (a) provided the results of the inspection conducted by Messrs. T.M. Tongue. T.E. Taylor, G.A. VanSickle, R.B. Landsman and Ms. D. ,

Calhoun on September 17, 1989. through October 3, 1989, of activities at  :

Braidwood Station. Reference (a) indicated that certain activities appeared .

to be in violation of NRC requirements and that a response is required. The Conunonwealth Edison Company response to the' Notice of Violation is provided in  ;

the Enclosure.

Commonwealth Edison believes that the circumstances surrounding the  ;

. bases.for the Notice of Violation may warrant further discussion.

Commonwealth Edison is willing to meet with the NRC Staff to discuss these at ['

your convenience.

If you have any questions regarding this response, please direct them  ;

to this office.

Very truly yours,

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M T.J. Kovach Q@ Nuclear Licensing Manager M 4h e

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$$b cc Stephan Sands-NRR NRC Resident Inspector-Braidwood i NRC Document Control Desk DEC 211989

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ENCLOSURE r COMMONWEALTH EDISON COMPANY'S RESPONSE TO BRAIDWOOD STATION INSPECTION REPORT Nos. 456/89026 and 457/89026 ,

VIOLATION: .

Technical Specification 3.8.2.1 action statement c.(2) requires that, "With a DC bus inoperable or not energized on a shutdown unit (Mode 5 or 6), the af fected bus may be energized f rom the operating unit (Mode 1, 2, 3, or 4) opposite DC bus via the crosstie breakers af ter limiting the DC loads on the af fected DC bus; operation may then continue for up to seven days or open the '

crosstie breakers.

Contrary to the above, on September 15, 1989, the seven day time limitation was exceeded by about five hours.

The DC crosstie was closed on September 8, 1989, at 3:58 a.m., and reopened on September 15, 1989, at approximately 9:10 a.m. This was done to provide power to bus 111 on Unit 1 in Mode 5 (cold shutdown) f rom bus 211 on Unit 2 in Mode 1 (operations) above $1.

RESPONSE

Commonwealth Edison acknowledges that on September 15, 1989 the DC bus crosstle between the operating unit (Unit 2) and the shutdown unit (Unit 1) was closed in excess of seven days. In response to the Braidwood Resident Inspector's concern over the potential applicability of Technical Specification 3.8.2.1, Braidwood Station verbally agreed to observe a seven day time limit for the closure of the D.C. crosstie breakers. This seven day period was inadvertantly exceeded, by about five hours, due to a miscanmunication among station management personnel.

Commonwealth Edison acknowledges the Braidwood Resident Inspector's concerns in that the potential for a mis-interpretation of the subject Technical Specification exists. This mis-interpretation results from the current wording of the subject Specification. The wording in the LCO of the Technical Specification does not provide a clear mechanism to directly implement the action statement of the Technical Specification. Braidwood Station intends to continue to review alternatives to the current Technical Specification wording. If developnient of an acceptable alternative is achieved, a Technical Specification change request will be submitted. However, it is Commonwealth Edison's position that the DC crosstle configuration is allowable by the current Technical Specifications. The basis for this position may not have been clearly presented to the NRC Staff previously. As a result, new information may be included in this response that supports Commonwealth Edison's position that may have not been reviewed by the NRC Staff.

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The DC crosstie configuration was issued in Ammendment 5, to the Braidwood I Station Technical Specifications, on January 27, 1938. On March 2, 1989, Braidwood Station wrote an interpetation of Amendment 5 based on the following references the Technical Specification itself, the Safety Evaluation Report issued with the amendment, and the technical information used to justify the change. Amendment 5 to the Braidwood Station Technical Specifications was issued to address two specific configurations. These configurations are addressed as, situation 1 and situation 2 in the licensee summary of the proposed change and the Safety Evaluation Report issuad with the change.

Situation 1 addresses the inoperability of a battery charger alone with both units operating in modes 1, 2, 3. or 4. In this situation action statement c.(1) of specification 3.8.2.1 will allow the DC crosstie breakers to be closed for the purpose of supplying DC power to the affected units battery and loads. In this configuration, both batteries are connected to their respective DC bus with a single battery charger supplying DC power. The j capacity of a single charger is sufficient to supply both units in this configuration. In the event of single failure and simultaneous accident with  ;

loss of offsite power, all equipment fed from the DC busses would be powered  ;

from a fully charged operable battery capable of meeting its analyzed load 1 profile, without having to impose crosstie limitations. j Situation 2 addresses the inoperability of a battery charger and its associated battery on a shutdown unit (modes 5 or 6). In this situation action statement c.(2) of specification 3.8.2.1 will allow the DC crosstie l breakers to be closed for the purpose of supplying DC power to the affected l units loads. In this configuration the DC loads must be limited to less than  ;

or equal to 63 amps to assure that the single remaining battery would have adequate capacity to supply power to the operating unit in the event of a ,

single failure and simultaneous accident with loss of offsite power.

On September 8, 1989 Braidwood Station Unit I was in mode 6 with Unit 2 operating at approximately 95% power. Battery 111 was fully operable and connected to its bus, the Unit 1 charger 111 was removed from service for maintenance, the Unit 2 battery 211 and charger were both fully operable and connected to their respective bus, and the crosstie between Unit 1 DC bus 111 and 211 was closed. This manipulation occurred at 0358 on September 8, 1989.

In this configuration, Unit I was in full compliance with the applicable Technical Specification requirements (i.e., Tech Spec 3.8.2.2) of.one fully OPERABLE division of DC power (Division 12), without reliance on the croustie l provisions. Unit 2 had the required number of OPERABLE DC buses, batteries, l and chargers as stated in Tech Spec 3.8.2.1. Again, this condition was achieved without benefit of the crosstie provision. Braidwood was not in a condition that required entry into Action Statement c.2 because DC Bus 111 was intact, unfaulted, and energized from its own battery. At no time was the DC bus inoperable or in a de-energized condition for the shutdown Unit (Unit 1).

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The use of the crosstie breaker in this instance had the net effect of  !

maintair.ing full, dual-train availability of DC controla and indications for Unit I without unnecessarily degrading the Division 11 battery. The configuration was within the design envelope of the DC system as described in Sections 8.1.1 and 8.3.2.1.1 of the Byron /Braidwood UFSAR (See Attachment A).

The battery charger with a rated output of 400A is designed and sized to i accomodate the additional loading imposed by the closure of the crosstie  ;

breakers. These Class 1E breakers offer redundant electrical isolation capability, and are coordinated with the the DC bus main breaker to ensure that the crosstie will open before the battery is isolated in the event of a -

fault.

The unit in operation, Unit 2, was not rendered vulnerable to any ,

single-failure considerations by this configuration, so the ability of the system to mitigate a design basis event was not impacted. Based on the above information Braidwood Station believed that there was no time restriction required in this configuration because (1) there were two fully charged  !

batteries associated with each unit, and (2) the configuration was one not specifically addressed by the Technical Specifications.

t It must be recognized that this configuration will be required during refuel outages to maximize the availability of main control room controls and indications during the performance of required DC charger and battery testing.

The duration of such events may differ from outage to outage based on testing and equipment repairs. As such, the latitude to crosstle DC buses with one unit in operation and the second unit shutdown will be required.

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l Because Unit 1 was in mode 6 with one fully OPERABLE train of DC power and in .

full compliance with Technical Specification 3.8.2.2, Commonwealth Edison requests that this violation be withdrawn for Unit 1. Based on the above discussion, Commonwealth Edison respectfully requests that the NRC re-review the facts as presented. Commonwealth Edison believes that Technical Specification 3.8.2.1 was not violated and that the configuration of the DC crosstie which Braidwood Station utilized was in compliance with the description in the Byron /Braidwood UFSAR. Commonealth Edison believes that this issue warrents further discussion and as such, Commonwealth Edison would like to meet with the NRC Staff prior to the NRC Staff's final disposition of l this violation.

CORRECTIVE ACTION TAKEN AND RESULTS ACilIEVED:

l Prior to exceeding seven days from the point of closing the DC crosstle breakers, Braidwood Station had conducted conversations with the resident inspectors on site outlining the stations position. It was agreed that the crosstie time frame would be limited to less than seven days until resolution could be reached.

Through a miscommunication error it was believed that the seven day time frame was to expire th morning of September 16, 1989. Upon notification by the Resident inspectors that the seven day time frame had been exceeded, Braidwood Station proceeded to supply temporary power to DC bus ill and open the crosstie breakers. This action was completed at 0910 on September 15, 1989.

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1 CORRECTIVE ACTIONS TAKEN TO AVOID TURTHER VIOLATION: j Within the week following this event a conference call was conducted between Braidwood Station, Byron Station, and NRR. It was concluded from the call 1 that the Technical Specifications did not specifically address the situation, I the specification was ambiguous in nature, and that from a technical  !

standpoint there is basis to pursue an amendment to the Technical l Specifications. Braidwood Station will attempt to develop an acceptable i alternative to the existing Technical Specification wording to govern the use of the D.C. crosstle treakers and, accordingly make an appropriate Technical Specification change request submittal. Until resolution of this matter is achieved, Braidwood Station will limit the use of the DC crosatie breakers, ,

when one unit is in operation (mode 1, 2, 3, or 4) and the other unit shutdown (mode 5, or 6) to less than or equal to 7' days.

To preclude the potential of a verbal commitment being missed, Braidwood Station will document these commitments using the existing Braidwood Station tracking system.

DATE OF FULL COMPLIANCE:

Braidwood Station believes it is currently in full compliance with Ammendent 5 of the Technical Specifications.

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l-i ATTACHMENT A TO ENCLOSURE COPMONWEALTH EDISON COMPANY'S RESPONSE TO BRAIDWOOD STATION INSPECTION REPORT NOS. 456/89026 and 457/89026 f

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Each unit:is provided with a 250-Vdc system for use with essen-  ;

tial non-safety-related auxiliaries as described in Subsection 8.3.2.1. [

Identification of Class 1E Loads ,

o Nuclear safety-related systems and components that require electrical power to perform their nuclear safety function are  ;

defined as Class 1E loads.  :

8.1.1 Indeoendence Between Redundant Standby (Onsitei Powgr Sources and Between Their Distribution System i An acceptable degree of independence between redundant standby i (onsite) power tources and between their distribution system is described in the following subsections. l

a. Independent Load Assianment ,

i Each Class 1E Load (a-c or d-c) is assigned to an ESF Division 11 or 12 (21 or 22) load group.  :

Assignment is determined by the nuclear safety I functional redundancy of the load. The loss of a single division does not prevent the performance of-the minimum safety functions required for a safe shutdown.

b. Indeoendent Class 1E A-C Sources  !

Each ESF division a-c loed group has a feed from two auxiliary transformers (offsite) and from one i diesel generator (onsite) as shown in Drawings 6E-0-4001 and 20E-0-4001, Section 1.7.

The diesel-generator circuit breaker will not close ,

automatically unless other source circuit breakers to that load group are open as shown in Drawings  ;

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6/20E-1-4030DG01 and 6/20E-1-4030DG02, Section 1.7.

c. Indeoendence of Class it'D-C Sources ,

Each ESF division d-c 16ad group has a feed from one battery charger and one battery as shown in Drawings 6E-0-4001 and 20E-0-4001, Section 1.7. 1 The redundant d-c load groups cannot be connected to each other. The d-c battery-charger combination of one ESF division cannotEach be connected to another d-c load group of one ESF redundant division.

unit can be connected to the corresponding nonredun-dant d-c load group of the second unit and satisfy the design load.

8.1-8 l

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d. Indeoendence of Standby sources i

The diesel-generator circuit breaker will close to j its associated load group automatically only if the i other source circuit breakers to the load group are l open.  !

1 When the diesel-generator circuit breaker is I closed, no other source breaker will close auto- i matica11y. Electrical interlocks ensure that no i means exist for connecting redundant load groups with each other.  ;

Each of the redundant load groups is fed from only one diesel generator. No means are provided for transferring loads between the redundant diesel  !

generators. l There is no direct tie provided that will allow the paralleling of the redundant diesel generator man-  !

ually by an operator error during loss of offsite ,

power. l i

e. Prime Mover Division 11 and 12 (21 and 22) diesel-generators are provided with only one prime mover for each  ;

generator. .

Compliance with Regulatory Guide 1.6 is discussed in Appendix A.

8.1.2 Selection of Diesel-Generator Set Cacacity For Standby l Power Sucolies Diesel-generator sets are selected as the onsite standby power '

supply with sufficient capacity and margin to assure that acceptable fuel design limits and design conditions of the j reactor coolant pressure boundary are not exceeded, that the core is cooled, and that containment integrity and other vital l functions are maintained in postulated accidents. l The diesel gener'ator load rating for continuous duty is 5500 kW (6875 kVA, 0.8 power factor). .

The 2000-hour rating of each standby diesel generator is 5934 kW, and the 2-hour rating is 6050 kW.

Table 8.3-5 shows the maximum expected coincidental loads for ,

each of the diesel-generator sets, for LOCA conditions, and for '

safe shutdown conditions.

During preoperational testing, the predicted standby diesel generator loads for each ESF division is verified, as well as i the capability of the diesel generators to carry these loads.

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s D-C Power System j 8.3.2

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8.3.2.1 Descrintion )

The d-c power' system provides d-c control and motive power for  !

vital equipment during all normal as well as emergency conditions of the plant. The system is designed to meet the  !

requirements of General Design Criteria (GDC) 17 and 18.  !

Figures 8.3-1 and 8.3-2 show the single line diagrams of Units l 1 and 2 125-Vdc systems. j The d-c power system consists of the following subsystems

a. Two non-Class 1E 250-Vdc systems (each with its own  !

battery, battery charger, and associated equipment)  !

which supply power to the generator air side seal  !

oil pumps, turbine d-c emergency bearing oil pumps, steam generator feed pump turbine emergency bearing .

oil pumps, and plant computer for Unit 1 and Unit 2 i respectively. j

b. One non-Class 1E 48-Voc system at the river screen house (with its own battery, battery charger, and ,

associated equipment) which supplies d-c control power to the river screen house switchgear.

c. Two non-Class 1E 125-Voc systems at the switchyard .

r(lay house which supplies d-c control power to the 345-kV switchyard circuit breakers,

d. One non-Class 1E 125-Vdc system which supplies  !

power to the technical support center computer and ,

peripheral loads and the security computer.  ;

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e. Four Class 1E 125-Vdc power systems which are described in the following sections.

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f. Two Class 1E 24-Voc systems which provide control j power and diesel engine starting capacity for the i diesel engine-driven auxiliary feedwater pumps, "

which are described in the following sections.

8.3.2.1.1 class 1E 125-Vdc Power Evstems Each. unit is provided with two sources of class 1E 125-Vdc power. They are electrically isolated and physically separated so that any failure involving one source cannot jeopardize the function of the other source.

The 125-Vdc batteries, racks, chargers, distribution panels, and battery room ventilation equipment are classified as Safety Category I and meet Byron /Braidwood seismic requirements.

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B/B-UFSAR f ;

The Class 1E 125-V battery systems supply power to Class 1E I

' loads without interruption during normal operations or DBA  !

conditions. Each Class 1E 125-Vdc system consists of one

. battery, one main distribution bus with molded-case circuit  !

breakers, one static battery charger, and local distribution  :

L i panels. Redundancy and independence of components precludes l l the loss of both systems as a result of a single failure. For -

Unit 1, Battery 111 supplies ESF Division 11 load requirements; f Battery 112 supplies ESF Division 12 load requirements. There are no bus ties, or sharing of power supplies between redundant t trains. j Each Class 1E 125-V battery, battery charger, and distribution panel ascociated with one ESF division is located in a Seismic Category I room, physically separated from the redundant equip-  ;

ment. Electrical separation is also maintained to ensure that a single failure in one train does not cause failure in the redundant train. There is no sharing between redundant Class ,

1E trains of equipment such as batteries, battery chargers, or J distribution panels. ,

Each Class 1E 125-Vdc system has the capacity to continuously  ;

supply all the connected normal running load while maintaining its respective battery in a fully charged condition. Each ,

battery has a nominal rating of 1200 ampere-hours and is capable of carrying the various loads continuously, for the time periods indicated in Table 8.3-9, in the event of a total loss of onsite and offsite ac power. The batteries are sized  :

in accordance with IEEE 485-1978. .

The primary sources of Class 1E d-c power system are the battery chargers. Every battery charger is rated to supply its associated d-c loads while fully recharging the battery. Each battery charger is fed from a 480-Vac ESF switchgear bus of the same division. This meets the recommendations of position C.1.b of Regulatory Guide 1.32.

One 400 ampere capacity static battery charger supplied by a  ;

Class 1E MCC, is provided for each Class 1E 125-V battery system. Protection is incorporated in the battery chargers to preclude the ac supply source from becoming a load on the battery as a result of power feedback upon loss of ac input power. Backup protection is incorporated by an overvoltage relay mounted on the charger, which trips the charger supply and annunciates the tripped condition in the control room.

9 Each battery charger is capable of floating the battery on the bus or recharging a completely discharged battery while supplying the largest combined demands of the various steady-state loads under all plant operating conditions.

• The battery chargers do not have the capability of supplying the loads if the battery is disconnected. Figures 8.3-1 and 8.3-44

B/B-UFSAR 8.3-2 show that the battery chargers are automatically discon- .

nected when the batteries are disconnected. i The batteries are located in separate rooms. The rooms are i i

described in the Byron /Braidwood Fire Protection Report, Subsection 2.3.5 (Reference 1). All battery areas are venti-lated to prevent the accumulation.of gases produced during charging operationss Each Class 1E 125-V battery area is  ;

provided with an independent safety-related ventilation system. A separate safety-related exhaust fan and duct is (

provided for each Class 1E battery area. The ventilation ,

system services the rooms housing the batteries and the battery  :

chargers and distribution panels are der,cribed in Subsection 9.4.5.3. ,

i Each 125-Vdc system has its own independent instrumentation:

a. d-c voltmeter at the MCB to measure.the voltage at the 125-Vdc distribution center bus; t b.

d-c voltmeter with a selector switch to measure the -

d-c output voltage of the battery charger and the bus voltage; .

c. d-c ammeter to measure the d-c output current of the battery charger;

d. d-c ammeter to measure the d-c current of the i battery; 1 e,

power failure alarm relay which indicates a loss of l a-c power to the battery charger (alarms at the main control room);

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f. charger d-c output failure alarm relay (alarms at the main control room); i

g. charger low d-c voltage alarm relay (alarms at the main control room); ,

h. charger high d-c voltage shutdown relay; l

i. recording ground-detector voltmeter and alarm (alarms at the main control room); l i

3 breaker trip alarma on the battery and battery charger breakers and an alarm indicating that the bus tie breaker is closed (alarms at the main control room); and l

k. 125-Vdc bus undervoltage alarm relay (alarms at the main control room). ,

[ 8.3-45 1

f6 . . i B/B-UFSAR i ,

p The following protection is provided against overcharging:

L a. A high-voltage shutdown relay opens the main supply L breaker to the charger when the d-c output voltage of the charger rises to approximately 15% over the 4 battery float voltage.

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b. A d-c voltmeter provides a visual check on battery voltage. No overvoltage alarms are provided.

The tie between buses 111 and 211 and the tie between buses 112 i and 212 (d-c buses for Unit 1 and Unit 2) are each provided {

with two normally locked open, manually operated circuit  !

breakers. The ties are provided so that the nonredundant d-c buses of Unit 1 and Unit 2 can be interconnected during mainte-nance and testing operations in the battery an6/or battery j charger associated with either bus 111 (211) or bus 112 (212).

No interlocks are provided since the interconnected buses are not redundant. However, procedural and administrative controls  !

are used to limit the corrective load to an allowable amount  !

(63 amps) based on not exceeding the battery capacity. Tie breaker closed alarms are provided.

The d-c power supplies are separate and independent for Unit 1  ;

and Unit 2. Each supply is of sufficient capacity to meet the loads normally connected to it in the event of-a loss of  ;

offsite power. While it is possible to interconnect the Unit 1 and Unit 2 power supplies, they will remain disconnected except for the following circumstances: (1) when a 6-c power supply must be taken out of service for the purposes of maintenance and/or' testing, or (2) in the event of a failure of a d-c supply source.

The interconnection between each Unit's Class lE 125-Vdc sys-tems, via the crosstie, is limited by procedural and admini-strative controls. These controls ensure that combinations of maintenance and test operations will not preclude the systems .

capabilities to supply power to the ESF d-c loads. The cri-  !

teria specifying the allowable combinations of maintenance and- ,

test operations are governed by the plant technical specifi-cation. Coordination between unit operations required during maintenance and testing are governpd by administrative -

controls. The provisions of administrative 1y controlled, ,

manually actuated, interconnections between the non-redundant Class 1E d-c buses affects (i.e., increase) the overall reliability and availability of the d-c systems for each unit in that it provides a means for manually providing power to a d-c bus at a time when it would otherwise have to be out-of-service (e.g., to perform a battery discharge test during a refueling outage, to replace a damaged cell, etc.).

During normal operation, the batteries are kept fully charged by the battery chargers. periodically, the voltage is raised for equalization of the charge on the individual battery cells.

8.3-46

B/B-UFSAR

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i Readings of the battery voltage level during the equalization l charge are recorded.

The instrumentation (and the related alarms) provides reliable- i supervision of the condition of the overall d-c system, but  !

does not (by itself) provide adequate information on the condition of the battery (a component). The condition of the ,

battery is tested initially as noted in Chapter'14.0 and i periodically monitored and tested as noted in Technical Speci- i fication 3/4.8. The time schedule for performing inspections, '

measurements, and tests is established in accordance with the requirements of IEEE Standard 450-1975 (as modified by the .

proposed 1978 revision issued for comments on November 7, 1977) l and 308-1971. I The batteries will be periodically discharge tested in accor-dance with the recommendations of Regulatory Guide 1.129. t The d-c power system is designed and applied so that when l operated within its rating under specified environmental conditions and when maintained in accordance with an approved schedule (including replacements of components when necessary),  ;

it will perform its functions for the 40-year life of the plant.

8.3.2.1.2 class 1E 24-Vdc AFW Pumn Diesel Batteries The d-c power' system for the diesel-driven auxiliary feedwater pump consists of two complete sets of 24-Vdc batteries, battery chargers, battery racks, cables, and necessary accessories.

The complete system is located in the room with the diesel-driven auxiliary feedwater pump.

The battery chargers are powered from two separate ESF motor control centers of the same division as the diesel-driven pump.

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, Each battery has sufficient capacity to run the diesel through l' four cranking cycles of 5 seconds each before the cranking i L timer times out and an overcrank and fail to start alarm is  !

initiated.

The battery chargers are of the full wave rectifier voltage regulated type with voltmeter, ammeter, and thermal cutout designed for continuous floating duty on the storage batteries. Chargers are for 120-V, 60 Hz, single-phase a-c power supply, and have an isolation transformer to ensure that the batteries are completely isolated from the a-c power system. Operation of the battery chargers is automatic and I includes regulation to maintain the output voltage substantially constant within the rated current range and independent of a-c supply voltage.

There is no separate ventilating system for the d-c power system. The diesel-driven auxiliary feedwater pump room 8.3-47

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