ML20059A723

Insp Repts 50-324/90-27 & 50-325/90-27 on 900709-12.No Violations or Deviations Noted.Major Areas Inspected: Electrical Sys Design & Maint & Follow Up to Potential Concerns Identified in Previous Insp

ML20059A723
Person / Time
Site:	Brunswick
Issue date:	08/01/1990
From:	Fillion P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:
Shared Package
ML20059A722	List: ML20059A720 ML20059A723
References
50-324-90-27, 50-325-90-27, NUDOCS 9008230192
Download: ML20059A723 (8)

See also: IR 05000324/1990027

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/pm M:pq'o NUCLEAR REGULATORY COMMISslON  ;

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• 101 MARIETTA STREET.N.W.

I e ATLANT A. GEORGI A 30323

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Report Ncs.: 50-325/90-27 and 50-324/90-27  :

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Licensee: Carolina Power and Light Company-  !

P. O. Box 1551 ,

Raleigh, NC 27602  !

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Docket Nos.: 50-325 and 50-324 License Nos.: DPR-71 and DPR-62

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Facility Name: Brunswick 1 and 2

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Inspection Conducted: July 9-12, 1990 L

Inspector:

P. Fillion

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Ditti Signed

Approved by:

M. D. Hunt, Acting Chief Date Signed

Plant Systems Section .

Engineering Branch

Division of Reactor Safety

SUMMARY

Scope:  ;

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This routine, announced inspection was conducted in the areas of electrical

systems design and maintenance. It was a follow-up to potential concerns

identified in a previous inspection. The NRC inspector reviewed engineering i

reports, Licensee Event Reports, procurement documents, interviewed engineering

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personnel and operators, and inspected equipment. ,

Results:

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l Six NRC identified issues covering a range of topics had been addressed by the

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licensee indicating good response to _NRC initiatives. Timeliness was -  :

satisfactory. A major part of the inspection was the review of engineering

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reports of various scopes and types. The brief reports were authored by

on-site engineers while the major _ comprehensive reports were prepared by

consulting firms. These reports varied in quality, but from ar. overall

balanced judgement viewpoint the engineering reports were of average quality.

Plant areas inspected were in good condition, and a special effort had obviously '

been made to control corrosion in the-service water pump house.

In the areas inspected, violations or deviations were not identified. +

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9008230192 000019

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- (Closed) IFI 324, 325/88-11-03, Electrical System Design Review SAT and  !

SKV Cable (Section 2.a) l

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- (Closed) IFI- 324, 325/88-11-04, Compliance with GDC-17 and Related TS  !

ChangeRequest(Section2.b)  !

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- (Closed)IFI 324, 325/88-11-05, Deficiencies Identified'During Walkdown of

Electrical Equipment (Section 2.c)- {

- (Closed)IFl 324,325/88-11-06, Blackout Services Battery Duty Cycle Study  ;

(Section2.d) l

- (Closed)IFI 324,325/88-11-07, DC Yoltage Profile Study (Section 2.e)- [

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- (Closed)IFI 324,325/88-11-08 THFKBreakerRating(Section2.f) l

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REPORT DETAILS

1. Persons Contacted

Licensee Employees

J. Cannon, Electrical Systems Engineer

• W. J. Dorman, Manager, Quality Assurance / Quality Control

D. Dotson, Lead Electrical Procurement Engineer

• J. L. Harness General Manager

• R. E. Helme, Manager, Technical Support

• T. Jones, Specialist, Regulatory Compliance

M. Kirkland, Electrical Systems Engineer

• W. Link, Sanior Reactor Operator

J. O'Connor, Supervisor, Electrical Systems Engineering

L. Rothman, Principal Engineer, Nuclear Engineering Dept.

M. Schall, Shift Foreman

W. Shade, Senior Engineer, Nuclear Engineering Dept.

Other licensee employees contacted during this inspection included

engineers and security force members.

NRC Resident Inspector

• W. Levis

• Attended exit interview

2. ActiononPreviousInspectionFindings-(92701)

During)a Probabilistic

(88-11 conducted Risk

by an NRCAssessment

-team duringBased

MarchOperational Safety

1988, several Inspection

potential

safety concerns were identified that related to electrical systems. Since

that time, each of these concerns has been addressed by the licensee. l

During this inspection (90-27), the NRC inspector reviewed engineering

analysis and corrective actions to confirm that the potential concerns  :

have been resolved. Relevant details and the rationale for resolving each

concern are discussed below,

a. (Closed) IFI 88-11-03, Electrical System Design Review SAT and 5KV j

Cable i

The 4160 Volt distribution system is a resonant grounded system (as l

defined by the IEEE) which limits ground fault current to 8 amperes, i

A properly designed resonant grounded system has at least two

advantages: damage due to a. ground fault would be limited, and

automatic tripping is not required for single ground faults. Having

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these two advantages, it may be possible to continue normal operation

for some time even if a ground fault exist. A disadvantage of the

resonant grounded system is that overvoltages, i.e.173 percent of

normal cperating voltage, will appear on the unfaulted phases. In

selecting cable insulation thickness for a resonant grounded system

overvoltage levels and expected time duration should be considered

(references 1 and 2). At the time of inspection 88-11, questions

remained about whether or not these considerations had been proper _ly

accounted.

Since that time, the licensee has addressed the questions, and

prepared a report._ Research of procurement documents indicates that

SKV cables installed in the plant have three different thicknesses of

insulation: 155, 140 and 115 mils.. The NRC inspector confirmed the

insulation thickness by checking two )urchase order packages.

Reference 1 calls for an insulation thic(ness of 115 mils (133 percent

level) for a Brunswick type system. Reference 2 calls for 90 mils of

insulation. The cable installed meets the more stringent standard.

Both references 1 and 2 state that 133 percent level insulation may

be applied where "there is adequate assurance that. the faulted

section will be deenergized in a time not exceeding one hour." The

NRC inspector interviewed operators, reviewed the annunicator

response procedure and operator training lesson plans and verified

that the plant operators interviewed understood the correct response

to a " ground fault" annunicator. Since most 4160 volt feeder

circuits have individual ground fault detection relays, the

information is available to carry out this action. For example, the

Shif t Foreman's Log for June 13, 1990, has an entry concerning a

ground fault on the 2B condensate booster pump motor. The 20 motor

was quickly started and the 2B motor secured.-

IFI 88-11-03 also included a concern that the startup/ standby

transformer could be subjected to tank heating should a ground fault

occur on the secondary side. Transformers connected grounded wye on i

both the primary and secondary and of the three-legged core type

construction are prone to this problem. NRC Report No. 88-11 cited a

reference to support the statement. The licensee did some research

on this phenomenon, and determined that the startup/ standby

transformer has a three-legged core. However, they reasoned that

because the ground fault current is limited the zero sequence flux is

also limited, and therefore, transformer tank heating is limited. No

supporting documentation was provided for this conclusion. It is

stated in the FSAR that the transformer tank is specially designed to

handle harmonic currents that may exist. Also, operating experiences

indicated that ground faults have occurred on the secondary side of

the transformer. LER 2-89-009 describes an event that took place in

June,1989, where a ground fault existed for 2.75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br />; and the

transformer did not sustain any) damage that could be detected by

inspection (blisteredpaintetc.

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The NRC inspector agreed that the 4160 volt distribution system is j

being operated within its design constraints, and IFI 88-11-03 is

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closed. The references cited in the discussion are: l

(1) AEIC CS6-82, Specifications for Ethylene. Propylene Rubber l

Insulated Shielded Power Cables Rated 5 through 69KV, 4th 1

Edition. 4

(2) ICEA PUB. NO. S-68-516. Ethylene-propylene-rubber-insulated Wire l

and Cable for the Transmission and Distribution of Electrical

Energy.

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b. (Closed) IFI 88-11-04, Compliance with GDC-17 and Related TS Change  ;

Request

In NRC Inspection Report 88-11, the discussion of this IFI states  !

that the NRC will review the Brunswick design with respect to the ,

requirement to have two independent sources of offsite power. A

Diagnostic Evaluation Team (DET) inspection conducted in April .and

May, 1989, identified a similar concern. The licensee has responded I

to the DET finding by reviewing the subject and submitting a report ,

or position paper. This report was transmitted by a letter from ,

A 8. Cutter, Vice President Nuclear Services ~ Department CP&L to NRC

Document Control Desk, serial No. NLS-90-074 dated March 30, 1990.

The matter is not yet resolved. However, the IFI is closed because -

the matter is being tracked by URI 89-34-04, i

c. (Closed) IFI 88-11-05, Deficiencies Identified During Walkdown of

Electrical Equipment

During the 88-11 inspection, several plant equipment deficiencies, or  !

potential deficiencies, were identified which are itemized in the

report for that inspection. The licensee has taken action on each of

these items. During this inspection (90-27). the- NRC inspector

l performed the following activities to resolve and-close-out these '

items:

(1) Walked down several motor control centers and observed that each

starter had one contactor status light illuminated as is proper. .

(2) Walked down the control room / reactor building wall penetration

area inspecting cables for bend radius, and no bend radius '

problems were observed.

(3) The service water pump house was inspected for corrosion of L

equipment, and it was observed that the licensee was doing a

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good job controlling corrosion in this building.

(4) The high-voltage transformer area was walked down, and it was

observed that the broken concrete trench covers mentioned in the

88-11 report had been replaced with new covers.

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In inspecting the above mentioned areas, and other areas, no )

safety-conceins were identified, and IFI 88-11-05 is closed. 1

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d. (Closed)IFI 88-11-06, Blackout Services Battery Duty Cycle Study J

This item was a concern that the licensee did not have a study

showing how long the battery would be able to maintain adequate l

voltage in a blackout scenario event though four hours was assumed in H

the. Probabilistic Risk Assessment study. Meanwhile, the Code of ,

Federal Regulations was amended to include Section 50.63, Loss of All .

Alternating Current Power. Pursuant to 50.63, the licensee submitted

their " Station Blackout Coping Analysis Report" by NUS Corporation on

April 1989, 8542-P-101 Rev.1. Section 7.2.2, Class IE Battery  :

Capacity, states: The capacity of the BSEP Class 1E batteries to

support decay heat removal during a station blackout of four hours

duration was checked. According to calculations [8S42-E-01 Rev. 3],

the battery has capacity to power coping loads for 70 minutas with no ,

operator action, or 126 minutes if action is taken to transfer the

UPS inverter demand at 30 minutes after the SBO. Using cross ties

between units sufficient power can be restored to the blacked out

unit to power the battery chargers.

Since the licensee now has a study of the blackout services battery

duty cycle, IFI 88-11-06 is closed. The results of that study will

be examined during review- of the licensee's compliance with the ,

" Station Blackout Rule", 50.62

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e. (Closed)IFl 88-11-07, DC Voltage Profile Study

During inspection 88-11, the NRC inspector asked to review the

licensee's voltage profile study for the DC system. Such a study

would demonstrate that each DC device could operate within its rated t

voltage range when battery voltage varies from 105-140 volts. The

licensee could not provide the study during the inspection. After

this deficiency was identified, the . licensee launched DC Voltage

Profile Study, PCN G0017A. Cognizant engineers at the Nuclear

Engineering Department in Raleigh, North Carolina, described the

nature and scope of this study to the NRC inspector. The study,

which is being carried out by NUS Corporation, will compare each

component's voltage rating to the maximum and minimum voltages seen

at the terminals of that device. These minimum and maximum voltages.

will be determined from a computer model of the DC system. For_each

component, the rated voltage range has been obtained from vendor I

supplied data. By December 1990 the Unit 1 portion of the study ,

should be complete, while the Unit 2 portion is just starting. Test I

cases already run on Unit I have not disclosed any problems. Also,

DC powered motor operated valves have already been addressed under a-

separate study which had a higher priority than PCN G0017A. Based on

the fact that a proper voltage profile study is well underway, IFI

88-11-07 is closed. ,

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f. (Closed)IFI 88-11-08 THFK Breaker Rating l

A 125/250 VDC System Coordination Study dated December 15, 1975, was  !

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l reviewed by the NRC inspector from the view point of the interrupting

l rating of the circuit breakers versus the short-circuit current that ,

the battery. can deliver. The study concluded that the available-  !

current was about 10,000 amperes. A . copy of the manufacturer's +

application data including a table of DC interrupting ratings was

presented. For the. THFK circuit breaker, the application data  ;

indicates the following DC interrupting ratings:

125 Volts,1 pole - 20,000 Amperes

250 Volts,1 pole - no rating given

250 Volts, 2 pole - 20,000 Amperes

Notes to the application data state: (a) Multipole ratings (2 or 3)

are based on midpoint grounded systems with one pole in positive leg

and one pole in negative leg, and -(b) Single-pole ratings are for

application in ungrounded systems. Brunswick has an ungrounded 250

volt system with one breaker pole in the positive leg and one ) ole in ,

the negative leg. Since Brunswick's case did not appear to tie NRC *

inspector to fit the application- data, an IFI was created so that

the licensee could review the particular application.  ;

In October 1988, the licensee discussed the interrupting ratings with

an application engineer employed by the breaker manufacturer. This

conversation, which clarified the situation, was summarized on a ,

memorandum-of-telephone-conversation. The basic. concept to keep in

mind is that each breaker pole is rated to interrupt 20,000 amperes at-

125 VDC. This concept brings consistency to the application data and

allows one to analyze the Brunswick situation. For a fault on the

load side of the breaker, the 250 volts would be equally divided

between the poles which means the breaker could interrupt 20,000

amperes.

If the fault occurred between the battery side of the breaker on one

DC leg and the load side of the breaker on the other DC leg, the

breaker would not be rated to break the fault current (10,000

amperes). In this case one pole would be required to break the

entire fault current with the full 250 volts across the breaker pole.

This type of fault, especially at maximum levels, is not a credible

event. Considering the information provided by the breaker l

manufacturer's application engineer, the NRC inspector no longer had

a concern, and IFI 88-11-08 is closed.

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8. Exit Interview j

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The inspection scope and results were summarized on June 12, 1990, with l

those persons indicated in paragraph 1. The inspector described the areas  :

inspected and discussed in detail the inspection results listed below. 3

Proprietary information is not contained in this report.  ;

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- (Closed) IFI 324, 325/88-11-03. Electrical System Design Review SAT

and SKV Cable (Section 2.a) ,

- (Closed)IFI 324, 325/88-11-04, Compliance with GDC-17 and Related TS

ChangeRequest(Section2.b)

- (Closed) IFI 324, 325/88-11-05, Deficiencies Identified During

Walkdown of Electrical Equipment (Section 2.c)

- (Closed) IFI 324, 325/88-11-06, Blackout Services Battery Duty Cycle

Study (Section 2.d)

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(Closed) IFI 324, 325/88-11-07, DC Voltage Profile Study

(Section2.e)

- (Closed)IFI 324,325/88-11-08, THFK Breaker Rating (Section 2.f)

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