ML20044C335

Forwards Addl Info Re Resolution of Medium Voltage Electrical Cable Bend Radius Issues,Per Suppl 2 to Vol 3 of NUREG-1232 Re SER on Util Nuclear Performance Plan.Requests Change to 920408 SE to Accept Revised Testing Plan

ML20044C335
Person / Time
Site:	Browns Ferry
Issue date:	03/17/1993
From:	Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RTR-NUREG-1232 TAC-M80681, TAC-M80682, NUDOCS 9303220248
Download: ML20044C335 (8)

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I Tenrem Vahey AoP% IV.t Cha hm MG Dewsr. Alaten ME 2E MAR 171993 O J W Zeongue' i Wre P:mmm; tw;mt f or'y %ciew hunt U.S. Nuclear Regulatory Commission '

ATTN: Document Control Desk Washington, D.C. 20555  :

Centlemen:

In the Matter of ) Docket Nos. 50-259 Tennessee Valley Authority ) 50-260 50-296 BROWNS FERRY NUCLEAR PIANT (BFN) - MEDIUM VOLTAGE CABLE BEND RADIUS ISSUES -

References:

1. Letter from TVA to NRC dated October 4, 1990, Revision to the Cable Installation Issues-Supplemental Report - Cable Pullby

2. NUREG-1232, Volume 3, Supplement 2 -' Safety Evaluation Report on Tennessee Valley Authority: ,

Browns Ferry Nuclear Performance Plan, January . i 1991

3. Letter from TVA to NRC dated May 10, 1991, Action Plan to Disposition Concerns Related to Units 1 and 3 Cable Installation Issues Including Cable  ;

Separations

4. Letter from NRC to TVA dated April 8, 1992, Safety Evaluation of TVA Plans to Resolve 't Electrical Cable Installation and Separation Issues for the-Browns Ferry Nuclear Plant Units 1

• and 3 (TAC Nos. M80681 and M80682)

This letter provides additional information regarding the resolution of 1 medium voltage electrical cable bend radius issues. The basic issue is that electrical cables can experience premature degradation of the '

insulation system if they are bent to an excessively tight radius. TVA's bend radius corrective action program was developed to ensure that i improper bends in safety-related electrical cables do not affect safe plant operations. The corrective actions for Unit 2 for the bend radius program were described in Reference 1. The NRC reviewed these corrective ,

actions and issued a Safety Evaluation on them in Reference 2. The ,

corrective actions for Units 1 and 3 were described in Reference 3. A' Safety Evaluation of the Units 1 and 3 corrective actions was also issued ,

(Reference 4). TVA subsequently determined that some of the corrective actions should be nodified. Enclosure 1 describes the program changes and  ;

the basis for making the changes. Enclosure 2 summarizes the commitments ,

associated' with the program efianges. l e

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'U.S. Nuclear Regulatory Commission  !

l ttAR 171993  !

Based on these changes in the corrective actions. TVA requests NRC issue a '

supplement to NUREC-1232 Supplement 2, Section 3.11.5. TVA also requests a change to the April 8, 1992, Safety Evalus. tion for Units 1 and 3 to-accept the revised Group 2 cable testing plan. ,

Please refer any questions to G. D. Pierce Interim Manager of Site I Licensing, at (205) 729-7566.

Sincerely, ,

lOsJ.'Zeringue

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i Enclosures  !

cc (Enclosures): l' NRC Resident Inspector '

Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35611 ,

Mr. Thierry M. Ross, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike '

Rockville, Maryland 20852  !

Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II

.101 Marietta Street, NW, Suite 2900 Atlanta, Georgic 30323 i

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ENCLO3URE 1 'l BROWNS FERRY CABLE BEND RADIUS CORRECTIVE ACTION FIRI CIULNCES I. BACKCROUND

1. Original action plan  ;

The Cable Issues Supplemental Report, Corrective Actions, ,

Revision 3 was provided as an enclosure to Reference 1. '

t In the report, TVA proposed an action plan to resolve the medium voltage bend radius issue for Unit 2. The NRC staff reviewed this plan and concluded that it was acceptable as documented in Reference 2. A similar plan ,

was issued for Units 1 and 3. Reference 3 contains the plan for Units 1 and 3 and Reference 4 contains a Safety Evaluation of the plan for Units 1 and 3. The action plans classified cables according to bend radius ratio (the ratio of bend radius to cable diameter). The cables were to be classified into Groups 1, 2 and_3; Croup 1 having the smallest bend radius ratio.  ;

2. Original disposition of Group 1 cables required to support Unit 2.

The action plan for Unit 2 identified 58 cables subject to medium voltage cable bend radius review.

Of the original 58 cables, there were 869 cable bends.  !

Sixteen of the original cables were determined to have i cable bends that had a radius less than 6 times the cable ,

diameter. These 16 were classified as Group 1 cables. '

Five of these cables were slated for replacement during the Unit 2 cycle G outage. l

3. Original Croup 2 cables testing plan. -,

The corrective action plan for all units required that high potential testing be used to verify that the affected cables were capable of maintaining the interfacial integrity of the shielding system. The 15 ,

worst case cables were to be tested to ensure adequacy for restart of the affected units. All Croup 2 cables  ;

would be tested and trended during subsequent outages to facilitate a trend analysis. Final dispositions of Group 2 cables were dependant-on the outcome of the trending information, Group 3 cables would be subject to normal maintenance testing.

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l Page 2 ENCLOSURE 1 (Continued)

II. ADDITIONAL INFORMATION

1. Another cable was added to the bend radius review list for Unit 2 due to a design change that reclassified a non '

safety cable to Class 1E status. The design change required that alternate board feeders to Class 1E applications meet Class IE requirements. The cable, PP434-1E, is to be replaced during the Unit 2 cycle 6' .

outage for reasons other than bend radius.

2. During constructability walkdowns in support of the replacement plans for Group 1 cables ES2550-II, ES75-1, ES88-I, and ES113-I, the observed bends were significantly i less severe th-in the values which had been recorded during the original walkdown program. These cables have been ,

i recategorized as appropriate.

3. Cable PP453-II, which is associated with the Group 1 Unit 2 action plan, has been reclassified as non safety related and no longer aubject to the bend radius program.

Cable PP453-II is an intertie cable which is used to parallel diesel generators D and 3D or to power Shutdown Board D during a Unit 2 Appendix R event. BFN does not -

take credit for this cable for shutdown of the. units from any design basis accident, therefore, it is classified as nonsafety related.

III. REVISED DISPOSITION.

1. Revised disposition of Group 1 cables.

The Group 1 cable, PP453-II, which has been reclassified as.

nonsafety related, will not require replacement. The other four Unit 2 Group 1 cables, ES2550-II, ES75-I, ES88-1, and ESil3-1, which were reclassified based on the constructability walkdown data have been redispositioned in accordance with the action plan requirements. These cables had been scheduled for i replacement during the Unit 2 cycle 6 outage, but will now be l 1 eft in service. l

2. Revision to the Group 2 cables testing plan.

BFN implemented a Group 2 Load Cycle and Corona Test  :

Program to replace the original high potential testing i program. The Load Cycle and Corona Test Program  !

demonstrated the capability to maintain interfacial 1 integrin of the shielding system. This approach-has been utilized by TVA in the disposition of similar issues ,

at Watts Bar (Reference 5). The procedure is a modified i Association of Edison Illuminating Companies j qualification test. The test, CSS-87, Specifications for Thermoplastic and Cross-linked Polyethylene Insulated Shielded Power Cables Rates 5 through 35 Kv, has been performed on a cable bent to the lower bound of Group 2 (i.e., bent to 6 times OD).

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Page 3 ENCIASURE 1 (Continued) i The testing confirmed that the Group 2 cables can meet their design  ;

requirements for interfacial shield integrity with no reduction in i life and without the need for further special high potential testing at each outage. Based upon the satisfactory results, the cables are  !

now subject to only routine maintenance tests as appropriate. The testing results are available, for NRC review, at our Rockville office (Reference 6). The Load Cycle and Corona Test' Program is superior to the hi-pot test program for 3 reasons:

(1) Cables are testod under accelerated voltage and  ;

temperature (aged) conditions rather than under normal conditions, (2) The integrity of the shielding system is physically inspected rather than making a determination by inference from voltage breakdown data, and (3) There is no potential to damage the plant equipment or cables as there is in hi-pot testing.

IV. EFFECTS OF REVISED DISPOSITION. ,

1. The five Group 1 cables which were slated for replacement during the Unit 2 cycle 6 outage will no longer require replacement.

2. The high potential testing and trending of Group 2 cables will be discontinued (except for normal maintenance and i modification activities).

V. JUSTIFICATION

1. Justification for reclassifying the Group 1 cables and for not reclassifying any Group 2 or 3 cables to Group 1: It  ;

is improbable that there are cables which should have had  ;

a lower group classification. The determination that observed bends were less severe than previous data led TVA to investigate the validity of the earlier walkdowns.

Additional walkdowns were conducted using a sampling plan to establish a 95% confidence that 95% of the original  ;

walkdown data would remain valid when remeasured (References 7, 3 and 9). To be considered valid, the original walkdown bend radius measurement would have to be smaller than, or equal to, the bend radius when remeasured l via the sampling plan. The sampling plan results are available for review at our Rochille Office, i

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ENCLOSURE 1 (Continued) l Of the 58 cables which were originally subject to bend radius review, 31 cables were available for reevaluation.

The 31 cables have 623 bends. The other 27 cables were not included in the sampling plan for the following  !

reasons: ,

a. Eleven were replaced by other programs f

b. Five were ground cables, and therefore evaluated as f not subject to the voltage stresses which lead to premature ageing.

c. Eleven are embedded cables. Embedded cables cannot be walked down. Since the conduit bend radius determines the cable bend radius, there is no -

concern for bend radius violations in embedded -

cables.

Of the 623 bends subject to the sampling plan, 54 randomly chosen bends were remeasured and reevaluated.

In all 54 cases, the original measurements were shown to be equal to or less than the remeasurements. This confirms the above 95/95 acceptance criteria to validate the original data.

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2. Justification for acceptin results of previous high potential testing: The hi potential testing which was ,

conducted to support Unit restart remains valid. It is possible that some bend radii were originally underestimated such that the related cables were included j in the 15 " worst case" test group, thereby eliminating l other cables with smaller bend radii from the " worst case" 3 group. Based upon the results of the sagling plan )

however, none of the displaced cables would meet Group 1 ,

criteria. Only Group 1 bends are expected to impact test  ;

results.

VI. CONCLUSIONS .

l Five cables which were slated for replacement under the l original correctivo action plan will not be replaced due to j corrected dispositions. The test plan, which would have required testing and trending for subsequent outages, has been replaced by a load cycle and corona test program. Cable PP434-1E has been reclassified so that it now is subject to the bend radius evaluation. Cable PP434-1E is being replaced due to identified insulation damage.

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ENCLOSURE 1 (Continued) i

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c VII. REFERENCES.

1. TVA's letter to the NRC dated October 4,1990, Revision to the Cable Installation Issues Supplemental Report - Cable <

Pullby .l

2. NUREG-1232 Volume 3, Supplement 2 - Safety Evaluation l Report on Tennessee Valley Authority: Browns Ferry Nuclear Performance Plan, January 1991

3. Letter from TVA to the NRC dated May 10, 1991, Action Plan.

to Disposition Concerns Related to Units 1 and 3 Cable Installation Issues Including Cable Separations

4. NRC letter to TVA dated April 8,1992, Safety Evaluation of TVA Plans to Resolve Electrical Cable Installation and Separation Issues for the Browns Ferry Nuclear Plant Units 1 and 3 (TAC Nos. M80681 and M80682) i

5. TVA letter to the NRC dated October 11, 1990, Watts Bar Nuclear Plant (WBN) - TVA Responses to NRC Comments Resulting From August 1-3, 1990 Meeting F

6. Group 2 Load Cycle and Corona Test Report

7. Samplin5 Plan; Cable Bend Radius Verification

8. Walkdown W41769 ,

9. Bend Radius Walkdown Data Sheets / Technical Review Data l Sheets (Calc ED-Q2999-920677 RO)  ;

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ENCLOSURE 2  !

SUMMARY

OF COMMITMENTS .I i

I. NEW COMMITMENT: l TVA will replace cable PP434-IE during the Unit 2 cycle 6 outage. ,

II. SUPERSEDED COMMITMENTS:  ;

1. TVA will replace cables ESil3-1, ES2550-II, PP-453-II, f ES75-I, and ES88-I during the next scheduled refueling outage. t

2. All cables in Group 2 will be tested to the requirements >

of SEMI-65 during the next scheduled outage and subsequent i outages to facilitate a trend analysis. BFN plans to  !

evaluate the trend analysis at the end of the third -l refueling outage following restart to assess the need for continued trending of these cables.

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