ML20140E057

Forwards Response to 970226 RAI Re GL 92-08,Item 2(c), Thermo-Lag Fire Barriers

ML20140E057
Person / Time
Site:	Grand Gulf
Issue date:	06/05/1997
From:	Hagan J ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20140E061	List: ML20140E057 ML20140J073
References
GL-92-08, GNRO-97-00022, NUDOCS 9706110226
Download: ML20140E057 (13)

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Entergy Operatione, Inc.

I T n PO Box 756 l

• I( Port G.oson, MS 39150 Tel 601437 6408 m Fax 601437 2795 June 5, 1997 J'

• J H***a VCe Pre $ dent i Oceranens Gtand Gulf Nuclear Staton U.S. Nuclear Regulatory Commission Document Control Desk Nail Stop Pl-37 Washington, D.C. 20555 Subjects Grand Gulf Nuclear Station Docket No. 50-416 License No. NPF-29 Response to the Request for Additional Information Regarding Generic Letter 92-08 Item 2 (c) : Thermo-Lag Fire ,

Barriers, dated February 26, 1997 GNRO-97/00022 Gentlemen Reporting Requirement Item 2 (c) of Generic Letter (GL) 92-08 requests information concerning the evaluation and application of test results performed to determine the ampacity dorating of cables enclosed in Thermo-Lag fire barriers. The most recent information that omad Gulf Nuclear Station (GGNS) docketed in response to GL Item 2(c) wre submitted by letter dated December 20, 1996 (Reference 1).

The December 20, 1996 submittal presented the GGNS response to questions raised from the Staff's preliminary review of GGNS Engineering Reports GGNS-96-0006, Revision 0 and GGNS-96-032, Revision 0 (Referencee 2 and 0}. These reports'were submitted to the Staff by letter dated June 28, 1996 (Reference 4) and provided the completed results of the GGNS Thermo-Lag evaluations for fire endurance and ampacity dorating parameters.

Following review of the GGNS December 20, 1996 submittal, the Staff identified information presented in our submittal that requires g clarification. The needed clarifications were discussed in a telephone g conference call between Entergy and the NRC on February 20, 1997 and g subsequently documented in the Staff's February 26, 1997 Request for g*

Additional Information (RAI) (Reference 5]. g' The Staff's RAI is segregated into three distinct questions. A contextual E*

synopsis of our response to each question follows below. Attachment 1 ~g provides the detailed GGNS response to the Staff's February 26, 1997 RAI, C including the supporting rationale for the conclusions drawn.

In Question 1, the Staff's RAI requests clarification of the grouping factors applied for multiple conduits in a common enclosure, Specifically, a breakout of the overall raceway dorating that is attributable to the conduit grouping factors versus the contribution by (k the Thermo-Lag cladding is requested. In accordance with the Staff's request, GGNS has separately accounted for dorating due to conduit grouping versus contributions from the Thermo-Lag overlay, as delineated in Attachment 1.

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GNRO-97/00022 i Page 2 of 4 l Question 2 concerns ampacity dorating considerations for continuously i energized constant KVA loads which may draw more than their nameplate full load amperes (FLA) on a steady state basie. The concerns a promulgated by this question envelopes eight circuits enclosed in two l '

cable trays at GGNS. The GGNS response provided in the December 20, 1996 submittal was based on equipment nameplate ratings and/or design information available at the time. Subsequently, GGNS has collected data

which is indicative of actual field conditions and based on review of

that data, we concur with the Staff's characterization that cable i

ampacity margin determinations should be based on worst case continuous  ;

) ampere loading rather than equipment nameplate data. We have revised our j approach to apply a bounding multiplier to the nameplate,FLA prior to determination of cable ampacity margins. Additionally, the 48% ampacity derating assumed for one of the affecte,d trays has been determined to be ,

44% based on industry information, rather than the overly conservative i j 48% as previously docketed by GG148. The 'ampacity dorating determinations I

[ for the other raceway remains unchanged.

! The recalculated ampacity dorating determination is based on a analytical j methodology. This represents a deviation from our previously utilized 4

similarity analysis approach, however, the resulting ampacity dorating 4

margin determination is consistent with ampacity margins that have been 3 analytically developed and supported by empirical testing. All other GGNS l j installed Thermo-Lag raceway are bound by corresponding empirical testa j that have been previously reviewed by the staff.

Question 3 requasted that the appropriate engineering report (s) previously docketed by GGN8 be revised to reflect a level of detail consistent with information docketed in our December 20, 1996 submittal with regards to ampacity dorating for cables encased in Flext-Blanket 330-660 material. This revision as well as other needed revisions to Engineering Reports GGN8-96-0006 and GGNS-96;0032 as delineated in the

' responses provided in Attachment 1 are planned to be completed by March 31, 1998. Ne understand, based on t.he February 20, 1996 conference call referenced above that revisions to the applicable engineering reports is l primarily focused on facilitating historical record keeping purposes and i that resubmittal of the revised repoxt(s) for NRC review is not required.

We acknowledge receipt of the staff letter dated April 21, 1997 which finds the GGNS program plan for resolution of GL 92-08 issues acceptable.

Your letter confirms that the attached clarifications to our December 20, 1996 RAI response and any future interactions regarding ampacity dorating of Thermo-Lag 330-1 raceway will be coordinated separately from Generic Letter 92-08 activities. ,

1 This information is being submitted under affirmation in accordance with 10 CFR 50.54(f)(Attachment 2).

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.GNRS-97/00022 i Page 3 of 4' I

Please contact Charles E. Brooks at (601) 437-6555 should you have any

questions, or require additional information.

Your truly, JJH/CES/

l attachments: 1. s response to the NRC Request for Additional l Information, dated February 26, 1997 1

2. Af firmation, per 10 CFR 50.54 (f) of the GGNS Response to 92-08 RAI Item 2 (c), dated February 26, 1997 ,

cca Mr. R. B. McGehee (w/a)

Mr. R. S. Reynolds (w/a)

Mr. J. H. Dixon (w/a)

Mr. H. L. Thomas (w/a)

Mr. J. W. Yelverton (w/a)

Mr. Ellis W. Merschoff (w/a)

Regional Administrator U.S. Nuclear Regulatory Comunission Region IV l 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 Kr. J. N. Donohew, Project Manager (w/2)

Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission ,

Mail Stop 13H3 I washington, D.C. 20555 l

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i Attachment 1 to r

, GNRO-97/00022 l

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Grand Gulf Nuclear Station Response to Generic Letter 92-08 Item 2 (c) RAI l

! dated February 26, 1997 '

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, .GNRO-97/00022 i Attachment 1 Page 1 of 7 i  !

The following items require clarification as delineated in the Staff's RAI dated February 26, 1997. These items were identified as a result of

f. the Staff's review of the GGNS response to the GL 92-08 Request for j Additional Information, dated December 20, 1996.

1. In the first part of the licensee's response to Question 1 j (attached to the submittal of December 20, 1996) regarding Multiple i Conduits in a Common Enclosure, it is not clear whe4ber the grouping factors given in Table IX of ICEA Standard P-46-426 are part of the design calculations for plant electrical raceways independent of the dorating factor for the Thermo-Lag fire barrier, installatione.and simply omitted from the subject calculations or are the subject grouping f actors being commingled into the overall dorating factor for the Thermo-Lag installations. If the latter case is true, clarify which factor applies for the Thermo-Lag contribution versus the grouping dorating factors when the spacing between the conduit surf aces is not ' greater than the conduit diameter or less than 1/4 of the conduit dian=ter. Also, discuss the applicability of industry standard grouping. factors in the subject calculations which were submitted in the licensee's letter of June 28, 1996.

In the second part of the licensee's response to Question 1 regarding Individually Enclosed conduits, it is not clear whether a conduit grouping factor will be applied to all applicable cables and applicable design calculations will be revised to reflect these dorating factors. Clarify the licensee's commitment in its submittal dated December 20, 1996.

GGHS Response Grouping factors given in Table IX of ICEA Standard p-46-426 are utilised in the original design calculations for plant electrical raceway and cable installations, which were performed by the AE to support original plant construction. The evaluations documented in Engineering Reports GGN8-96-0006 Revision 0 and GGNS-96-0032 Revision 0., are independent of the original design calculations, and the scope of the evaluations documented in these Engineering Reports is limited to ampacity derating for only those raceways that are protected by Thermo-Lag fire barrier installations.

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i i Nultiple conduits in a comunon enclosure

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An ampacity dorating factor of 48% was used for M ccaligurations tiaere two l horizontal conduits (1 x 2) are ep la==d within a emman -la=rre fabricated by 1

installing themoo-Lag 330-1 rw e nal 1-W" thick penals directly on the surface of '

these ocmchits. The h==4a for utilizing this dorating factor is da-ted in l l Engineering Report G35-96-0032 Rev4airm 0, and reitsrated within m' h  !

{ 20, 1996 sukumittal. W14=tica of the 48% dorating to collectively =~v==* for j conchit gmeing as well as for the Thaneo-Iag installation &es *=le the 1 two factors. Indivi& al accounting of the two desating factors will require applicatics of a Thesm-Lag installatica dorating factor, and an w e iste canchit grouping factor separately. Gas ~==4dare it overly conservative to -

apply an additional '=Ai4t gmging factor to the 48% dorating. However, Gas will conservatively apply an addieinn=1 conchit gmeing factor to the 48%

dorating. Although a factor of 0.94 (6% dorating) would appropriately =~w==>

for the conchit gmping ocmfiguration for the two cases at Gas, a conchit gmging facter of 0.91 (9% dorating) will be ~===rvatively utilised to acecr.mt for the oczuhit gmging in this ccafiguratien. The minianan aspecity margin for cables within conchits =ar'1a==d in commcm enclosures d4 =i===d above after application of separate dorating factors to individually =~ ==* for The mo-Zag installatica and conchit gmeing, is approxiestely 10%. This aspecity margin determination includes an aspecity correction facter of 1.09 to account for the actual d4aat temperature within the recum idiere these Thaumo-tag installations are located, as well as a 1.15 unitiplier to nameplate FIA values to accomt for variations between nasoplate FIA and actual in-situ currents dra m by the loads.

The bases for the latter two facters are d4====d under Gam' response to questien 2 of this Request for Jddi>4r==1 Inicematien.

'GGNS considers it prudent to apply conduit grouping factors for all applicable conduits within the scope of Engineering Reports GGNS-96-0006 Revision 0 and GGNS-96-0032 Revision 0. Absent Staff guidance to the contrary, these reports will be revised to address conduit grouping factors within the body of the reports as well as to reflect the application of these factors on the dorated cable ampacities documented within Attachment I to these reports. The appropriate revisions are planned to be incorporated by March 31, 1998.

Individually enclosed conduite In response to the second part of Question 1, GGNS confirms that a conduit grouping factor of 0.91 will be applied to all applicable individually wrapped Thermo-Lag clad conduits. Engineering Reports GGNS-96-0006 Revision 0 and GGNS-96-0032 Revision 0 will be revised to reflect these changes. The approp'riate revisions are planned to be incorporated by Narch 31, 1998.

2. In the licensee's response to Question 2. the licensee stated the following = continuously energized constant KVA loads powered by cables within the scope of this evaluation are sized to drive no more than 100% of their horsepower. Therefort, overloading of cables connected to constant KVA loads, due to continuous operation

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at 115% of rated horsepower, does not require additional ampacity dorating consideration."

The staff believes that ampacity margin determinations should be l'

based on worst case continuous ampere loading, instead of using equipment nameplate data which may not reflect actual field 1

] conditions. This question is not intended to address ampacity '

dorating due to transient voltage conditions. The staff's concern pertains to the potential understatement of final ampacity margins l l (i.e., after dorating for Thermo-Lag and other typical design  !

, factors (e.g., cable fill, temperature) based on the use of non-conservative ampere loading values (i.e., using equipment nameplate

data when the load is operated above its full load ampere rating).

l The licensee is requested to clarify its December 20, 1996, ,

i response in terms of the above stated concern. I I

The worst-case non-transient condition is having the voltage at the

! load terminals at 90% of rated voltage because the current will then be at its highest for the load. This condition is not a concern to the staff if the licensee can verify that the voltage at the load temminals will never be below 100% of rated voltage. The staff requests if the licensee can verify that this is true for the unit.

GGNS Response:

In order to adequately address the concerns raised by-the NRC Staff in question 2 of the RAI dated February 26, 1997, GGNS performed current and voltage measurements on constant KVA loads within the l scope of Engineering Reports GGNS-96-0006 Revision 0 and GGNS l 0032 Revision 0, that had margins of less than 15%. Power circuits with less than 15% margin were targeted since that bounds  !

the 11% increase in FLA corresponding to having 90% of rated l voltage at constant KVA load terminals. Measurements were taken on I a total of eight dual speed motors. These dual speed motors are  ;

part of two redundant 100% capacity ventilation trains that provide l cooling to Baergency Switchgear and Battery Rooms (177 system).

Each train is designed to operate at either the low speed or the high speed settings, depending on temperature permissives.

Therefore, each motor has two sets of power cables, one for low speed operation and another for high speed operation. As a result of the system operation described, these cables experience a duty cycle of significantly less than 100%.

Of the 16 cables providing power _ to the Z77 System motors, eight have less than 15% margin based on the evaluations documented in Engineering Reports GGNS-96-0006 Revision 0 and GGNS-96-0032 Revision O. Note that these eight circuits constitute the total population of power cables that have less than 15% margin within the population of cables evaluated within Engineering Reports GGNS-96-0006 Revision 0 and GGNS-96-0032 Revision 0. These circuits have at least two points of commonality:

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e These eight circuits are enclosed in Thermo-Lag clad trays located in Room OC302.

• Seven of the eight circuits are connected to the low speed windings of the dual speed Z77 system ventilation motors.

One of the eight circuits is connected to the high speed windings of one of the dual speed 177 system ventilation motors. Note the cable connected to the high speed winding has a margin of approximately 10%, and the other cables connected for high speed operation of the dual speed 177 I system ventilation motors have margins in excess of 15%.

The measured data revealed that in some cases i:he current drawn by these motors varied from the nameplate FLA for the respective motor. This confirms the impact of_ configuration variations

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contributing to constant KVA devices drawing currents that are different from their nameplate FLA on a steady state basis, and it also validates the Staff position that these variations should be explicitly accounted for. In view of these results, GGNS considers it apprcpriate to apply a bounding multiplier to the nameplate FLk, to account *or configuration variations, prior to the determination of cable ampacii.y margins.

In addition to the results discussed above, GGNS. revisited the development of dorating contributors in order to achieve conservative but realistic ampacity margin determinations. One of l the factors that GGNS has not taken credit for within the evaluations documented in Engineering Reports GGNS-96-0006 Revision 0 and GGNS-96-0032 Revision 0 is ambient temperature. Base cable ampacities utilized in these reports implicitly assume an ambiene temperature of 40'C, which bounds the temperatures typically experienced in rooms containing Thermo-lag clad raceways at GGNS, under normal operations. However, Room OC302 has an average temperature of approximately 80'F and is typically at a temperature of less than 86*F (30*C) . Coincidentally, this room has the bulk of Thermo-Lag clad raceways, including the Thermo-Lag clad cable trays, as well as the two installations of multiple conduits within single enclosures (discussed under GGNS' response to question 1 of the RAI).

Therefore, the ampacity evaluations will be revised to take credit for the lower ambient temperature in this room, which translates into an ampacity correction factor of 1.09 for cables within the raceways within this room versus the factor of 1.0 implicitly assumed in Engineering Reports GGNS-96-0006 Revision 0 and GGNS 0032 Revision 0.

The other dorating contributor revisited is the 48% dorat3mg utilized for the one mas tray clad with Thorne-Lag 330-1 r-inal 1-M* thick penals. This 48%

dorating factor is overly conservative since it is based on a tested

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5 l cczsfiguration of Thesmo-Tag 330-1 nominal 1-M" thick pan =1= with two emplete

] overlays of Thermo-lag 770-1 as ocupared to the Gas design idnich utilizes

, Thermo-Iag 330-1 nadnal 1-W" thick pan =1= with r=4nfarcement of joints with W" i of trouni grade anterial and wire mesh. To re-evalusta this overly <===rvative j dorating factor, Gas again canvassed indi%hals within the nue1==r utility

] inchastry (4a-1'd47 test facilities and industry coordinating organizations) idao

. are knowledgeable en Thereo-Lag issues, and in scus cases have been at the 1 l forefront of both, the testing and analytical approaches to the resolutics of i these issues. This effc.rt becught to atas' attentica an inAmtzy paper entitled

, " Fire Bukarence And Anpacity 1% sting Of One And Three-Hour Rated Thermo-Iag

, Electrical Racommy Fire narrier Systems' , authored by Messrs. Mark H. Salley )

i and Kent W. Brossa, both of the Tennessee Valley Authority idaan the paper was i presented. The salley-aroist paper is relevant to this d4=m==4r= ha-== cne of its topics is an analytical model idnich predicts derating factors for Thaneo-Iag j clad cable troy installaticsis. The analytical andal d4== ===d within the

Salley-arones paper is built w

st work previcualy dczin by Messrs. Phil Save and i j Gary Engmarus (presented in their paper entitled " Fire Protection Mrapped Cable {

Trey Aspecity") . j 3

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The salley-arcass paper lists camparisons between the original save-magmenn analysis, the edified Analysis (Save-Raymann with salley-arones modifications),

and av=41=hle test results. Table 18 of the paper shone that the Itx11fied

Analysis model yields an ACF of 0.67 versus the 0.68 ACF based en TtE's tasted configuration. This ocuparison desenstrates that the model yields a acam

conservative decating then the actual test. Note that this model utilized the .l actual TUE heat intensities rather than heat ineana4 ties derived fztza ICEk P 440. men heat intensity values derived fztza ICEk P-54-440 were substituted, the model ytaldad an As of 0.7, idnich is less <===rvative then the actual TUR test results by 2%.

Table 19 of the salley-Recent paper, idsich is calculated with heat titanaity values frca IGk P-54-440 shcus that the ocuparable ACF to TVA's tygraded 1ree- ,

m ur configuration is 0.55 versus the 0.52 ACF yielded by the tasted  !

configuration. However, review cf the tested ocnfiguration shows that the ndniansa measured thickn=== of the configuration is 2.54" versus the 2.0* assuend by the andel. een the model was re-analysed with a thicknees of 2.56", it yielded an As of 0.5, idsich is more conservative then the actual tasted data by 2 %. Table 13 shows that the worst case ACF based on the 2 dified Analysis for 1.25" thick 330-1 Themun-Iag is 0.58 (42% dorating) . Addition of a 2 % sergin to marw==t for variaticme in the nodel, based on d4=m==iczis in the previous pg .J., yield an ACF of 0.56. It is G35' position that in the absence of actual test data for cable trays erela==d solaly in Thermo-Zag 330-1 :=rin=1 1-M" thick pan =1=, the 44% dorating figure obtain=d analytically, and 4aa1"d47 an error margin of 2% represents a realistic approach.

Affected cable ampacities were recalculatode taking credit for the 30'C ambient temperature within Room OC302, and incorporating the more realistic 44% dorating in place of the overly conservative 48%. Additionally, as discussed earlier, a far; tor of 1.15 was applied to all power cable (nameplate) FLA values to account for variations between in-situ FLA and nameplate FLA values. Ampacity

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q Page 6 of 7 margin determinations based on the above revisions revealed that eight circuits have ampacity margins below 10%, with the minimum j margin being 2.27%. As a comparison, ampacity margin i' determinations factoring in the ambient temperature correction and revised Thorne-Lag installation dorating factor compared to the in-j situ FLA (measured) was performed. This determination indicated i that only two circuit had a margin below 10% (9.24%), as opposed to 3

j eight circuits falling under 10% when utilizing an FLA correction factor of 1.15%. This comparison shows that the 1.15 factor is j j appropriate and allows a conservative and bounding e, valuation. '

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f The Staff stated their belief that ampacity margin determinations j should be based on_ worst case continuous loading, instead of using j equipment nameplate data which may not reflect actual field

! conditions. By performing final ampacity margin determinations on j j corrected FLA values obtained by applying an FLA correction factor ,

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(1.15) which bounds measured FLA values for the seven worst case 1 3 circuits, GGNs believes that the concerns raised by the NRC Staff i

! regarding overstatement of final ampacity margins have been j addressed.

l 1 j In order to evaluate the worst case non-transient conditions for i constant KVA loads, GGMS performed evaluation to calculate the FLA l that would be drawn by constantly energized constant KVA loads at j the lowest anticipated grid voltage, based on measured currents for j the worst case circuits. The GGN8 UFSAR provides 496 kV (0.992 Per

Unit) as the min 4=nma anticipated grid voltage on the 500 KV grid.

! This revealed that at the lowest anticipated grid voltage, the j loading on one cable could exceed its dorated ampacity by i approximately 2%. If the grid voltage were t.o consistently be at 496 kV for the life of the plant, and if the motor fed by this cable (Q1Z77C001AA - low speed) had a 100% dity cycle for the life of the plant, the cable may experience thermal damage towards the end of its life. However, the nominal voltage on the grid is 510 MV (1.02) per unit, and any excursions to t).e lowest anticipated g; rid volte.ge are expected to be of a temporary nature.

Additionally, this actor has a duty cycle of significantly less than 100% due to the fact that it is the los speed application of 3

I the two redundant 100% capacity ventilation trains that provide cooling to Emergency Switchgear and Battery Rooms, as discussed earlier.

The abov's evaluation supports the conclusion that even with the minimum anticipated steady state voltage (which would represent a

" transient from the nominal grid voltage) the worst case cable should Aupport the required operation of its respective motor for the design life of the plant. In order to ascertain the physical condition of cables in trays, GGNS performed a visual inspection on ,

cables within one of the trays while modifications we're being made i to GGNS' Thermo-Lag installations during Refueling Outage 8 (fall 1996). Each cable within the tray segma:st available for inspection was individually inspected, and all cables within the inspected i

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, Attachment 1 Page 7 of 7 tray section were pliable and their insulation showed no signs of l l hardening or cracking, confirming the conclusion reached by the l above evaluation.

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l~ Absent Staff guidance to the contrary, appropriate changes to document the revised evaluation within~Rngineering Reports GGNS l 0006 Revision 0 and GGNS-96-0032 Revision 0, are planned to be l incorporated by March 31, 1998.

3. In the licensee's response to Question 6, a technical rationale was presented by the licensee to explain how the insta31ed

! configurations are bounded by referenced ampacity dorating tests. -

The staff requests that the applicable engineering reports be revised to reflect the use of the Thermo-Lag Flexi-Blanket 330-660 fire barrier material and the associated technical justification for the its ampacity dorating factor, GGNS Responses Ao previously stated, Engineering Reports GGNS-96-0006 Revision 0 and GGNS-96-0032 Revision 0 will be revised to reflect a level of detail consistent with information docketed in our December 20,

! 1996 submittal with regards to *,he Flexi-Blanket 330-660 material.

The needed revisions are planned to be incorporated by March 31, 1998.

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References:

1. Letter J. J. Magan to the U. S. Nuclear Regulatory Commission, dated December 20, 1996 Response to the " Request for Additional Informacion Related to Ampacity Derating issues for Thermo-Lag Fire Barriers for Grand Gulf Nuclear Station" .

2. Engineering Report No. GGNS-96-0006 Revision 0, " Grand Gulf Nuclear Station Engineering Report for Evaluation of Ampacity Deratings for Thermo-Lag Fire Barrier Enclosed Cables in Fire Aream/ Zones OC202, OC402, OC702 and 1A316" .

3. Engineering Report No. GGNS-96-0032 Revision 0, " Grand Gulf Nuclear Station Engineering Report for Evaluation of Ampacity Deratings for Thermo-Lag Fire Barrier Enclosed Cables in Fire Areas / Zones OC214, OC3 02, OC3 0 8 and 1A53 9 " .

4. Letter C. R. Hutchinson to the U. S. Nuclear Regulatory Commissionf dated June 28, 1996 Response to the " Request for Additional Information Regarding Generic Letter 92-08 (GL) Item 2(c): Thermo-Lag Fire Barriers" dated November 6,1995.

5. Letter U. S. Nuclear Regulatory Commission to J. J. Hagan, dated February 26, 1997 " Request for Additional Information Related to I Ampacity Derating issues for Thermo-Lag Fire Barriers for Grand Gulf Nuclear Station" .

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l Attachment 2 to l GNRO-97/00022 Grand Gulf Nuclear Station l

Response to Generic Letter 92-08 (Item 2C) RAI dated February 26, 1997 l

! Af firmation per 10CFR50.54 (f) l

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