ML20216C344

Rev 0 to, Review of Wolf Creek Nuclear Operating Corp, Analysis of Fire Barrier Ampacity Derating Factors

ML20216C344
Person / Time
Site:	Wolf Creek
Issue date:	04/19/1996
From:	Nowlen S SANDIA NATIONAL LABORATORIES
To:	Ronaldo Jenkins NRC (Affiliation Not Assigned)
Shared Package
ML20216C234	List: ML20216C232 ML20216C264 ML20216C323 ML20216C344
References
NUDOCS 9804140396
Download: ML20216C344 (30)

Text

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1 '. . ,

. A Review of the Wolf Creek Nuclear Operating Corporation Analysis of Fire Barrier Ampacity Derating Factors

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I A Letter Report to the USNRC j l

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Revision 0 l l April 19,1996  !

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Prepared by:

Steve Nowlen Sandia National Laboratories Albuquerque, New Mexico 87185-0737 1 (505)845-9850

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.p Prepared for.

Ronaldo Jenkins  ;

, Electrical Engineering Branch Office of Nuclear Reactor Regulation

! U. S. Nuclear Regulatay Cc2 mission Washington,DC 20555 ATTACHMEN1 3 9804140396 980406 1

• PDR ADOCK 05000482 '

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TABLE OF CONTENTS:

.g Section F.att FORWARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

1.0 INTRODUCTION

. . . . . t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Obj ective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 1.2 Overview of the Utility Ampacity Derating Approach . . . . . . . . . . . . I 1.3 Organization of Report . . . . . . . . . . . . . . ., . . . . . . . . . . . . . . . . . 2 4

2.0 REVIEW OF UTILITY CALCULA110N F-10A AND XX-E-008 . . . . . . . 3 2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Basic Assumptions of the Ibermal Model . . . . . . . . . . . . . . . . . . . 3 2.2 Formulation of the Thermal Model . . . . . . . . . . . . . . . . . . . . . . . . 4 4 2.3 Summary of Thermal Model Errors . . . . . . . . . . . . . . . . . . . . . . . 9

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2.4 Review of Calculation Results . . . . . . . . . . . . . . . . . . . . . . . . . . 10  !

2.5 Review Summary and Findings . . . . . . . . . . . . . , . . . . . . . . . . . 12  !

3.0 REVIEW OF UTILTIY CALCULATION XX-E.010 . . . . . . . . . . . . . . . 14 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2 Review of the Conduit Margins Methodology . . . . . . . . . . . . . . . 14  ;

3.3 Review of Utility Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . 17 i 3.4 Summary of Review Findings . . . . . . . . . . . . . . . . . . . . . . . . . . 18  !

4.0 REVIEW OF UTILITY CALCULATION XX-E-011 . . . . . . . . . . . . . . . 19

_ j 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

, 4.2 Summary of Cable Tray Margins Methodology . . . . . . . . . . . . . . 19

- 4.3 Review of Utility Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 ,

4.4 ' Summary of Review Findings . . . . . . . . . . . . . . . . . . . . . . . . . . 22 .l 4

5.0

SUMMARY

OF REVIEW FINDINGS . . . . . . . . . . . . . . . . . . . . . . . . . 24 '

$.1 Calculation F-10A and XX-E-008 . . . . . . . . . . . . . . . . . . . . . . . . 24 5.2 Calculation XX-E-010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 5.3 Calculation XX-E.411 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

- 5.4 Omission of Conduit Barriers 6" or IASs . . . . . . . . . . . . . . . . . . . 25 e

6.0 REFERENCES

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n

,, FORWARD ne United States Nuclear Regulatory Commission (USNRC) has solicited the support of Sandia National Laboratories (SNL) in the review of utility submittals associated

, with fire protection and electrical engineering. This letter report documents the results of a SNL review of a set of submittals from the Wolf Creek Nuclear Operating Corp. l (WCNOC). Dese submittals deal with the issue of ampacity loads for cable trays and I conduits protected by Hermo-Lag 330-1 fire barriers. These documents were submitted by the utility in response to USNRC Generic Letter 92-08. His work was performed as Task Order 7 of USNRC JCN J2017.

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1.0 INTRODUCTION

1.1 Objective

. In response to USNRC Generic Letter 92-08, the Wolf Creek Nuclear Operating Corp. I (WCNOC) provided documentation of the utility position regarding ampacity derating factors associated with its installed fire barrier systems. The objective of this review was to assess the adequacy of the utility submittal to ensure that cables at WCNOC are operating within acceptable ampacity limits. In particular, the submittals included documentation of two distinct analytical methodologies used to assess the adequacy of in-plant cable ampacity factors for its various Appendix R cable tray and conduit fire

, barrier systems.

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De submittals reviewed were documented in a utility response to a USNRC Request i for Additional Information (RAI). The relevant documents reviewed are: j

- Letter, March 10,1995 (item ET 95-0013), F. T. Rhodes, WCNOC, to the USNRC Document Control Desk, with enclosures as follows:

- Enclosure 1: WCNOC Calculation F-10A, " Power Cables with Fire Protection Wrapping - Temperature Calculations for Determining Derating Requirements," Revision 0,5/30/85. l 1

- Enclosure 2: WCNOC Calculation XX-E-010, " Determine / mpacity Margin of Conduits with Hermo-Lag 330-1 Fire Wrapping," Revision 0, Release Date 3/24/94. j

- Enclosure 3: WCNOC Calculation XX-E-Oll," Determine Ampacity Margin of Trays with normo-Lag 330-1 Fire Wrapping," Revision 0, Release Date 3/24/94.

- Enclosure 4: WCNOC Calculation XX-E-008, " mpacity Deratings for Conduits with normo Lag 330-1 Fire Wrapping," Revision 0, '

Release Date 3/24/94.

SNL was requested to review ease submittsls under the terms of the general technical

, support contract JCN J-2017, Task Order 7. His letter report documents the initial results of this review. De intent of this review was to provide support to the USNRC in determining the adequacy of the utility submittals, and in the potential development of a supplemental RAL Based on the results of this review, it is recommended that such a request be pursued.

1.2 Overview of the Utility Ampacity Derating Ayyn,ach he consideration of ampacity derating factors for fire barriers at WCNOC is based on essentially two analytical approaches. He first involves pure analytical assessments of the thermal behavior of a fire barrier protected conduit, and the second involves an analytical margins assessment of cable ampacity factors. Rese two approaches are

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i separate and distinct. He utility submittals do provide some limited citatiens to 7- ampacity derating tests perf nned by industry. H: wever, the overall approach is analytical. No testing has apparently been performed by the utility, and at the current time, no such testing is planned.

nose portions of the submittal based on the direct analysis of thermal behavior are documented in WCNOC Calculations F-10A and XX-E-008. . Rose analyses are based on rather simple correlations-based calculations of the heat transfer behavior. In particular, the more recent XX-E-008 document states that the purpose of these calculations is to " determine a worst case ampacity derating for power cables used in various conduit sizes employing a 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> or 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> rated normo-Lag 330-1 fire wrapping." He analysis is based ~on a pair of calculations, one without the barrier and one with the barrier, with a derating factor determined by comparing the calculation results.

In contrast, the margins analyses, as documented in WCNOC calculations XX-E-010 and XX-E-011, do not assess the ampacity derating factors for specific applications, but rather, assess the available ampacity margin for specific cables. Dat is, under this approach, the actual ampacity values for a cable are compared to the tabulated ampacities for that situation to determine tha available ampacity margin. Presumably, so long as the available margin exceeds the fire barrier derating impact, then the actual ampacities would be considered W.ble.

1.3 Organization of Report his review has focussed on an assessment of the acceptability of the utility ampacity margins analyses and on a review of the a selection of the specific case analyses documented by the utility. Section 2 presents a review of the utility analyses presented in Calculations F-10A and XX-E-008. Section 3 provides a review of the utility analyses presented in Calculation XX-E-010. Section 4 provides a review of the utility analyses presented in Calculation XX-E-011. Section 5 summarizes the j SNL recommendations regarding the need for additional information to support the l final me=====ent of the utility analyses. j i

.1 2

l 2.0 REVIEW OF UTILITY CALCULATION F-10A AND XX-E-008 ,

2.1 Overview De utility submittal has included two " Calculations" in which analytical assessments I are based on heat transfer modeling of the thermal behavior of fire barrier protected conduits. Dese are Calculations F-10A and XX-E-008. Note that the newer XX-E- ,

008 calculation is cited as superseding the older F-10A calculation. However, it is l also stated at the outset of XX-E-008 that the " Calculation F-10A methodology has been incorporated into this calculation. He major equations used in this calculation have been taken from F-10A." Hence, the importance of the basic model formulation

, as presented in the older F-10A documents must not be overlooked.

2.2 Basic Assumptions of the Thermal Model The basic formulation of the WCNOC thermal model, as presented in F-10A and as implemented in XX-E-008 is quite simplistic in its approach. He thermal model consists of a series of cylindrical shells of various composition (air, steel conduit, Hermo-Lag) surrounding a central core of copper which represents the powered cables. In developing this thermal model, there are several assumptions made which j will contribute to the overall quality of the results. Rose which are considered most '

important are: -

Assumntion 1 All of the cables are lumped together into a single composite mass. His approach significantly simplifies the overall formulation because the heat transfer behavior within the cable mass need not be treated as a complex geometry. In general, this is not a significant point of concem.

However, as discussed further below, the utility has apparently made certain errors in the implementation of this simplification.

Assumption 2: The lumped cable mass is assumed to be located in the center of the conduit. De impact of this assumption is to eliminate any contact between the cables and the conduit itself. On the surface this may seem to be a conservative assumption, and in fact, the calculation cites this as a conservative assumption (see F-10A, pg 1, item 2.5). However, this assumption is only conservative if one considers the effects on just a single

, calculation of ampacity (either a clad or baseline calculation). When the relative effect of the fire barrier is assessed, this becomes a non-conservative assumption. His most significantly impacts the calculations of XX-E-008 in which estimates of the smpacity derating factor are derived. i nat is, contact between the cables and conduit will tend to improve the rate of heat transfer, and hence, would tend to increase allowable ampacities for ;

a given situation. Assuming that there is no such contact in the thermal model  !

would tend to result in more conservative ampacity values being calculated for l a given situation. l However,in the case of the derating relculations, the purpose of the model is to assess the relative impact of the fire barrier in comparison to the baseline case. In this case, the assumption of no cable-to-conduit contact for l

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both the baseline and clad cases would mean th:1 the rel-tive impact cf the fire

,. barrier would be less significant than might actually occur. Th:t is, the assumption acts to inhibit the flow of heat in the baseline case, and hence, the relative impact of the fire barrier is made less significant.

His effect can be illustrated by considering an extreme comparison between a clad conduit versus a clad air drop. For the conduit, the fact that the conduit itself significantlyvestricts heat transfer from the cable means that the l relative iinpact of the fire barrier is smaller. For an air drop there is no initial i restriction in the rate of heat flow from the cable, and hence, the relative impact of the fire barrier is much greater. His situation is analogous in that the utility model has artificially restricted heat flow in the baseline case, and 4 hence, has potentially underestimated the relative impact of the fire barrier. )

Assumption 3: Here is no air gap between the fire barrier inner surface and  !

the conduit outer surf:.co. This may be a reasonable assumption, but only if the utility can document that its own installation procedures required that the gap which would normally be formed between the conduit and fire barrier be filled I with trowel-grade Thermo. Lag 300-1. We note that such practices were common for at least some TVA plants, but would not be considered typical of either the manufacturer's installation procedures nor general industry practice.  !

If this naturally occurring air gap was not specifically filled during the WCNOC installations, then the thermal model would be non-conservative. The presence of an air gap would act to increase the thermal impact of the fire barrier. He utility must document specific plant procedures which might justify this assumption, or should include an additional air gap in the formulation.

Assn u don 4: Radiative heat transfer has been incorporated into the analysis for both internal and external heat transfer. His is generally an appropriate analysis approach. (As noted below, there are concerns regarding the manner in which radiative heat transfer was implemented in the model.)

2.2 Formulation of the normal Model In formulating its thermal model, WCNOC has made a number of apparent mistakes which compromise the validity of the final equations. In order to illustrate these mistakes, one must follow through the formulation from W==i g to end.

To begin, it is useful to note that the utility analyses as presented in F-10A begin with a calculation of the actual heat load per unit length of cable. Using this actual heat load and an assumed ambient temperature condition, the various temperature rises through the fire barrier, conduit, air gaps and cable are calculated. De final " answer" is an estimated cable conductor temperature. If this temperature does not exceed the rated temperature of the cable then the ampacity is considered W.lt,le. He analyses provided in XX-E-008 take a somewhat different approach, as discussed further below, but are based on the same fundamental thermal model.

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The thermal model defines 6 Iscati:ns f:r which the t:;mperature can be assessed.

nese are (1) the middle of the cable, (2) the outer cable surface, (3) the inside surface of the conduit, (4) the outside surface of the conduit which is also assumed to be the inside surface of the barrier, (5) the outside surface of the fire barrier, and (6 or 'a') the ambient. Dese points are ultimately set up as a set of one-dimensional thermal nodes with specified thermal resistance values between adjacent nodes:

T1 T2 T3 T4 T5 Ta Rrra l R1-2 l R2-3 lRS4 lR44

.-W-.4.-W-.+IlWVL.l I I I

. , , . Cable Cable Conduit Conduit Barrier Ambient Oster Core Surface inner Outer Surface Surface Surfecs Figure 2.1: Simplified representation of final utility thermal node network.

He formulation of the utility starts from the outside and works its way inward. Dat I is, the ambient temperature is defined, and the final cable core temperature is calculated. Hence, this review will follo~w this same progression. .

l Heat transfer from the outer surface of the fire barrier (or for the baseline cases, from the outer surface of the conduit) to the ambient is assumed to occur by convection and .

radiation. He convection coefficient (h)is based on a simple text book correlation (from Keith,1976):

h, = 0. 27 = 0.27

• }5 ,

His correlation is appropriate to the analysis conditions. However, as implemented by the utility, an error has been made. The overall rate of heat transfer is given in the utility submittal as:

, 9, = h,(Ts - T,)

, In reality the correct expression must also account for the available surface area as l follows: I De " hes A (Ts - T.)

where (A,) is the area of the outer surface of the Sre barrier system (or area per unit length of conduit). In a very similar way, radiation is modelled using apparently straight-forward radiative heat transfer correlationsr l

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., Oz = Ge (Tl - Tl) where an emissivity (c) of 0.9 is used for the nermo-Lag, a value consistent with published literature on the subject. However, this calculation also suffers from the same problem as that noted above for the convection term. Dat is, this expression ignores the important effect of the available surface area. In fact, the radiative heat transfer should be given as-0, = esA,(Tl - Tl)

Since the utility is basing its analysis on a one foot section of the conduit (because the total heat flow is based on a calculation of heat generated per foot of cable length), it is

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inherently assuming that the available surface area of the conduit is one square foot of l l surface area per linear foot of conduit (1ft'/ft). His is not generally correct. In {

reality, the surface area of the fire barriers for the smaller conduits will be '

, significantly smaller than Ift'/ft, while several of the larger conduits will exceed Ift'/ft.

l Each conduit must be considered individually. His is a significant error in this step of the utility analysis. I l

, Heat transfer through the fire barrier and through the conduit are both based on simple

thermal resistance factors for an annular region:  !

In(r,/r s)

Rg,= 2d 4

l where r, is the outer radius, r, is the inner radius, and k is the thermal conductivity of the material. He temperature drop is then given by the simple correlation:

A T = O/R his aspect of the analysis appears to have been properly implemented.

ne next step is to assess the temperature drop from the inside surface of the conduit l to the outer surface of the cable. De analysis again includes consideration of both convection and radiation heat transfer. However, in both treatments mistakes have i been made.  !

One error common to both modes of heat transfer is the same problem identified for

the outer surface. nat is, both the convection and radiation correlations fail to include the effects of surface aran in the calculation. His becomes even more significant for the inner surfaces because the available surface area decreases sharply as one moves towards the center of the conduit. In particular, note that the equation for radiative heat transfer between coneantric cylinders is given by the utility as

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1..

g, o (T!-T!)

1+ 1 -

82 ( Az ;(Es  ;

nis expression should read:

~

g, cA(Tf-Tf) 3 ,

1.

s 3Y1_

Me a f,

where (A i ) is the outer surface area of the cable (note the inclusion of Ai in the numerator of the corrected expression). Note in particular that the (Ai/A2 ) term in the denominator of each expression does not fully account for the surface area effect.

It was also noted that the utility has assumed a value of emissivity for the cables of 0.94, and of the conduit of 0.80. While the cable value is appropriate, the assumed emissivity of the conduit should be viewed as an upper bound value. De impact of using an upper bound value in this case depends on how the thermal model is applied.

If one considers only the individual calculations of thermal behavior for a clad or baseline case, as in the F-10A calculations, then the effect is non-conservative (i.e. it would tend to over-estimate ampacity limits). If, however, one is considering the rela.tive impact of the fire barrier on ampacity limits, such as in the XX-E-008 calculations, then the effect is conservative (i.e., it would tend to maximize the estimated Islatiy.a impact of the fire barrier).

With specific regards to the treatment ofinterior convection, two additional mistakes have been made. First, the utility assumes that the same beat transfer coefficient can be applied to the inside surface of the conduit as.that applied to the outside surfa's of the fire barrier material (as given above). His is a fundamentally flawed assumption.

Convection currents within the interior of the conduit would be severely restricted in comparison to those present on the exterior of the conduit. Use of the exterior surface heat transfer coefficient for the inner surface could severely overestimate the rate of heat transfer. His treatment is inappropriate to the physical situation. Second, the

, utility formulation accounts only for the transfer of heat from the conduit to the internal air gap, and does not treat the additional thermal resistance associated with the subsequent transfer of heat from the internal air gap to the cable. Dat is, convection is an exchange between a solid surface and an impinging gas. The heat must flow from the conduit to the air, and from the air to the cable. He utility has only accounted for one part of this process.

He final step taken by the utility was to treat heat transfer within the cable itself.

Dat is, up to this point the utility has estimated only the outer surface temperature of the cable. The hot spot is assumed to occur at the core of the cable. However, the geometry of even a single three conducto cable is thermally complex, and hence, some simplification was clearly needed. De utility has attempted to simplify the 7

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• eeumene mus anwGmes *

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physical geometry by treating the cable itself as a simplified annular configurtti:n. ,

. Hat is, the utility approach to thermal analysis of the cable itself was to convert a single three-conductor cable to an " equivalent" configuration of a single cylindrical copper core surrounded by an " equivalent" air gap. This is presented on pages 7 and 8 of F-10A.

While this approach has potentialeerit, the utility implementation includes certain mistakes. First, the equivalent thermal resistance for the copper core is cited as:

1. 888*' " 1 4xksusser his equation is attributed to Holmann,1976. However, a review of this text shows that the equation should be written as follows (see Holmann's Equation 2-25):

~

r8

• • "' 4keusser i l

De reason for the discrepancy is unclear. In the treatment of the air gap, the thermal '

resistance is cited as:

1. 2 1

=

his also appears in error, ne resistance of this " equivalent" air gap should be assessed using the general annular region thermal resistance relationship given above and repeated here:

1. • L' ,

in (r3 /r,,,,,)

2xk Again, the reason for this discrepancy is unclear.-

De final error in this step appears on page g of F-10A, subsection (f). His section states that these two resistances, the copper core and equivalent air gap, act in parallel, and the analysis sums them accordingly (as parallel resistors)' In fact, the two resistances are in series, and the net effect should be the simple sum of the two individual values. His is a serious error because when the resistances are summed as if acting in parallel, the not resistance is actually lower than either of the two individual values (adding resistors in parallel reduces the not resistance). In reality,

{

i the not effect should be the simple sum of the two, and hence, is greater than either value individually (adding resistors in series increases the not resistance). l It was also noted in this review that this final step of the analysis, simplification of the j cable thermal geometry, was handled in a very alightly different manner in the XX-E-  !

008 calculation. In this updated calculation the cable was modelled using the simple average of two cable models. He first was as described above, a copper core g

_ . . . . . _ . . . . _ _ . _ . - - ~

i surrsunded by a ring cf air. He second was a revtrsal cf this model, thtt is, an air

" core surrounded by a copper ring. He basis for this reversal is unclear. His.

modification appears to be rather arbitrary and is not based on any identified physical insights. It was also noted that the errors made in the simplification process, as noted above, are retained in the updated XX-E-008 calculation.

2.3 Summary of normal Model Errors As discussed in Section 2.2 above, a number of errors have been made in the formulation of the thermal model as described in Calculation F-10A. Because this same model is used as the basis for Calculation XX-E-008, these same errors impact the results of this calculation as well. Dese errors are summarized briefly here for the sake of clarity: -

Error E ne treatment of convection and radiation from the outer surface of the fire barrier has omitted the outer surface area from the relevant heat transfer equations. In effect the utility %s inhsrently assumed that the available surface area of all conduits under analys's is one square foot of surface for each linear foot of conduit. His overestimatu the available surface area of smaller conduits, and may under-estimate de available area of larger conduits.

Error 2: De utility has assumed thtt the same convection coefficient correlation can be applied to heat transfer inside of the conduit as that applied 1 to the outside of the conduit. His treatment significantly over-estimates the rate of heat transfer within the conduit. Convection within the conduit will be highly restricted in comparison to that outside the conduit.

Error 3! De conduit intemal convection term, even neglecting the concern cited as Error 2 above, is inappropriately treated. He relationship used describes only the resistance associated with exchange between the conduit and the air inside the conduit, and neglects the additional resistance associated with

. the subsequent transfer of energy from the air to the cable itself.

Error 4: Similar to Error 1, the treatment of radiative and convective heat transfer within the conduit fails to include surface area factors in the heat transport equations. His error becomes even more signi6 cant as the much

. smaller inner surface areas, as compared to the larger outer saface areas, are considered.

i Error 5: .In the simplification of the cable geometry, the effective thermal resistance of the equivalent copper core appears to have been improperly

, calculated. The citation for this calculation was reviewed, Holmann 1976, and L

the utility implementation is in apparent conflict with this citation.

Error 6: In the simpli6 cation of the cable geometry, the thermal resistance of the equivalent air gap has been improperly calculated. It would appear that this equivalent air gap should be treated as a simple annular region. De basis for ,

the utility treatment is unclear. i 9 i

Error 7: In the simplificati:n cf the cable geometry, the equivalent thermal

• resistances of the copper core and the equivalent air gap have been summed as parallel resistance elements. Dese resistances act in series, not in parallel.

Hence, the net resistance should be the simple sum of the two resistances. His treatment could significantly under-estimate the net thermal resistance associated with this element of the model.

2.4 Review of Calculation Results In the initial analysis of F-10A, the operating conditions of specific cable applications were evaluated. Dat is, the objective of the F-10A calculations was to estimate the operating temperatures of actual cables installed in the plant. Hence, no analyses were .

performed to assess baseline ampacity conditions. Rather, all of the analyses focussed only on clad conduits. His is quite distinct from the objectives cf the XX-E-008 calculations. In these later calculations, the objective became the estimation of ampacity derating factors associated with a fire barrier system based c.c 4e thermal

. model of F-10A. Hence, the calculations were based on a relative comparison of corresponding baseline and clad cases Because the utility has stated that XX-E-008 supersedes F-10A, SNL has focussed its attention on the results presented in XX-E-008.

In performing the calculation of XX-E-008, the utility has made certain conservative assumptions. Dese include:

- Ambient temperature assumed to be 50*C for all cables,

- Results for 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> barrier used as a bound for the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> barriers, and Barrier thickness assumed to be 1.5" rather than nominal 1" for 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> barriers.

However, as noted in Section 2.2 above, there is one assumption which is cited by the.

utility as conservative, which is in reality non-conservative as applied to the XX-E-008 calculations. Dat is:

De conductors are assumed to be located in the center of the conduit.

As discussed in Section 2.2, when the objective of the calculation is to assess the relative impact of the fire barrier on ampacity limits, this is actually a non- .

conservative assumption.

He primary result of the XX-E-008 analyses are presented as a tabulation of estimated ampacity dorating factors for a range of conduit sizes. He estimated ampacity derating factors range from a low of 14% for a 6" conduit to a high of 49% for a 1/2" conduit (see page 13 of 23 of XX-E-008). Both the variation in values for nominally similar physical systems (differing only in conduit diameter) and the actual values seem in sharp contrast to experimental results available to date. Most of the experiments to date have shown only modest variation in the derating factors for conduits of various sizes. Further, the most severe conduit derating factors noted to date are significantly lower than these estimated values. In particular, note that TVA 10  !

. _ . . _ _ _ . = . . . . ._

Wctts Bar perf:rmed a test cf a single 1" conduit in a boxed barrirr configurcti:n (a

".. very thick one-h:ur barrier) which demo'nstrated a derating factor of just 12%. The TVA tested configuration should be far more severe than that modeled by WCNOC, and yet, the WCNOC estimate for a 1" rigid conduit was 39%.

On the surface, one might conclude that the WCNOC calculations are quite conservative, sed hence, acceptable. However, SNL would caution against such a conclusion. In particular, it is SNL's conclusion that the WCNOC calculations are in significant error, and hence, should not be cited as the basis for analysis. De ampacity dorating factors derived by WCNOC are in significant conflict with known experimental results. Even though a poorly based calculation ends up giving a

. conservative resu't, this should be viewed as a fortuitous event only. Fundamentally the calculation remains a poorly based assessment, and should not be credited. Given the significant formulation errors noted in this review, and the concems raised regarding certain of the base assumptions, these analytical results should not be credited.

Based on this finding, SNL does not consider it fruitful to review, in detail, the 351 pages of specific calculations provide as an attachment to XX-E-008 at this time.

Because all of these calculations are based on a fundamentally flawed thermal model, the insights to be gained as a result of such a tedious review are minimal. Hence, SNL has not pursued the review of these specific analyses. However, SNL did " spot check" some of the calculation sheets. While SNL did not attempt to reproduce the actual calculation, this " spot check" of the results provided further indications of modeling inadequacy. Dese will be illustrated through a brief discussion ofjust 2 of the cal:ulation sheets:

, Case 1: See Sheet 139 of 351: his sheet describes the calculation for a 1-1/4" conduit with a single 1/0 AWG cable. We note that WCNOC calculated an allowable baseline current for this cable of 436.12 Amps. His can be compared to the value from the NEC handbook (at 50*C) of 139.4. Amps, as

, cited at the bottom of the WCNOC sheet. Clearly, the WCNOC calculation is generating highly optimistic estimates of the cable ampacity limits for this application. It is unreasonable to assume that there is, in fact, & much margin in the NEC tables. Rather, this is a clear indication of errors in the WCNOC thermal Inodel. In this case, because the conduit is relatively small,

, the errors associated w:th trestment of the available surface area were likely the predominant source of the overall error in this particular calculation.

l Pa** 2: See Shaat 10 of 351: his sheet describes the calculation for a single 2000 MCM cable in a 6" rigid conduit. In this case an allowable baseline current of 469.8 Amps is calculated by WCNOC. This is compared to the NEC value of 615 Amps. In &is case the not effect of the WCNOC model is somewhat conservative. Two aspects of the WCNOC model could account for this apparent conservatism. First, for the 6" conduit considered, the available surface area would actually be larger than the Ift'/ft inherently assumed by WCNOC in its calcufstions. Use of the actual surface areas would have increased the heat transfer rates slightly. Second, WCNOC's assumption that 11 l

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the cable was in the cetter cf the conduit would also tend as decrease the calculat:d ampacity f:r this case.

Dese two simple cases illustrate that the WCNOC model can result in either conservative or non-conservativa results depending on the particular application. His is because the errors made in fonnulation of the model can act as either conservative or non-conservative depending orMvhich error is considered and on the actual physical system modeled.

It was also interesting to note that in its Attachment 4 to XX-E-008, WCNOC has plotted its derived ampacity limits in comparison to the NEC ampacity limits for a range of cable sizas. Dere is a very clear pattern of error illustrated by these plots.

For the smallest conduit sizes (1/2"-1"), the WCNOC calculated ampacity limits are consistently 2.5-4.0 times the NEC values. He utility however, states that "his calculation doe not specify an ampacity for the conductors, but only specifies an ampacity derating for a Thermo-Lag configuration. Herefore, it is not the intention of this calculation to be in exact agreement with the NEC or any other document (which) specifies ampacities." he utility then concludes that "nese charts add additional assurance of the validity of the results of this calculation as the shapes of the graphs have the same approximate shape." SNL finds this conclusion to be of questionable merit. It is SNL's finding that these charts are a further indication of serious problems with the WCNOC thermal model.

2.5 Review Summary and Findings Numerous errors in the formulation of the WCNOC thermal model which forms the basis of both Calculations F-10A and XX-E-008 were identified in this review. Also identified were potential concems regarding certain of the fundamental modeling i

assumptions. The competing effects of various errors and assumptions makes it l impossible to assess the not effect of the formulation errors and the questionable  ;

modeling assumptions explicitly. However, a review of the utility.results did provide l aome insights as to how these problems impacted the calculations.

Many of the errors and assumptions could result in either conservative or non-conservative results, depending on how the model is applied and on the physical  !

characteristics of the particular situation being modeled. Regarding the how the model l' is used, the utility has used the model either to calculate actual operating conditions, as in F-10A, or to estimate ampacity derating factors, as in XX-E-008. He effect of a given error or assumption could be conservative or non-conservative depending on which mode of application is considered. As discussed above, the assumption that the I cable is in the center of the conduit is one case in point. Further, one of the most

. critical errors made involved the failure of the formulation to appropriately include surface area facsons into the beat tranrprt equations. For smaller conduits this would result in an over-estimation of ampacity limits for a given situatiun, and for larger conduits it would result in under-estimation of ampacity limits. Hence, physical characteristics of the particular situation under analysis will also influence the degree of conservatism in the final' answer.

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In one particular case, an assumptirn made by the utility will be unifermly con.

conservative unless this assumption can be explicitly justified. Dat is, the thermal model assumes intimate contact, with no air gap, between the inner surface of the fire barrier and the outer surface of the conduit. His would only be a valid assumption if the utility procedures explicitly required that the gap which would naturally form between the barrier and conduit be filled with trowel grade Hermo-Lag 330-1 during the installation. Such practices we not unknown, but are not considered typical of industry practices. De utility should provide explicit justification for this assumption. !

Overall, the ampacity dorating factors as presented in XX-E-008 appear to range from potentially reasonable (for the larger conduits) to grossly conservative (for the smaller

. conduits). In contrast, the actual calculated ampacity limits appear to range from potentially reasonable (again for the larger conduits) to grossly non-conservative (for the smaller conduits). - In general, SNL finds that the results are in significant error, and should not be credited. Of particular concern is the fact that the errors in model formulation identified in this review are quite significant. Certain of the errors will also be difficult to correct. His thermal model is considered an inappropriate basis  ;

for analysis. Analyses of this type should be based on a more thorough and more '

reasoned approach to the thermal modeling problem. Given the significance of the errors identified, it is recommended that the calculations based on this thermal model should not be credited in any way. De compounding and conflicting errors render this model of little value as currently implemented.

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3.0 REVIEW OF UTILITY CALCULATION XX-E-010 3.1 Overview He purpose of calculation XX-E-010 as cited by the utility is to determine the available baseline ampacity margin for cables installed in fire barrier protected conduits at WCNOC. Dat is, the-intent of the calculation is to compare the actual in-plant cable ampacity values to the tabulated ampacity limits without consideration of the fire barrier system impact. If the available margin is sufficient to cover the anticipated fire barrier ampacity derating impact, then the cable ampacity is considered acceptable.

In general, SNL finds the approach taken by the utility to be an acceptable means of resolving the ampacity derating questions. In fact, this type of margins analysis is potentially the most simple and straight-forward approach to the assessment of fire barrier ampacity derating issues. Dat is, provided that the utility can demonstrate adequate margin in its cable ampacities to cover any anticipated fire barrier impact, then they could correctly assume that their ampacity values are acceptable. However, the implementation of this process must, of course, be correct.

As noted in Section 2 of this review, SNL takes issue with the thermal model used by WCNOC to estimate fire barrier ampacity derating factors. He numerous errors in the model render the results of no real value. Fortunately, a body of testing is available upon which a conservative estimate of the worst-case ampacity derating factors can be based. His exercise is, however, more appropriately the domain of the utility, not of this review. It is recommended that the utility revisit its ampacity margins analysis in light of the available ampacity derating test results. Assumption of a conservative upper bound impact for conduits based on current tests,in particular those now available from TU and TVA, would likely be acceptable to the utility given the available margins demonstrated in this calculation.

. Given this, the focus of this part of the SNL review has been placed of an assessment of the utility margins analysis approach and results. SNL has not attempted to establish an acceptable upper bound barrier derating impact because relatively little information on the physical characteristics of the WCNOC barriers is provided by the utility. Hence, there is no basis for SNL to establish a reasonable derating limit.

3.2 Review of the Conduit Margins Methodology ne utility calculation includes an assessment of all Hermo-Lag clad conduits.

However, the consideration of ampacity margins is limited to " power service level conduits." nat is,IAC cables are considered to add no thermal load to the system and are not evaluated. His is a reasonable assumption which is typical of such analyses. However, SNL does take exception to the utility statement that "the IAC cables will help to dissipate heat from the power cables because the thermal conductivity of the I&C cable is higher than that of air" (see page 7 of 29,Section V, paragraph 4). IAC cables can,in fact, degrade the rate of heat transfer through two effects:

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- First, if an I&C cable is installed such that it comes between a power

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, cable and the surface of the conduit, or if such a cable cause a periodic ,

interruption of the power cable-to-conduit contact (due to mutual twisting l within the conduit), then an insulating effect is introduced which would not be ' l present if the I&C cable were not present.

- Second, if a power cable 3 partially or fully surrounded by I&C cables ,

within a conduit, then radiative heat transfer between the power cable and the  !

conduit will be reduced. R,adiative heat transfer is a very important aspect of i 6e overall heat transfer process, and hence, this could also degrade cable I arapacity limits.

Even given that SHL disagrees with this one aspect of the utility assumptions, this

" difference of opinion" would not significantly impact the balance of the utility calculation. In particular, the utility conduit analyses include the use of a derating l factor associated with the installation of more that three conductors in a conduit (this  !

is based on the NEC method and is consistent with ICEA methods as mWI).' De  !

utility interpretation of this derating factor counts only the number of power cable i conductors, and neglects I&C cables in the process. SNL agrees that this is, in fact, j the intent of the standard. Dat is, the intent of the " conductor count" derating factor  ;

is to account for additional heat loads within a conduit, not to account for the  ;

insulating effects of unpowered cables. His item is noted "for the record" only, and l no specific actions are recommended on the basis of this finding.

He utility has also stated that "This calculation will not evaluate non-continuous loads which are seldom energized (such as MOV's)." nis, again, would appear to be a reasonable assumption. In particular, even when called upon, MOV power loads will 1 be of very short duration. Hence, the exclusion of MOV power cables from the  ;

analysis is both reasonable and typical of such analyses. (ne utility has provided a list of conduits eliminated on the basis of only containing MOV power cables.)

- However, the utility has eliminated two additional conduits from consideration because they contain non-MOV power cables considered "non-continuou ? Dese are .

Conduits 134U3033 and 114U3C4G (see page 8 of 29). Clari6cens are needed to  !

justify the elimination of these conduits from the analysis. In particular.

De tables in Attachment 2 show that conduit 134U3033 contains two power cables for a backup transformer, each carrying 45.1 amps. While the cables may not be energized during normal power operations, other modes of plant operation might require the activation of these cues for extended periods of time (i.e. hours to days). De utility should provide a description of the conditions under which these esbles might be called on to operate and further justify the elimination of this conduit from analysis. If there is a possibility of operation of these cables for extended periods (i.e., bours or days), then an analysis of their ampacity margins should be provided.

- Conduit 114U3C4G is listed in Attachment 2 as housing a single power cable ofindeterminate size carrying a load of 3 amps. Given this very light load, this cable / conduit is unlikely to be a source of significant ampacity 15

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,' concern. (Typical practice would imply use cf a conductor size cf at least  ;

12AWG, and 3 amps on a 12 AWG cable would leave significant margin.) l However, the utility should provide a further justification of the elimination of l this conduit from analysis consistent with the discussion for conduit 134U3033 i provided immediately above. I i

One point oflikely conservatism in the WCNOC analysis is that the ambient l environment was unifonnly assumed to be at 50*C. His was based on the original I cable purchase specifications, and would likely be a conservative upper bound for l

typical plant installations. His assumption should add a fairly substantial level of  ;

conservatism to the WCNOC margins assessments. )

ne utility analysis begins by considering the actual ampacity loads for'its cables in  :

comparison to the allowable ampacity from either the ICEA or NEC ampacity tables. I He tabulated values are corrected for both ambient temperature and for grouping effects. An ampacity margin (AM) is defined as:

r y***3 3 AAf = 1 *1004 Isam

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l Dis is an appropriate basis for comparison to ampacity derating factors (ADFs) because ADF is given by a quite similar expression:

ADF = *2*#

• 100%

g1 IwW  !

Hence, a direct comparison of the utility AM to known ADF values as an appropnate basis for the assessment of ampacity factors at WCNOC.

1 It was noted that the utility calculation includes a number of attachments. One of.

l these, Attachment 3, includes a letter from TVA in which an altemative method of .

calculating ampacity derating factors is described. In this method, apparently based on  !

a TVA standard, the test results for a clad conduit or cable tray are compared to the tabulated values of ampacity for the same cable from the NEC or ICEA tables (as apposed to comparing a clad test to a baseline test of the same item). His approach to ampacity derating has been identified by the USNRC as an inappropriate basis for analysis. That is, the objective c,f the ampacity derating tests is to determine the relative impact of the fire barrier on ampacity, regardless of the tabulated ampacity limits for a given cable. De 'IVA approach documented in this letter is not an accepted means for assessing fire barrier ampacity limits, and should not be credited in the WCNOC analysis. TVA values, apparently based on this approach to analysis, have been cited in the final section of the WCNOC. This is not considered appropriate. WCNOC should compare its margins to derating factors derived using approved methods of analysis.

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3.3 Revisw of Utility Calcul:tirns ne utility has provided the calculations for 20 conduits, each of which may contain more than one cable. In the utility approach, each cable would be analyzed individually, and hence,'there may be several calculations for a given conduit. (For example, a conduit with three power cables would receive three separate calculations.)

De available margin for each of1he power cables in each of these 20 conduits is evaluated separately.

In myiewing the utility calculations, SNL has not verified each and every calculation.

Rather SNL " spot checked" several of the individual calculations (about 5-10% of the individual calculations). For each of the calculations checked, the tabulated ampacities were veri 5ed, as were the subsequent margin calculations. He SNL check included

, both NEC-based and ICEA-based ampacity calculations. In this process no discrepancies of significance were noted. One very minor discrepancy which will have no impact on the analysis but should be noted wm For the calculations based on the ICEA tables, the " notes" column along the right edge of each page identified an "NEC temperature correction factor,"

typically 0.82. However, for the ICEA-based calculations, this NEC correction is not used. Rather, the temperature correction is based on the equation presented on page 9 of 29, and is typically found to be 0.894. His is,in fact, the correct approach and the NEC value is not applicable to these cases. Citing of this NEC value in ranjunction with the ICEA-based calculations is somewhat distractinr,, but not a point of significant concern.

De utility calculations show that the available ampacity margin for the protected conduits range from 33.04 to 99.68%. It is clear from the calculations that significant margin is available for all of these applications. Given that the lowest available conduit margin was about 33%, and given that no Dermo-Lag conduit ampacity derating test to date has produced a dorating impact even approaching this value, it is likely that the WCNOC conduit applications are well within W.ble ampacity limits. However, SNL does not credit the comparison of the calculated ampacity margins to the estimated derating factors from EE-X-008 as the basis for such a conclusion. This is because of the errors identi5ed in the formulation of the EE-X-008 thermal model.

He utility has made some comparisons to available test data from Underwriters

, Laboratory (UL), TVA, and TU. As noted above, the TVA comparison is not l considered appropriate due to the manner in which TVA calculated the ADF values. i nis also impacts the UL data comparison because the values cited by WCNOC are l taken from the TVA re-analysis of the original test results. De TU values are considered a valid basis for comparison. As noted by WCNOC, the TU ADF of 11%

is well within is available margin. Hence, while SNL agrees with the final conclusion that WCNOC is not "at risk" for improper ampacity derating, the basis for this  :

conclusion should be reconsidered by the utility. i i

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3.4 Summary cf Review Findings De utility conduit margins analysis as presented in calculation XX-E-010 has demonstrated that significant margin exists for those cables considered in the ' analysis.

It is the judgement of SNL that even the lowest of these margins, about 33%, is well within the worst-case derating impact anticipated for hermo-I.ag protected conduits.

Hence, it is likely that the utility een easily argue on the basis of the margins analysis that its conduits are operating well within acceptable limits. However, because of the problems with the thermal model, SNL does not credit the comparison of the available margin to the XX-E-008 calculated ampacity derating factors as the basis for this conclusion. The utility has also compared their margins to data as analyzed by TVA using a calculation method which has been rejected by the USNRC.

It is recommended that the utility be asked to reconsider the basis for its overall conclusion of acceptability. It is anticipated that an altemate basis could easily be derived by the utility, without the need to resort to correcting the thermal model of the XX-E-008 analysis. In fact, given the nature of the problems identified in the WCNOC thermal model, it would be much simpler for the utility to abandon calculation XX-E-008 and simply base its final assessments on a comparison to the available experimental data.

It is also recomrnended that the utility be asked to provide a further justificatic for the exclusion of conduits 134U3033 and 114U3C4G from the analysis. ' Ibis exclusion is based on the non-continuous nature of the current loads for these cables. However, the utility has not justified its assmnption in this case that the cables can never be called on to operate for extended periods, and hence, that no analysis is needed.

While no particular anticipation of problems with these conduits was identified, the utility should clarify its analysis, particularly for the more heavily loaded cables in conduit 134U3033.

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I 4.0 REVIEW OF UTILITY CALCULATION XX-E-011 J

i 4.1 Overview he purpose of WCNOC Calculation XX-E-011 is quite similar to that of XX-E-010.

. In XX-E 011 the calculations are designed to assess the available margin in the actual ampacity factors for cables housed in Hermo-Iag protected cable trays. He available margins are then compared to ampacity derating factors, and an assessment of acceptability is made.  ;

As with the conduit analyses of XX-E-010, the cable tray margins analysis approach is

, potentially one of the most simple and straight-forward possible approaches to the I assessment of ampacity factors. Fundamentally, SNL considers this to be an 4 acceptable approach to resolution of the ampacity derating questions. As noted above, this assumes that the margins analysis is performed properly. It is this question which is the focus of the SNL review documented here.

It should also be noted that the concerns raised related to calculations F-10A and XX-E-008 will have no impact on the cable tray calculations of XX-E-Oll. Dat is, the WCNOC thermal model was only developed for the asressment of conduits, and has no impact on the cable tray calculations.

4.2 Summary of Cable Tray Margins Methodology As in the conduit analyr s, the cable tray assessments consider only power cables.

Again, the utility states that the presence ofI&C cables will help to dissipate heat from the power cables, and again, SNL takes exception to this assumption. He presence ofl&C cables for a cable tray can only act to inhibit heat flow away from the powered cables in comparison to an equivalent situation in which the IAC cables are not present. Any additional cables, whether or not they contribute to the heat load, will act to thennally isolate ths powered cables from the ambient environment, and bence, will reduce ampacity limits. As in the case of the conduit analysis, given the manner in which the utility calculations have been performed, this issue will not significantly impact the final results or conclusions of the WCNOC analyses.

he cable tray analyses uniformly assume a 50*C ambient temperature for all cables.

, his will likely be a conservative assumption for most applications.

As with the conduits, cables which are not continuously energized are not considered as heat sources. While SNL agrees that not considering MOV cables is appropriate, other component cables which are operated for extended periods but only during  :

" abnormal" modes of operation may also require analysis. Here are six specific applications involving 11

• schemes" described by the utility in its submittal. Of these, three may require additional consideration:

- De utility cites two power cables for MOVs which utilize "modutronic controllers", AIJIV09 and AIRVil. It is implied that during the operation of i the Auxiliary Foodwater System, these cablas would be continuously energized.

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ne utility states that AFW pumps would enly be cperated during test or accident conditions, and hence, these cables are excluded from analysis. His is considered a potentially inappropriate assumption which requires clarification. The utility should consider the maximum length of time'this system might be called on to function. If the system might be called on to q operate for several hours or longer, then an ampacity analysis would bo appropriate. Even in this time frame an overloaded cable could overboat and fault.

- De utility identifies three ' schemes" involving building unit heaters, l 16 GLY 15LA,16 GLY 15LB, and 16GKG20LA.~ Dese are cited as non- '

continuous loads because they are only active in cold weather, and are tied into a thermostatic system which will cycle the power. Given the location of

. WCNOC, Kansas, there is a distinct possibility of extended periods of extreme cold in which such heaters might operate at near continuous levels for extended periods. It is recommended that the utility should provide additional information to justify these assumptions, or attematively, to perform a margins analysis including these cables. In particular, even given that the heaters j themselves may not be safety critical, any other cables housed jointly with l these power cables may be impacted by their operation. _ SNL does note that l under the postulated circumstances, the ambient temperature would also drop i below the 50*C assumed by the utility. Hence, an additional margin may be available to cover this situation. However, it is recommended that additional consideration of this assumption is needed.

- Similarly, there is a " heat trace circuit" identined for scheme

, 16QJG10BA. As with the discussion immediately above, additional l .

justification is needed to assess the validity of neglecting this cable as a heat l aource in the calculations.

1 It is recommended that the utility be asked to provide additional support for its I assumptions in these three cases, or alternately, to pmvide a margins analysis which includes consideration of these cases.

4.3 Review of Utility Results In reviewing the actual results of the utility analyses, SNL has not explicitly reviewed each and every one of the many calculations presented. Rather, SNL ' spot checked" about 5-10% of the calculations pmvided. For each of the calculations, SNL  !

attempted to reproduce the calculation as shown, and assened the basic f

appropriateness of the various calculation steps in the context of both the tabulated  ;

ampacity tables, and accepted ampacity analysis practices. It is on this basis that the following insights were developed:

- SNL was able to reproduce the calculations as shown by the utility. I nat is, no gross mathematical errors were observed in the calculations.

However, some difficulty in reproducing the results was experienced because the utility has not explicitly identified either the characteristics of the cables 20

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, being analyzed (such as diameter, wheth:r er n:t the individual conductors are jacketed, jacketing of the cable, triplexing versus multi-conductor configuration; these factors determine which of the ampacity tables should be applied), nor the actual table from which the cable ampacity limits have been taken. To complete this review, SNL used a " trial and error" process until a match to the values cited by the utility was obtained.

- As the cable ' ray depth of fill increases, allowable ampacity limits decrease. In general, he cable tray depth of fill will not fall precisely on the values cited in the ICEA tables. Hence, WCNOC has used a depth of fill correction factor to calculate ampacity limits for actual calculated cable tray

. depths of fill. In general, this is an acceptable methodology.

However, it must also be recognized that the P-54-440 tables limit ampacities for cables in trays to 80% of the ICEA P-46-426 open air ampacity limits. This is explicitly called out in P-54-440 Section 2.2, " Calculated Depth of Cables in Trays," which states "Ampacities .. are calculated ... with maximum limitations of 80 percent of the ampacities ofindividual cables isolated in free air . taken from ICEA Publication No. P-46-426,IEEE S-135".

His limiting factor has not been incorporated into the WCNOC analyses. For each case, the calculated base ampacity should be compared to the 80% of open air ampacity limit, and the lesser of the two values used. This will only impact those cable trays with a calculated depth of fill which is less

. than 1", the minimum value covered by the ICEA P-54 440 tables. For these cases, ampacities greater than the tabulated values are derived, and hence, should be checked against the "80% of open air" limit. Two of the cable trays considered by WCNOC fall into this category; trays 116USD30 end 116U$E30.

To illustrate the impact, consider tray 116U$E30, Scheme 16GLG17BA as presentsi on page 17 of 23 of the utility calculation. He depth of fill for this tray is calculated as 0.44", and the baseline ampacity of a 3/C,2/0 cable corrected for this depth of fill is cited as 232.76 amps. His value is apparently based on the extrapolation of the 1" depth of fill value from P-54-440 Table 3-5. He ICEA P-46-426 tables give the open air ampacity limit for a triplexed cable of this size with a voltage rating of IKV or less as 247 amps'.

Using the '80% of open air" limit wov1 ' give an upper bound cable tray j ampacity of 197.6 amps. His is much len Aan the 232.76 amps cited by the utility. If the calculation is carried through to the end, this would result in a

- final calculated margin of about 34% rather than the 44% value cited by the

. utility.

1 8 ne open air ampacity limit does depend on the voltage rating of the cable which is not given by the utility. SNL has inferred the rating to be 0-600V based on the observation that the ampacity limit value cited by the utility appears to be derived from Table 3-5 of the 54-440 standard which covers 0-600V triplexed cables. He values from this table are the only ones which resulted in a match with the value cited j by the utility. Hence, the open air value was taken from the limits of a IkV triplexed i cable as given on pg 260 of the ICEA P-46-426 standard. 4 l

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Each cf the two trays with less than 1" depth cf fill shsuld be

(* rer, valuated. De utility analysis should include consideration of the "80% of open air" limit to cable tray ampacities as specified by P-54-440. The most

. significant potential impact will likely involve the larger cables.

- De utility has compared its calculated margins to ampacity derating test results from three sources;-namely, Texas Utilities, TVA, and a UL. Of these three sources, only the TU results are considered an appropriate basis for comparison. As noted above, the early TVA test results cited by WCNOC and the "UL with IPCEA values for baseline" results were dei,ved using a methodology which is not considered appropriate by the USNRC (see

! discussion in Section 3.3 above). Further, the UL test results cited were ,

J performed as a "special investigation" at UL by the manufacturer TSI. These tests are not supported by UL and have been discredited as a pct of the general investigation into the normo-Lag issues. Hence, these results are not an appropriate basis for comparison.

In general the utility margins analysis has demonstrated a significant erargin for all of ,

its cables. Even given the failure of WCNOC to include consideration of the '80% of i open air" ampacity for cable trays, significant margin is expected to remain. The one l case cited above by SNL as illustrative of this concern resulted in an estimated  !

modified margin for one cable of 34% as compared to the utility value of 44%. This value is still bounded by the TU 1-hr derating test which showed a ADF of 32%.

Given this, it is likely that all of the WCNOC cables are operating within acceptable limits. However, the final assessment should be deferred until all of the cables impacted by this concem have been reevaluated.

4.4 Summary of Review Findings -

ne basic approach to analysis taken by the utility in Calculation XX-E-011 is -

considered an appropriate methodology for resolution of ampacity derating concerns

- for cable trays at WCNOC. However, the utility elimination of three cable trays which house heating circuit power cables and one tray associated with the AFW system should be further justified, or analyses for these cables should be provided.  ;

Also an apparent oversight in the analysis of two of the three cable trays considered by WCNOC was identi5ed. His involved the failure to masider the '80% of open air" ampacity limit which is specified in ICEA P-54-440 for cables in cable trays.

When incorporated into the analysis, this limit could reduct the calculated margins for certain of the cables analyzed by WCNOC.

It was also noted that the utility has used ampacity tr.st results which are not considered appropriate as the basis for its final =======ent of margins %;.ll,ility. In particular, the utility has cited the discredited TSI results from the special investigation it performed at UL (these results are not supported by UL and were discredited during the USNRC/DOJ investigation of TSI), and has cited early TVA test results which were based on an analysis methodology which is not considered acceptable by the USNRC (use of the tabulated ampacities for the baseline ampacity assessment). De only test cited by the utility which is considered an appropriate basis of comparison is 22

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[ that perfsrmed recently by TU. It is neommended th:2 the utility consider more recent test results now available from TVA in addition to the TU tests. j i

In general, the utility has demonstrated that significant margin is available for the l cables at WCNOC.' It is expected that the utility will be able to successfully demonstrate that their cables are operating within acceptable limits, even given the concems cited in this review. However, it is recommended that a final assessment be i deferred pending utility resolution of the concerns raised here.

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5.0

SUMMARY

OF REVIEW FINDINGS 5.1 Calculation F-10A and XX E-008 De F-10A and XX-E-008 calculations include many very significant errors which )

render the results of no real value. He formulation is also based on certain I questionable assumptions which may lead to non-conservative results given the manner in which the utility is attempting to apply these analyses, in particular, in XX-E-008.

De comparison of the ampacity derating factors calculated in XX-E-008 to available l experiments revealed that, while the calculations on the surface appear to provide l conservative results, in reality, the calculations should be viewed as in significant error, and the conservative nature of the results as fortuitous only.

Certain of the errors and limitations in the WCNOC thermal model formulation are  !

considered fundamental and not easily amenable to correction. It is not expected that this thermal model can be easily corrected by the utility. SNL recommends that, for the record, the USNRC inform the utility of the concerns raised as a result of this  ;

review, but SNL does not recommend that the USNRC attempt to solicit any  ;

modification or corrections from WCNOC. k is secommended that this calculation not be credited in any manner.

In a very fundamental sense, this calculation is not needed by the utility to demonstrate that its cables are operating within acceptable limits. Sufficient experiments are now available such that the simplistic calculations being made with  !

this thermal model are rendered obsolete. He utility should be encouraged to abandon this calculation, and to rely instead on the available ampacity test results.

5.2 Calculation XX-E-010 De utility conduit margins analysis as presented in calculation XX-E-010 has demonstrated that significant margin exists for those cables considered in the analysis.

. Even the lowest of these margins, about 33%, is well within the worst-case derating impact anticipated for Hermo-Lag protected conduits.

However, SNL does not credit the comparison of the available margin to the XX-E-008 calculated ampacity derating factors (see discussion in 5.1 above). De utility has also compared their margins a data as analyzed by 'IVA using a calculation method which has been rejected by the USNRC. Hence, the basis for the final conclusion that the ampacity factors at WCNOC are acceptable is not considered appropriate.

Given the margins which have been demonstrated, it is likely that th: utility can easily argue that its conduits are operating well within acceptable limits. It is recommended that the utility be asked to reconsider the basis for its overall conclusion of acceptability. It is anticipated that an alternate basis could easily be derived by the utility, without the need to resort to correcting the thermal model of the XX-E-008 analysis. For example, the utility should consider the TU and more recent TVA test results in formulating its final assessment.

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.. It is also recommended that the utility be asked to provide a further justificatien for N* the exclusion of conduits 134U3033 and 114U3C4G from the analysis. His exclusion is based on the non-continuous nature of the current _ loads for these cables. However, the utility has not justified the implied assumption that these cables can never be called on to operate for extended periods, and hence, that no analysis is needed.

While no particular anticipation of problems with these conduits was identified, the utility should clarify its assessment, particularly for the more heavily loaded cables in conduit 134U3033. Given the nature of the calculations, even the performance of a margins analysis for these cables would be a very simple undertaking.

5.3 Calculation XX-E-011 De basic approach to analysis taken by the utility in Calculation XX-E-011 is s

considered an appropriate methodology for resolution of ampacity derating concerns for cable trays at WCNOC. However, an apparent oversight in the analysis of two of the three cable trays considered by WCNOC was identified. His involved the failure to consider the '80% of open air" ampacity limit which is specified in ICEA P-54-440 for cables in cable trays.

It was also noted that the utility has used ampacity test rescits which are not appropriate as the basis for its final assessment of margins acceptability. In particular, the utility has cited the discredited TSI results from the special investigation it performed at UL (these results are not supported by UL and were discredited during the USNRC/DOJ investigation of TSI), and has cited early TVA test results which were based on an analysis methodology which has been identified as unacceptable by

, the USNRC (use of the tabulated ampacities for the baseline ampacity assessment).

De only test cited by the utility which is considered an appropriate basis of comparison is that performed recently by TU. It is recommended that the utility consider more recent test results now available from TVA in addition to the TU tests.

He utility elimination of six cable " schemes" (ALHV09, ALHV11,16 GLY 15LA, 16 GLY 15LB,16GKG20LA, and 16QJG10BA) involving either heating circuit power cables or power cables to a unique type of MOV should be further justified or j analyses for these cables should be provided. l i

In general, the utility hu demonstrated that significant margin is available for the cables at WCNOC. It is expected that the utility will be able to successfully demonstrate that their cables are operating within acceptable limits, even given the

, concerns cited in this review. However, it is recommended that a final assessment be deferred pending utility resolution of the concerns raised here. .

1 5.4 Omission of Conduit Barriers 6" or less One specific question asked by the USNRC in its original RAI related to the utility j practice of not analyzing any conduit fire barrier system which runs less than 6" along l

the length of a conduit. He utility was asked to provide a further explanation of this '

assumption. This item was not addressed explicitly in the review of the individual  ;

calculations documented above, and hence, will be addressed briefly here.  !

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The utility cover ! citer cites that natural convecti:n currents within the conduit s,' combined with the thermal mass ef the cables would dissipite heat adequately to ensure that there would be a minimal rise in temperature. SNL considers this to be a reasonable assessment. In particular, the effects of thermal conduction along the l length of the cables and conduit, combined with convection within the conduit would .

effectively dissipate any effects on such a localized level. It is also relevant to note that the overall impact on ampacity limits of even a continuous "Ihermo-Lag fire barrier of the type used by WCNOC is relatively modest as demonstrated by testing (on the order of 10% or less). This combined with the very localized nature of the effect under consideration would render any local increases in cable temperature of )

only very minimal impact. Extensive analysis of these situations in not warranted.

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6.0 REFERENCES

fs 6.1 Power Cable Ampacities Volume 1 - Copper Conductors, ICEA P-46-426, IEEE S-135-1,1962 6.2 Ampacities of Cables in Open-top Cable Tnn's, ICEA P-54-440, NEMA WC 51,1986. -

6.3 The Naionaf Electried Code Handbook, NFPA,1993 edition.

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