ML20204E800
| ML20204E800 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom, Limerick  |
| Issue date: | 03/12/1999 |
| From: | Geoffrey Edwards PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-92-08, GL-92-8, TAC-MA3370, TAC-MA3371, TAC-MA3404, TAC-MA3405, NUDOCS 9903250134 | |
| Download: ML20204E800 (35) | |
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GNL 92-08 PECO NUCLEAR ecco cee<2v ce,eoeev 965 Cteterbrook Boulevard
/. Unit of PECO Energy wayne. PA 19081-5691 March 12,1999 4
Docket Nos. 50-277 50-278 50-352 50-353 License Nos. DPR-44 DPR 56 NPF-39 NPF-85 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Peach Bottom Atomic Power Station, Units 2 and 3, Limerick Generating Station, Units 1 and 2, Request for Additional information Regarding Generic Letter 92-08, "Thermo-Lag 330-1 Fire Barriers" (TAC Nos. MA3370, MA3371, MA3404 and MA3405)
References:
Letters from PECO Nuclear to USNRC Document Control Desk dated April 16, 1993, December 29,1993, February 4,1994, December 19,1994, March 29,1995, August 2,1995, May 2,1996, March 24,1997, January 14,1998, and March 13,1998.
Dear Sir / Madam:
The subject request for additional information (RAl) regarding Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," dated November 14,1997, requested that PECO Energy Company (PECO Energy) respond with additional information regarding l
Thermo-Lag 330-1 fire barrier systems. This RAI was in response to previously submitted information regarding ampacity derating parameters for installed Thermo-Lag fire barriers at Peach Bottom Atomic Power Station and Limerick Generating Station.
'! 4 0 0 00 On March 13, 1998, a written response to this RAI was submitted to the NRC for j
review. Several questions identified during the review of this response were discussed during a meeting between the NRC and PECO Energy representatives that was conducted on November 18,1998. During this meeting, PECO Energy committed to providing written confirmation of the new validation results for the TVA-tested configurations and a detailed description of the ampacity derating methodology for conduits to be used by PECO Energy. PECO Energy had also committed to provide 1
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March 12,1999 Page 2 i
examples showing how ampacity derating factors are determined and applied to actual plant configurations for a conduit and a cable tray as well as information regarding a revision to the heat generation rate modeling of cables in selected gutters and cable trays. Attachments 1 and 2 to this letter provide this information.
If you have any questions, please do not hesitate to contact us.
Very truly yours, 4
w_.
G. D. Edwards Director-Licensing i
Enclosures:
PECO Affidavit, Attachments cc:
H. J. Miller, Administrator, Region I, USNRC A. C. McMurtray, USNRC Senior Resident inspector, PBAPS A. L. Burritt, USNRC Senior Resident inspector, LGS 1
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' COMMONWEALTH OF PENNSYLVANIA ss.
]
COUNTY OF CHESTER i
J. J. Hagan, being first duly swom, deposes and says:
That he is Senior Vice President of PECO Energy; the Licensee herein; that he has read i
I the enclosed response to a Request for Additional Information Regarding Generic Letter 92-08, for Peach Bottom Atomic Power Station, Unit 2 and Unit 3, Facility Operating License Nos. DPR-44 and DPR-56, and Limerick Generating Station, Unit 1 and Unit 2, Facility Operating License
(
Nos. NPF 39 and NPF 85, and knows the contents thereof; and that the statements and matters set forth therein are true and correct to the best of his knowledge, information and belief.
l W
nior ice P esident Subscribed and swom to 1
j before me this/jd day o
1999.
duaaAaro
/
Notary Public mm Carol A.Wunon Notary Putsc
, ic@ n % ue"a %
Member,Penneyhenn Am at Notettes
March 12,1999 Docket Nos. 50-277/278 50-352/353 RAI Response Regarding GNL 92-08 Thermo-Lag Related Ampacity Derating issues Confirmation of Validation Results for the TVA-Tested Configurations The purpose of this document is to provide clarifications to the March 24,1997, and March 13,1998, PECO Energy Company submutals regarding the heat transfer model and validation studies performed to determine the ampacity derating factors of cables that are routed in fire protected conduits. The information provided is a summary of the November 18,1998 meeting discussion between the NRC staff and PECO Energy.
1.0 MODEL VALIDATION PECO Energy Company uses a heat transfer model to derate the ampacity of cables enclosed in Thermo-Lag, a fire protection material, for the configurations installed at Limerick Generating Station (LGS) and Peach Bottom Atomic Power Station (PBAPS) that are different from the ones analyzed / tested by the industry. As requested by the NRC Staff, the model has been validated against the seven cases that were tested in the TVA Watts Bar tests. Two different levels of validation were performed. For five of the seven cases, l
the validation was performed by modeling the specific configuration that was tested (i.e.,
1 TVA test cases 7.6a,7.6b,7.4,7.5, and 7.8). The remaining two of the seven cases have a similar configuration and use a unistrut frame to which the Thermo-lag material is attached (i.e., TVA test cases 7.7a and 7.7b). These two configurations were only approximately modeled by neglecting the blockage effect of the unistrut frame. These two cases are not used by PECO Energy at either PBAPS or LGS. The modeling for these two configurations (modeling the unistrut)is a complex undertaking relative to the benefit that would be gained in performing the additional work required. Since PECO Energy does not use these configurations, there is no relative benefit to refining the model to address the j
v 1 figuration in a precise manner.
The results of the validation show that the heat transfer model used by PECO Energy predicts conservative ampacity derating factor (ADF) values for the PBAPS and LGS applications.
2.0 CALCULATION OF PROTECTED AMPACITY AND ADF Methodology i
A fire protected conduit is viewed as a system with two component parts. One component j
of the system is the conduit with the cable inside; providing the heat source. The second i
I part of the system is the Thermo-Lag fire protection material wrapped around the conduit or a group of conduits. The objective of the modeling approach is to assure that a value of cable ampacity is calculated such that the cable insulation temperature meets its design life requirements.
The presence of the fire barrier material is accounted for in terms of an ampacity derating factor which represents the percent reduction of the baseline ampacity due to the insulation
March 12,1999 Docket Nos. 50-277/278 50-352/353-Page 2 of 7
'effect of the barrier. The baseline ampacity is determined from applicable industry standards by proper consideration of the cable conductor size, ambient temperature, the number of conductors in the conduit and, if any, the presence of other adjacent conduits.
Output Parameter The protected ampacity, I, is the parameter of interest for a cable in a raceway enclosed with a fire protective materia!. The main output of the heat transfer model is a value for the
+
protected ampacity, I,, for the model cable such that when the cable load is limited to this value, the cable insulation temperature is kept at or below its design life temperature. The model cable type used in the model is 600 volt,3/C No. 6 AWG with XLPE insulation and i
neoprene Jacket. An ampacity derating factor (ADF) is then calculated from this value of 1, I
' and the baseline ampacity. Th.is ADF is then applied to baseline ampacities of different cables to determine their protected ampacitics.
Input Parameters i
The input parameters to the model include the raceway and the fire barrier data, the cable fill data, and the baseline ampacity,1. The heat transfer model uses these data to 3
calculate a protected ampacity of the cable. The baseline ampacity is determined tsy applying appropriate correction factors to the nominal ampacity of the cable. The nominal 1
ampacity is obtained from the IPCEA P-46-426 except for No.10 AWG which is determined from the NEC Table 310-16.1 is calculated based on the following equation:
3 1 = lm X '(ATCF)X (MCCF) X (CGF) where 3
ATCF Ambient Temperature Correction Factor from NEC Table 310-16 MCCF Multiple Conductor Correction Factor from NEC Article 310-15, paragraph 8a CGF Conduit Grouping Factor from IPCEA P-46-426 1
The method for determining 1 for input to the model differs from lEEE Standard 848.1 per 3
3 the_lEEE Standard is a measured value whereas,1 for the heat transfer model is a 3
calculated value based on the industry standards. This approach ensures consistency with
- the plant calculations used for sizing the cables.
1 Heat Transfer Equations A description of the heat transfer equations is provided beginning on page 7 of the March 24' 1997 submittal regarding PECO Energy's ampacity derating methodology. A significant point made on page 8 of the submittal as it relates to conduits is that the overall heat tmnsfer coefficient for a conduit, is back-calculated from the baseline ampacity,13 This everall heat transfer coefficient applies in the region from the cables in the conduit to the surface of the conduit. The process of the back calculation uses the known cable fill and baseline ampacity based on the industry standards, the conduit size, and the temperature conditions in a heat balance equation to solve for the overall heat transfer
g March 12,1999 Docket Nos. 50-277/278 f
50-352/353 Page 3 of 7 coefficient for the conduit. Tia overall heat transfer coefficient for the conduit is then used, in conjunction with the barrier and ambient heat transfer coefficients, to perform a heat balance for the protected conduit and determine a protective ampacity.
l Amp 3 city Derating Factor (ADF)
The ADF is defined as a percentage by IEEE standard 848:
ADF = [(1 - 1,)/1 ] X 100 3
3 As noted above, ADF is the additional ampacity derating that must be applied due to the fire wrap only.
Test vs. Model Comparison The two readily apparent measures to compare the model with the test results for model validation are I, and ADF. As noted previously,1,is the limiting value that assures that the cable insulation temperature criteria is met. The second readily apparent measure that could be used is ADF. Also as noted previously, ADF is the ampacity derating that must be applied due to the fire wrap only.
I,is the primary prameter of concern in assuring the cable insulation temperature objective is met regardless of the method used to determine its value, either the IEEE test method or a heat transfer model. The ADF is a derived value based on two parameters, I, and I,.
A comparison of the values of 1, based on the test and the heat transfer model provides a valid conclusion regarding the adequacy of the heat transfer model. ADF of the test and the model can only be compared if 1 has the same value for both the test and the heat 3
transfer model.
3.0 MODEL VALIDATION RESULTS Overview of Tables Tables 1 through 3 provide the model validation results as discussed with the NRC Staff on November 18,1998. Table 1 is a comparison of the results of the heat transfer model with test data using a baseline ampacity from the TVA test results. Table 2 is the same comparison but instead of using a baseline ampacity from the TVA test results, it uses a l
baseline ampacity from the industry standards. Table 3 is a composite of the data from 1
l Tables 1 and 2 and it provides a comparison of 1, and ADF.
l i
A general discussion of the tables' content is provided for convenience of comparison
)
between them. The header row in each table provides the physical description of the specific test cases. Immediately below this row is the corresponding test case number.
The test cases with unistrut frame configuration are shown in the last two columns. For
March 12,1999 Docket Nos. 50-277/278 50-352/353 Page 4 of 7 both Tables 1 and 2, Test Results are provided in terms of 1, I,, and ADF. The difference 3
between Tables 1 and 2 is the value of 1. In Table 1,1 used in the model, is based on 3
3 TVA test results. In Table 2,1 is based on industry standards.
3 The first five cases beginning with TVA 7.6a through TVA 7.8 are applicable to the PBAPS and LGS p! ant designs. Test cases TVA 7.7a & 7.7b are not used in the PBAPS and LGS plant designs. As identified previously, these cases were only approximately modeled by ignoring the unistrut frame portion of the configuration.
Table 1 - Comparison of Results of the Heat Transfer Model with Test Data (Baseline Ampacity from Tests)
Table 1 compares the test to the model by using a value for 1 as input to the heat transfer 3
model that is equal to the measured value of 1 from the test. A comparison of 1, between 3
the Test Results and the Model Results across the columns shows that the I, value r.alculated by the model is lower (and therefore more conservative) for the first five test cases, which are the applicable cases for PBAPS and LGS fire barrier designs.
Table 2 - Comparison of Results of the Heat Transfer Model with Test Data (Baseline Ampacity from industry Standards)
Table 2 compares the test to the model by using a value for 1 as input to the heat transfer 3
model that is equal to the calculated value of 1 from the industry standards. An important 3
point to note is that this is the value of 1 as it would be used in the design process for the 3
fire barrier configurations for Peach Bottom and Limerick. A comparison of 1, between the Test Results and the Model Results across the columns shows that the I, vaius calculated by the model is lower (and therefore more conservative) for all cases including those that are not cpplicable.
Table 3 - Test vs. Model Comparison of 1,/(ADF)
Table, !s a composite of the data from Tables 1 and 2 and it provides a comparison of 1, ano nJF. The compariscn of 1, calculated by the model based on industry standards against the I, based on the test results shows that the model calculates a conservative value of 1, for all cases. Comparison of the ADF calculated from the results of heat transfer model with ADF obtained from the tests shows that the heat transfer model conservatively bounds the test cases for the configurations used at LGS and PBAPS.
Conclusion The model results bound the test results in terms of both protected ampacity and ADF for all the test configurations that are applicable to LGS and PBAPS. The model results bound the test results in terms of protected ampacity regardless of whether the baseline ampacity is taken from the tests or determined from the industry standards. Therefore, the calculation of ADF values based on 1 calculated from the industry standards is appropriate.
3 Application of the ADF that is calculated in this manner will result in a conservative and correct value fer I, for the PBAPS and LGS applications.
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l DRAFT 1Marcli 11.1999 10 CFR Q 50.80 i
U.S. Nuclear Regulatory Commission ATTN:- Document Control Desk Mail Stop O-P1-17 :
. Washington, DC 20555-0001 Re:
Three Mile Island Nuclear Station, Unit 1 (TMI-1)
Facility Operating License No. DPR-50, Docket No. 50-289 License Amendment Request No. 278 Proposed License Transfer and Conforming Administrative License Amendments
Dear Sir / Madam:
AmerGen Energy Company, LLC (AmerGen) and GPU Nuclear, Inc. (GPUN), acting for itself
- and on behalf of Metropolitan Edison Company (Met-Ed), Jersey Central Power & Light Company (JCP&L), and Pennsylvania Electric Company (Penelec), the joint applicants in connection with the proposed transfer of the TMI-1 license to AmerGen, hereby submit the comments set forth in Attachment I hereto on the proposed Order, proposed conforming amendment, and draft safety evaluation with respect to the proposed license transfer which were provided to the applicants by letter dated March 4,1999.
~
AmerGen and GPUN appreciate the opportunity to review and comment on these drafts in order.
to assure that these documents accurately reflect the terms of the proposed sale of TMI-1 and the commitments made by AmerGen and GPUN in connection with the proposed license transfer. If L you have any questions about any of these comments, please call John Matthews at 202-467-7524.
Sincerely, Kevin P. Gallen David R. Lewis Morgan, Lewis & Bockius, LLP Shaw Pittman Potts & Trowbridge ATTORNEYS FOR AMERGEN ATTORNEYS FOR GPUN Enclosure (As stated) cc:
Administrator, Region I TMI Senior ResidentInspector l
TMI-1 Senior Project Manager l
GPUN File No. 98152 :
WA03A/2232.1
=
V March 2,1999 Docket Nos. 50-277/278 r-50-352/353 l-RAI Response Regarding GNL 92-08
' Thermo-Lag Related Ampacity Derating Issues Detailed Description of the Ampacity Derating Methodology This document provides detailed descriptions of the ampacity derating methodology and clarifications to the March 24,1997, and March 13,1998, PECO Energy Company
'submittals regarding the determination of ampacity derating factors for cables that are routed in fire protected raceways. The information provided is in response to the November 18,1998, meeting between the NRC staff and PECO Energy on this subject.
l Section 2.2 provides new information regarding the use of a revision to the method for calculating the heat generation rate for cables in an encapsulated gutter accounting for diversity of the loading of the cables.
1.0 INTRODUCTION
4 1.1 Ampacity derating factors for protected raceways at LGS and PBAPS that are not similar to those tested or analyzed by the industry are determined by performing heat transfer analysis. The essential criteria used in the heat transfer analysis is that the heat generated within the cables in the raceway must be dissipated to the ambient without causing the cable temperature to exceed a specified temperature limit, typically 90 C. The equations and definitions used in the heat transfer model were provided in L
PECO Energy to NRC submittal dated March 24,1997, and the equations used are also i
repeated in the examples included in this attachment. These equations describe the heat generation rate in the raceway, the heat transfer areas of the components involved, and the associated heat transfer coefficients. Determination of the allowable heat generation rate in the raceway is accomplished by simultaneous solution of the applicable heat transfer equations. The solution procedure involves an iterative process since the convective and radiative heat transfer coefficients are temperature dependent.
After the allowable heat generation rate is determined, a matching ampacity and a corresponding ampacity derating factor (ADF) are calculated. Calculations to determine the ADF are performed for a model cable identified in IEEE Standard 848 [Ref. 2]. The solution procedure and the calculation of the ampacity derating factor are discussed in Section 3.0. This ADF value is then used to determine the protected ampacity of the various size plant cables. Example calculations for cables in protected cable trays and protected conduits are given in Section 4.0.
1.2 Some of the raceways at LGS and PBAPS have power and control cables in them.
The. load current of the power cables vary over a wide range from nearly zero to the maximum allowable. The load current of the control cables is negligible. Therefore, unlike a raceway with uniformly loaded power cables, the raceways containing large number of control cables or lightly loaded power cables are diversely loaded. The approach described below applies to diversely loaded raceways.
March 2,1999 Docket Nos. 50-277/278 50-352/353 Page 2 of 24 Diversity, as used in this document, refers to non-uniform current loading of the cables in the same raceway. A diversely loaded raceway will allow some of its cables to be loaded at a current level higher than that of a uniformly loaded raceway by constraining the current level of the remaining cables. The heat transfer aspect of a diversely loaded raceway is identical to that of a uniformly loaded raceway except that the cable mass is divided into distinct regions, each generating heat at a rate dictated by the current level allowed in it. The diversity model applied at PBAPS and i
LGS is a modified version of the model described by Black [Ref. 9,10] The modification involves imposing restrictions on region dimensions and ampacities so that hot spot effects are properly accounted for and ampacity limits set by the industry 1
standards are complied with. With these exceptions recognized, the heat transfer modelis formutated using the method of uniformly loaded racewaye described in PECO March 24,1997 submittal to NRC [Ref.1]
2.0 BASIS AND ASSUMPTIONS 2.1 The basis and assumptions for the model which does not use diversity is described in PECO March 24,1997, submittal to NRC [Ref.1].
2.2 The diversity model is applied to selected cable trays and gutters exhibiting a marked non-uniformity in their current loads. This non-uniformity is accounted for by dividing the cable mass in the raceway into three distinct regions. The first region contains the heavily loaded cables in the center, the second region contains the moderately loaded cables and envelopes the first region, the third region contains the lightly loaded cables and envelopes the second region. Within each region heat is generated uniformly. Placing the heavily loaded cables at the core of the cable mass increases the thermal resistance of the raceway and results in a conservative, i.e.,
high, ampacity derating factor.
The model distinguishes between two types of raceways: a raceway where the cables are arranged in a cable bed with a rectangular geometry as in a cable tray, and a raceway where the cables are arranged in a round bundle with a cylindrical geometry as in a gutter. Assumptions pertaining to the diversity model are listed below:
1.
The cables are assumed to form a rectangular slab, herein referred to as " cable bed," or a round bundle, herein referred to as " cable bundle," with the heavily e.aded cables enveloped by the lightly loaded cables. This configuration minimizes the allowable heat generation rate for a givers cable insulation temperature and results in a conservative ampacity derating factor.
March 2,1999 Docket Nos. 60-277/278 54 352/353 i
Page 3 of 24 2.
One-dimensional steady state conditions apply. This is assumption is consistent with accepted industry practices such as those used by ICEA [Ref. 5] and Stolpe [Ref.11].
3.
Within each region, heat is generated uniformly at a rate dictated by the Diversity parameter which is assigned based on the current loading of the most heavily loaded cable in that region. The term Diversity refers to the ratio of the actual current load of the cable to its nominal ampacity.
)
l 4.
The thickness of any region cannot be less than the diameter of the thickest cable in that region.
5.
For cables in trays, the calculated ampacity may not exceed 80 percent of the ampacity of the individual cable in free air as specified in the appropriate tables in IPCEA [Ref. 4] or NEC [Ref. 3].
6.
For cables in gutters, the calculated ampacity may not exceed the ampacity of the individual cables in free air as specified in the appropriate tables in IPCEA
[Ref. 4] or NEC [Ref. 3].
Assumptions 3 and 4 ensure that hot spot effects are accounted for in the unlikely event that some highly loaded cables are formed into a cluster. Assumptions 5 and 6 ensure that the cable ampacity limits established by the industry standards are preserved.
3.0 CALCULATION PROCEDURE 3.1 Non-Diversity Model 1.
Calculate the number of cables in the raceway based on the percent fill (or till depth)of the raceway.
2.
Determine the baseline ampacity using the applicable industry standards.
3.
Calculate the surface area of the raceway that actively participates in the transfer of the heat generated in the raceway.
4.
Calculate the overall heat transfer coefficient of the raceway, U,. The overall heat transfer coefficient for cable trays and cable bundles is calculated directly from the thermal property and geometric data of the cable mass. For conduits, U,is back calcu;ated from the baseline ampacity data as described in steps 4.1 I
and 4.2 below.
P l
t March 2,1999 Docket Nos. 50-277/278 50-352/353 i
Page 4 of 24 4.1 Calculate the heat generation rate corresponding to the baseline ampacity and j
the number of cables in the conduit.
i Calculate the conduit surface temperature and the corresponding heat transfer 4.2 coefficient U,. This is accomplished by solving the heat balance equation which requires that the heat generation rate in the conduit is equal to the heat dissipation rate from the conduit.
Steps 4.1 and 4.2 require iteration over the surface temperature of the conduit since the heat transfer coefficient from the conduit to the ambient is a function of the surface temperature. The heat transfer coefficient is also a function of the l
emissivity of the conduit surface. The industry standards NEC [Ref. 3] or IPCEA
[Ref. 4] where the baseline ampacity is obtained, do not specify a value for the L
conduit emissivity. Accordingly, a conservative approach is taken in applying 1
the model to plant-specific conduits by assuming that the emissivity (c), upon which the baseline ampacities in the industry standards are based, is at the high end of the range (0.4 to 0.8) given in [Ref. 6, page A4-5), i.e., emissivity = 0.8.
This is conservative since choosing a high emissivity value for the conduit (for the purpose of determining U,,) lowers U,and thus increase the ADF value, 5.
Calculate the surface area (outside) of the fire barrier.
6.
Calculate the heat transfer coefficient of the fire barrier.
~ 7.
Estimate a reasonable fire barrier inside wall temperature corresponding to the specified cable conductor temperature, baseline ampacity, and the ambient temperature, and calculate the corresponding barrier outside wall temperature.
This step involves several sub-steps including iteration over the assumed barrier wall temperature until the heat transfer rate through the barrier is balanced by the heat dissipation rate from the barrier to the ambient.
8.
Calculate the raceway surface temperature and the heat generation rate within the raceway corresponding to the barrier wall temperature determined in Step 7.
For raceways with a large air gap between the raceway and the fire barrier, this step involves several sub-steps including iteration over the enclosure air
. temperature until the heat generation rate in the raceway matches the heat l
transfer rate from the raceway to the barrier.
L
L' March 2,1999 L
Docket Nos. 50-277/278 50-352/353
)
l Page 5 of 24 9.
Compare the heat dissipation rate from the barrier determined in Step 7 with the heat generation rate determined in Step 8. These quantities must agree within
{
a reasonable limit. If not, the barrier wall temperature is adjusted and Steps 7 l
and 8 are repeated until the solution converges.
l L
1
' 10. Calculate the current corresponding to the heat generation rate in the raceway.
- 11. Calculate the Ampacity Derating Factor (ADF).
- 12. Calculate the available ampacity margin. The ADFs calculated in Step 11 and other correction factors per industry standards are applied to the nominal ampacity of specific cables in plant receways to calculate the protected ampacity of the cable. This protected ampacity of the cable is then compared to the load current to calculate the margin. If the margin is equal to or greater than 10% then the ampacity of the cable in the encapsulation is considered acceptable.
The calculation procedure is illustrated in Section 4.1 for a protected cable tray and in Section 4.2 for a protected conduit. These raceways are plant-specific raceways coming from the LGS Ampacity Derating Calculation [Ref. 8) and use an Im,y,,, calculated from industry standards. The equations or derivation from equations and equation numbers included in each calculation step are the same as previously provided in the PECO Energy to NRC submittal dated March 24, i
1997 [Ref.1). All calculations are performed on a per-unit-length of cable basis.
Tables 4.1 and 4.2 show the final results of the model obtained after a significant number of iterations. The calculation involves iterative computations to calculate final values. The results shown in the body of Sections 4.1 and 4.2 i
are slightly different from the results in Tables 4.1 and 4.2 because the number of iterations performed in these sections is less than that performed for the final results provided by the model.
3.2 Diversity Model The diversity model assigns each ind;vidual cable in a raceway to one of the three regions according to its relative current load, and produces a distinct ampacity derating factor for each of the three regions. The calculctions are performed in three main steps: defining the region parameters, calculating the allowable heat intensities (heat generation rate per unit volume)in each region, and determining the ampacity derating factors for each region. A brief summary of each step is described below, o
a March 2,1999 Docket Nos. 50-277/278 50-352/353 Page 6 of 24 1.
Define The Region Parameters The region parameters, namely the physical dimensions, are determined by ranking the cables according to their diversity and assigning the region j
i boundaries. Typically, power cables are assigned to the first and the second regions, and control cables are assigned to the third region. Region boundaries are assigned based on actual cable areas subject to the restriction imposed by assumptions 3 and 4 in Section 2.2. Each region is assigned the diversity of the most heavily loaded cable contained in it, l.o., the maximum value of diversity encountered in the region.
1 2.
Calculate the Allowable Heat Generation Rate in the Raceway The allowable heat generation rate in the cable mass is calculated using the heat transfer model described in PECO March 24,1997 cubmittal to NRC [Ref.
1). The multi-region cable mass is handled separately by applying the familiar conduction equation with intemal heat generation. The problem is formulated j
such that a diversely loaded raceway can be analyzed as a uniformly loaded i
raceway by defining an equivalent thermal conductivity and an equivalent l
average hest generation rate in the cable mass.
l 3.
Calculate the Ampacity Derating Factors for Each Region l
The allowable heat generation rate in each region is calculated using the average heat generation rate determined in Step 2 in conjunction with the diversity parameters assigned in Step 1. The corresponding ampacity derating factors are, then, determined using the method described in PECO March 24, i
1997 submittal to NRC [Ref.1].
1 4.
The available ampacity margin is calculated as in Step 12 of Section 3.1 "Non-Diversity Model."
l The diversity model produces a low ampacity derating factor in Region 1 in the i
center, and high ampacity derating factor in Region 2 enveloping it. This is
)
expected since the cables in Region 2 are constrained to a low ampacity level consistent with the diversity factor assigned to them. In other words the low current load in Region 2 enables a high current load in Region 1. Nc ampacity derating factor is defined for the control cables in Region 3 since the current load of these cables is very small.
i l
I_
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March 2,1999 l
Docket Nos. 50-277/278 l
50-352/353 Page 7 of 24 4.0 EXAMPLE CALCULATIONS 4.1 Protected Cable Tray (24 Inch Tray - 3 Hour Rated)
J This example is for a 24 inch ladder type cable tray protected by a three-hour rated fire barrier. The calculations performed by the Model are tabulated n Table 4.1 in a spread sheet format. The essential data used in the calculation is listed below. The calculation results may differ slightly from those in Table 4.1 due to round off errors and because the I
number of iterations performed in this section is less than that provided by the Model.
Fire Barrier Data w3, wid th, (in)................................ 2 7.0 ho, h eig ht, (1n)............................... 8.3 c3, emissivity [Ref. 6].................... 0.90 to, thickness (1n)............................ 1.50 k, (Btu /hr-ft-F) [Ref. 6]................ 0.122 F,, s h a pe fa ctor........................... 1.00 Raceway Dimension And Cable FIII Data w,, tray width, (in)......................... 24 h,, tray heig ht, (in)......................... 4
)
d,, fill depth, (in)............................ 1.00 c,, raceway emissivity [Ref 5]...... 0.80 F,3, sha pe factor.......................... 1.00 Model Cable Data Ca ble Size................................... 3/C #6 d,,y,, Cable Diameter (in)............. 0.74 n,,, no. of conductors per cable..... 3 km, (Btu /hr-ft-F) (Ref. 6].............. 0.090 R, resistance, (Ohm /1000ft)......... 0.535 Temperature Data T,,, conductor temperature, ( F)....194.0 T, ambient temperature, ( F).......104.0 1
March 2,1999 Docket Nos. 50-277/278 50-352/353 l
l Page 8 of 24-l Step 1 Calculate the number of cables, n,,3,,, in the raceway using Equation 3 d,f,' =. # * *
44 (3) n,,,,,
0.74, Step 2 Determine the baseline ampacity, l,,,,,,,,, for the 3/C #6 cable with 0.74 inch e
diameter and 1.0 inch cable depth from the applicable industry standards
.74 I,,,,,,,, = 44 x
= 45.2 Amps (ICEA, Ref 5, Table 3.3) 0.72 Step 3 Calculate the surface area, A,, of the raceway per unit length using Equation 6.
Only the top and bottom surfaces are counted j
A, = 2w, = 2 x(24 /12) = 4.0ft' /ft (6)
Step 4
. Calculate the heat transfer coefficient, U,, for the cable bed using a portion of
{
Equation 4
- 0 U, =[ d, ]= [1.00/12]= 4.32 Btu /hr-ft' *F (4)
Step 5 Calculate the surface area, A, of the barrier per unit length 3
A, = 2(w, + h,) = 2(27 + 8.3)/12 = 5.88 ft' /ft Step 6 Calculate the heat transfer coefficient, U, of the barrier wall using a portion of 3
Equation 12 U,=h=0'I
= 0.98Bru/hr-ft'
- F (12) t, 1.5/12 Step 7 Estimate a barrier wall temperature This step involves iteration over the barrier wall temperature such that the heat L
transfer rate through the barrier wall reasonably matches the heat dissipation l
rate from the barrier to the ambient. The iteration starts by estimating an inside wall temperature, Two, and solving for the outside wall temperature, T, and the corresponding heat dissipation rate, go. Only the final values of the iteration variables are shown below.
F
.l, l
March 2,1999 Docket Nos. 50-277/278 50-352/353 AMachment 2 Page 9 of 24 L
- Step 7 (continued)
T,.;, = 154.3 *F (final value)
T,.,,, = 123.7 *F (calculated from simultaneous solution of Equations 12 and 13)
Step 7.1 Calculate the heat dissipation rate through the barrier wall, q,.
q, = U, A,(T, g,, - T,,,)= 0.98 x 5.88(154.3 - 123.7) = 176 Blu / hr -ft
(_ 12)
Step 7.2 Calculate the heat dissipation rate from the barrier wall to the ambient, qu. This involves calculating the convective heat transfer coefficient, ha, and the radiative heat transfer coefficient, hm, from the barrier surface to the ambient.
Calculate the convective heat transfer coefficient from Equation 9 h, u = a AT* "
'123.7 - 104 *'"
= 0.20
= 0.34 Btu /hr -ft' *F (9)
<L, 27/12 i
Calculate the radiative heat transfer coefficient from Equation 8 h,,s.,, = F,,e,a[(T,.,,, + 460J' + (T, + 460J'][(T,.,, + 460) + (T, + 460)]
= 1.0 x 0.9 x 0.1714 x 10 x (8)
[(123. 7 + 460J' + (104 + 460J'][(123. 7 + 460) + (104 + 460)]
= 1.17 Btu / hr - ft' *F Calculate the combined heat transfer coefficient from the barrier wall to the ambient, Uu Uu = (h,.,, + h,,s.,,) = 0.34 + 1.17 = 1.51 Btu /hr -ft' *F Calculate the heat dissipation rate from the barrier wall to the ambient, q3, qu = Uu A,(T,.,,, - T, ) = 1.51 x 5.88(123. 7 - 104) = 175 Blu /hr-ft (13)
f'
)
)
March 2,1999 Docket Nos. 50-277/278 50-352/353 Page 10 of 24 Step 7.3 Compare the heat transfer rate through the barrier wall, q, with the heat j-dissipation rate from the barrier wall to the ambient, q,. The two quantities must be in reasonable agreement. Otherwise adjust Ta and repeat Step 7.
i q,(175 Btu /hr-ft)is within 0.6 % of q,(176 Btu /hr-ft). This is considered a reasonable agreement.
l Step 8 Calculate the raceway (or cable mass) surface temperature T, corresponding to the cable conductor temperature (194 F) and the barrier inside wall temperature Tm. This step requires iteration over the enclosure air temperature T, as described below.
Estimate a reasonable value for the heat generation rate in the raceway based on the baseline ampacity and the heat dissipation rate from the barrier. For barriers with multiple raceways, a reasonable value of the heat generation rate in each individual raceway may be obtained from an estimate of the protected ampacity. For barriers containing a single raceway, the heat generation rate in j
the raceway is equal to the heat dissipation rate from the barrier.
Step 8.1 Calculate the raceway surface temperature corresponding to the heat generation rate, g,, in the raceway using Equation 4. For single raceways q,= go determined in Step 7.1.
I T' = T*
4'
= 194 -
= 183.8 *F (4)
U,A, 4.32 x 4 Step 8.2 Estimate a value for the enclosure air temperature, T,, based on barrier inside wall temperature, Ta, and the raceway surface temperature, T,. This involves simu:taneously solving equations 4 and 5.
q, : U, A,(T, - T,) = U,, A,(T, - T,.,, )
Since the convective heat transfer coefficient from the surface of the raceway to the barrier is dependent on the raceway surface temperature, T,, and the enclosure air temperature, T, an iterative process is used to calculate T,.
{
T, = 167 *F (final value)
Lr l
q i
March 2,1999 Docket Nos. 50-277/278 50-352/353 Page 11 of 24 Step 8.2 (continued) i Calculate the convective heat transfer coefficient, ha, from the raceway to the barrier 1
'h,.,, = 0.20 AT * *
'183. 8 - 167 ' "
= 0.20
= 0.34 Btu / hr -ft' *F (9)
<L, 24 /12 h,.,, = 0.20 A T' "
'167 - 154.3 * "
f
= 0.20
= 0.32 Btu /hr-ft' *F (9)
<L, 25 /12 h
0.34 h,.,, =
1+.A'(",h j+
4 3,0.34 3 = 0.19Blu /hr-ft
- F (11) 3=
c-n
<A,,,yh,.,,,
< 5.88> < 0.32,.
Calculate the radiative heat transfer coefficient from Equation 8 h"'- ~ "I ' + 460 + (T,_;, + 460f][(T, + 460) + (T,.,, + 460)]
(g) j-c, 3.1-e,'$'
S E
r vb b < b)
,'"'~'* _ 0.1714 x 10~'[(183.9 + 460J' + (154.3 + 460J'][(183.9 + 460) + (154.3 + 460)]
~
1 - 0.8 1 1 - 0.9 ' 4
- 0.8 1
0.9
<5.88, h,,s.,, = 1.29 Btu / k - p' -T Calculate the combined heat transfer coefficient from the raceway to the barrier, U,s U,, = (h,.,, + h,,s.,,) = 0.19 + 1.B = 1.# Blu / hr - p'-T )
Calculate the heat transfer rate from the raceway to the barrier, q.
q,, = U,, A,(T, - T,.,,) = 1.48 x 4 x (183.9 - 154.3) = 175 Btu /hr-ft (5)
I
7 March 2,1999 Docket Nos. 50-277/278 L
50-352/353 l
Page 12 of 24
, ~
Step 9 Compare the heat transfer rate from the raceway to the barrier wall, q,3 with the l
heat dissipation rate from the barrier wall to the ambient, q3,. The two quantities l
must be in reasonable agreement. Otherwise adjust Tu,, and repeat steps 5
)
j through 7.
]
q,(175 Btu /hr-ft) is the same as q (175 Btu /hr-ft) to within three significant
- figures. This is considered a reasonable agreement.
L Step 10 Calculate the protected ampacity, I,,,,,,, using Equation 2 C=j 17 1
',,,,a =
n,n, R 144 x 3 x 0.515 x 10~' 0.2931 = 27.0 Amps (2)
F
' Step 11 Calculate the Ampacity Derating Factor using Equation 1 ADF = # ' ~
x100 = 40.3% (Round up to 41%)
(1) l 45.2 l
Step 12 Calculate the Available Ampacity Margin for a Specific Cable in a Plant Raceway l
Plant LGS Tray No.
1ACXA94 Depth of fill 1.53 inches Cable No.1 AB21306A Cable Size 3/C #8 AWG Cable Diameter-0.75"
/,,,,,,,,
27.7 Amps (ICEA [Ref. 5, Table 3.12))
I 3
Ambient Temp. 50 C ATCF 0.89 (Ambient Temperature Correction Factor)
'ADF 41 %
/,,,,,,,
I.,,,,,,, x(1-ADF/100) x ATCF = 27.7 x (1-0.41) x 0.89
=14.5 Amps 1,,a 12.6 Amps (Cable Load)
Ampacity Margin = {(1,,,,,,u- /,,,,/ I,,, }x 100% =
{(14.5 - 12.6) /12.6 } x 100% = 15% > 10%
l Therefore, the ampacity of the protected cable is acceptable.
I
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March 2,1999 Docket Nos. 50-277/278
(
50-352/353 t
Page 13 of 24 Table 4.1 24 Inch Tray - 3 Hour Rated FIRE BARRIER DATA AIR GAP HEAT TRANSFER DATA PARAMETERS w, width, (in) 27.0 t,, (in)
N/A a 0.20 e
h, height, (in) 8.3 n
0.25 3
c, emissivity 0.90 T,
104.0
( F) to, thickness (in) 1.50 k, (Btu /hr-ft-F) 0.122 3
F,, shape factor 1.00 3
RACEWAY DIMENSION AND CABLE FILL DATA RacewayID TRAY j
w,, tray width, (in) 24 d,, tray height, (in) 4 fill depth, (iri) 1.00 c, cat,le surface emissivity 0.80 c
F,3, shape factor 1.00 Cable size (model cable) 3/C #6 d,3,,, cable dia, (in) 0.740 l
e n,,, no. Of conductors (per cable) 3 l
km, (Btu /hr-ft-F) 0.09 R, resistance, (Ohm /1000ft) 0.535 I,,,,,,,,, baseline amp., (Amp) 45.2 3
CALCULATED PARAMETERS l
Unprotected Raceway (baseline) n,3,,, number of cables
[3]
44 e
2 A,, heat transfer area, (ft /ft)
[6]
4.0 q,, heat gen. Rate, (Btu /hr-ft)
U,, (8tu/hr-ft - F)
[4]
4.32 l
2 T,, surface temp., ( F)
N/A 2
U,,, (Btu /hr-ft - F)
N/A j
Protected Raceway I,,,,,u, protected amp., (Amp) [2]
27.02 g
q,, (Btu /hr-ft )
[5]
175.24 T,,, conductor temp., ( F)
Input 194.0 T,, surface temp., ( F)
[4]
183.9 l
l l
y March 2,1999 Docket Nos. 50-277/278 50-352/353 Page 14 of 24 Table 4.1 24 inch Tray - 3 Hour Rated CALCULATED PARAMETERS (cont'd.)
Enclosure Air Space T., enclosure air temp., ( F) l167 l
(A/A),
0.68 (A/A),,s 0.68 2
h,,, (Btu /hr-ft - F)
[9]
0.34
{
2 h,43, (Blu/hr-ft - F)
[9]
0.31
]
2 h,4, (Btu /hr-ft - F)
[11]
0.19 2
h,,,,, (Btu /hr-ft - F)
[8]
1.29 2
U,3, (Btu /hr-ft - F) 1.48 q,3, (Btu /hr-ft)
[5]
175.30 Barrier & Ambient 2
A, area, (ft /ft) 5.88 Entries in boxes designate the parameters over 2
U, (Btu /hr-ft - F)
[12]
0.98 which iterations are carried out.
3 Only the final values are shown.
Tw, inside temp., ( F) l154.3 l
Tw, outside temp., ( F)
[12, 13] 123.7 2
h,#,, (Btu /hr-ft - F)
[9]
0.34 Entries in [ ] show the applicable equation number in PECO submittal to NRC [Ref.
11 h,,u,, (Btu /hr-ft'- F)
[8]
1.17 2
U,, (Btu /hr-ft - F) 1.51 3
T., ambient temp., ( F)
Input 104.0 ADF
[1]
40.2 %
i l
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March 2,1999 Docket Nos. 50-277/278 l
50-352/353 Page 15 of 24
- 4.2 Protected Conduit (5 Inch Conduit - 3 Hour Rated)
This example is for a single conduit in a round enclosure. The calculations performed by the Model are tabulated in Table 4.2 in spread sheet format. The essential data used in the calculation is listed below. The calculation results may differ slightly from those in
{
Table 4.2 due to round off errors and because the number ofiterations performed in this
{
section is less than that provided by the Model.
I Fire Barrier Data do, outside diameter, (in).............. 8.813 h, height, (in)............................... N/A 3
c, emissivity [Ref. 6]................... 0.90 e
f, thickness, (1n).......................... 1.5 3
k, (Btu /hr-ft-F) [Ref. 6]................ 0.122 3
F,, sha pe factor......................... 1.0 3
Raceway Dimension And Cable Fill Data I
d,noy,,, outside dia., (in)................. 5.563 e
t,,,gy,,, wall thickness, (in).............. 0.258 pe rce n t fill..................................... 4 0.0 %
c, raceway emissivity [Ref. 6]...... 0.40 c
F,3, shape factor.......................... 1.00 Model Cable Data Cable Size (model cable)............ 3/C #6 d,,3,,, Cable Diameter (in)............ 0.74 n, no. of conductors per cable..... 3 o
k,,, (Btu /hr-ft-F) [Ref. 6].............. 0.090 3
R, resistance, (Ohm /1000ft)......... 0.535 Temperature Data T, conductor temperature, ( F)....194.0 T,, ambient temperature, ( F).......104.0 1
March 2,1999 Docket Nos. 50-277/278 50-352/353 Anachment 2 Page 16 of 24 Step 1 Calculate the number of cabics, n,,3,,, in the raceway using Equation 3
" " ' " " ~ ' " " ' " " E""'IIII b'5 ~ *0'2##
- 0
- n, =
= 18.6 (3) d 100 ag, 0.74 100 Step 2 Determine the baseline ampacity,1,,,,,,,,, for the 3/C #6 cable using the nominal 3
ampacity and multiple conductor correction factor from the applicable industry standards.
Is,,,,u,,, = 69 Amps [IPCEA, Ref 4) x 0.35[NEC, Ref 3]
= 24.2 Amps Step 3 Calculate the surface area, A,, of the raceway per unit length A, = mi
,s,,, = x(5.563 /12) = 1.456ft' / ft (6) n Step 4 -
Calculate the heat transfer coefficient, U,. of the raceway using a portion of Equation 4. U,is back calculated from the baselinc ampacity data. This requires an iterative process where Equation 4 and Equation 5 (with Ts,, replaced by T,)
are solved simultaneously for an unprotected conduit. The steps involved are shown below:
Step 4.1 Calculate the heat generation rate for the unprotected conduit using the baseline ampacity in Equation 3
[q,]w,u,,=(nai,n,,[1]L,u,,,R)/ C = (18.6 x 3 x 24.2' x 0.535 x 10*')/ 0.2931 (3)
= 59.6Blu / hr -ft Step 4.2a Estimate the surface temperature of the unprotected conduit
[T,]w,u,,, = 127.3 *F (final value)
Step 4.2b Calculate the convective heat transfer coefficient from the unprotected raceway to the ambient using Equation 9 with a = 0.27 and n = 0.25 h"" = 0.27 AT *
'12 7.3 - 104 '
= 0.27
= 0. 719 Btu / hr - ft' *F (9)
<L,
< 5.563/12,
w March 2,1999 Docket Nos. 50-277/278 50-352/353 Anachment 2 Page 17 of 24 Step 4.2c Calculate the radiative heat transfer coefficient from the unprotected raceway to the ambient. The radiative heat transfer coefficient, h,
, is based on an upper-bound estimate of the emissivity of the conduit surface. The value used is 0.8.
This results in a conservative ampacity derating factor by lowering the conduit heat transfer coefficient, U,, which is calculated later in this step.
h,a.,, = e,.u,u,p[(T, + 460)' +(T, + 460)'][(T, + 460) + (T, + 460)]
= 0.80 x 0.1714 x 10~* x (8)
[(127.3 + 460)' + (104 + 460J'][(127.3 + 460) + (104.0 + 460)]
= 1.047 Btu / hr - ft' *F Step 4.2d Calculate the overall (combined) heat transfer coefficient, U,,
U,, = (h,.,, + h,,s.,,) = (0.719 + 1.047) = 1.766 Btu /h -ft' *F Step 4.2e Calculate the heat dissipation rate, g,,, from the unpdected conduit q,, = U,, A,(T, - T, ) = 1. 766 x 1.456 x (127.3 - 104) = 59.9 Btu / hr-ft (13)
The calculations above are repeated by adjusting the conduit surface -
temperature, T,, until q,, and q,are within an acceptable range of each other. For the values used above, the heat dissipation rate from the conduit, q,,(=59.9 Btu /hr-ft), is within 0.5% of the heat generation rate in the conduit, q,(=59.6 Btu /hr-ft). This is considered a reasonable agreement.
- Step 4.2f Calculate the overall heat transfer coefficient, U,, of the' conduit using a portion i
of Equation 4 I"'E""""
U' =
=
(Micoaa )[T, - T,],,,,u, (x5.563 /12)[194-127,3]
(4)
= 0.614 Blu / hr - ft' *F Step 5 Calculate the surface area, A, of the barrier per unit length 3
A, = nd, = n8.813/12 = 2.31ft'/ft L-
y March 2,1999 Docket Nos. 50-277/278 50-352/353 j
Page 18 of 24
(
Step 6 Calculate the heat transfer coefficient, U, of the barrier wall using a portion of Equation 12 k
0.122
/
s
=.80Blu &-f *F (12)
- d,In d
8.813/12 8.813 s
in 2
d - 2t, 2
8.813 - 2 x 1.5 s
Step 7 Calculate the barrier wall temperature This step involves iteration over the barrier wall temperature such that the heat transfer rate through the barrier wall reasonably matches the heat dissipation rate from the barrier to the ambient. The iteration starts by estimating an inside wall temperature, T.,,,, and solving for the outside wall temperature, T m, and the 3
3 i
corresponding heat dissipation rate, q,. Only the final values of the iteration variables are shown.
T,.;, = 136.8 *F (final value)
T.,,, = 115.2 *F (calculated from simultaneous solution of Equations 12 and 13) s Step 7.1 Calculate the heat transfer rate through the barrier wall, q, q, = U, A,(T.,, - T,.,,,)= 0.80 x 2.31(136.8 - 115.2) = 39.9 Btu /hr-ft (12) s Step 7.2 Calculate the heat dissipation rate from the barrier wall to the ambient, q,. This involves calculating the convective heat transfer coefficient, h,4,, and the radiative heat transfer coefficient, h,#,, from the barrier surface to the ambient.
Calculate the convective heat transfer coefficient h,.u = a AT ' *
' 115.2 - 104 '"
= 0.20
= 0.40 Btu /hr-ft' *F (9)
<L, q 8.813/12,
T March 2,1999 Docket Nos. 50-277/278 50-352/353 l
Page 19 of 24 I
Step 7.2 (continued) l Calculate the radiative heat transfer coefficient l
l h,,s.u = F,,e,a[(T.,,, + 460)' +(T, + 460)'][(T.,,, + 460)+(T, + 460)]
s s
= 1. 0 x 0.90 x 0.1714 x 10~"[(115.2 + 460)' + (104 + 460)')
(g) x[(115.2 + 460)+(104 + 460)]
= 1.14 Btu /hr -ft' *F Calculate the combined heat transfer coefficient from the barrier wall to the ambient. U,
3 U,, = (h,_u + h,,s.u ) = 0.40 + 1.14 = 1.54 Btu / hr -ft' *F Calculate the heat dissipation rate from the barrier wall to the ambient, go, qu = U A,(T,.,,, - T,) = 1.54 x 2.31(115.2 -104) = 39.8 Btu /hr-ft (13) u 3
Step 7.3 Compare the heat transfer rate through the barrier wall, q, with the heat dissipation rate from the barrier wall to the ambient, q,. The two quantities must be in reasonable agreement. Otherwise adjust Tu,, and repeat Step 7.
l q.,(39.8 Btu /hr-ft)is within 0.3% of q (39.9 Btu /hr-ft). This is considered a reasonable agreement.
l Step 8 Calculate the raceway surface temperature, T,, corresponding to the cable conductor temperature, T,,(=194 F) and the barrier inside wall temperature, Tu,,.
Estimate a reasonable value for the heat generation rate in the raceway based on the baseline ampacity and the heat dissipation rate from the barrier For barriers with multiple raceways a reasonable value of the heat generation rate in each individual raceway may be obtained from an estimate of the protected ampacity. For barriers containing a single raceway, the heat generation rate in the raceway is equal to the heat dissipation rate from the barrier.
i
o.
March 2,1999 Docket Nos. 50-27'7/278 50-352/353 Page 20 of 24 Step 8.1 Calculate the barrier surface temperature corresponding to the heat generation rate, q,, in the raceway using Equation 4. For single raceways q,= q, determined in Step 7.1.
T' = T"
"' = 194 -
= 149.6 *F (4)
U,A, 0.617 x 1.456 Step 8.2 Calculate the convective heat transfer coefficient from the raceway to the barrier.
Because the air gap between the conduit and the fire barrier is so small, the convective heat transfer coefficient is calculated based on pure conduction only.
'~b~
h,.,, =
= 1.536 Btu /hr-ft' *F (11)
=
t, 0.125/12 Calculate the radiative heat transfer coefficient using Equation 8
_ a[(T, + 46'O)' +(T,_u + 460J'][(T, + 460)+(T,_u + 460))
i
" ' ' ' ' ~
1-c, J 1-e,'A,'
c, F
c A
eb 3 g bj
_ 0.1714 x 10[(149.6 + 460J' + (136.8 + 460)'][(149.6 + 460) + (136.8 + 460)]
" ' ' ' ' ~
1 - 0.4 [ 1- 0.9 '1.46' O.4 1
0.9 < 2.31, h,,s.,, = 0.586 Blu / hr - ff-T Calculate the combined heat transfer coefficient from the raceway to the barrier, Um U,, = (h,.,, + h,,s.,,) = (1.536 + 0.586) = 2.12 Btu /hr-ft' *F Calculate the heat transfer rate from the raceway to the barrier, q,,
q,, = U,, A,(T, - T,.u ) = 2.12 x 1.456 x (149.6 -136.8) = 39.5 Blu / hr-ft (5)
I L
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March 2,1999 l
Docket Nos. 50-277/278 50-352/353 Page 21 of 24 l
Step 9 Compare the heat transfer rate from the raceway to the barrier wall, g,3, with the heat dissipation rate from the barrier wall to the ambient, g3,. The two quantities must be in reasonable agreement. Otherwise adjust Tu,, and repeat steps 7 through 9.
q,3 (39.6 Btu /hr-ft)is within 0.5 % of q,(39.8 Btu /hr-ft). This is considered a reasonable agreement.
I l
Step 10 Calculate the protected ampacity, I,,,,,c,u, using Equation 2 l
I"'",,s = k n,n,R y 18.6 x 3 x 0.535 x 10 0.331 = 19.8 Antjn Q)
C=
\\
i Step 11 Calculate the Ampacity Derating Factor ADF = #' ~
x 100 = 18.2% (Round up to 19%)
24.2 Step 12 Calculate the Available Ampacity Margin for a Specific Cable in a Plant Raceway l
Plant LGS Conduit No.
1CP123 Conduit Size 6" Rigid steel conduit. Contains 22 current carrying conductors Cable No.1CY16306A Cable Size 2/C #10 l,,,,,,,,,,, a w e 40 Amps (NEC, Ref. 3) Nominal Ampacity l
.,a40 c
=40 x 0.91 = 36.4 Amps (NEC, Ref. 3) o MCCF 0.45 Multiple Conductor Correction Factor from NEC [Ref. 3]
Ambient Temp. 50 C ATCF 0.89 (Ambient Temperature Correction Factor)
ADF 19%
1,,,,,,,
/,,,,,,,, x MCCF x (1-ADF/100) x ATCF= 36.4x0.45x (1-0.19) x 0.89 3
l
=11.8 Amps l
I,,,
6.7 Amps (Cable Load)
Ampacity Margin ={(I,,,,,c,u- /,,,/ /,,u }x 100% =
{(11.8 - 6.7) /6.7} x 100% = 76% > 10%
Therefore, ampacity of the protected cable is acceptable.
L
1 o
i March 2,1999 Docket Nos. 50-277/278 50-352/353 4
Page 22 of 24 1
Table 4.2 5 inch Conduit - 3 Hour Rated FIRE BARRIER DATA AIR GAP HEAT TRANSFER DATA PARAMETERS d, outside diameter, (in) 8.813 t,, (in) 1/8 a
0.20
)
3 h, height. (in)
N/A n
0.25 3
. c, emissivity 0.90 T, ( F) 104.0 e
f, thickness (in) 1.5 3
k, (Blu/hr-ft-F) 0.122 3
i F,, shape factor 1.0 3
RACEWAY DIMENSION AND CABLE FILL DATA RacewayID Conduit d,ongu,,, outside dia., (in) 5.563 t
ou,,, wall thickness, (in) 0.258 eon percent fill 40.0%
l c,, conduit surface emissivity 0.40 F,3, shape factor 1.00
)
cable size (niodel cable) 3/C #6 d,y,, cable dia., (in) 0.740 e
n, no. Of conductors (per cable) 3 o
k,,, (Btu /hr-ft-F) 0.09 3
R, resistance, (Ohm /1000ft) 0.535
/,,,,,,,,, baseline amp., (Amp) 24.2 3
CALCULATED PARAMETERS Unprotected Raceway (baseline) n,y,, number of cables
[3]
19 e
2 A,, heat transfer area, (ft /tt)
[6]
1.46 g,, heat gen. Rate, (Btu /hr-ft)
[2]
59.7 2
U,, (Btu /hr-ft - F)
[4]
0.614 T,, surface temp., ( F) 1127.3 l
2 U,,, (Btu /hr-ft - F)
[8,9J 1.77 Protected Raceway l
,,c,,,, protected amp., (Amp)
[2]
19.73 y
q,, (Btu /hr-ft )
[5]
39.67 T, conductor temp., ( F)
Input 194.0 n
T,, surface temp., ( F)
[4]
149.64
s o
March 2,1999 Docket Nos. 50-277/278 50-352/353 Page 23 of 24 Table 4.2 5 inch Conduit - 3 Hour Rated l
CALCULATED PARAMETERS (cont'd)
Enclosure:
Air Space (or Gap)
(A/A),
1.00 (A/A),,,
1.00 2
h,,, (Btu /hr-ft - F)
[9]
N/A 2
h,43, (Btu /hr-ft - F)
[9]
N/A J
2 h,4, (Btu /hr-ft - F)
[11] 1.54 2
h,,,.,3, (Btu /hr-ft - F)
[8]
0.58
)
2 U,3, (Btu /hr-ft - F) 2.12 g,3, (Btu /hr-ft)
[5]
39.65 i
Barrier & Ambient 2
A, area, (ft /ft) 2.31 Entries in boxes designate the parameters 3
over which iterations are carried out.
2 U, (Btu /hr-ft - F)
[12J 0.80 Only the final values are shown.
Tu,,, inside temp., ( F) l136.8 l
Tw, outside temp., ( F)
[12, 115.2 13]
2 h,_3,, (Stu/hr-ft - F)
[9]
0.40 Entries in [ ] show the applicable equation number in PECO submi*tal to NRC [Ref.1]
2 h,,g.3,, (Btu /hr-ft,op) ggy 4,14 2
U,, (Btu /hr-ft - F) 1.54 3
T,, smbient temp., ( F)
/nput 104.0 ADF
[1]
18.5%
k-
r
" o March 2,1999 Docket Nos. 50-277/278 50-352/353 Page 24 of 24
5.0 REFERENCES
- 1. to PECO Submittal to NRC dated March 24,1997.
2.
1EEE Standard "lEEE Standard Procedure for the Determination of the Ampacity Derating of Fire-Protected Cables," lEEE Std 848-1996.
3.
Early, M. W. et al., National Electric Code Handbook, National Fire Protection Association,1993.
4.
IEEE/IPCEA Standard S-135/P-46-426, Power Cable Ampacities: Volume I-Copper Conductors and Volume II-Aluminum Conductors,1964.
5.
ICEA Standard Publication, "Ampacities of Cables in Open-top Cable Trays,"
ICEA P-54-440 (Third Edition), NEMA WC 51-1986.
6.
Safety Evaluation Report by the Office of Nuclear Reactor Regulation, "Ampacity Issues Related to Thermo-Lag Fire Barriers, Texas Utilities Electric Company, Comanche Peak Steam Electric Station, Unit 2, Docket No. 50-446,"
Enclosure to US Nuclear Regulatory Commission letter dated June 14,1995.
7.
Omega Point Laboratories Report Titled, "Ampacity Derating of Cables Enclosed in Conduits with Thermo-Lag 330-1/770-1 Upgrade Electrical Raceway Fire Barrier Systems (ERFBS)," Project Nos. 11960-97332,97334-6, 97768-70, Tennessee Valley Authority, March 28,1995.
8.
DESS Calculation, "Ampacity Derating Factors of Cables in Thermo-Lag Protected Raceways,"VU2800-LGS-01, Rev.1, January 11,1999.
9.
Harshe, B. L. and W. Z. Black, "Ampacity of Cables in Single Open-Top Trays,"
lEEE Transaction on Power, December 1994.
- 10. Black, W. Z. and B. L. Harshe, "Ampacity of Diversely Loaded Cables in Covered and uncovered Trays," IEEE Paper No. PE-269-PWRD-0-05-1998.
- 11. Stolpe, J., "Ampacity for Cables in Randomly Filled Trays," IEEE Trai.sactions on Power Apparatus and Systems, IEEE Paper No. 70 TP 557-PWR.
- b..
J