ML20217H577
| ML20217H577 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 03/27/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20217H561 | List: |
| References | |
| GL-92-08, GL-92-8, NUDOCS 9804030397 | |
| Download: ML20217H577 (14) | |
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p & UNITED STATES j
s* NUCLEAR REGULATORY COMMISSION 2 WASHINGTON, D.C. 20066 0001
,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ILLINOIS POWER COMPANY AMPACITY DERATING ISSUES CLINTON POWER STATION DOCKET NO. 50-461 BACKGROUND By letter dated July 24,1997, Illinois Power Company (IPC) (the licensee) submitted a response to the NRC Request for Additional Information (RAI) related to Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," for Clinton Power Station (CPS).
The licensee's original analyses which were the subject of the NRC RAI dated August 16,1996, were based on an application of the " Watts per foot" methodology. The preliminary review had indicated that the subject methodology was inherently inadequate to demonstrate the acceptability of derived ampacity load limits for the cables installed at CPS. In addition, the licensee submittal dated March 31,1997, included a number of supplemental ampacity i i
assessments based on a direct comparison of the cable design heat intensity for plant {
installations to those observed in one cladded ampacity test [ test results cited in SNL Report SAND 94-0146, "An Evaluation of the Fire Barrier System Thermo-Lag 330-1," September 1994]. The subject methodology provided no assessment for the ampacity limits for an individual cable.
In its submittal dated July 24,1997, the licensee informed the staff that it would abandon any further application of the " Watts per foot" methodology to assess the performance of individual cables located within the Thermo-Lag wrapped electrical raceways.
Enclosure 1 9804030397 900327 5 PDR ADOCK 05000461 -
F PDR u
The staff evaluation of the ampacity derating methodology for. CPS follows.
EVALUATION After reviewing the licensee's submittals and Sandia National Laboratories (SNL) Technical-Evaluation Report (TER) and SNL Letter (see Enclosures 2 and 3), the staff agrees with the SNL analyses and conclusions. The ampacity derating analysis questions, the licensee's ,
responses, and the staff's evaluation of the responses follow.
Amoacitv Deratina Analysis Revieg
. Question 1
-- The licensee needs to specify the assurned ambient temperature for each fire area with .
adequate justification for the assumption. The ICEA tables for cable ampacity are based on 40*C ambient and adjustment will be required for a different ambient temperature.
Licensee's Response in its submittal of March 31,1997, the licensee stated that all of the licensee
. assessments have been based on an assumed ambient temperature of 50*C with the exception of Area D-8 which assumed an ambient temperature of 40*C.
Staffs Evaluation The clarification by the licensee fully resolves the staffs concerns.
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. Question 2 The' licensee needs to provide details of baseline ampacity for tray and conduit including pertinent information (cable types, characteristics, outside diameter, ambient temperature, depth of fill or percentage fill, conduit size, conduit fill, etc.) used to
- determine the baseline ampacity. Also, specify the fire barrier ampacity derating factors for each raceway configuration.
Licensee's Resoonse in its submittal of March 31,1997, the licensee provided Ca'culations 19-G-01 and 19-G-02 as the basis for its baseline ampacity assessments which included information on cable types and characteristics. The licensee also included Calculation 19-Al-08 which establishes an ampacity derating factor of 32% 'to screen the impact of the installed fire barrier systems at CPS.
Staffs Evaluation The clarification by the licenses fully resolves the staffs concern. A review of the licensee's calculations is shown in Enclosure 2.
. Question 3 Provide the basis of baseline ampacity value for #19/22 AWG and #19/25 AWG cables in cable tray and conduit. These cable sizes are not available in ICEA P-54-440 tables.
Licensee's Resoonse in its submittal of March 31,1997, the licensee clarified that the subject cable designations are equivalent to #9 AWG and #12 AWG cables respectively.
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- Staffs Evaluation 4
The clarification by the licensee fully resolves the staffs concems.
. Question 4 The " heat intensity" method is a departure from the accepted ampacity dera'ing approach. Generally accepted practices are determination of ampacity derating factors based on the results of either experiments or analysis. The following concerns were
- identified in the " heat intensity" analysis method (see SNL report dated May 16,1996,-
for details):
a) Inadequate treatment'of depth of fill.
J b) Removal of the conservatism from the ICEA tabulated ampacity values without adequate justification, c) Inadequate justification for the assumption that 32% derating of ICEA tabulated values will bound the derating impact of all fire barrier systems installed at Clinton Power Station (CPS).
d) Deviation from the ampacity derating test approach without adequate justification.
e) Inadequate justification for the applicability of " heat intensity" analysis method.
Licensee's Response
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In its submittal of March 31,1997, the licensee provided the following responses to the -
subject concerns:
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'a) The licensee contends that their analysis did not directly compare different depth of '
cable fills with CPS design.3The subject analysis attempted to compare CPS .
raceway configurations with SNL test specimens on a consistent basis by normalizing the CPS design values to a one and one-half inch depth of fill standard.
. b) The licensee expanded on its treatment of ICEA tabulated ampacity values and stated that their intent was not to compare actual installed cables to the subject SNL cladded test but to illustrate that the plant design approach yields more conservative results than those measured in the subject SNL test.
c) The licensee provided an explanation why it was not necessary to test the subject
- fire barriers and clarified the process by which assessments were made regarding the fire barriers. The licensee also included a discussion of its " Watts per foot" analysis of its cladded cable trays and conduits.
d) The licensee expanded upon the basis for its " heat intensity" analysis by discussing the methodology cited in Stople's paper, "Ampacities for Cables in Randomly Filled Trays."
Stafs Evaluation Although the licensee's response did not adequately address staff concems on the " heat intensity" method, no further followup is required since the licensee has abandoned this
= approach. Additional discussion of the licensee's response is provided in Enclosure 2,
'Section 5.2.
" i Question 5 The ampacity margin analysis approach is generally considered an appropriate approach to the resolution of the ampacity derating issue. The available margins in the cable ampacity should be compared against the fire barrier derating impact which may g;
be derived from well-founded and validated thermal calculations, or from appropriate experiments. The NRC-sponsored test should not be used as the basis for assessment of in-plant cable ampacity effects. TVA and TU have submitted a range of ampacity derating tests which have been reviewed and accepted by NRC. The staff recommends that the licensee should rely on the available ampacity test results of TU and TVA.
However, the licensee must demonstrate that the ampacity derating values are appropriate (or conservative) to the CPS barrier systems, or must provide for appropriate methods of extrapolating those results to the CPS installations.
Licensee's Resoonsa in its submittal of March 31,1997, the licensee stated that the process utilized for resolution of the ampacity derating issue followed the process outlined in the subject question. The actual loads on the power cables in Thermo-Lag wrapped raceway were reviewed and compared to the projected ampacity values established in Calculations 19-G-01 and 19-G-02 for the same size cables. This analysis determined the available margin for each applicable cable. The estimated margin was then compared to the ampacity derating factor of 32% which was developed by Calculation 19-Al-08. The licensee contends that the 32% ampacity derating factor is a conservative parameter to bound all Thermo-Lag wrapped cable trays and conduits.
Staff's EvaluatiSD i'
The clarification by the licensee clearly identifies its intent to apply a single ampacity derating factor to bound all of the fire barrier installations. However, the cited value of 32% will not adequately bound the 3-hour Thermo-Lag wrapped cable tray systems.
- Question 6 l l
l The analysis of cables 1DG29A and 1DG30A in fire area CB-1e is considered i insufficient. The licensee indicated that these cables are not impacted by derating
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based on the observation that the cables are not continuously energized. However, the -
- non-continuous loads must consider the maximum possible duration of cable operation under worst case conditions and should consider power cycling. If the maximum run -
time is short and power cycling time is long in comparison to the temperature rise time of the cable mass, then the licensee's justification would have merit. Additional documentation should be provided for the subject two cables regarding operating history.
Licensee's Response
. in its submittal of March 31,1997, the licensee provided information on the specific
. operating conditions for the subject cables. Specifically, the licensee states that the subject cables operate for approximately 5 minutes each day and concludes that the period of operation is too short to permit significant heating to ' occur within the cables.
Staff's Evaluation
-l he clarification by the licensee fully resolves the staff's concems.
. Question 7 The licensee indicated several cable tray barrier installations are designed to protect a
" fire break" (to establish a 20 foot combustible free zone) and are not specifically iritended to protect the cables in the tray. The licensee should describe any differences in the construction or configuration of barriers installed as fire breaks as compared to those installed to protect installed cables from fire damage. If there are differences in construction, the licensee should assess how these differences would impact the cable ampacity derating results.
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- Licensee's Resoonse in its submittal'of March 31,1997, the licensee stated that there are no differences in
- construction between the two subject installations. The licensee noted that for the installations referenced, the fire break installed on the tray consists of an application of
- Thermo-Lag material over a twenty foot length of cable tray and only the fire break in the C-2 fire area includes a power cable tray.
Staff's Evaluation The clarification by the licensee fully resolves the staff's concems.
. Question 8 The constant KVA loads will draw 11% more current at 90% of rated voltage available at its terminals. Additionally,'some loads may operate at overload or at a service factor of 15%. Accordingly, the full load current (FLA) could be as high as 125% of FLA at nominal voltage. The licensee needs to address this aspect of system operation in its ampacity derating analysis.
Licensee's Response
. In its submittal of March 31,1997, the licensee provided the requested reassessments
- which were initially based upon an increase in total heat generation rate for each tray
- and conduit which were followed by supplemental analyses for any cable which was found to be over 40% of the nominal " project ampacity" (i.e., the nominal base line ampacity of the cable without the Thermo-Lag fire barrier) s
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Stars Evaluation
. Although the " Watts per foot" approach which were utilized for the initial assessments did not provide an adequate analysis of the performance of individual cables, the -
licensee's supplemental analyses did show that all cables have adequate margin to allow for potential undervoltage and motor overload condition. Therefore, the Information provided by the licensee fully resolves the stafs concerns.
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.. Question 9 The use by the licensee of the ampacity test results as presented in SAND 94-0146 is inappropriate given that the subject test was intended to reproduce a specific manufacturer's test conditions which when compared to currently accepted test procedures suffers from a number of experimental deficier.cies.
Licensee's Response
- In its submittal of July' 24,1997, the licensee did not provide a specific response to the subject question.
Staff Evaluation
- As documented in the licensee's submittal dated July 24,1997, the licensee agrees with the stars recommendation not to utilize their " Watts per foot" methodology but instead to use the existing ampacity margin analysis as the basis that the applicable cables are operating within acceptable ampacity design values as detailed in Enclosure 2.
- Therefore, the commitment made by the licensee fully resolves the stafs concerns.
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-.~ Question 10 In general, the ' Watts per foot" methodology provides an inadequate treatment of the impact of cable loading on the allowable heat loads and assumes those effects are largely irrelevant to the overall heat rejection capacity of the cable tray or conduit system.
Licensee's Response in its submittal of July 24,1997, the licensee stated that the " Watts per foot" review which had been performed for various Thermo-Lag wrapped cable raceways installations will not be utilized to assess the performance of individual cables within the
' wrapped raceways.
illaff Evaluation l The commitment made by the licensee fully resolves the staffs concems.
. Question 11 d
See SNL's discussion in Section 5.2 of the SNL Letter Report dated May 2,1997,
[ Enclosure 2 of staff RAI dated June 30,1997] of the following concerns:
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- Inadequate Treatment of Depth of Fill
- Removal of Conservatism from the Insulated Conductor Engineers Association
~ Ampacity Tables -
- ' . Inadequate Justification for 32 Percent Ampacity Derating Factor As A Bounding Limit 1
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-~ Analysis Failed to Use the Appropriate Ambient Temperature.
- Inadequate Justification for Applicability of the Analysis Method 3 I
' Licensee's Response
-In its submittal of July 24,1997, the licensee did not provide a specific response t'o the subject question.
Staff Evaluation As documented in the licensee's submittal dated July 24,1997, the licensee agrees with the staff's recommendation not to utilize their " Watts per foot" methodology but instead
. the existing ampacity margin analysis will be used as the basis that the applicable cables are operating within acceptable ampacity design values (see Enclosure 3).
Therefore, the commitment made by the licensee fully resolves the staff's concems.
Application of Amnacity Derating Methodology ;
The licensee ampacity analysis is performed in two parts using two different methods of analysis. As detailed in Enclosure 2, the first part of the analysis is based on the following ,
ampacity margin assessment approach:
' Method 1: The licensee assesses the baseline ampacity limits of its installed cables using tabulated ampacity values. These values are then compared to the actual plant ampacity loads, and an available ampacity margin is determined. if this margin is sufficient to bound the ampacity derating impact of the fire barriers, then the licensee appropriately concludes that the plant ampacity loads are acceptable.
- The second part of the licensee analysis or Method 2 was based on a comparison of cable heat l intensity values under various conditions or a " Watts per foot" methodology. As documented ,in irj
the licensee's submittal dated July 24,1997, the licensee agrees with the SNL's recommendation not to utilize this " Watts per foot" methodology but instead the existing ampacity margin analysis will be used as the basis that the applicable cables are operating within acceptable ampacity design. The shortcomings which have been identified regarding the
" Watts per foot" approach far exceeds the advantages of using this method for ampacity derating determination. Further discussion of the concerns regarding Method 2 is detailed in Enclosure 2.
Upon completion of the above analyses the licensee originally assumed that an ampacity
- derating factor (ADF) of 32% would bound all installed Thermo-lag fire barriers. As discussed in Enclosure 2 for the cable tray application the licensee has actually applied a 35.4% ADF to tabulated ampacity limits to allow for both a fire barrier and a solid steel tray cover plate.
In addition, the licensee's response to Staff Question 5 (see above question and response)
. Indicates that the available margins in cable ampacity would be compared against the fire barrier derating factor which was derived from well founded and validated thermal calculations
, or from appropriate experiments. Given the rejection of the thermal calculations associated with the " heat intensity" or " Watts per foot" approach the 32% ADF selected must be consistent with available test data.
The following finding is applicable when the licensee's selection of 32% ADF is compared with available industry test data:
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- The licensee assumption of a 32% ADF is adequate to bound the impact for both one-hour cable tray installations and all conduit applications. For conduits, a range of test results are available, and all indicate conduit ADF values well below the cited 32%. For a one-hour cable tray system, the Texas Utilities Electric (TUE) test results indicate an ADF of 31.6%.
However, the licensee assumption of a 32% fire barrier ADF is not adequate to bound the y impact for a 3-hour cable tray installation. Two sources are cited for this assessment:
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- Florie Nor Corporation (FPC) tested a nominal single layer 3-hour Thermo-Lag cable a
' tray fire barrier system with no upgrades and no tray cover for Crystal River, Unit 3. The -
test results for the subjec* 3-hour Thermo-Lag system was 41.4%.
- Tennessee Valley Authority (TVA) tested an upgraded 3-hour Thermo-Lag cable tray fire barrier system that included a solid tray cover (the upgrade was installed over a nominal single layer 330-1 installation). The test results for the subject 3-hour Thermo-Lag system was 48%.
1 The actual ADF appropriate to the CPS 3-hour tray systems will likely lie somewhere between these two values (41.4% and 48%).~ That is, the FPC result would underestimate the net impact at CPS because it did not include tray covers while the TVA results would be conservative for -
CPS because it involved both covers and an upgrade to the base installation.
Given these observations, the staff recommends that the margin results for a 3-hour cable tray installations at CPS be compared to an ADF impact of 44.3% for the combined cover plus barrier configuration. Given that the licensee has already included a 5% derate penalty for the solid covers in its assessment of the nominal" project ampacity," the cited margins results can be compared directly to the FPC test result of 41.4% for a final assessment of acceptability.
Although a verification had been performed by the licensee based upon the 3-hour fire barrier cited in SNL report SAND 94-016, a review of the licensee's responses on the use of industry
. tested fire barrier results indicates that the licensee ddi not directly confirm that the installed Thermo-Lag enclosed raceways at CPS are representative of the TUE and FPC tested configurations. The licensee should verify and document the applicability of tested fire barrier configurations to installed applicable CPS fire barrier systems.
CONCLUSIONS From the above evaluation, the NRC staff concludes that no significant safety hazards are .
introduced at CPS for. (1) a net 32% ADF for the one-hour and 3-hour conduit fire barrier i
. 2 systems and the one-hour cable tray fire barrier systems; and (2) a net 41.4% ADF for 3-hour cable tray fire barrier systems. Therefore, the staff requests that the licensee respond in writing addressing this issue. In addition, the staff finds that the licensee should verify that the -
Thermo-Lag enclosed electrical raceways are installed and constructed in a manner representative of the applicable tested fire barrier configurations (i.e., TUE and FPC ampacity derating test configurations) from which the 32% and 41.4% ADF values were derived. Include a discussion of your approach in this area in you
- response.
Principal Reviewer: R. Jenkins Date: March 27, 1998 4
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A Technical Evaluation of the Clinton Power Station Fire Barrier Ampacity Assessments A Later Report to the USNRC Revision 0 May 2,1997 l
Prepared by:
Steve Nowlen
, Sandia National Laborsfries Albuquerque, New Mexico 87185-0747 (505)845-9850 l
I Prepared for:
Ronaldo Jenkins Electrical Engineering Branch OfEce ofNuclearReactor Regulation U. S. Nuclear Regulatory Commission Washington,DC 20555 USNRC JCN J-2503 Enclosure 2 wem,m
. TABLE OF CONTENTS:
I SAGlion P.agn 4 FORWARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
1.0 INTRODUCTION
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 l .1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .
1.3 Organization of Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 2.0 OVERVIEW OF THE UTILITY AMPACITY APPROACH . . . . . . . . . . . . . . . 2 2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.2 Basis for Estimated Fire Barrier Derating Impact . . . . . . . . . . . . . . . . . . . . . 3 2.3 A Summary of the CPS Margins Analysis Results. . . . . . . . . . . . . . . . . . . . . 4 -
. 2.4 The Licensee Heat Intensity Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.0 REVIEW OF THE LICENSEE RAI RESPONSES . . . . . . . . . . . . . . . . . . . . . . 6 3.1 RAI Item 1: Ambient Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 RAI Item 2: Cable Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3 RAI Item 3: Cable Designations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.4 RAI Item 4: The Heat Intensity Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.5 RAI Item 5: Appropriateness ofBarrier ADF Values . . . . . . . . . . . . . . . . . . 7 3.6 RAI Item 6: Cables IDG29A and IDG30A . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.7 RAI Item 7: Fire Breaks Versus Protective Barriers . . . . . . . . . . . . . . . . . . . 8 3.8 RAI Item 8: Under-Voltage and Motor Overloads . . . . . . . . . . . . . . . . . . . . 8 3.9 Summary ofFindings on RAI Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.0 A REVIEW OF THE LICENSEE MARGINS ASSESSMENTS . . . . . . . . . . . 10 4.1 Overview and Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2 Fire Zone A-l a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3 Fire Area C-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 4.4 Fire Zone CB-l e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1
" 4. 5 Fire Zone CB-i f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 l 4.6 Fire Zone CB-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.7 Fire Area D-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.8 Summary ofMargins Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1
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- FORWARD The 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 ofsubmittals from the Clinton Power Station (CPS) nuclear plant. These 1 submittals deal with the assessment of ampacity loads for cable trays and conduits !
. protected by Thermo-Lag 330-1 fire barriers.' This report represents the second in a series ofreports for the CPS ampacity assessments. The original documents reviewed by SNL were submitted by the utility in response to USNRC Generic Letter 92-08. An initial i review report was prepared by SNL May 16,1996, and in August 1996 an RAI was forwarded by the USNRC to the licensee requesting resolution of the review findings.
The current report focuses on an assessment of the licensee's RAI response, and on an overall assessment of the adequacy of the licensee's ampacity treatment. This work was perfonned as Task Order 2, Subtask 5 of USNRC JCN J-2503.
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1.0 INTRODUCTION
1.1 Background
In response to USNRC Generic Letter 92-08, the Clinton Power Station (CPS) nuclear plant provided h=aawton of the utility position regarding ampacity derating factors associated with its installed Thermo-Lag 330-1 fire barrier systems. His information wu contained in a letter dated November 3,1995 from J. G. Cook, Blinois Power / CPS, to the USNRC Dw=aa' Control Desk, item U-602512 and included six eMe#--T =& SNL was requested to review the ampscity derating aspects of these submittals under the terms of the general technical support contract JCN J-2017, Task Order 8, Subtask 5.
A letter report d&-ting the results of SNL's review was submitted to the USNRC on May 16,1996. Iargely on the basis of the SNL review findings, an RAI was forwarded by the USNRC to the licensee on August 16,1996. Helicensee response to this RAI was provided on March 31,1997.
1.2 Objectives This letter report documents SNL's findings and recommendations resulting from a review of the licensee RAI response. The report also provides an overall assessment of the adequacy of the licensees treatment of ampacity loads for fire barrier clad cables.
It is important to note that, consistent with the statement ofwork for this effort, the SNL review has been limited to those portions of the utility submittals directly related to the issue of ampacity derating only. The utility submittals include documentation of other aspects of the Thermo Lag issue including quality control and fire performance issues.
SNL has not reviewed these portions of the documents.
1.3 Organization ofReport This review has focused on a review of the licensee's specific RAI responses, and on an overall assessment of the adequacy of the licensee's treatment. Section 2 provides a summary overview of the licensee's ampacity derating process and results. Section 3 of this report provides a point-by-point review of the licensee's RAI responses. Section 4 provides SNL's findings regarding the acceptability of the individual fire area ampacity assessments cited in the licensee study. Section 5 provides for a r'eview of the licer.see calculation of fire barrier ADF, Calculation 19-AI 08, and also discusses in more detail the licensee response to RAI item 4 and those aspects of the licensee " heat intensity" analysis method that have not been adequately resolved by the RAI process. Section 6 summarizes the SNL findings and recommeadalons.
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'2.2 Basis for Estimated Fire Barrier Derating Impact The licensee has assumed a fire barrier derating impact of 32% for all installed fire barriers including both I-hour and 3-hour and both tray and conduit barriers. As discussed above, in practice for cable trays the licensee has actually applied a 35.4% ADF to tabulated ampacity limits to allow for both a Sre barrier and a solid steel tray cover plate. The basis for the 32% fire barrier ADF is a licensee calculation,19-AI-08, which was provided as Enclosure 4 to Attachment 2 of the licensee RAI response and is reviewed in more detail in Section 5.3 below. The value is cited as an estimate of the ADF impact of a 3-hour cable tray Sre barrier syuem which bounds the impact for the 1-hour tray and the conduit applications.
In summary, SNL Snds that the licensee calculation has resulted in a non-conservative estimate of the derating impact of a 3-hour Thermo-Lag cable tray Sre barrier system.
This finding is based on a comparison of the licensee results to available test data. Based on this comparison SNL makes the following SaMa==:
The licensee assumption of a 32% ADF is adequate to bound the impact for both 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> cable tray installations and all conduit applications. This Snding is based on a comparison to available test results. For conduits, a range of test results are available, and all indicate conduit ADF values well below the cited 32%. For a 1-hour tray system the Texas Utilities Electric (TUE) results are cited as indicating an ADF of 31.6%.
The licensee assumption of a 32% fire barrier ADF is not adequate to bound the impact for a 3-hour cable tray installation. SNL cites two sources for this assessment:
Florida Power and Light (FPL)' Crystal River tested a nominal single layer 3-hour Thermo-Lag cable tray fire barrier system with no upgrades and no tray cover. The tested ADF was 41.4%.
Tennessee Valley Authority (TVA) Watts Bar' tested an upgraded 3-hour Thermo-Lag cable tray fire barrier system that included a solid tray cover (the upgrade was installed over a nominal single layer 330-1 installation).
The tested ADF was 48%.
The actual ADF appropriate to the CPS 3-hour tray systems will likely lie somewhere between these two values (41.4% and 48%). 'Ihat is, the FPL result would underestimate the net impact at CPS because it did not include tray covers while the TVA results would be conservative for CPS because it involved both covers and an upgrade to the base installation.
' Aspects of the FPL tests are proprietary, but a non-proprietary version of the test report is available in the USNRC public document room.
8 See TVA submittal to the USNRC document control desk of Apnl 25,1995.
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- However, as discussed further in Sectisn 5.2 belsw, SNL remains unconvinced that this is an appropriate basis for analysis. SNL must continue to recommend that this aspect of the licensee analysis not be credited by the USNRC, and that this approach to analysis be viewed with significant scepticism.
However, SNL also Snds that this part of the analysis is not needed to support an assessment of the licensee's cable ampacity. Rather, the margins analysis is sufficient in and ofitselfto support the conclusion that cables at CPS are operating within acceptable limits. It is SNL's recommendation that further interactions to resolve our concerns related to this analysis method are not warranted. SNL has concluded on the basis ofthe margins analysis that the licensee has demonstrated adequate margin for all ofits fire barrier clad cables. SNL recommends that our concerns simply be noted for the record.
4 Svnopsis of Licenea, Raennnae The licensee has clarified that these two designations are equivalent to #9 AWG and #12 AWG cables respectively.
Findinen and R=.c.....endations This response is adequate to resolve the identified concern. No further actions on this RAI item are recommended.
3.4 RAIItem 4: The Heat Intensity Method Svnopsis of Can-n: h licensee was asked to further clarify and justify its heat intensity -
based cable ampacity analysis method and results. Five specific points ofconcern were identified:
a) inadequate treatment ofdepth offill, b) removal of conservatism from tabulated ampacity limits, c) inadequatejustification for an assumed 32% ADF as a hanadian limit, d) deviation from a testing based approach without adequatejustification, and e) inadequatejustification for applicability of the heat intensity analysis method.
Synopsis of Licennee Rennonte: The licensee has provided an extensive response to the identified concerns (over eight pages of additional discussion). Hence, providing a concise synopsis of this response is rather difficult. A detailed discussion of the licensee response will be deferred to Section 5.2 below.
Findings and Recommendations A detailed review of the licensee response to this RAI item is provided in Section 5.2 below. In summary, while SNL finds that the licensee response has not adequately resolved certain of the most critical concerns, SNL also recommends that no further actions to resolve these concerns is warranted at the current time. In particular, a review of the licensee margins analysis has shown that all of the cables considered are operating within acceptable ampacity limits. The licensee heat intensity analysis is not needed to reach this conclusion, and hence, resolution of the identified concerns will not significantly cont.ibute to an assessment of the ultimate acceptability of the licensee's ampacity loads.
3.5 RAIItem 5: Appropriateness of Barrier ADF Values Synopsis of Concern: The licensee was requested to furtherjustify the applicability of the cited ADF factors for the fire barrier installations at CPS.
Synopnin of Licennee Ra=nanaa The licensee response again cites the supporting calculation for ADF 19-AI-08, and provides limited discussion explaining that this value was considered to bound all of the CPS conduit and tray "mstallations.
Findinen and R=.....c.2ndatta== This response is adequate to resolve the identified concern as expressed in this RAI item. 'Ihat is, the licensee has made clear that its intent was to apply a single ADF value that would bound all of the fire barrier installations including both trays and conduits. While SNL does not consider the cited value of 32% to adequately bound the 3-hour tray systems, the value will bound both I-hour trays and all conduit installations. No further actions on this RAI item are recommended.
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, ps response is adequate to resolve the identified concern. No further actions on this RAI stem are recommended.
3.9 Summary ofFindings on RAIResponses SNL Snds that with the exception of RAIitem 4, the licensee has provided responses that 4 adequately resolve all of the identified concerns. With regard to RAI item 4, this item dealt exclusively with the licensee heat intensity analysis methodology. As is discussed in Sections 2.3,2.4, 4, and 5.2, SNL Bnds that the heat intensity analyses are not needed to support the conclusion that all of the cables considered are, in fact, operating at acceptab ampacity levels. Hence, SNL recommends that further actions to resolve the open items with respect to this methodology are not warranted. No further actions on any of the RAI items have been recommended.
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3 .
- e operation and construction. Fan motors are sized to handle the maximum rated flow rate under unrestricted operation. Unlike pumps, when the air Bow rate of a fan is restricted, the motor load actudy decreases because the fan itself will tend to " free wheel" and will actudy move less air and hence do less work.) Given this, SNL finds that only the under-voltage condition is considered probable. This might result in a minor overload for a limited time period, but given the times and intervals involved as well as the demonstrated tray load diversity, SNL recommends that the cited margin of 31.4% is acceptable.
Hence, for this fire area, SNL finds that the licensee had demonstrated an adequate margin for the installed cables.
4.3 Fire Area C-2 Fire Area C-2 contains several cables in both trays and conduits, all wrapped with 1-hour fire barriers. Hence, screening based on a 32% ADF is appropriate for all clad cables in this area.
All but one of the cables in this area were identi6ed as having an available margin in excess of 50% based on the nominal current loads with one exception. The licensee has also considered a re assessment that includes a 1.25 load factor for all non-resistance type loads. The one exception is considered by the licensee as follows:
Cable ISC02B is a pump motor feed cable for the Standby Liquid Control system.
The cited nominal margin for this cable was 23.75%. This is signi6cantly reduced i if a 1.25 load factor is applied. However, the licensee has provided two alternative assessment bases for this cable. The Erst is based on the limited time operation of l this cable; no more than two hours at a given time under any conditions 'Ihe second is based on a relaxation of the depth of fill assumption to actual depth of fill. This second assessment yields a modified margin of 36.5%, even including the 1.25 load factor. SNL finds these reassessments acceptable, and finds the second reassessment especially telling in this regard given the more solid quantitative nature of the result. SNL recommends that given that a margin of 36.5% has been
- demonstrated, even including a 1.25 load factor, that this cable is operating under
. acceptable conditions.
SNL Snds that the licensee assessment for the clad cables in this area has demonstrated an acceptable margin for d cases.
4.4 Fire Zone CB-le !
All of the Sre. wraps in CB-le are 1-hour barrier systems. Hence, screening based on a 32% ADF is appropriate for the clad cables in this zone. The initial licensee assessment for this area iemonstrated a minimum margin of 35% for all cables based on nominal load ratings and operation. Hence under nominal operating conditions all cables are found to L be acceptable based on the screening against a 32% ADF.
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nominal margin cf 37.71%. Ifthe ADF is raised to 41.4% as recom SNL then these cables would bejudged to be nominally overloaded SNL does not recommend that additional interactions on thes warranted for the following reasons:
A note to the licensee's original submittal analysis cites that these cables are each carrying a common load in parallel with other cables (IVLolB and 1VLO2B) Hence each cable carries nominally 50% of the device load.
However, the base analysis assumed that each cable carried 55% of the device load to allow for a conservative bound on length mis-match. This -
implies an additional 10% margin of conservatism in the analysis (55%
50% implies the assumed is 110% of the actual). Hence, if this conservatism is relaxed, impact. the actual cable margin would, in fact, exceed the anticipa In addition SNL notes that the nominal overload for these two cables f modest, on the order orjust 3-4%. Further SNL notes that this tray has a very significant level orload diversity, even if all of the cables in the tray operating at the full load currents. Based on the information provided in the licensee's submittal of11/3/95 there are a total of26 cables in this tray 3 these 26 cables half (13) are operating at less than 25% of the nominal ra ampacity limit. In fact six cables are operating at less than 1% ofthe rated ampacity, and an additional three are operating at less than 10% of the rated ampacity. While it is dif5 cult to quantify the actual ampacity gain that would result from this diversity, it is SNL'sjudgement that for this case it would be sufBeient to allow for the modest overload on these two cables.
SNL this particular recommends case. that the licensee demonstrated ampacity margin is ac Two additional cables are shown to have margins in excess of 41.4%, even considering a 1.25 load factor.
One additional cable is dismissed based on the relaxation of the assu condition to reflect the actual cable load. This case involves c l is a DC load feeder for a calibration lab. The cable is used only to provide cunents in calibration activities. Ncrmally there is no load on the table, but the
. licensee assessment is based on an assumed load of 12 amps, or 80% of the I
breaker rating. When a 1.25 load factor is applied, a 15A load is postul the available margin is reduced to 6.2%. SNL concurs with the licensee assessment that this cable is unlikely to ever be loaded to this level. Further, obviously a non-safety grade cable and hence is ofno real safety significanc recommends that this assessment be accepted as adequate.
The last cable, IVWO3A is shown to have a nominal margin of almost 50%
normal load conditions, but only 37.3% if a 1.25 load factor is considered. SNL recommends that this is sufficient margin in this case because the load is assoc with a motor driven fan. As noted above, fans are not likely to experience {
significant motor overloads due to the nature of the fan design andl opera 13
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. 5.0 A REVIEW OF THE LICENSEE SUPPORTING CALCULATIONS 5.1 Overview j i
The licensee has provided two principal suppoinng calculations as a part ofit submittal )
package. The first hmaaved an alternate licenace analysis approach based on cable heat intensity. This calculation was provided as a part orthe original licensee submittal of I 1/3/95, and was the subject ofconsiderable discussion in SNL's review report of l
5/16/96. Section 5.2 provides a brief summary discussion of those areas of the calculation I that SNL Snds remain open (unresolved) even given consideration of the licensee's RAI responses.
1 The second caled4 was performed by the licensee in order to estimate the ADF impact of a 3-hour cable tray Sre barrier system. This calculation was requested in the RAI, and was provided by the licensee in its RAI response. A review of this calculation is provided in Section 5.3. j 5.2 The Licensee Heat Intensity Analysis 1'
One part of the licensee submittals had documented an analysis approach based on a comparison ofplant design cable heat intensity limits to those observed in one SNIJNRC clad case ampacity test. In its previous review, SNL had raised a number of points of concem associated with this methodology. The licensee was asked to respond to these concerns in RAI item 4. The objective of this section is to review the licensee RAI response for item 4, and to reassess the SNL position regarding this approach to analyris.
RAI item 4 had requested clarification of and additional justification for the proposed methodology. In particular, the licensee was specifically asked to address five points of concern:
a) inadequate treatment of depth of fill, b) removal of conservatism from tabulated ampacity limits, c) inadequatejustification for an assumed 32% ADF as a bounding limit, d) deviation from a testing based approach without adequatejustification, and e) inadequatejustification for applicability ofthe heat intensity analysis method.
The licensee response included both a general response to the SNL identi6ed concerns, and speci6c responses for each of the Eve specific points identified in ths RAL The following six sub sections, 5.2.1-6 provide for a brief review of each of these parts of the response. The final sub-section,5.2.7, provides a summary of SNL's current findings and recommendations regarding this method.
5.2.1 Insights Based on the Licensee's General Response
'Ihe first point addressed in the licensee's general response appears to be based on a 7' misunderstanding of SNL's 6ndings. That is, the licensee provides a redefinition of the i
term heat intensity and discusses the fact that this approach derives fre,m Stolpe's work.
SNL is well aware of this fact, and indeed cited this in its own reviev;. SNL has no 15
the net results cf the licensee heat ary ,
intensit to ampacities are based on the ICEA tables can be made more transparent by similarly evaluating the measu SNUNRC clad case test in comparison to these same ICEA ta two cases can then be compared directly. Consider:
In effect the licensee has taken the tabulated ampacity (or hea for an assumed 50*C versus 40*C ambie the licensee has applied a net ACF of(ACF,,=0.95*0.90*0.68=
ADF of41.9%. This is the ultimate basis for the licensee cite ampacity" or" CPS design" limits.
- The licensee compares these limits to the SNUNRC clad test am intensity) ss taken directly from the test measurements. Ifthose res compared to the same ICEA tables then the SNUNRC test results re derating of the ICEA limits by 17.0-28.8% depending on the cable siz intensity comparisons are simply showing na th 17.0-28.8% ADF, and nothing more. All ofthe intermediate dis confuse this ultimate result. All of the licensee resul on this difference in ADF values.its individual case analyse Whether or not the 41.9% ADF is sufficient to conservatively boun{
ambient temperature, the tray covers, and the fire barrier ha this analysis unless one accepts that (1) the SNUNRC pa eclad cas as a direct mem=re of the actual clad case ampacity limits fully i ampacity tables or any ADF values (2) the licensee relaxation of the 5 and (3) that the direct extrapolation of these r ,
the SNUNRC test results is insufficient to s interpretation and extrapolation of the results.
- Ihese values use the licensee calculated mNEMA s or the
/ICEA amp j
as the base line condition, and the measure , .
.thethe SNUNRC base line test were higher inherent conservatism in the ampacity tables.
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)
b___. -
.' SNL also noted that the licensee re+;+3= has included a discussi:n cf a "Wttts per foot"
, analysis ofits clad cable trays and conduits. SNL does not credit this aspect of the analysis. "Ihe licensee cites that this step is perfonned to assess whether or not the total load on the system is sufficient to cause general aging concerns. SNL NamaMiy disagrees with this assessment. The licensee also cites its individual cable assessments as determining whether on not individual cables are loaded sufficient to damage themselves.
It is this aspect of the licensee assessments that SNL considers appropriate. If all of the individual cables are operating within acceptable limits, then the tray or conduit as a whole is acceptable. If an individual cable is operating at excessive ampacity loads, then all ofits co-located neighbors are also potentially subject to accelerated aging (because they may came into contact with the overloaded cables at some point, and at that point premature aging could be experienced). The " Watts per foot" method, in SNL's view, provides no new or useful information and should not be credited.
5.2.6 Inadequate Justi6 cation for Analysis Method.
The licensee response to this concern cited that the method was based on the methods of Stolpe. While this is nominally true, Stolpe did introduce the concept of heat intensity, the licensee application of this concept is not consistent with accepted ampacity derating approaches. The licensee has not adequately addressed this concern in its response.
In particular, it was SNL's concern that the licensee has not validated its approach to direct application of test-based heat intensity limits for clad cable trays to actual cable ampacity assessments. While the licensee cites a long passage from Stolpe's paper, the licensee apparently fails to appreciate that Stolpe's work is backed up by a whole series of tests as well as thermal modeling results. The licensee comparison to a single test with significant and known shortcomings cannot compare to Stolpe's extensive validation efforts. The additional explanations offered by the licensee have offered no new information to alter SNL's finding that this approach lacks a sufficient basis for validation to allow for its general application as an ampacity assessment method for clad cables.
5.2.7 Summary of Findings and Recommendations In summary, while the licensee has provided some new insights into its intentions and approach to analysis, SNL stands by its earlier recommendations. SNL recommends that this aspect of the licensee analyses should not be credited without significant additional review and validation, and that this approach to the analysis ofclad cable ampacity limits should be viewed with scepticism. The licensee has not addressed SNL's most fundamental concems which are:
The licensee comparisons are inappropriate in that the compared limits represent a mixture ofinstallation conditions.
The licensee =4~I, in effect, results in the comparison of project design ampacity limits for a clad cable to a single clad case ampacity test result, and in fact, to a test result with known significant shortcomings.
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3 m In principal, this cpproach can be made to work acceptably under the prope circumstances It is for example somewhat similar to the approach taken by its own ampacity assessments.' However, there appear to be very significant d that have the potential to seriously compromise, orsven invalidate, the CPS implementation of this approach. Fundamentally, the licensee las not demonstr this approach to analysis is appropriate for CPS as will be discussed further below The bottom line on this calculation is that it has yielded a non-conservative estimat fire barrier ADF. The licensee results have found an ADF of32% fo system. However, in recent years a number ofampacity tests have been performed, hence, a set ofdirect experimental results are available. Ofthese, three are conside especially relevant (as cited in Section 2.2 above):
TUE tested a 1-hour Thermo-Lag cable tray Sre barrier system and found an A of 31.6%. A three-hour system should yield an ADF somewhat larger than this value. ,
FPL tested a 3-hour single layer Thermo-Lag cable tray fire barrier system wit upgrades and no tray covers and found an ADF of41.4% for this configuration The CPS barrier should have a modestly higher ADF impact because of the presence of the solid tray covers not included in the FPL test.
TVA tested a 3-hour single layer Thermo-Lag cable tray barrier system that included both material upgrades and solid tray covers and found an ADF of4 This test would be conservative in comparison to the CPS barrier because ofth material upgrades.
Given these results, SNL finds that the licensee's conclusion that 32% would bou impact of a 3-hour barrier is not conservative and is not acceptable. Th limit would, however, be adequate to bound for the 1-hour tray installations, a CPS conduit installation.
In its review SNL has not attempted to provide a thorough and complete asse aspects of the licensee model. In panicular, SNL has made no attempts to confirm the actual numerical results, to reproduce the model as implemented by the licens implement a modified version of the analysis model.
There are many factors that might have contributed to the licensee's non-conse result. Based on SNL's limited review, it is suspected that the following factors ha likely contributed to the non-conservative nature of the final ADF estimates:
The licensee base line condition is based on a direct application of tabulated
' intensity limits, presumably derived from Stolpe's work, to a specific test re and to a speci6c thermal model. However, the licensee has not demonstrate
'See Braidwood submittal to the USNRC document control desk of , .
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s The licensee has assumed a relatively low value for the emissivity of the galvanized tray surfaces and covers (0.23). Galvanized materials will have emissivity values as high as 0.8 under realistic conditions. It is unclear based on SNL's review which extreme would be more conservative in this context. Some demonstration that the licensee treatment is conservative should be provided as a part of the analysis.
1 In calculating the allowable heat load the licensee has applied an area correction J factor of n/4 to it's total cable mass cross-sectional area calculation (AMa*wgx/4) which may be inappropriate. nere are two ways to calculate depth of fdl, one used by Stolpe based on the circular cross-section of a cable, and ) '
the second used in the ICEA tables based on a surrounding square section for each cable. De difference between the two is, indeed, s/4. However, the depth offill and heat intensity limits should be self-consistent at the outset. Applying an ,
additional correction at this stage of the analysis appears inappropriate, but )
because the licensee has cited a LaSalle Station calculation not provided for SNL i review as the basis of the heat intensity, this aspect cannot be verified as correct or incorrect. (Note that this cannot account for the heat intensity discrepancies ;
identified immediately above as correction of the heat intensity limit using the same n/4 factor still yields a significant discrepancy in comparison to either Stolpe or the ICEA).
One additional discrepancy that was noted is that in the thermal model the licensee ,
has assumed a 15% derating for its solid steel covers, but in the development of j the licensee " project ampacity" limits, only a 5% derating was applied for the solid tray covers (see licensee Calculation 19-G-1). In this sense, the two calculations ,
appear inconsistent and incompatible. )
i It is likely that a combination of these factors has led to the licensee's non-conservative j
ADF result. Of most significance are the issues of thermal model self-consistency. This is an especially critical aspect of an ampacity model. An analysis of this type should, at a minimum, provide for a direct validation ofits self-consistency. In this case, this would require a direct validation of the assumptions made regarding the base line heat intensity limits and the licensee treatment of extemal heat transfer procesa (the correlations for convection, crediting of the sides in the heat transfer process, and the values of emissivity chosen in the model).
As was noted above SNL does not recommend that any additional licensee interactions be undertaken to resolve these concerns. SNL has determined that the CPS cables that are housed in the 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> cable tray barriers do have adequate margin to allow for a 41.4% or higher derating. Hence, the licensee has demonstrated adequate ampacity based on the margins analysis approach. Given this, the role of these results in the licensee analysis is rendered moot.' It is recommended that these concerns be noted "for the record" only.
.~., ,
. identical fire barrier system was found to be 41.4%. Several points of potential concern in
, the licensee model have been identi6ed by SNL in text above.
It is SNL's recommendation that this calculation not be credited as a realistic estimate of the Src barrier ADF impact. However, no specific interactions to resolve these concerns are recommended. This is because:
SNL finds that the 32% ADF assumed by the licensee is adequate to bound the 1-hour cable tray barriers and all of the conduit barriers that represent the bulk of the licensee installations, and
- For the one fire area containing 3-hour cable tray barriers SNL has compared the licensee margins results to the higher screening value of 41.4% ADF and found that all cables did have adequate margin.
In the broader context, while the licensee has itself applied a non-conservative screening value to its 3-hour tray barriers, the supplemental SNL assessments have concluded that all of the cables do have adequate margin. Hence, the resolution of SNL's concerns regarding the licensee ADF calculation is not considered especially important. SNL recommends that these concerns simply be noted "for the record."
6.4 Summary of Findings on Licensee Heat Intensity Analysis The licensee submittal included a number of supplemental ampacity assessments based in essence on a direct comparison of the heat intensity from a single SNUNRC clad case ampacity test to the heat intensity obtained using the licensee cable design method. While the licensee has provided some additional insights into their intent and approach, SNL finds that a number of the most critical concerns have not been addressed adequately.
SNL's recommendations regarding this method have not changed substantially. SNL continues to recommend that this aspect of the licensee analysis not be credited without significant additional review, assessment and validation. Further, while SNL has no difficulty with appropriate applications of the heat intensity method, this particular 1 approach to a heat intensity analysis should be viewed with scepticism.
Offsetting this finding is the fact that, fundamentally, SNL considers this aspect of the analysis to be entirely unnecessary. As noted in 6.1 above, the margins approach is sufEcient in and ofitself to resolve the ampacity load concerns, and has in fact demonstrated adequate margin for all of the Ere barrier clad cables at CPS. No further I analysis is required to demonstrate adequacy of the cable loads.
Given these findings, SNL does not recommend additional interactions with the licensee at this time to resolve the open concerns related to the heat intensity approach as applied by the licensee. Only if the same methodology is invoked by another licensee, or if the methodology is re-introduced by CPS for subsequent analyses that do not satisfy the margins analysis approach would a need arise to resolve the identified concerns. It is recommended that SNLs concerns regarding this method should be noted for the record only.
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