U-602720, Provides Response to NRC Request for Addl Info Re Thermo-Lag for Ampacity Derating Issues for GL 92-08, Thermo-Lag 330-1 Fire Barriers & IE Info Notice 94-022
| ML20137L106 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 03/31/1997 |
| From: | Connell W ILLINOIS POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20137L112 | List: |
| References | |
| GL-92-08, GL-92-8, IEIN-94-022, IEIN-94-22, IEN-94-22, U-602720, WC-158-97, NUDOCS 9704070156 | |
| Download: ML20137L106 (22) | |
Text
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tihnois Power Compsny -
~f Clinton Power Station --
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P.o. Box 678 - ;
. Clinton,IL 61727 i
' P{ , - Tel 217 935-5623 1l lJ i (
, s Fax 217 935-4632 - l
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'l Wilfred ConneH E NMS' -
PGWER v'c' El "s'**d*"'
March'31', 1997 WC-158-97 i
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r Docket No. 50-461 ,
i Document Control Desk ~ .
Nuclear Regulatory Commission !
Washington, D.C. 20555
Subject:
Illinois Power's (IP's) Response to the NRC's !
Request for Additional Information (RAI) Regarding Thermo lio Related Ampacity Deratine Issues !
i
Dear Madam or Sir:
j This letter provides IP's response tc the NRC August 16,1996, RAI regarding l Thermo-Lag related ampacity derating issues for Generic Letter (GL) 92-08, "Thermo- i Lag 330-1 Fire Barriers." This response was committed to in IP letter U-602646 dated j October 9,1996.
IP believes that more than an ample ampacity derating has been applied to Thermo-Lag wrapped cable at Clinton Power Station (CPS). This was discussed in the IP response to the 1995 RAI(U-602512 dated November 3,1995). This is due to the fact that the cables are rated using a conservative methodology. Although the
. percentage of derating applied for Thermo-Lag is less than that reported in NRC IE Information Notice 94-22, the total overall derating of cable at CPS limits allowable curret to ensure low heat production. Therefore, accelerated aging of the cables due to tl e hermo-Lag wrap will not occur.
1 Due to the technical nature of this issue, the information requested is included in l Attachment 2. The eight NRC questions are quoted in bold and IP's response follows the question. If there are any questions or areas needing clarification, please have the NRC Clinton Power Station Project Manager contact Paul Telthorst of my staff. It is I IP's desire to answer or clarify any portion of this response as needed. d f(D71 <
9704070156 970331 P
M ADOCK 050004611 PDR[" M.U N N
a 4 e e U-602720 .i Pagc2 {
Attachmen: 1 provides an affidavit supporting the facts set forth in this letter. ;
- i Sincerely yours, i
l
/. Connell V 1 l ;
Vice President .
) JSP/krk Attachment i t
cc: NRC Clinton Licensing Project Manager !
NRC Resident Office, V-690 '
Regional Administrator, Region III, USNRC ;
- Illinois Depanment of Nuclear Safety e
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. /1.achment 1 to U402720 J
John G. Cook, being first duly sworn, deposes and says: That he is the Senior Vice '
President at Illinois Power; that this letter supplying information for this Request for Information to Generic Letter 92-08 has been prepared under his supervision and . !
direction; that he knows the contents thereof', and that to the best of his knowledge and belief said letter and the facts contained therein are true and correct.
P Date: This 3 I day ofMarch 1997.
Signed: .
U John G. Cook r
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Subscribed and sworn to before me this dl day ofMarch 1997. j j
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Attachment ?
to U-602720 Page 1 of14 4
Responses to NRC Requests for Additional Information on Ampacity Deratina Issues Related to Thermo-Lam Installations
- 1. Specify the assumed ambient temperature for each fire area and provide justification for each assumption. The ICEA tables for cable ampacity are based on 40'C ambient and an adjustment will be required for different ambient temperatures.
There are five fire areas under discussion. These areas are A-la, C-2, CB-le, CB-If and D-8. The normal ambient temperatures for these areas is from 65 F to 104"F (18'C to 40*C) except for area D-8 which has a normal ambient of-2 F to 97'F (-19 C to 36 C). These values are taken from DC-ME-09-CP Revision 11, Equipment Environmental Design Conditions, Design Criteria and are listed in Section 3.11 of our Updated Safety Analysis Report (USAR). For areas CB-le, CB-If, and D-8 there are no area temperature changes as a result of accidents. For area A-la, a loss of off-site power event lasting for 100 days will result, during summer, in a maximum temperature of 128 F (53'C) and, during winter, in a minimum temperature of 47'F (8 C). For area C-2, a Drywell LOCA will result in a peak temperature of 185'F (85'C) in the first day of the event and this will then decrease to the normal temperature over the 100 day post-accident duration.
From the Sandia letter report attached to this RAI, it appears that the Sandia personnel ,
believe that Clinton Power Station (CPS) has assumed an ambient of 40 C in our baseline l ampacity calculations. The following should clarify ambient temperature concerns. The l CPS project ampacities are based on an assumed ambient temperature of 50 C. This ambient temperature value is shown in our calculations and stated in our USAR (Table 8.3-12). Per the guidance ofICEA P-54-440, this results in a lower allowed ampacity.
The additional 10 C was added in the ampacity calculations to account for any cable routing that might pass through a plant area with a higher ambient temperature. As indicated above, all of the areas with Thermo-Lag have a upper ambient temperature value of 40"C. This represents an additional conservatism in the CPS analysis of Thermo-Lag impact on ampacity for all zones except D-8 (where the 40 C value was utilized in the analysis). 1
- 2. Provide details of baseline ampacity for tray and conduit including pertinent information (cable types, characteristics, outside diameter, ambient temperature, I depth of fill or percentage fill, conduit size, conduit fill, etc.) used to determine the baseline ampacity.
The baseline ampacity for cables in tray is established in calculation 19-G-01 (copy included as Enclosure 2 to this Attachment). This is also where the ampacity values in USAR Chapter 8, Table 8.3-12 come from. The ampacity values for cable in conduits were documented in calculation 19-G-02 (copy included as Enclosure 3 to this Attachment).
- A Attachment 2 to U 602720 Page 2 of14 l ,
i
) Also, specify the fire barrier ampacity derating factors for each raceway configuration.
Calculation 19-AI-08 (copy included as Enclosure 4 to this Attachment) established the derating factor for a three-hour Thermal Science Inc. (TSI) tray wrap to be 32%. This is the only configuration for which CPS has a site specific calculation. The installations in t areas A-1a, C-2, and CB-le are trays with one-hour wraps of Thermo Lag and D-8 is a conduit installation with a one-hour wrap of Thermo-Lag. The tray in area CB-If has a
' three-hour wrap of Thermo-Lag. Since most of the installations are of the one-hour value with thinner layers of Thermo-Lab, the use of the derating factor established for the thicker three-hour wrap will provide a conservative review standard.
- 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 "
440 tables.
The cables referenced are #9 AWG and #12 AWG respectively, with class C stranding (19 strands) of the tinned copper conductor. They have EPR insulation and CSPE jacketing on the conductor with an overalljacket of CSPE on the cable. The ampacity values for
- 19/22 AWG and #19/25 AWG are based on the values listed for #9 AWG and #12 AWG cable sizes in the relevant tables in ICEA P-54-440. The diameters of these CPS cables i are as follows:
i
- . 3/C,19/22 AWG,1KV has a diameter of 0.723";
i 3/C,19/22 AWG,600V has a diameter of 0.656";
2/C,19/22 AWG,'600V has a diameter of 0.62";
2/C,19/25 AWG,600V has a diameter of 0.514",
- 4. The " heat intensity" method is a departure from the accepted ampacity derating
- approach. Generally accepted practices are determination of ampacity derating j factors based on the results of either experiments or analysis. The following
- concerns were identified in the " heat intensity" analysis method (see attached report for details):
Before responding to the concerns a. through e., listed below, some clarification needs to be made with respect to the methodology used in the CPS evaluation. The purpose of the analysis performed was to determine if there were any installations where the cables
- produced enough heat to cause a potential concern requiring more detailed examination.
~
Sandia's comn ents seem to indicate a concern with the use of the term " heat intensity" and any reference to the ampacity derating values published by the NRC in IE Information
. Notice (IEIN) 94-22 and Sandia in SAND 94-0146.
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Attachment 2 i
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The first issue to consider is " heat intensity. This term is utilized by Stolpe in his paper .
"Ampacities for cables in randomly filled trays." _ Stolpe uses the concept of standardizing the maximum allowable heat generation throughout the cable mass in the tray to avoid j localized hot spots.- This assumes that every cable in the tray is energized. Since the value established is the allowable value when every cable in the tray is energized to the derived l limit and producing the maximum allowed heat, this provides a conservative point to !
evaluate against.' When an evaluation of cables in a tray shows the majority of the cables unloaded and producing a negligible amount of heat while the heaviest loaded cable (s) is still below that derived limit, the lack of heat from the unloaded cables represents another .
conservatism in the evaluation process. !
l The next issue to address is the objections of references to the derating numbers from the l NRC in ISIN 94-22. The Sandia letter spends almost half a page quoting disclaimers from !
SAND 94-0146. Similar reservations were voiced about the results of these tests in the j
- ampacity evaluations attached to the 50.59 reviews. However, the NRC did not include !
similar disclaimers within IEIN 94-22. IEIN 94-22 ampacity derating values were j significantly larger than the values used at most sites, including CPS. At CPS, the smaller derate values were compared to the IEIN 94-22 deratings. This presented several !
problems including lack of physical data on the cables listed in the IEIN and that CPS does !
not use one conductor (1/C) cables in their trays. Presented with the question, the !
Nuclear Station Engineering Department (NSED) decided to compare the data derived by l Sandia in their tests with the values that would have bcen established at CPS for the same cables. On page 7 of their May 16,1996, letter, Sandia discusses this evaluation and '
basically rejects it. Part of this rejection appears to have been the result of an incorrect assumption concerning how that the data comparison was made. ;
The NRC was contacted to obtain the physical dimensions of the conductors (the Sandia f SAND 94-0146 report had not been issued at this time). Based upon the values and ,
description provided, Table 3.1 (Ampacities of 0-600 volt copper single-conductor non- ,
jacketed cables) and instmetions ofICEA P-54-440 (NEMA WC-51) were used to l establish ampacity values for the cables. Site ampacities for power cables had been :
established in calculation 19-G-1 using Table 3.12 of the same standard. In order to make ;
the comparison to SAND 94-0146, two deviations from the 19-G-1 methodology were taken: !
1
- The first deviation taken was for the depth of fill. The depth of fill was taken as one !
. and one-halfinch rather than the standard two inches. This was not explicitly stated in l IP's response to the 1995 NRC Thermo-Lag RAIs (Attachment 4 to U-602512). l However, the individual evaluations for each 50.59 which were provided as Attachment 5 to that letter contained the depth of fill statement. This was because the depth of fill for the test sample prepared by Sandia calculates out as 1.41 inches (per Section 2.2 ofICEA P-54-440). ,
I The second deviation taken was that ampacity values derived were rounded to tenths rather than'whole numbers.
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to U402720 i Page 4 of14 i
- The second deviation taken was that ampacity values derived were rounded to tenths l rather than whole numbers. j i
The two cable deratings (for tray covers and 50 C ambient) imposed as part of calculation )
19-G-1 were applied to the ampacity values. As an additional point of comparison,'non- l derated values from the ICEA standard were also tabulated. Review of this data showed !
that the methodology utilized at CPS resulted in lower allowable ampacity values for the same 1/C cables despite applying a smaller Thermo-Lag derating value. This was clearly j{
shown on the table contained on page 4 of Attachment 4 in the 1995 IP response to the.. !
'first RAI (U-602512, dated November 3,1995). The non-derated ICEA values also ,l resulted in lower ampacity values than the Sandia test which is indicative of the conservative nature of sizing guidelines of the standard. The ampacity values thus established were then converted to watts / foot and heat intensity. These units showed the consistency of the allowed heat production for the various cables which is an expected l result of the Stolpe equations that the ICEA standard had used to develop their ampacity j tables. These values show that cables of different sizes can be compared to one another :
once their ampacity value has been converted into heat intensity.
The results of this initial evaluation of the data contained in IEIN 94-22 were discussed !
with Management and Licensing personnel. Since this evaluation indicated that the CPS !
design process had been conservative with respect to cable selection and ampacity margin, l engineering continued with the 50.59 evaluations for the five areas where the Thermo-Lag !
- was to be left in place. !
, a) Inadequate treatment of depth of fill. l
, The inadequate treatment of depth of fill appears to be based on the paragraphs starting the middle of page 7 in the Sandia review dated May 16,1996. In this section of the white- i up, Sandi:: assumes that the comparison between the Sandia National Laboratories (SNL) j test values, the ICEA values, and the CPS design values utilize different depths of fill. l
- l. This assumption is not true. While the CPS project ampacity numbers for cables in tray i are based on a 2 inch depth of fill, the cables utilized in the SNL test are not pan of our i L design. Accordingly, the values shown for the CPS design in these comparisons had to be l derived and the derivation was done using a 1.5 inch depth of fill so that the results could j be compared directly. To make the values representative of CPS design, the same deratings for tray covers (5%) and higher ambient temperature (10%) were applied to the l ICEA 1.5 inch depth of fill values as are applied in the tray ampacity calculations for our j site. These additional deratings (conservatisms) are why the CPS values are lower than l
<- the ICEA values. l
}
The chan that is attached to each evaluation was first developed as part of the review of l IEIN 94-22. The chart's purpose was to demonstrate that the numbers published in IEIN i 94-22 did not mean that our derating value was unacceptable, Depending on the starting i
. ampacity value, a 32% derate could result in a lower overall heat intensity than the larger l derating values listed in the IEIN.
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Attachment 2 to U-602720
- Page 5 of14 4
b) Removal of the conservatism from the ICEA tabstated ampacity values l without adequatejustification. j i The removal of conservatism concern appears to be based on paragraphs staning on page ;
- eight of the Sandia review. The section states
- "The CPS assessment practice of j
! comparing measured clad ter,t " heat intensity" values to those ofin-plant cables will -l
]
remove any potential conservatism which derives from the ampacity tables." This _
l statement does not describe the evaluation process that was performed at CPS. As part of !
the review ofIEIN 94-22, comparisons were made between the clad test values published -
in IEIN 94-22 and SAND 94-0146 and calculated ampacity values which were derived by 1- use ofICEA standard P-54-440 and the CPS ampacity calculation methodology. These i
comparisons indicated that the ICEA standard's methodology produces conservative ampacity values for cables and that use of these values would result in operation at t i
temperatures well below the normal 90'C upper limit since operation at the elevated current levels as reported in IEIN was necessary for the conductor temperature to reach 90*C. The comparison further indicated that the CPS methodology added more ,
conservatism to the ICEA standard and concluded that the CPS methodology would result !
in cable temperatures further below the 90 C limit. j i
i In the evaluations of cables that was done as part of the 50.59 evaluations on Thermo-Lag i
! installations, each cable was reviewed and verified to fulfill the derating value established in the CPS calculations. After this review was complete, there was still a need to address i the derating values reported in IEIN 94-22, which were higher than the 32% value obtained by calculation 19-AI-08. This was done by referring back to the IEIN review and the conclusions which indicated the CPS methodology would produce cooler cables. f i '
After restating the review and its' conclusions, a comparison was then made between the most heavily loaded cable (s) in the Thermo-Lag wrapped raceway under review and "the lowest values shown in the right hand column" of the table prepared during the IEIN review. These " lowest values" were the values derived during the IEIN review by applying .
- the methodology of calculation 19-G-01 and the derating of calculation 19-AI-08 to cables !
of the size used in the testing done by Sandia for the NRC. This comparison demonstrates ;
two things. First, that the methodology discussed in the IEIN review has actually been ;
followed in the CPS design and installation process. Second, the hottest (most heat j
. intensive, greatest heat producing) cable (s) in the raceway being reviewed is cooler than i the coolest (least heat intensive, lowest heat producing) cable postulated in the IEIN l review.
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i Attachment 2 to U-602720 Page 6 of 14 The statements by Sandia in their letter to the NRC seem to indicate a belief that the comparison discussed above was between the heat intensities of the installed cables in the ;
plant and the heat intensities of the clad cables from their tests. By combining the IEIN conclusions (the derived ampacity values have a lower heat intensity than the clad cables in the test) and the evaluation statements (the plant cables have a lower heat intensity than the ampacity values derived during the IEIN review) it would be possible to establish such a comparison. However, concentrating on this comparison removes the focus from the rationale of the two activities performed:
- In the IEIN review, the derived ampacity values and the clad test reported values are both dealing with every conductor being energized. If the conductors of the clad test assembly were energized to the derived values, the resultant conductor temperature would have to be lower than 90 C.
- In the evaluation of actualloads on installed plant cables, most of the cables are lightly loaded. By looking at the most heavily loaded cable in the tray and finding it acceptable, the acceptability of the lightly loaded cables is demonstrated.
c) Inadequate justification for the assumption that 32% derating ofICEA tabulated values will bound the derating impact of all fire barrier systems installed at Clinton Power Station (CPS).
The statement ofinadequatejustification for use of the 32% derating factor to bound all CPS fire barrier systems is actually stated in the Sandia write-up as such," . . . this value is apparently CPS calculation 19-Al-8. * *
- should be reviewed to assess the appropriateness of this assumption." This calculation (19-AI-8) determines the derating required for a tray with a three-hour wrap of Thermo-Lag. The calculation does this by considering the heat production allowed for a 24 inch wide tray section (using heat intensity) and then determining the reduced heat production that would be allowed based on dissipation of the heat through a layer of Thermo-Lag.
The installations in areas A-la, C-2, and CB-le are trays with one-hour wraps of Thermo- ,
Lag and D-8 is a conduit installation with a one-hour wrap of Thermo-Lag. The tray in area CB-If has a three-hour wrap of Thermo-Lag. Since most of the installations were of the one-hour value, the use of the derating factor established for a thicker wrap was deemed to be both a bounding and a conservative decision. The fact that these !
installations have one-hour wraps is noted in the safety evaluation attachments but there is not a clear statement that the 32% derating value listed is for a three-hour wrap. However ;
this point was explicitly stated in Attachment 4 ofIP's response to the NRC's 1995 RAI '
regarding Thermo-Lag (letter U-602512, dated 3 November 1995) where this was described as an additional conservatism in the evaluation process.
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- [ . l Attachment 2 '
to U-602720 ;
Page 7 of14
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- Furthermore, there is an added conservatism related to the use of the derating value . l established in calculation 19-AI-8. The heat production values utilized in the calculation i are based on an open top tray in an ambient temperature of 40*C (ICEA P-54-440 values). !
These values are not derated as the Clinton project ampacities are in calculation 19-G-1 l (see previous statements concerning derating for tray covers and higher ambient i 1 temperature). The calculation therefore starts out with a larger heat value in the tray then !
.would exist in the design of CPS. The derating value established in the calculation is for !
this larger initial heat value. Using this same derating against the CPS project ampacity i values adds conservatism since the actual allowed heat in the tray by project ampacity l numbers is less than the initial heat of the 19-AI-8 calculation. !
I To illustrate, j ifI, is the NEMA ampacity for a cable l and I. is the CPS project ampacity for the same c .ble j and R is the resistance of the cable j then the heat produced in the initial step of the 19-AI-8 calculation is l
l I'R !
- The 32% derate results in an allowable derated NEMA ampacity of 0.681, which produces heat of (0.681 )2R =0.46241,2R. ,
The CPS project values are derated by 5% and 10% from the NEMA values so i
l' I =(0.95)(0.9)l, =0.8551, j i
-and the initial heat produced by a cable at project ampacity is l I.'R =(0.8551.)2R =0.731I.2R. j Applying the 32% derate to the project ampacity therefore produces an allowable derated l project ampacity of j i
0.68I = (0.68)(0.8551.) =0.58141, l and a heat production of.
i I (0.681.)'R =(0.58141.)'R = 0.3381,'R ' l l
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Attachment 2 to U-602720 Page 8 of14 The ampacity ratios stated here are shown on the graph in Attachment 4 to letter
, U-602512. i
. I j d) Deviation from the ampacity derating test approach without adequate ,
justification. l l
- The ampacity derating test approach was not chosen since the Thermo-Lag installation at !
CPS is a known, definable quantity. Rather than establish a derating value used on l potential new Thermo-Lag installations, an examination of the presently installed cables in .j wrapped raceways was performed. The stated concern expressed in GL 92-08 is that inadequate derating of Thermo-Lag wrapped installations might result in cables being l operated at temperatures above their ratings which would accelerate the cable aging i
. process. This concern was addressed directly by considering two points. - First, is any l single cable loaded so heavily ths.t it could damage itself? Second, is the overall heat j production in the wrapped raceway high enough to create an aging concern? The manner i in which these questions were addressed by the review process is discussed below. j The evaluations performed reviewed each cable's actual load and compared it to the i
e project ampacity value for that ' cable type. The project ampacity values are cable in tray l
- values and were derived using ICEA/ NEMA methodology with deratings applied for tray 1
covers and ambient temperature.
1 i The comparison indicates the amount of margin that exists for each cable between actual load and project values and identifies which cables are the most heavily loaded. The attachments to the 50.59 evaluations discuss the most heavily loaded cables and indicate
> that they meet the calculated (calculation 19-AI-08) derating value of 32% for wrapped cables at CPS. Since the derating value was established for a three-hour wrap, it provided a conservative value to compare the one-hour wrap installations. In the CB-lf zone where i the tray actually has a three-hour wrap, the review indicated that none of the cables approaches the established limit.
l Once the individual cables were reviewed and shown to be acceptable, the second point was addressed. While the analysis of the individual cables indicates that no problems exist, looking at the overall heat production provides a simple validation that the results are
. realistic. With the cable sizes and loads already listed, it's a straight forward matter to determine the heat production from the cables. In addition to the margins discussed in item c. response above, the dominance oflightly loaded cables provides assurance that ,
there is no potential for the heat concentration necessary to cause accelerated thermal aging of the cables.
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Attachment 2 to U-602720 Page 9 of 14 The following wattages (production from the cables in the raceway) were calculated with the conductor impedance at 90 C. Since the heat production is so low, the conductors would not reach this temperature so the wattage value shown is conservative with respect to actual heat being generated by the cables. Note that the values shown are per running
' foot of raceway; therefore, for a 24 inch wide tray the wattage shown is over two square feet and for the 36 inch tray it is over three square feet.
Zone A-la, 36" wide tray, 5.9 watts per foot of tray Zone C-2, 24" wide tray, 1.6 watts per foot of tray 3" conduits, 0.14 watts per foot ofconduit Zone CB-le, 36" wide tray, 11.1 watts per foot of tray 24" wide tray, 4.1 watts per foot of tray 24" wide tray, 7.0 watts per foot of tray Zone CB-lf, 24" riser, 4.1 watts per foot of riser 36" tray, 21.5 watts per foot of tray Zone CB-Sa, 1-1/2" conduit, 0.1 watts per foot of conduit 2" conduits, 0.18 watts per foot of conduit 3" conduit, 1.0 watts per foot of conduit Zone D-8, 5" conduits, 7.5 watts per foot of conduit e) Inadequate justification for the applicability of " heat intensity" analysis method.
In Stolpe's paper "Ampacities for cables in randomly filled trays," he states:
" Cable ampacities in randomly packed trays must be based on the assumption that cables are tightly packed and that we cannot depend on heat being carried out of the bundle by air flowing through it. Without question, this tightly packed condition does not exist in every cable tray, but it does randomly occur often enough that, for safety, each cable tray must be designed as though it was going to be tightly packed. It is not even necessary that the entire cable tray be tightly packed, since packed width ofonly about three inches is suflicient to produce a hot spot in an otherwise cool tray.
With the criterion of tight cable packing established, it is then required to determine how the heat generation is distributed in the tray cross-section. The many cable sizes possible, both single and multi-conductor, and each carrying a different current apparently makes it quite difficult to place allowable currents on such a heterogeneous mixture. However, looking at the problem from the standpoint that we do not want any hot spots in the cable tray, the problem can be solved.
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Attachment 2 !
to U-602720 I j: .. Page 10 of14 l j
- Hot spots in a thermal system are produced by locally intense heat sources; thus, in every' area of the cable tray we'must eliminate such conditions. In other words, the heat I
4
. generated in every area of a tray cross-section must be uniform. This is the key to the .
entire problem of ampacities for randomly arranged cables in cable trays, and the concept i of uniform heat generation cannot be overemphasized. j
- - Consider Figure 1 showing a hypothetical slice of area from a typical, tightly packed cable ;
. tray. The heat intensity within each unit area, expressed in watts / foot per square inch of !
t cross-sectional area, must be constant all the way down to the smallest unit area inside the !
I tray, which is the smallest cable in the tray. We therefore place ampacities of cables, such l 4
as shown in Figure 1, in proponion to the overall cross-sectional area of the individual l cables, including the conductor and insulation. .!
l If we know the allowable heat intensity for a given cable tray, we can immediately place [
t ampacities on every cable in the tray by knowing the cross-sectional area of each 4
composite cable. Thus, the problem now remains to establish the allowable heat intensity l for various cable tray configurations. ;
i This portion of Stolpe's document is clear in that the goal is to assign ampacity values l which will not allow hot spots in the cable mass. The method by which this is to be l accomplished is to first determine how much heat can be dissipated from a cable mass j w!2ch is assumed to be homogenous and producing heat evenly throughout its mass j (allowable heat intensity). After this determination, assign ampacity values to cables such j that they do not produce more heat per unit area than the homogenous mass (place i ampacities in proportion to the cable's cross-sectional area). This does not mean that .i cross-sectional area is the only parameter to consider when assigning ampacities. Stolpe is l clear in pointing out the fallacy of trying to treat large round cables as though they were l thin rectangular shapes. An example would be that a cable with a diameter of 2.75 inch !
placed in a tray with a depth-of-fill of 1/2 inch will not be able to dissipate heat as though !
i it were 12 inch wide and 1/2 inch thick. This is why larger diameter cables have limitations on their ampacity as the tray depth-of-fill goes below their diameter. These l limitations are incorporated in the ICEA/ NEMA tables. {
The CPS method for assigning project ampacities follows the ICEA/ NEMA guidelines :
(see calculations 19-G-01 and 19-G-02). For Thermo-Lag wrapped tray sections, the ;
allowable ampacity was determined by calculation (see 19-AI-08). The review of wrapped !
cables that was performed as part of the 50.59 reviews in response to GL 92-08 confirmed !
that the actual loads on the cables did not exceed these values or provided justification for j why this was acceptable.
As a means of demonstrating the conservatism of this methodology, the most heavily j loaded cables in each wrapped raceway (which in turn means the cables with the highest j heat intensities) were then compared to the calculated ampacity values derived in the !
review ofIEIN 94-22 (using the CPS methodology of calculation 19-G-01) for single !
conductor cables of the same dimensions as the cables tested by Sandia. l l
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. Attachment 2 to U-602720 i
- Page 11 of14 Note: The review ofIEIN 94-22 compared CPS methodology against the Sandia results. i However, the comparison made at this point of the Thermo-Lag 50.59 evaluations is against the derived CPS values of that review (values extrapolated using the CPS .
methodology), not the Sandia test result values. j Since the cables actually installed in our plant are not the same size nor of single
, conductor construction, the comparison was done through heat intensities. As stated ,
above, the goal is to not have potentially damaging hot spots in the tray and the heat intensity represents the actual heat production. Therefore the comparison shows that the hottest location in the tray is still cooler than the coolest calculated point in the 94-22 review. ;
The Sandia remarks do make a valid point with respect to this comparison. Since the project ampacities are based on a 2 inch depth of fill, it k an expected result that the '
comparison will show a lower heat intensity than the values derived for a 1.5 inch depth of fill. However, it is also true that the actual depth of fill in more than half of the wrapped power tray (zones A-la, C-2, and one of the 24 inch wide legs in CB-le) is less than 1.5 inch. Further, as indicated in the discussion above, there are restrictions on the ampacity oflarge diameter cables. These cables therefore produce less heat per unit area when installed in trays whose depth-of fill is less than the diameter of the cable. The result of ,
this is that the large cables (3/C, 350 MCM) installed in the tray sections reviewed represent an additional (albeit small) conservatism in the actual overall heat generation in the tray versus the calculated allowable heat generation in the tray.
- 5. The ampacity margin analysis approach is generally considered an appropriate approach to the resolution of ampacity derating issue. The available margins in the cable ampacity should be compared against the fire barrier derating impact which may 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 ofin-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,it must be demonstrated that the ampacity derating values are appropriate (or cor.servative) to the CPS barrier systems, or provide for appropriate methods of extrapolating those results to the CPS installations.
As indicated in response four above, the process utilized by CPS in the resolution of the ampacity derating issue follows the process outlined in the NRC statement. The actual loads on the power cables in Thermo-Lag wrapped raceway were reviewed and compared to the project ampacity values established in calculations 19-G-01 and 19-G-02 for the same size cables. This shows the available margin in each cable. This margin was then compared to the derating factor established in calculation 19-Al-08. As stated above, the 19-AI-08 derating factor of 37% is for a three-hour wrap of Thermo-Lag on tray.
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Attachment 2 to U-602720 Page 12 of14 Therefore, it was deemed to be conservative for the one-hour installations on trays in zones A-la, C-2, and CB-le, and bounding for the three-hour installations on trays in zone CB-1f.
No calculations were performed at CPS to establish derating factors for conduits wrapped in Thermo-Lag. In order to evaluate the one-hour wraps on conduits in zones C-2 and D-8, the 32% derating developed for three-hour tray wrap was used. While there is no direct correlation between trays and conduits, the 32% derating factor was developed for open cable trays so it should be conservative with respect to conduits.
- 6. The analysis of cables 1DG29A and IDG30A in fire area CB-le is considered insufficient. Additional documentation should be provided for the subject two cables regarding operating history.
These cables feed the air compressors (1DG02CA and IDG02CB) for the Division II Diesel Generator Air Stan skid. The air compressor's function is to maintain the air pressure in the air receiver tanks within a specified range. The compressors operate in response to pressure switches (IPS-DG004A, IPS-DG006A) mounted on the skid, turning on when the receiver tank is at 215 psig and turning off at 250 psig. These motors are fed from the safety bus, but are shunt tripped during accident conditions. The operating time required for these compressors to rise the tank pressure from 215 to 250 psig is approximately five minutes and the frequency of operation is daily. This operating profile is too short for the cables to warm up, stabilize, and become a heat source for themselves and the other cables in the tray.
i 7. Describe any dilTerences in the construction or configuration of barriers installed as fire breaks as compared to those installed to protect cables from fire damage. If there are differences in construction, describe how these differences would impact the cable ampacity derating results.
There are no differences in construction between the two installations. For the installations referenced, a fire break installed on tray consists of an application of Thermo-Lag over a twenty foot length of cable tray. Only the fire break in the C-2 fire area includes a power tray.
- 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 fullload carent (FLA) could be as high as 125% of FLA at nominal voltage. Describe how this aspect of system operation was included in the ampacity derating analysis.
Standard design practice is to provide margin during the selection of cables to account for variances of voltage, temperatiire, etc., during plant operation. This is why cables are not operating at rated temperaturer Similarly, proper specification of motors for motor driven equipment allows the movn to operate in its normal range. Selection of a motor
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. Attachment 2
. to U-602720 Page 13 of14 that will need to operate in the service factor range is a departure from standard practice f and requires separate analysis to account for changes in mnning temperature, efficiency, !
power factor, speed, etc., of the unit being so operated. The possibility does exist for ;
- intermittent operation of a motor above its rated horsepower but within its stated service, ;
factor due to degraded connected equipment. !
1 With respect to the analysis performed for ampacity derating of Thermo-Lag wrapped 1 raceway, the consequences of degraded voltage and overload conditions on these >
installations is reviewable in the same manner. First, the consequences of every cable in !
the wrapped raceway carrying 125% ofits load current is considered. The heat !
production in the tray would increase by the square of the current which would mean l 156.25% of the original wattage. Recalling the heat production values listed in the - :
response to 4.c. above, such an increase would result in the following changes. ;
FROM TO l Zone A-la, 36" wide tray, 5.9 watts /ft 9.2 watts /A . j I
Zone C-2, 24" wide tray, 1.6 watts /ft 2.5 watts /A j 3" conduits, 0.14 watts /ft 0.22 watts /ft Zone CB-le, 36" wide tray, 11.1 watts /ft 17.3 watts /ft [
24" wide tray, 4.1 watts /A 6.4 watts /A i 24" wide tray, 7.0 watts /A 10.9 watts /ft ,
Zone CB-If, 24" riser, 4.1 watts /ft 6.4 watts /A !
36" tray, _ 21.5 watts /ft 33.6 watts /ft Zone CB-Sa, 1-1/2" conduit, 0.1 watts /ft 0.16 watts /ft 2" conduits, 0.18 watts /R 0.28 watts /ft 3" conduit, 1.0 watts /A 1.6 watts /ft Zone D-8, 5" conduits, 7.5 watts /ft 11.7 watts /A As these values indicate, the overall heat production even with 25% overload is still quite low. The installations would still need to be checked to see if the additional current resulted in hot cables. While all cables could be checked, some simple steps can limit the number of reviews needed. The postulated 25% increase would change a cable canying 40% of project ampacity to 50% of project ampacity. The 50% number was treated as a
- cut-offin the original analysis.. Therefore, a review of all wrapped cables with a loading of 40% or more of project ampacity would be sufficient to identify if any individual cables could be subject to accelerated aging as a result of the postulated overload condition.
This review is included as Enclosure 1 to this attachment.
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- Attachment 2 to U-602720 f
- Page 14 of14 i
' After performance of the individual cable reviews, clearly the actual heat production in the trays is not subject to a 56% increase from postulated overloads since many individual !
loads are not subject to the postulated overload. In addition, the heat production shown i for the various fire zones includes loads that the analyses have shown are not normally energized so the baseline heat numbers are conservatively high. Accordingly, the design margins account for potential overload conditions. The possibility of overloads does not
. impact the conclusion of the original cable review that accelerated aging of cables due to -
Thermo-Lag wrapped raceway is not a valid concern at CPS. !
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- Enclosurs 1
, to Attachment 2 to U 602702 Page1of5 Review of Thermo-lag Wrapped Raceway with Respect to Potential Adverse Effects on the Enclosed Cables From a Postulated 25% Overload Inasmuch as this review is looking at the effects of an overload condition, part of the review has to include whether the connected equipment is subject to such overloads. Resistive loads such as heaters and lights do not create the type of overload condition referenced in request eight of the RAI. Once cables are identified as feeding such loads, they would not require further review since the previous analysis has already established acceptability.
I) In fire zone A-la, there are three cables loaded over 40% of project ampacity, IDG21J, IRD31B and IVD02A.
Cable IDG21J has a load of 40 amps which results in 50 amps with a 25% increase. This cable is the DC feed to Diesel Generator (DG) control panel IPL12JB so only two of the three conductors are energized. Accordingly, the cable ampacity could be increased from 97 to 118 amps and the cable would be loaded to less than 50% even with the postulated 25% overload so there is no concern with accelerated aging for this cable. (This allowable increase was not stated in the original analysis since it was not required for acceptance of the cable at that time.)
Cable IRD31B has an assigned load of 25 amps so increase of 25% would result in 31.25 amps. However, this is a 120 VAC circuit fed by a 30 amp breaker so the maximum current without tripping the breaker is 30 amps. The original analysis took credit for the fact that this cable is in a tray with a depth-of-fill ofless than one inch which allowed the cable ampacity to be increased from 32 to 49.3 amps. If the additional ampacity increase for using only two of the three conductors is applied, the ampacity can be increased from 49.3 to 60.3 amps and the cable is shown to be loaded to less than 50% even with maximum overload. (The allowable ampacity increase due to two of three conductors being energized was not stated in the original analysis because it was not required for acceptance of the cable at that time.)
Cable IVD02A has a load of 120 amps which results in 150 amps when increased by 25%.
Original analysis showed the cable ampacity could be increased from 175 to 192.7 amps based on the one inch depth of fill for the tray. A current of 150 amps represents a 78%
loading against this ampacity. However, IVD02A feeds DG ventilation fan IVD01CB which is only started when the Division II DG is running. During normal plant operation, this results in two hours of fan operation (one while the DG runs and one while room cools down) per month (two hours per week during accelerated DG surveillances). Every 18 months there would be a full day of fan operation during the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run of the DG.
The two hour monthly (weekly when accelerated) runtime is too short for the cable to stabilize and produce significant heat. The 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of continuous operation every 18 month is too infrequent for the potential heating of the cable due to overload to cause a concern with accelerated aging against a predicated operable life of forty years. (The
h
. Enclosure 1
[ to Attachment 2 to U402702 Page 2 of 5 operating cycle and duration of the load for cable 1VD02A was not discussed in the original analysis since it was not required for acceptance of the cable.)
- 11) In fire area C-2 there are five cables loaded over 40% of project ampacity, ISC02B, lHG25L', lHG25M,1HG25N, and lHG25P.
- Cables.1HG25L,1HG25M,1HG25N, and 1HG25P all are feeding hydrogen igniters which are resistive loads and not subject to the postulated overload condition.
Cable ISC02B feeds the motor for pump IC41-P001B (Standby Liquid Control). This motor draws 48.8 amps so a 25% increase would result in a current of 61 amps which represents 95.3% of the cable project ampacity. In the original analysis it was noted that this cable was not a concern since 1) the pump is only run for short periods to perform surveillances during nonnal plant operation and 2) in an accident scenario that required the pump to inject into the vessel the maximum run time would be less than two hours. This analysis is still valid so even with a postulated overload the cable will not be subject to accelerated aging. (This cable could also be analyzed based on the allowable ampacity increase from 64 to 96 amps due to the depth-of fill in the tray being less than one inch.
The postulated overload of 61 amps would only represent 63.5 % of this value so the cable could accept a derate of 36.5%. However, this was unnecessary since the load does not operate for sufficient time for accelerated aging to be a concern.)
III) In fire zone CB-le there are eleven cables loaded over 40% of project ampacity, 1 CM09H, 1 CM09K, 1DG21 J, 1DG26B, 1DG27B, 1 DG29A, 1 DG30A, 1 VD02A, IVD05A, IVG38A, and IVG40A.
Cables IDG21J and IVD02A were discussed under zone A-la above.
Cables ICM09H, ICM09K, IDG26B, and IDG27B feed heating circuits and therefore would not be subject to the postulated overload.
Cables IDG29A and IDG30A feed the air compressors (IDG02CA and IDG02CB) for the Division II DG Air Start skid. These units draw 27 amps so a 25% overload would result in a current of 33.75 amps which represents 105% loading of the cable ampacity. l This current would trip the 30 amp feed breaker during extended operation. However, as }
r discussed in response six above, the operating time for these compressors is approximately five minutes on a daily basis so the breaker would not be expected to trip. The short duty cycle (see response six above) would prevent heat up and eliminates any concern over i accelerated aging of the cable from the postulated overload.
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- - Enclosure I to Attachment 2
. to U-602702 l Page 3 of 5 j Cable IVD05A feeds the motor for fan IVD02CB. This motor draws 6.5 amps so a 25% :
increase would result in a current of 8.125 amps. This represents a loading of 50.8% - i against the project ampacity of 16 amps for this size cable. This means that the cable i could be assigned a 49.2% derate against the project ampacity during a 25% overload ;
condition. Accordingly, accelerated aging from the postulated overload condition will not - l be a concern for this cable. !
[
Cables IVG38A and IVG40A feed the motors for fans OVG01CB and OVGCf"B l respectively. These motors draw 7 amps each so a 25% increase would result in a current ;
of 8.75 amps. This represents a loading of 54.7% against the project ampacity of 16 amps l for this size cable. This means the cables could be assigned a 45.3% derate against the j project ampacity during a 25% overload condition. Accordingly accelerated aging from j the postulated overload condition will not be a concern for this cable. !
IVa) In fire zone CB-If there are four cables in the 24-inch wide Division II power tray which
' are loaded over 40% of project ampacity, ICM09H, ICM09K, IVG38A, and IVG40A. !
i These cables were discussed under zone CB-le above.
IVb) - In fire zone CB-1f there are eleven cables in the 36-inch wide BOP power tray which are j loaded over 40% of project ampacity, lEH06B, ILV53D, ITO15A, IVLOI A, IVL01B, ;
IVLO2A, IVLO2B, IVLO4A, IVWO3 A, lWY11 A, and IWY1IB. ;
Cables 1VLO1 A,1VLO1B,1VLO2A,1VLO2B,1VLO4A, IWYl1 A, and 1WYl1B all feed i heating loads so they would not be subject to the postulated overload.
L ~ Cable IEH06B carries up to 19.2 amps so a 25% increase would result in 24 amps which !
represents a loading of 54.5% against the project ampacity for this cable. This would allow the cable to accept a derate of 45.5% against the postulated overload. However, -
2 this cable feeds through 20 amp breakers in the Electrohydraulic Control (EHC) cabinet so l'
- if the postulated overload occurred, the breakers would trip and the cable would be de-energized. Therefore, this cable does not have an accelerated aging concern due to i postulated overloads. l i
i Cable ILV53D has an assigned load of 12 amps so a 25% increase would result in a load i of 15 amps which represents 93.8% of the project ampacity for this cable. In the initial
! analysir; this cable was identified as carrying a 120V circuit and since only two conductors :
are energized the cable ampacity could be increased from 16 to 19.2 amps. The 15 amps !
, would represent a 76.5% loading against this value. The assigned load on this cable !
4 comes from the feed breaker rating of 15 amps and an assumption of 80% of breaker l'
- rating. In actuality there is no design load for this circuit since it is a DC source for the calibration lab on the 781 foot level of the radwaste building. When DC power is required ;
- for test equipment or for a device being tested in the lab, this circuit provides it. Since the .
- circuit is to support calibration testing as needed, the current draw will vary according to ;
usage and it would be unlikely that the circuit would be operating at maximum draw (15 i
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Enclosure 1 i
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Page 4 of 5
. amps per the breaker rating) for any significant length of time. . Based on the usage for this I circuit there should not be an accelerated aging concern for this cable. ;
I Cable ITOISA feeds the motor of pump ITOOSP (Emergency Bearing Oil Pump). Cable i ITOO5P has a DC motor so only two conductors are energized This cable is paralleled ,
. with ITOISE and is assigned 55% of the rated current or 143 amps for analysis purposes. i A 25% increase results in a current of 178.8 amps which is 53,7% of the project ampacity l for this cable. If the additional ampacity increase for using only two of the three !
- conductors is applied, the ampacity can be increased from 333 to 407 amps and the cable is shown to be loaded to less than 50% even with the postulated 25% overload. Further, !
> since this pump is an emergency backup to maintain the turbine oil pressure in the event of !
loss of AC power, it is normally de-energized. Aside from verification of operation of the ;
pump, which is performed during startup of the turbine, this pump is not run. In the event ofloss of AC power, the pump will actuate on pressure drop and remain operating as the ;
turbine is brought to a stop. The pump is required to be able to operate for 30 minutes to cover this coastdown interval and this duration is too short to have a thermal impact on i the cable. Therefore there is no thermal aging concern for this cable. (The DC nature of the circuit and the standby nature of the load was not discussed in the original analysis since it was not required for acceptance of the cable.) ,
i Cable IVWO3A feeds the motor for fan OVWO4CA. This motor draws 134.9 amps so a i 25% increase results in a current of 168.7 amps which represents 62.7% of the project ,
ampacity rating. This means the cable could be assigned a derate of 37.3% against the
. postulated overload. This should be sufficient to prevent accelerated aging of the cable even in the event of such an overload.
The 36-inch wide BOP tray on 762 foot level of the control building (zone CB-1f) shows l j the highest heat production value and for evaluation purposes this could be addressed in several other ways. For example, by discussion of the short length (4 feet) of the Thermo- !
lag installation on the tray. Since the tray is wrapped for such a short length, additional 4
heat dissipation through the mass of the cables and out to the unwrapped tray lengths
- could be postulated. This could then be used as part of a specific calculation for the heat j retention / dissipation for this specific installation. Alternately, the actual maximum ambient ;
temperature in this area (40*C) could be used to justify an 11% increase in the allowable !
- ampacity of all the cables in the zone since the project ampacities are based on an assumed ambient of 50'C. However, since the individual review and analysis process has not found any unresolvable concerns there is no purpose in pursuing further margin for the cables in
]
this tray. 3 V) In fire zone CB-Sa, there are two cables (of three in a 3 inch conduit) which have loads ,
greater than 40% of the project ampacity value, ICM09G and ICM09J. (Since three cables are sharing a conduit, the lower project ampacity value of 32 amps for the cable size rather than the conduit ampacity value cf 62 amps is used for the review.). .
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j . These cables are feeding resistive loads so they are not subject to the postulated overload. i VI) In fire area D-8, there are two cables in conduit which are loaded to greater than 40% of i
- the project ampacity for cables in conduit, IDG31 A and IDG31B. j These cables carry the output of the Division II DG to the Division II 4KV bus and the >
current evaluated is for the maximum designed load. Since the DG has its own voltage regulation, these cables will not see sustained current variations from degraded voltage. l The automatic loading of the DG during accident conditions is limited by design and }
protective relaying. CPS operating procedures require monitoring of the DG output to ,
limit the total load on the DG so as not to exceed the designed value during manual !
operation. These conditions preclude the postulated overload condition for these cables. ;
Further, as described in the analysis of cable IVD02A in area A-la above, the DG is only ;
operated for surveillance purposes during normal plant operation. This entails one hour of
, operation per month (one hour per week during accelerated testing) and a twenty-four j hour run of the DG every eighteen months. This is insufficient time to create a concern for ,
accelerated thermal aging of the cables. (The limited time frame in which the DG is expected to operate during normal plant operation and that these cables will be energized i
, was not discussed as part of the original analysis since it was not required for acceptance i
of the cables.)
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