Text

Forwards Request for Addl Info Re Thermo-Lag-related Ampacity Derating Issues,In Order to Resolve Concerns on Ampacity Derating Factor Determinations for Plants,Per GL 92-08
	ML17311A474
Person / Time
Site:	Palo Verde
Issue date:	12/07/1994
From:	Brian Holian; Office of Nuclear Reactor Regulation
To:	Stewart W; ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
References
	GL-92-08, GL-92-8, TAC-M85583, TAC-M85584, TAC-M85585, NUDOCS 9412080247
	Download: ML17311A474 (28)
	v • d • e

Hr. William L. Stewart Executive Vice President, Nuclear Arizona Public Service Company Post Office Box 53999

Phoenix, Arizona 85072-3999 December 7,

1994

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION REGARDING THERMO-LAG-RELATED AHPACITY DERATING ISSUES fOR PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2 AND 3 (TAC NOS.

H85583, M85584, AND M85585)

Dear Hr. Stewart:

By letter dated September 27,. 1993, Arizona Public Service Company (APS) submitted a response to the NRC Request For Additional Information (RAI) dated July 21, 1993, related to Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," for the Palo Verde Nuclear Generating Station (PVNGS).

Further, you indicated in your responses related to GL 92-08 (dated February 7,

1994, and March 15, 1994), that your original analytical approach will be supplemented by the Nuclear Energy Institute ampacity test results.

You then propose to determine what revisions, if needed, are to be made to the original ampacity derating determinations for existing or future upgraded Thermo-Lag configurations.

In conjunction with its contractor, Sandia National Laboratories (SNL), the NRC staff has completed its preliminary review of your original analytical approach as documented in the September 27, 1993, submittal, and has identi-fied a number of open issues and concerns that require clarification before our review can be completed.

We request that you submit your responses to the enclosed request for additional information in order to resolve our concerns on the ampacity derating factor. determinations for PVNGS Units 1, 2 and 3.

The reporting requirements contained in this letter affect fewer than 10 respondents; therefore, Office of Management and Budget clearance is not required under Public Law 96-511.

Sincerely, ORIGlNAL SIGNED BY.Linb N. Tran for:

Brian z. no>ian, Senior vroject Planager Project Directorate IV-2

++>~080247 9412p7 j

I Division of Reactor Projects III/IV

~

O ~ 05OOo5~8 Office of Nuclear Reactor Regulation Docket Nos.

STN 50-528, STN 50-529, and STN 50-530

Enclosure:

As stated I

cc w/encl:

See next page DISTRIBUTION Docket File JRoe LTran Public PD IV-2/RF ACRS (4),

TWFN DFoster-Curseen TQuay Region IV

KPerkins, WCFO

OGC, 015B18 BKolian DOCUMENT NAME:

PV85583.rai PH/PDIV-2 BHolian:

OFFICIAL RE 0 Y'FC LA/DRPW NAME Dfoster-rseen DATE l~ / 94 twj!pg t"'"jILP> 7jpEITER CljPV

h

Hr. William L. Stewart Executive Vice President, Nuclear Arizona Public Service Company Post Office Box 53999 Phoenix, Arizona 85072-3999 December 7,

1994

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION REGARDING THERMO-LAG-RELATED AMPACITY DERATING ISSUES FOR PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2 AND 3 (TAC NOS.

M85583, H85584, AND H85585)

Dear Hr. Stewart:

By letter dated September 27, 1993, Arizona Public Service Company (APS) submitted a response to the NRC Request For Additional Information (RAI) dated July 21, 1993, related to Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," for the Palo Verde Nuclear Generating Station (PVNGS).

Further, you indicated in your responses related to GL 92-08 (dated February 7,

1994, and Harch 15, 1994), that your original analytical approach will be supplemented by the Nuclear Energy Institute ampacity test results.

You then propose to determine what revisions, if needed, are to be made to the original ampacity derating determinations for existing or future upgraded Thermo-Lag configurations.

In conjunction with its contractor, Sandia National Laboratories (SNL), the NRC staff has completed its preliminary review of your original analytical approach as documented in the September 27, 1993, submittal, and has identi-fied a number of open issues and concerns that require clarification before our review can be completed.

We request that you submit your responses to the enclosed request for additional information in order to resolve our concerns on the ampacity derating factor determinations for PVNGS Units 1, 2 and 3.

The reporting requirements contained in this letter affect fewer than 10 respondents; therefore, Office of Management and Budget clearance is not required under Public Law 96-511.

Sincerely, ORIMNAL SIGNED BY.Linb N. Tean for:

Br>an l;. notlan, Senior project manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos.

STN 50-528, STN 50-529, and STN 50-530

Enclosure:

As stated cc w/encl:

See next page DISTRIBUTION Docket File JRoe LTran Public PD IV-2/RF ACRS (4),

TWFN DFoster-Curseen

KPerkins, WCFO Tguay

OGC, 015B18 Region IV BHolian DOCUMENT NAME:

PV85583,rai OFC LA/DRPW.~~

PM/PDIV-2 BHolian:

DATE 7/94 C~l 94 OFFICIAL RECORD COPY NAME DFoster-rseen

/i' p

Mr. William L. Stewart Arizona Public Service Company Palo Verde CC'r. Steve Olea Arizona Corporation Commission 1200 W. Washington Street

Phoenix, Arizona 85007 T.

E. Oubre, Esq.

Southern California Edison Company P. 0.

Box 800

Rosemead, California 91770 Senior Resident Inspector USNRC P. 0.

Box 40 Buckeye, Arizona 85326 Regional Administrator, Region IV U. S. Nuclear Regulatory Commission Harris Tower E Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Mr. Charles B. Brinkman, Manager Washington Nuclear Operations ABB Combustion Engineering Nuclear Power 12300 Twinbrook Parkway, Suite 330 Rockville, Maryland 20852 Mr. Aubrey V. Godwin, Director Arizona Radiation Regulatory Agency 4814 South 40 Street

Phoenix, Arizona 85040 Mr. Curtis Hoskins Executive Vice President and Chief Operating Officer Palo Verde Services 2025 N. 3rd Street, Suite 220

Phoenix, Arizona 85004 Roy P.

Lessey, Jr.,

Esq.

Akin, Gump, Strauss, Hauer and Feld El Paso Electric Company 1333 New Hampshire Avenue, Suite 400 Washington, DC 20036 Ms. Angela K. Krainik, Manager Nuclear Licensing Arizona Public Service Company P. 0.

Box 52034

Phoenix, Arizona 85072-2034

Chairman, Maricopa County Board of Supervisors ill South Third Avenue

Phoenix, Arizona 85003

Enclosure RE VEST FOR ADDITIONAL INFORMATION PALO VERDE NUCLEAR GENERATING STATION AMPACITY DERATING ISSUES TAC NOS.

MS55S3 MS55Sa Ma55SS GENERAL MODELING CONCERNS The Bechtel/PVNGS total heat rejection capacity analysis methodology as documented in the licensee submittal dated September 27, 1993, provides an assessment of the overall behavior of the protected system only, and provides no assessment of the behavior of individual cables within that system.

The "Watts/ft" analysis methodology utilized by Bechtel serves as a general design tool to assess the general limits of allowable cable loading within a given cable routing system.

Bechtel recognized the limits of this methodology in

'he following statement (See Enclosure 3 of the licensee submittal, Sheet 21 of the Bechtel TPO Design Guide E2.6.4, Revision 2):

CAUTION: Since "watts per foot" or "watts per foot per unit width" correlates with AVERAGE temperatures,-

each such case should be analyzed to ensure against hot-spots.

If many of the cables are lightly loaded, one or a few small cables can be overloaded to the point of damage without the "watts per (square) foot" limitation being exceeded.

The above statement also implies that the analysis methodology provides an overall assessment of the average cable behavior assumin certain eometric and cable loadin conditions a

1 That is, the statement that the heat rejection capacity correlates to "average" cable temperatures can be somewhat misleading.

The experimental data used to establish the heat rejection capacity of cable trays is based on the testing of heavily loaded cable trays, and the measurement of hot-spot temperatures within the cable mass.

Hence, the correlation is actually between the overall heat generation rate and a

hot-spot temperature rise as measured within a ti htl acked cable mass.

Therefore, this correlation is not strictly between average temperature and the heat rejection capacity.

In addition, the extrapolation of these results to other, less densely packed cable installations has not been demonstrated by the licensee.

Overall, the licensee analyses do not address potential hot spot temperatures which could arise due to the use of the fire barrier material or provide any assessment of the anticipated heat transfer behavior for the individual cables.

Therefore, the licensee analyses have not demonstrated that the ampacity values associated with an individual cable protected by the fire barrier material, Thermo-Lag 330-1, will remain within acceptable limits.

The licensee is requested to provide supplemental analyses to ensure that individual cable ampacities remain within acceptable limits when enclosed by the fire barrier material.

CABLE LOADING EFFECTS In general, the "Watts/ft" method assumes that cable loading effects are largely irrelevant to the overall heat rejection capacity of the cable tray or conduit system.

One exception noted in the licensee analysis was that, in

I,

some of the cases involving "overloaded trays," the estimated maximum allowable total heat load was reduced in proportion to the increase in the calculated depth of the cable fill introduced by the overloading of the tray.

Further, the reduction in the individual cable ampacity limits which were imposed to compensate for increased cable tray loading do not necessarily mean that the overall system heat load has been reduced in value.

A densely

packed, uniformly powered cable tray would be expected to have a higher overall heat rejection capacity than a sparsely loaded tray, even though the individual cable ampacity values would be lower in the sparsely loaded tray case.

The principal requirement is to ensure that the hot spot temperature is less than 90 C.

The increased number of cables present would more than compensate for the individual ampacity reductions.

In general, the increased cable load would lead to reduced power densities (volumetric heat generation rate) because the ampacity value would be reduced for the individual cable.

This reduction in power density would tend to reduce the hot spot temperatures, and hence, an overall increase in the total heat load could be tolerated, at the same time that individual cable ampacity limits are reduced.

In contrast, the licensee methodology reduces the allowable heat load for overloaded trays.

This issue is of particular importance when considering the PVNGS analyses.

Host of the cable tray applications involve very sparsely loaded trays where in some cases there is as few as a single set of power cables present in a tray.

Use of the heat rejection capacity values which are based on the testing of heavily loaded trays would yield nonconservative estimates of the overall heat rejection capacities of the sparsely loaded trays, and hence, nonconservative assessments of cable ampacity adequacy.

It is expected that the total tray heat rejection capacity would be dependent on various factors, especially the power density within the cable mass.

These factors should be accounted for in the methodology, or it should be demonstrated that these factors are not important to the analysis.

The basis for the correction by the licensee for the overloaded trays appears

unclear, and the staff requests further clarification by the licensee on the methodology used for these exceptions.

CABLE TRAY DIVERSITY EFFECTS The "Watts/ft" analysis method does not appear to provide significant treatment of cable tray diversity effects on the total allowable heat loads.

All of the available ampacity tests cited by the licensee are based on cable trays in which all of the cables are powered uniformly.

In the PVNGS applications, many cable trays contain a diverse or mixture of loaded and unloaded cables.

In general, where there are unloaded cables present in a cable tray there will be more margin in the cable design.

This assumption is true so long as one is considering the heat transfer behavior of individual cables.

However, since the "Watts/ft" method provides an assessment of the overall behavior of the cable system only, this methodology may lead to erroneous results for cases involving diverse loads.

For example, consider two cases where one cable tray is loaded with 50 power cables (Case I) and another cable tray contains a single cable (Case 2).

In Case I, all 50 of the cables are powered uniformly.

In Case 2, the single cable carries the same power load as in Case I.

The "Watts/ft" methodology would assume that the overall heat rejection capacity in these two cases would be identical.

Further, in Case I, the heat load generated by one cable could be increased by a factor of 50 assuming that the other 49 cables are deenergized and the cable remains within its original heat load capacity.

This result would imply a 7-fold increase (i.e., heating load is proportional to the square of current) in the ampacity value is allowable based upon the above example.

This conclusion is clearly unrealistic.

As the current of a cable is increased a limit would quickly be reached beyond which the insulating effects of the surrounding non-powered cables would increase the powered cable temperature beyond its operating limits (90'C).

However, the "Watts/ft" methodology would conclude that the ampacity'alues determined in each of the above two cases were equally acceptable.

The total overall heat rejection capacity of the cable tray system may be reduced in those cases involving diverse cable loads, even though the ampacity of the individual cables which are powered could be increased as a result of a diversity analysis.

However, it is not clear how the "Watts/ft" methodology would determine the allowable ampacity increase for individual cables in a cable tray due to diverse cable loads.

The staff requests that the licensee clarify how the "Watts/ft" methodology as employed by PVNGS will incorporate cable tray diversity effects.

EXTRAPOLATION OF EXPERINENTAL RESULTS Another concern regarding the licensee's methodology is the extrapolation from a very limited database to all of the licensee's plant applications.

In particular, it would appear that the extrapolation of the experimental results has been performed without adequate technical justification or validation.

The use of the experimental values of the total heat load associated with referenced ampacity tests appears to distort the intent of the ampacity derating test approach for the draft IEEE Standard

P848, "Procedure for the Determination of Ampacity Derating of Fire Protected Cables".

The intent of the industry ampacity derating test methodology is to provide a relative measure of the impact of the fire barrier system on the performance of the cables.

In this relative assessment, many factors "wash out."

That is, the ampacity correction factor, the ratio of two currents (cladded and baseline currents) causes many physical parameters to become secondary in importance.

These parameters become "self-cancelling" in nature so long as the parameters remain consistent between the baseline and cladded test specimen.

In contrast, the licensee's methodology is based on use of the absolute thermal load measured during the ampacity test of a cladded test specimen.

Parameters which may have only secondary importance when considered based upon relative performance can be of primary importance when the absolute thermal loads are used to determine ampacity limits.

This includes factors such as cable size, cable loading density, diversity, insulation thickness,

jacketed versus unjacketed

cables, conductor type, and insulation material.

Each of these factors would be expected to have an impact on the measured absolute thermal

loads, but would not be expected to significantly impact the relative cladded versus baseline ampacity performance.

The use of the absolute measured values of cable tray heat rejection capacity would appear to raise significant concerns regarding many of the factors which had been minimally addressed under the IEEE P848 procedure.

The intent of the IEEE P848 procedure, a relative performance test, is to isolate the insulating effect due to the fire barrier material.

Therefore, the test data referenced by the licensee must be carefully evaluated to ensure that consistent, conservative, and technically defensible results are obtained which compensate for the site specific difference in cable parameters.

The measured values of the total heat rejection capacity can vary widely, even in the case of the open baseline cable trays used in many ampacity tests.

In

fact, even the limited set of test data cited by the licensee indicates a very wide range in measured absolute heat rejection capacities.

For the Thermal Sciences Inc./Underwriters Laboratories tests, the heat rejection capacity value measured was 23.7 W/ft per 6-foot length (the 6-foot length of cable tray represents a normalized value necessary to compare the various tests).

In the Bechtel Los Angeles Power Division tests, the heat rejection capacity value measured was approximately 31-34 W/ft per 6-foot length (this value was calculated by our contractor SNL based on various other reported results, but is not reported directly).

Another data point referenced in a Bechtel supplement dated February 3,

1981, based on a test performed for a nuclear power plant had a measured heat rejection value of 17.91 W/ft per 6-foot length.

All of these values are for nominally similar open cable trays with no fire barrier protection.

This wide variation illustrates the sensitivity of the absolute heat rejection capacity to experimental parameters.

DOCUMENTATION OF CABLE TYPES AND PROPERTIES During the review of the PVNGS submittal, considerable difficulty was encountered in order to characterize the various cables cited by the licensee.

That is, the documentation provides one table with cable sizes and resistance values for various "cable codes" (see Sheet 8 of 18 of Bechtel Calculation 13-EC-ZA-300).

In a second table (see Sheets AI-A36, Bechtel Calculation 13-EC-ZA-300) the individual cables of interest at PVNGS are identified by a plant "cable ID" and the individual load ampacities.

However, no listing is provided which connects the "cable codes" to the plant "cable ID."

Hence, it is not possible to positively identify the characteristics of all of the individual cables cited in the PVNGS analysis.

Attempts were made by our contractor, Sandia National Laboratories (SNL), to "back out" cable types based on the heat load and ampacity values presented in the subject analysis.

Given these two values, a calculation of the cable'resistance can be made, and the resistance calculated can then be compared to the tabulated resistance values.

For example, consider the citation of Cable Tray 2EZA2CNTFAg and Cable ID 2EgA17NCIFD in the subject analysis.

The cable has a heating value of 5.92

W/ft (Sheet C118 of C443, Bechtel Calculation 13-EC-ZA-300) and the current load is 213.4 amperes (Item number 1015 on Sheet A21 of A36, Bechtel Calculation 13-EC-ZA-300).

Using these values yielded an estimated cable conductor resistance value of 0.0433 ohms/1000 ft.

This value does not match any of the values presented in the tabulated cable resistance

table, and

hence, no match could be made.

The staff requests that in any future submittal that the licensee provide a

direct identification of each cable of interest which includes the physical characteristics of each cable, the tabulated nominal ampacity rating of the

cable, and the actual in-plant ampacity factors.

VALIDATIONOF THE "WATTS FT4 METHOD The licensee submittal references the paper by J. Stolpe entitled "Ampacities for Cables in Randomly Filled Trays" as the basis for the validation of the total heat load (or "Watts/ft") methodology, and presumably, for the extrapolation of the test results (see PVNGS response to RAI, Enclosure 1,

Item 1C).

However, the Stolpe paper only refers to the extrapolation of the test results to other similarly loaded cable trays.

That is, Stolpe was only concerned with extrapolating his test results to other heavily loaded cable trays (trays with full layer, no gaps coverage) with uniform heating of the cables.

This reference does not address the more complex issues associated with variations in cable loading density and cable diversity issues as discussed above.

This paper does not provide adequate support to justify the extrapolation of subject data to sparsely loaded trays and conduits which are installed at PVNGS.

The licensee is requested to provide additional technical basis for the subject extrapolation of data results to sparsely loaded cable trays and conduits.

0 t

Hr. William L. Stewart Executive Vice President, Nuclear Arizona Public Service Company Post Office Box 53999

Phoenix, Arizona 85072-3999 December 7,

1994

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION REGARDING THERMO-LAG-RELATED AMPACITY DERATING ISSUES FOR PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2 AND 3 (TAC NOS.

M85583, H85584, AND H85585)

Dear Hr. Stewart:

By letter dated September 27, 1993, Arizona Public Service Company (APS) submitted a response to the NRC Request For Additional Information (RAI) dated July 21, 1993, related to Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," for the Palo Verde Nuclear Generating Station (PVNGS).

Further, you indicated in your responses related to GL 92-08 (dated February 7,

1994, and March 15, 1994), that your original analytical approach will be supplemented by the Nuclear Energy Institute ampacity test results.

You then propose to determine what revisions, if needed, are to be made to the original ampacity derating determinations for existing or future upgraded Thermo-Lag configurations.

In conjunction with its contractor, Sandia National Laboratories (SNL), the NRC staff has completed its preliminary review of your original analytical approach as documented in the September 27, 1993, submittal, and has identi-fied a number of open issues and concerns that require clarification before our review can be completed.

We request that you submit your r'esponses to the enclosed request for additional information in order to resolve our concerns on the ampacity derating factor determinations for PVNGS Units 1, 2 and 3.

The reporting requirements contained in this letter affect fewer than 10 respondents; therefore, Office of Management and Budget clearance is not required under Public Law 96-511.

Sincerely, ORIMNAL SIGNED BY.Linb N. Tran for:

Br>an t., notsan, Senior t'roject Planager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos.

STN 50-528, STN 50-529, and STN 50-530

Enclosure:

As stated cc w/encl:

See next page DISTRIBUTION Docket Fi1 e JRoe LTran Public PDIV-2/RF ACRS (4),

TWFN DFoster-Curseen Tguay Region IV

KPerkins, WCFO

OGC, 015818 BHol i an DOCUMENT NAME:

PV85583.rai OFC LA/DRP NAME DFoster-rseen DATE E

//94 PH/PDI V-2 BHolian:

C~/1 94 OF CIAL RECORD COPY 7t'I'

~ 7

)i I

t

'll

Mr. William L. Stewart Arizona Public Service Company Palo Verde CC Mr. Steve Olea Arizona Corporation Commission 1200 W. Washington Street

Phoenix, Arizona 85007 T.

E. Oubre, Esq.

Southern California Edison Company P., 0.

Box 800

Rosemead, California 91770 Senior Resident Inspector USNRC P. 0. Box 40

Buckeye, Arizona 85326 Regional Administrator, Region IV U. S. Nuclear Regulatory Commission Harris Tower 8 Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Mr. Charles B. Brinkman, Manager Washington Nuclear Operations ABB Combustion Engineering Nuclear Power 12300 Twinbrook Parkway, Suite 330 Rockville, Maryland 20852 Mr. Aubrey V. Godwin, Director Arizona Radiation Regulatory Agency 4814 South 40 Street Phoenix, Arizona 85040 Mr. Curtis Hoskins Executive Vice President and Chief Operating Officer Palo Verde Services 2025 N. 3rd Street, Suite 220

Phoenix, Arizona 85004 Roy P.

Lessey, Jr.,

Esq.

Akin, Gump, Strauss, Hauer and Feld El Paso Electric Company 1333 New Hampshire Avenue, Suite 400 Washington, DC 20036 Ms. Angela K. Krainik, Manager Nuclear Licensing Arizona Public Service Company P. 0.

Box 52034

Phoenix, Arizona 85072-2034

Chairman, Maricopa County Board of Supervisors ill South Third Avenue

Phoenix, Arizona 85003

~/

Enclosure RE VEST FOR ADDITIONAL INFORMATION PALO VERDE NUCLEAR GENERATING STATION ANPACITY DERATING ISSUES TAC NOS.

885583 885584 885585 GENERAL NODELING CONCERNS The Bechtel/PVNGS total heat rejection capacity analysis methodology as documented in the licensee submittal dated September 27, 1993, provides an assessment of the overall behavior of the protected system only, and provides no assessment of the behavior of individual cables within that system.

The "Watts/ft" analysis methodology utilized by Bechtel serves as a general design tool to assess the general limits of allowable cable loading within a given cable routing system.

Bechtel recognized the limits of this methodology in the following statement (See Enclosure 3 of the licensee submittal, Sheet 21 of the Bechtel TPO Design Guide E2.6.4, Revision 2):

CAUTION: Since "watts per foot" or "watts per foot per unit width" correlates with AVERAGE temperatures each such case should be analyzed to ensure against hot-spots.