ML17355A279
| ML17355A279 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point, Saint Lucie  |
| Issue date: | 03/26/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17355A277 | List: |
| References | |
| GL-92-08, GL-92-8, NUDOCS 9904020215 | |
| Download: ML17355A279 (18) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON> O.C. 20555-0001 Op o~
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SAFETY EVALUATIONBYTHE OFFICE OF NUCLEAR REACTOR REGULATION GENERIC LETTER 92-08 AMPACITYDERATING ISSUES FLORIDAPOWER & LIGHTCOMPANY ST. LUCIE PLANT UNITS 1 AND 2 TURKEYPOINT PLANT UNITS 3 AND4 DOCKET NOS. 50-335 50-389 50-250 AND 50-251
1.0 BACKGROUND
By letters dated December 19, 1996, and March 7, 1997, Florida Power and Light Company (FPL) submitted responses to the NRC Request for A'dditional Information (RAI) dated November 6, 1996, and January 29, 1997, related to Generic Letter (GL) 92-08, "Thermo-Lag 330-1 Fire Barriers," for St. Lucie Plant (SLP), Units 1 and 2, and Turkey Point Plant (TPP),
Units 3 and 4, respectively.
The licensee approach to ampacity assessment is similar for each of these two plants, and one of the supporting calculations submitted by FPL was common to both plants.
However, in assessing the adequacy of these submittals each plant's documentation was independently reviewed by the staff.
The original FPL submittals were provided in response to two preliminary staff Requests for Additional information (RAls); one for SLP dated 11/6/96, and one for TPP dated 1/29/97. The RAls in each case were quite direct and requested (1) the supporting calculations cited as the basis for the licensee assessments and (2) additional justification for the extrapolation of Texas Utilities Electric Company (TUEC) test results to the FPL fire barriers.
The licensee responses were provided under FPL cover letters dated 12/19/96 (SLP) and 3/7/97 (TPP).
Each licensee response included an extensive set of supporting calculations for SLP; Calculation SPL-OFJE-96-001, "Cable Derating in Conduits with Fire Barrier Coatings:, Revision 1, Approved 12/96.
Calculation PTN-BFJM-96-005, "Fire Barrier Ampacity Correction Factors-Extrapolation of Tests Results for 3 Hour Barrier," Revision 0, Approved 4/96.
Calculation JPN-PSL-SEES-96-059, "Engineering Evaluation of the Application of Thermo-Lag to Meet R.G. 1.75 requirements," Revision 0, Approved 8/96.
ENCLOSURE 1
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and for TPP:
Calculation PTN-BFJE-93-001, "Ampacity Derating Response to NRC GL 92-08 for Cables Routed in Conduit and Tray with Thermo-Lag 330-1 Fire Barrier System Coating," Revision 0, 7/90.
Calculation PTN-BFJM-96-028, "Fire Barrier ACF for T-Lag 330-1/770-1 Assemblies,"
Revision 6/94.
Calculation JPN-PTN-SEEP-96-011, "Review of Ampacity Ratings for Power Cables in conduits and Travs with Thermo-Lag 330-1 Covering," Revision 6/94.
Calculation PTN-BFJM-96-005, "Fire Barrier Ampacity Correction Factors - Extrapolation of Test Results for 3 Hour Barrier," Revision 6/94.
Calculation PTN-BFSE-96-006, "Ampacity Derating for Cables in Raceways and Boxes
'ith Thermo-Lag 330 and with Thermo-Lag 330 w/Layer of Thermo-Lag 770 Fire Barrier Coating," Revision 6/94.
It should be noted that Calculation PTN-BFJE-93-001 had been superseded by Calculation JPN-PTN-SEEP-96-001 and Calculation JPN-PSL-SEES-96-059 did not relate to the ampacity assessments performed by the licensee.
Therefore, the above mentioned calculations were not reviewed by the staff in the subject calculation.
The subject staff RAI had identified a number of open issues and concerns requiring clarification by the licensee.
The subject licensee submittal contained the response to staff questions regarding its ampacity derating methodology.'he staff evaluation of the ampacity derating methodology for SLP and TPP follows.
2.0 EVALUATION After reviewing the licensee's submittals and SNL Technical Letter Report (see ),
the staff agrees with the SNL analyses and conclusions.
The ampacity derating analysis questions, the licensee's responses, and the staff's evaluations of the responses follow.
Am acit Deratin Anal sis Review Question 1
St. Lucie Plant (SLP) Submittal a.
For the nominal 1-hour Thermo-Lag cladded conduit fire barriers, the licensee has assumed a fire barrier ampacity derating factor (ADF) of 11% (or an ampacity correction factor (ACF) of 0.89). This value apparently derives from the Texas Utilities Electric Company (TUEC) ampacity derating tests conducted for Comanche Peak Steam Electric Station (CPSES), Unit 2. Similarly, for the nominal 3-hour Thermo-Lag cladded fire barriers, the licensee has assumed an ADF of 20% (or ACF of 0.80). This value also appears to be derived from a thermal extrapolation of the TUEC 1-hour conduit ampacity derating tests,
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However, the maximum 11% ADF value selected by the licensee is inconsistent and nonconservative with the staff findings regarding the subject TUEC 1-hour conduit barrier tests [see Reference 1 below].
The licensee is requested either to consider more recent ampacity'erating test data compiled by Florida Power Corporation (FPC) for Crystal River, Unit 3 [see Reference 2 below] or the applicable modified TUEC ADF values as stated in the subject staff Safety Evaluation [Reference 1] as the basis for one-hour conduit ADF values.
It should be noted that the referenced FPC test ADF values compare favorably with the 11% ADF value initiallyselected by the licensee.
In the event that the licensee adopts the FPC test ADF values, the licensee should confirm that all fire barrier constructions for the applicable configurations are representative of the barrier construction used in the FPC ampacity derating tests.
b.
The staff finds that the licensee's use of the Institute of Electrical and Electronics Engineers (IEEE) "no sun - 2 ft/s" conduit baseline ampacity limits in its Calculation PSL-OFJE-001 is contrary to the accepted practice in nuclear power plant ampacity assessments for general indoor applications.
It is recommended that:
(1) baseline ampacity should be assessed on the basis of the "no sun - 0 ft/s" condition, or (2) an explicitjustification should be provided for the assumption that all cables will be subject to continuous air flowcurrents of a least 2 ft/s velocity.
The licensee is requested to consider the above information for further modification or correction of the subject calculation.
The licensee in Calculation PSL-BFJM-96-005 has assumed that inductive heat losses are not relevant to the SLP applications.
However, this does ignore the fact that the TUEC tests did experience apparent problems with inductive heating that will be reflected in the test data.
This introduces'a considerable but unquantifiable level of uncertainty into these analyses.
The licensee has taken the measured test currents as reported by TUEC directly as the basis for analysis.
However, in approving the TUEC test results [see Reference 1], the staff concluded that there was considerable uncertainty in the test results because of both the inductive heating problem and the fact that
'ifferent physical test specimens were used for the baseline and clad tests.
The licensee calculation has failed to bound this uncertainty. As recommended in Question 1.a above, the licensee is requested to consider:
(1) the use of the more recent ampacity derating test data obtained by FPC for Crystal River, Unit 3 [See Reference 2 below]; or (2) the applicable modified TUEC ADF values as stated in the subject staff Safety Evaluation [Reference 1] as the basis for conduit ADF values.
Licensee Res onse In its submittal dated June 26, 1998, the licensee responded as follows:
1.a &c The subject calculations have been updated using the FPC test results rather than the TUEC test results and the licensee indicated that the
FPC test results were applicable to SLP installations.
The licensee determined that all cables were operating within acceptable ampacity limits.
1.b The subject calculations had been revised to use the "no sun - 0 ft/s" conditions. The licensee determined that all cables were operating within acceptable ampacity limits.
The information provided by the licensee fullyresolves the staff's concerns.
Question 2 Turkey Point Plant (TPP) Submittal a.
The same concern as stated in Question 1.a above is also applicable for Calculation PTN-BFJM-96-005 and applicable conduit fire barriers installed at TPP.
b.
SNL made the following observations regarding the subject calculations:
Calculation PTN-BFJM-96-028 1.
For the cable tray case, the licensee appears to have mistaken TVAtest article 7.1 as a 3-hour barrier system with a nominal thickness of 1.25" when in fact TVAtest article 7.1 involved a test of a 1-hour system of nominal 5/8" thickness.
As a result, the licensee thermal model has understated the relative impact of the change in barrier thickness for the upgraded 3-hour barrier system in comparison to the tested 1-hour barrier system.
2.
The licensee table cites a value of 0.75" for the assumed thickness of the 3-hour plus upgrade cable tray fire barrier system.
This appears to be a simple typographical error and the calculation seems to have been performed using the correct 2" thickness.
The licensee is requested to consider the above information for further modification or correction of the subject calculation.
Calculation JPN-PTN-SEEP-96-011 1.
The licensee assessment of baseline ampacity limits for cable trays were not documented in the submittal; hence, a definitive review of these values was not possible.
Based on a simple comparison of the licensee cited values to those obtained by SNL using the ICEA P-54-440 methodology SNL found that certain licensee cited values appeared non-conservative.
Although SNL re-analyzed each of the six licensee cable tray applications using accepted methods, and based on this re-analysis, all of the cable tray applications
0 appear to have an adequate ampacity margin the licensee should document their assessment of the baseline ampacity limits for cable tray applications.
2.
In one particular cable tray case study, tray 4AXT10, the licensee has applied the methodology of IPCEA P-46-426 for cables in trays without maintained spacing.
This methodology has been superseded by the ICEA P-54-440 methodology; hence, its use in this study appears to be inappropriate.
SNL also noted that the licensee application of this method had cited open air ampacity limits for a single conductor cable when in fact the values for a 3-conductor cable should have been used.
SNL re-analyzed the case in question using the P-54<40 method, and as a result it appears that the subject ampacity loads are acceptable.
However, the licensee should re-examine the use of the IPCEA P-46426 methodology in this case.
3.
In the assessment of conduit ampacity limits, the licensee has applied conduit conductor count correction factors that inherently credit 50% diversity without explicitlyjustifying that this level of diversity does in fact exist in the applicable conduits.
This concern only impacts those few conduits with a conductor count of ten or more. Although SNL has re-analyzed the affected conduits, and it appears that even including the more conservative conductor count correction factor, the affected cables are operating within acceptable ampacity limits there should be an explicitjustification for the 50% diversity assumption.
The licensee was requested to consider the above information for further modification or correction of the subject calculation.
Licensee Res onse In its submittal dated June 26, 1998, the licensee provided the following responses for TPP:
Calculation PTN-BFJM-96-005 See response to Question 1.a above.
Calculation PTN-BFJM-96-028 uestion 2.b 1.
The licensee response clarified that the test being simulated in the subject calculation is not TVATest Item 7.1 as had been assumed in the question.
The licensee used an alternate TVAIOmega Point Laboratories test described in a journal article attached to the subject calculation. The licensee stated that the thickness values cited are appropriate given the referenced test.
2.
The licensee response clarified that each case cited in Sheet 6 was presented in a "cumulative effect" format. That is, the 0.76 inches thickness cited in the last line of the referenced table is actually added to the previous lines 1.25 inches thickness to obtain the full 2 inches thickness.
The apparent discrepancy was a misinterpretation of the subject table values.
I Calculation JPN-PTN-SEEP-96-011 uestion 2.b 1.
The licensee states that the baseline ampacity values were taken from the original design calculations prepared in 1985 and 1990 and notes that "Itis common practice to use prior calculation results as a basis for new calculations in lieu of performing duplicate calculations.
As such, these values are consistent with the design basis forTurkey Point and are considered reasonable and conservative."
2.
The licensee acknowledges that the P-46-426 methods were used in early design calculations, and that the resulting values have been retained in more recent calculations.
The licensee concludes that, "The use of IPCEA P 426 in lieu of IPCEA P-54-440 is considered appropriate in order to remain consistent with the methodology used in the original calculation." The original licensee calculation 5177-304-E005 (date unknown) was not provided in the subject submittal. The licensee did not address either the concern regarding the use of P-46-426 or the use of single conductor ampacity limits in the evaluation of 3 conductor cables.
3.
The licensee response states that the conductor count correction factors were those used in an earlier Calculation 5177-EF-15 (date unknown) and that, "justification for load diversity has been established in the original design calculations."
Staff Res onse The information provided by the licensee for Calculations PTN-BFJM-96-005 and PTN-BFJM-96-028 fullyresolves the staff's concerns.
The information provided by the licensee for Calculation JPN-PTN-SEEP-96-011 is considered to be non-responsive for the resolution of the staff's concerns.
The disposition of the associated open items are discussed in the following section.
A lication of Am acit Deratin Methodolo The licensee utilized an ampacity margins assessment based on a direct comparison of actUal in-plant service loads to derate ampacity limits for the cables.
The licensee analysis excluded the consideration of instrument, control, and intermittent load power cables (such as valves) due to the transient nature of the heat loads.
St. Lucie Calculation PTN-BFJM-96-005 is entitled "Fire Barrier Ampacity Correction Factors-Extrapolation of Test Results for 3 Hour Barrier." The purpose of the calculation is to estimate the fire barrier ADF for the 3-hour fire barriers at SLP based on the extrapolation of 1-hour system test results.
In practice, calculations were performed for both conduits and cable trays, although for SLP'it would appear that only the conduit results have been applied (no clad cable trays are identified in the SLP margins analysis).
The cable tray results were used in the TPP assessments.
Calculations PSL-OFJE-96-001 is entitled, "Cable Derating in Conduits with Fire Barrier Coatings." This calculation represents a relatively straight-forward ampacity margins assessment for the fire barrier clad cables at SLP. Allof the clad cables are housed in conduits, and there are no clad cable trays. The fire barriers include both 1-hour and 3-hour configurations.
Most installations are of a standard configuration with the exception of certain cases where multiple conduits have been clad using a common fire barrier system.
The referenced STP calculations have been revised to resolve the uncertainties associated with the application of TUEC best results and the assumption of 2 feet/second continuous air flowfor the subject application.
Given that the licensee methodology utilizes the appropriate industry test data which has been reviewed and accepted by the staff in its margins assessment, the staff finds that the submitted information supports the conclusion that the Thermo-Lag protected cables at SLP are operating within acceptable ampacity limits.
Given that the revisions to the SLP calculations have addressed all of the identified concerns, the staff finds that the licensee has provided adequate information to resolve the ampacity-related points of concern raised in GL 92-08.
Turke Point Calculation PTN-BFJM-96-028 is entitled, "Fire Barrier ACF for T-Lag 330-1/770-1 Assemblies." The stated purpose of this calculation is to extrapolate TUEC ampacity test results for nominal 1-hour and 3-hour Thermo-Lag 330-1 single layer installations for cable tray and conduits to the TPP installations involving Thermo-Lag 770-1 overlay upgrades.
This calculation is essentially identical in terms of approach and implementation to the thermal model employed in Calculation PTN-BFJM-96-005.
Calculation JPN-PTN-SEEP-96-011 is entitled, "Review of Ampacity Ratings for Power Cables in Conduits and Trays with Thermo-Lag 330-1 Covering." The objective of the calculation is to assess ampacity loads on individual cables when clad with nominal (non-upgraded) 1-hour and 3-hour Thermo-Lag barrier systems.
This assessment includes consideration of the fire barrier ACF factors as estimated in the supporting Calculation PTN-BFJM-96-005. The approach for direct ampacity margin analysis is virtually identical to the methodology applied to SLP as described above.
The licensee has determined the ampacity load and physical installation characteristics of each of the identified power cables of interest.
Baseline ampacity limits are determined, and applicable derating factors are applied to estimate the derated ampacity limit.
For cable trays it appears that only the fire barrier ACF has been applied. The resulting actual load ampacity is then compared to the estimated derated ampacity limitfor a final assessment of acceptability.
In addition, the licensee has also documented certain supplemental calculations of the heat load for the individual cables and for each cable tray or conduit as a whole. These calculations have not been utilized as a primary basis for acceptability assessment.
Essentially, the licensee conducted a "Watts per foot" type of analysis.
As the staff has cited in past reviews, the "Watts/foot" method of analysis has not been demonstrated to be technically adequate to assess individual cable performance.
Therefore, the staff does not credit the use of the "Watts/foot" analysis in these supplemented calculations for ampacity assessment.
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The open items for TPP Calculation JPN-PTN-SEEP-96-011 and their disposition with respect to the impact on safety are listed below 1.
The licensee did not verify that the cited baseline ampacity values are appropriate and consistent with accepted engineering practice.
Based on a simple comparison of the licensee cited values to those obtained using the ICEA P-54-440 methodology several licensee cited values appeared to be non-conservative.
~Dts osition:
SNL re-analyzed each of the six licensee cable tray applications using accepted methods, and based on this re-analysis, all of the cable tray applications appear to have an adequate ampacity margin.
In certain cases, the licensee cited specific use of IPCEA P-46-426 values which had been superseded by ICEA P-54-440 methodology.
Further, in one particular case, the licensee evaluated a 3-conductor cable based upon single conductor ampacity limits instead of the more restrictive 3-conductor ampacity values.
~Dis osition:
SNL re-analyzed the case in question using the P-54-440 method, and as a result it appears that the subject ampacity loads are acceptable.
In the assessment of conduit ampacity limits, the licensee has applied conduit conductor count correction factors that inherently credit 50% diversity without explicitlyjustifying that this level of diversity does in fact exist in the applicable conduits.
This concern only impacts those few conduits with a conductor count of ten or more.
~Dls osition:
SNL has re-analyzed the affected conduits, and it appears that even including the more conservative conductor count correction factor, the affected cables are operating within acceptable ampacity limits.
Calculation PTN-BFSE-96-006 is entitled "Ampacity Derating for Cables in Raceways and Boxes with Thermo-Lag 330 and with Thermo-Lag 330 w/Layer of Thermo-Lag 770 Fire Barrier Coating." The objective of this calculation is to re-assess the ampacity margins for cable in applications that have been upgraded beyond the nominal 1-hour or 3-hour barrier installations (i.e., those considered in Calculation 96-011). The cited ACF factors for the upgraded barriers are listed as derived from both Calculation 96-028 and 96-005.
The licensee approach for analysis is nominally identical for calculation PTN-BFSE-96-006 to the margins assessments performed in Calculation 96-011 as discussed above.
The primary difference lies in the nature of the fire barriers under analysis.
The only other significant difference between the subject calculation and the previous margins assessments is that an alternative definition of the margin has been employed by the licensee.
In fact, in this calculation the licensee does not present the results in the form of an available margin, but rather, cites the actual installed ampacity load as a fraction of the allowable ampacity load.
This is, in effect, a margins assessment, but should be viewed as an ACF-based margin as compared to an ADF-based margin. That is, the cited load fractions can be viewed directly as the maximum allowable ACF above and beyond the nominal assumed fire barrier derating that could be accepted by a given cable. This approach is both unusual, and different from the method used in the other FPC margins assessments.
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, It should be noted that the Open Items for Calculation JPN-PTN-SEEP-96-011 is also applicable for Calculation PTN-BFSE-96-006.
Calculation PTN-BFSE-96-006 is dependent on the use of baseline ampacity values from earlier design calculations.
As in the case of Calculation JPN-PTN-SEEP-96-011, the licensee provided sufficient information for independent verification, using currently accepted methods, that the Thermo-Lag protected cables at TPP are operating within acceptable limits.
Calculation PTN-BFJM-96-005, "Fire Barrier Ampacity Correction Factors - Extrapolation of Test Results for 3 Hour Barrier," Revision 6/94 is common to both SLP and TPP submitttal was previously discussed for SLP. Allof the findings in the context of the SLP submittal also apply for TPP.
In summary, for all of the referenced TPP calculations above, the licensee provided sufficient information for the staff to independently verify, using currently accepted methods of analysis, the assertion that the Thermo-Lag protected cables are operating within acceptable ampacity limits. Therefore, the open items associated with TPP Calculations JPN-PTN-SEEP-96-011 and PTN-BFSE-96-006 represent the potential that design engineering of future changes in the plant, as well as equipment life extension assessments (e.g., cable aging) could lead to nonconservative safety decisions.
However, it should be noted that future design changes and life extension assessments are beyond the scope of GL 92-08.
3.0 CONCLUSION
S From the above evaluation, the staff concludes that for St. Lucie Plant, all of the ampacity related concerns have been resolved and the licensee has provided an adequate technical basis to find that all of the Thermo-Lag fire barrier enclosed cables are operating within acceptable ampacity limits. Therefore, the staff finds that there are no outstanding safety concerns with respect to GL 92-08 ampacity issues.
Due to the nature of the issues raised during this review, it is recommended that the subject safety evaluation be used in any followup inspection at St. Lucie Plant.
From the above evaluation, the staff finds that although the licensee has provided sufficient information to conclude using currently acceptable methods of analysis, that the Thermo-Lag fire barrier enclosed cables at Turkey Point Plant are operating within acceptable limits, there remain open items which could impact the technical validity of the licensee's design documentation.
These open items. could impact future design changes to the plant as well as any plant life extension issues (i.e., cable aging). Although no further action is necessary at this time, the staff plans to use this safety evaluation in any followup inspection at Turkey Point Plant.
4.0 REFERENCES
1.
NRC Letter from T. Polich to C. Lance Terry dated June 14, 1995, [contains "Safety Evaluation of Ampacity Issues Related to Thermo-Lag Fire Barriers at Comanche Peak Steam Electric Station, Unit 2 (TAC NO. 859990)"]..
2.
Florida Power Corporation Ampacity Derating Tests for Crystal River Unit 3 as documented in "Ampacity Test Investigation of Raceway Fire Barriers For Conduit and Cable Tray Systems," Underwriters Laboratory Report No. 95NK17030NC1973, May 7, 1996.