ML17311B100
| ML17311B100 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 08/01/1995 |
| From: | Stewart W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 102-03433-WLS-A, 102-3433-WLS-A, NUDOCS 9508080325 | |
| Download: ML17311B100 (6) | |
Text
PRIORITY 1 (ACCELERATED RZDS PROCESSING)
REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS) r ACCESSION NBR:9508080325 DOC.DATE: 95/08/01 NOTARIZED: NO DOCKET FACIL:STN-50-528 Palo Verde Nuclear Station, Unit 1, Arizona Publi 05000528 p
STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi 05000529 STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTH.NAME AUTHOR AFFILIATION R
STEWART,W.L.
Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Responds to NRC 941207 RAI re Thermo-Lag-related ampacity derating issues.
DISTRIBUTION CODE:
A029D COPIES RECEIVED:LTR ENCL SIZE:
TITLE: Generic Letter 92-008 Thermal-Lag 330 Fa.re Barr er NOTES:STANDARDIZED PLANT Standardized plant.
Standardized plant.
05000528 I
05000529 05000530 T
INTERNA RECIPIENT ID CODE/NAME PD4-2 LA HOLIAN, B THOMAS,C NRR/DRPW/PD3-1 RGN4
.FILE EXTERNAL: NOAC COPIES LTTR ENCL 1
0 1
1 1
1 1
1 1
1 1
1 1
1 RECIPIENT ID CODE/NAME PD4-2 PD TRAN,L NRR/DE/EELB NRR/DSSA/SPLB NRC PDR COPIES LTTR ENCL 1
1 1
1 1
1 2
2 1
1 D
N NOTE TO ALL "RZDS" RECIPIENTS:
PLEASE HELP US TO REDUCE WASTE!
CONTACT THE DOCUMENT CONTROL
- DESK, ROOM OWFN 5D8 (415-2083)
TO ELZMZNATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED.'OTAL NUMBER,OF COPIES REQUIRED:
LTTR 13 ENCL
Arizona Public Service Company P,O. BOX 53999
~
PHOENIX, ARIZONA85072-3999 WILLIAML. STEWART EXECVTIVEVICEPAESIDENT NUCLEAR 102-03433-WLS/AKK/NLT August 1, 1995 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-37 Washington, DC 20555-0001
References:
1)
Letter dated December 7, 1994, from B. E. Holian, Senior Project Manager, Project Directorate IV-2, USNRC/NRR, to W. L. Stewart, Executive Vice President - Nuclear, APS 2)
Letter No. 102-02658, dated September 27, 1993, from W.
F.
Letter No.
102-03211, dated December 22,
- 1994, from W.
L.
Stewart, Executive Vice President, Nuclear, APS, to USNRC
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Units 1, 2, and 3 Docket Nos. STN 60-528/529/630
Response
to the Request for Additional Information Regarding Thermo-Lag-Related Ampacity Derating tssues By letter dated December 7, 1994 (Reference 1), the NRC requested Arizona Public Service Company (APS) to submit additional information to resolve open issues and concerns regarding the original analytical approach for ampacity derating determinations described in APS letter dated September 27, 1993 (Reference 2).
Specifically, in Reference 1, the NRC questioned several aspects of the "watts-per-foot" methodology for ampacity derating determinations at PVNGS.
APS is in the process of revising the cable derating analysis as part of the PVNGS design basis reconstitution effort.
This effort recognized the need to utilize the latest industry-recommended cable derating methodologies and has, therefore, eliminated the watts-per-foot methodology previously utilized.
The revised analysis constitutes a review of power cables in trays, including those which are routed through raceways enclosed in Thermo-Lag, to verify that the respective ampere loadings do not exceed the derated ampacities.
First, the ampere loading is being determined based on the characteristics of the downstream load equipment.
The rated ampacity without the fire-barrier material will be determined for each power cable AC,'A4 ~ 8 9508080325 '95080i
J i"
C Yy h
U. S. Nuclear Regulatory Commission ATTN: Document Control Desk
Response
to the RAI on Ampacity Derating Issues Page 2,.
based on PVNGS design information. This approach utilizes industry-recognized cable sizing methodologies in conjunction with as-built variables such as cable size and tray fill.
The ampacities are based'on a
maximum cable insulation design criteria temperature of 90 degrees Celsius.
Finally, a derating factor will then be applied to account for the thermal effect of the fire-barrier material.
As discussed in our December 22, 1994 letter (Reference 3), derating factors utilized for Thermo-Lag at this time, will be based on the latest available industry data.
Recent industry tests, consistent with draft IEEE P848 methodology, indicate derating factors in the range of 12% to 38%.
Prior to applying the derating factors based on industry test
- results, APS will evaluate the configurations installed at PVNGS to those tested configurations for applicability.
APS is following the resolution of NRC issues associated with the draft IEEE P848 standard and the potential generic applicability of industry tests performed to date.
Upon resolution, APS will determine to what extent specific details of cable, raceway, and fire-barrier features must be reconsidered to demonstrate specific test applicability to installed configurations.
Detailed evaluations of the tested configurations will be performed in the future, as necessary, to justifythe use of the existing tests and resulting data for derating PVNGS cables enclosed in Thermo-Lag.
PVNGS does not intend to perform ampacity testing for Thermo-Lag enclosures at this time, and is resolving ampacity issues separately from the fire endurance issues.
However, the revised analysis will be formatted in a manner that will permit rapid re-evaluation of conclusions as required.
PVNGS willalso consider whether or not the fire-barrier material is required to meet regulatory requirements and commitments and may remove Thermo-Lag barriers as warranted.
Please note that during the design basis reconstitution effort, cases have been identified where the load current through the cable exceeds the standard ampacity values derived utilizing the ICEA Standard P-54-440.
Conservatisms inherent in this standard and more rigorous analytical methods of performing the calculation, including cable diversity considerations, are being evaluated.
APS has documented and is evaluating these cases in accordance with the PVNGS corrective action program.
Should it be determined that a reportable condition or an operability concern exists, APS will take appropriate action(s).
The NRC concerns documented in Reference 1 are addressed by adopting the new methodology as follows:
~
General Modeling Concerns:
The thermal behavior of individual cables is considered with the new methodology, in contrast with the watts-per-foot method which considered only the overall behavior of the system.
U. S. Nuclear Regulatory Commission ATTN: Document Control Desk
Response
to the RAI on Ampacity Derating Issues Page 3
Cable 'Loading Effects:
The power density within the cable mass is accounted for in the new methodology by the selection of the appropriate ampacity for the particular configuration prior to the application of the derating factor, thereby accounting for power density and tray fill. Power density and tray fill parameters are readily available in design documents and databases at PVNGS.
3.
Cable Tray Diversity Effects: The new methodology will consider the heat transfer behavior of individual cables thereby eliminating the concerns regarding cable diversity.
Extrapolation of Experimental Results:
Experimental results which were the basis ofthe watts-per-foot methodology are not applicable with the new methodology. More recent tests which utilize draft IEEE P848 methodology more accurately isolate the insulating effect of the fire-barrier material as stated in Reference 1.
Documentation of Cable Types and Properties:
APS recognizes the NRC's difficulty in identifying cable sizes with the information contained in the analysis previously provided to the NRC.
APS will clearly identify each cable of interest, including the physical characteristics of each cable and the actual in-plant ampacity factors, in the revised analysis.
Validation of the "Watts/Ft" Method:
As discussed above, APS is in the process of adopting a
new methodology for ampacity derating determinations as part of the design basis reconstitution effort and, therefore, willnot be extrapolating Stolpe data to validate the watts-per-foot method.
Should you have any questions, please contact Scott A. Bauer at (602) 393-5978.
Sincerely, WLS/AKK/NLT/rv
.cc:
L. J. Callan K. E. Perkins B. E. Holian K. E. Johnston
~ l
~
1