ML17305B007
| ML17305B007 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 08/16/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17305B006 | List: |
| References | |
| NUDOCS 9008230100 | |
| Download: ML17305B007 (6) | |
Text
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION USE OF NYLON CABLE TIES AT PALO VERDE NUCLEAR GENERATING STATION UNITS I 2 AND 3 DOCKET NOS. 50-528 50-529 AND 50-530
1.0 INTRODUCTION
In NRC Inspection Report No. 50-528/88-01 pertaining to the Palo Verde Nuclear Generating Station (PVNGS) dated March 30, 1988, the NRC Safety System Functional Inspection (SSFIj team identified a concern regarding the seismic adequacy of nylon cable ties which are used to support electrical cables in vertical cable trays at PVNGS, Units I, 2 and 3.
Arizona Public Service Company (APS or the licensee
) provided a response to this issue in a submittal to the NRC dated June 10, 1988.
Based on its review, the staff requested additional information on February 7, 1989 to complete its evaluation.
APS responded to the request by submitting further information for clarification of its previous submittal on April 4, 1989.
During a conference call on September 26, 1989, and by letter dated January 26, 1990, APS provided further confirmatory information to assure the staff that all vertical cable tray locations and their environmental conditions were duly examined and the design basis for their analysis was complete and adequate.
On May 7, 1990, APS also telecopied additional information from the Design Criteria Manual, as referenced in their January 26, 1990 submittal, in support of its analysis.
Two additional conference calls between APS and the staff took place on May 8, 1990 and June 15, 1990 (Refs.
3 and 4), which facilitated the resolution of the nylon ties issue.
Our safety evaluation is provided below.
- 2. 0 EVALUATION The staff reviewed the analysis initially submitted by APS to investigate the potential for (I) the nylon ties used to tie vertical run cable bundles at PVNGS to break during a Safe Shutdown Earthquake (SSE),
and (2) the cables to slip and produce tension on the terminal connections.
The assumptions and modeling used by the licensee to determine seismic response of the ties are based on the multi-element lumped mass method and the modeling parameters used are found reasonable and consistent with established practices.
The horizontal seismic demand on the nylon ties determined from the analysis during a safe-shutdown earthquake is compared with the tensile capacity of the ties.
Also the column action of the cables, independent of the vertical support from the ties, was assessed to have adequate stiffness to sufficiently limit the vertical displacements in the ties to levels below the available slack at the terminal connections; thus avoiding potential disengagement of vertical cable connectors.
The results of the licensee's analysis showed that the nylon ties have a
considerable safety margin against failure during SSE; and, that there will be no net tension on the terminals due to SSE loads on the cables.
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~ The staff raised a concern that the analysis might not have fully considered environmental conditions (moisture, temperature and radiation) resulting from a Design Basis Accident.
The licensee's analysis
- showed, however, that consideration of applicable environment, with respect to relative humidity, would still provide ample margins of safety; thus, the integrity of the ties would be maintained.
In regard to the acceptable temperature design basis for the ties, APS confirmed that the locations selected for temper-ature effect analysis were the worst case conditions, i.e., abnormal "mild" environmental conditions.
Other locations existed where temper-atures exceeded these conditions.
- However, APS considered these har sher temperature environments not applicable because they apply to areas where; either, (I) nylon cable ties were not utilized (Containment Building), (2) all safety-related cables were routed through conduit (Hain Steam Support Structure),
or (3) the safety-related cable trays were mounted in a horizontal position (Diesel Generator Building).
The Control Building and Fuel Building are the only areas where vertical run cable trays with nylon ties are located and the qualified temperatures for the ties (i.e.,
120 degrees F at 20% relative humidity and 185 degrees F
maximum continuous temperature) are higher than that due to the Design Basis Accident conditions (104 degrees F).
Therefore, the temperature issue is considered resolved.
The licensee has indicated that the most radiation exposure of nylon ties will be in the Fuel Handing Building where they could be exposed to an integrated 40 year dose as high as 3.5E4 rads.
The threshold for damage of nylon ties has been determined as 8.6E5 (Ref. 2).
There is an adequate margin against the threshold of damage of nylon ties.
Therefore, the radiation exposure concern for nylon ties is considered resolved.
3.0 CONCLUSION
Based on the staff's evaluation of the licensee's submittals, the results of seismic analysis of nylon tie response, and the assessment of pertinent environmental conditions (humidity, temperature and radiation exposure) for vertical run cable trays which use nylon ties, we conclude that the ties are adequately designed and installed to perform their safety functions under various conditions and their characteristics are consistent with those presented in the PVNGS's updated FSAR (Ref. I).
Therefore, the staff concludes that the use of nylon cable ties at PVNGS is acceptable.
Principal Contributors:
W. Thompson D. geng Dated:
August 16, 1990
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ADDITIONAL
REFERENCES:
1.
PVNGS UPDATED FSAR, Appendix 3E, Environmental and Seismic Qualification Parameters of Safety-Related Equipment.
2.
EPRI NP-1558 dated September 1980 "A Review of Equipment Aging Theory and Technology," table 7-10.
3.
May 8, 1990, Conference Call between APS and NRC staff as a result of questions having to do with whether the cables were considered a part of the overall structural design criteria of the cable tray structures, and whether there were locations wher e temperatures would be exceeded during a
design basis accident that would be unacceptable.
4.
June 15, 1990, Conference Call between APS and NRC staff.
This conference call confirmed May 8, 1990 question and APS submittal dated January 26, 1990, regarding possible locations of where unacceptable temperature could be found in vertical cable risers, and confirmed that areas that'might be exposed to unacceptable high temperatures were in areas where cables were within a conduit and therefore not an applicable nylon tie concern.
5.
PVNGS Design Criteria Manual, "Project General Design Criteria, Table 1-3, Design Basis Event Combinations",
as referenced in APS submittal dated January 26, 1990.
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