05000390/FIN-2010007-02
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Finding | |
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| Title | INSTALLED INSULATING FLUID IN INTERIOR TRANSFORMERS POTENTIALLY DEVIATES FROM LICENSE/DESIGN CRITERION IN SSER 10 AND POSITION D.1.g OF APPENDIX A TO BTP (APCSB) 9.5-1 |
| Description | The inspectors opened an URI related to questions regarding the licensees compliance with all provisions of their NRC-approved FPP. Specifically, the inspectors raised questions regarding the dielectric insulating liquid used for indoor power transformers as specified Appendix FF, Section 5.10.2 of SSER 18 and NRC Position D.1.g of Appendix A to BTP APCSB 9.5-l, Guidelines for Fire Protection for Nuclear Power Plants, dated August 23, 1976. Fire Area FA 37 (AV-064) contained four liquid-insulated 6.9kV to 480V shutdown board transformers, in groups of two inside containment curbs. These medium voltage transformers were insulated with a silicone-type dielectric insulating fluid. Three of the four transformers (1-OXF-212-A2-A, 1-OXF-212-A1-A, and 1-OXF- 212-A-A) contained an estimated 317 gallons of insulating fluid and the other transformer (0-OXF-206-A) contained approximately 205 gallons. Near these transformers were combinations of redundant safety-related cable trays or conduits or both. While performing the review of FA 37 (AV-064), the inspectors identified the indoor power transformers dielectric insulating liquid was not consistent with that described in SSER 18, section 5.10.2, Askarel-Insulated Transformers and NRC Position D.1.g of Appendix A to (BTP) APCSB 9.5-l, Guidelines for Fire Protection for Nuclear Power Plants. Section 5.10.2 of SSER 18 specified that indoor transformers would be either a dry type or insulated with non-combustible liquid. Section 5.10.2 of SSER 18 further stated that Askarel was used as the noncombustible liquid for indoor transformers. The inspectors determined that the SSER reference was based on transformer insulating liquid being noncombustible material (negligible combustible loading) which did not represent an ignition source. However, during the inspection the inspectors found that the transformers in FA 37 did not contain the specified dry type or non-combustible dielectric insulating material, but were insulated with a silicon-based combustible dielectric liquid. Furthermore, Position D.1.g. (ii) of Appendix A to (BTP) APCSB 9.5-l specified that safety related systems that are exposed to flammable oil-filled transformers should be protected from the effects of a fire by enclosing the transformer with a three-hour fire barrier and installing an automatic water spray protection. The transformers had not been enclosed with such a barrier. The inspectors reviewed Part VI of the WBN FPR (Revision 39) and found that the fire rating of the regulatory barriers for the floor and walls in FA 37 was two-hours. The inspectors also reviewed WBN FPR, Part 1, Table 1-1, Summary of Fire Protection Conformance, (Revision 27) which specified that safe shutdown equipment cables were located in FA 37 and were protected with a credited one-hour rated fire resistive wrap. Table 1-1 of the FPR also identified that the area total fixed combustible load fire severity for a 3-hour rated barrier was classified as Moderately Severe, e.g., less-than 240,000 Btu/ft2. The inspectors reviewed the combustible loading summary calculationEPM-DOM-012990, (Revision 41) for FA 37 and found that the fuel load in the area was 164,549 Btu/ft2, which exceeded the 2-hour rated barrier criteria of 160,000 Btu/ft2. Additionally, the review of WBN FPR, Part VII, Deviations and Evaluations, (Revision 10) noted that the licensees evaluation for deviation 2.4 concerning intervening combustibles did not specifically consider the transformers in the area (insulated with a combustible dielectric liquid) as a potential intervening combustible located between redundant components. The licensee was not able to provide a documented technical evaluation which justified the use of the combustible dielectric insulating liquid and its associated contribution to the area combustible load fire severity or intervening combustible evaluation. In response to the inspectors questions, the licensee stated that, although SSER 18 did address Askarel oil, no additional evaluations of the type of oil used in indoor transformers was required since the SSER did not reflect the latest information provided by TVA in Revisions 4 and 5 of their FPR submitted to NRC on September 28, 1995, and November 1, 1995, respectively. The licensee stated that these submittals identified that transformers installed within safetyrelated buildings are either dry-type or insulated and cooled with high fire point (650F) liquid. Based upon the review of the WBN FPR and EPM-DOM-012990, the inspectors concluded that the transformers in the area (insulated with a combustible dielectric liquid) contributed to a total fixed fuel load fire severity that exceeded the credited fire resistive rating of the room fire barriers and could potentially challenge either the credited one-hour barrier for the safety related cables, the walls separating the adjacent FAs or both. The inspectors discussed this issue further with licensee personnel on June 13, 2011 during a teleconference. The licensee personnel stated they would provide additional information related to questions raised by inspectors regarding when the change to the combustible dielectric was made. Based upon questions raised by the inspectors, 40 additional indoor transformers were identified in Unit 1 and areas of Unit 2 (under construction) to have the same combustible dielectric liquid and located within ten (10) additional AVs (AV-1, AV-51, AV-63, AV-64, AV-68, AV-69, AV-89, AV-94, AV-95, and AV-96) at WBN. The licensee initiated service request (SR) 263312 and problem evaluation report (PER) 265331 to address the issues described in this section. Further review and consultation with NRC experts in the Office of Nuclear Reactor Regulation will be needed to determine the regulatory impacts of this issue. As a result, this issue is identified as URI 05000390/2010007-002, Installed Insulating Fluid in Interior Transformers Potentially Deviates from License/Design Criterion in SSER 18 and Position D.1.g of Appendix A to BTP (APCSB) 9.5-1. |
| Site: | Watts Bar  |
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| Report | IR 05000390/2010007 Section 1R05 |
| Date counted | Dec 31, 2010 (2010Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.05 |
| Inspectors (proximate) | N Staples G Wiseman R Fanner R Nease L Suggsd Faillae Patterson J Hamman K Miller M Speck R Baldwin R Lanyi R Monk S Shaeffer |
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Finding - Watts Bar - IR 05000390/2010007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Watts Bar) @ 2010Q4
Self-Identified List (Watts Bar)
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