05000390/FIN-2018010-03
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Finding | |
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| Title | Potential Failure to Maintain Design Requirements of RTDs |
| Description | The TAS RTD receipt documents specified design criteria identified in EQOP-ESE-7 in WCAP 8587 and the EQTR WCAP-8687 Supp. 2-E07A. The installed condition of the RTDs did not appear to meet the qualification performance specifications. Testing performed indicated that a gap existed between the RTDs and installed thermowells creating a large thermal resistance. Westinghouse document FDR-WBT-2015-01, Field Deviation Notice for Watts Bar Unit 2, indicated that the RTD/thermowell fit for the tip was outside the maximum tolerance listed in design drawing 1847E83 Rev. 4. The performance specifications were to ensure that the RTD time response across the thermowells thermal resistance was within tolerance. The higher thermal resistance increased the response time. The deviation appeared to be accepted as is. The Westinghouse equipment qualification data package, WCAP 8587/EQOP-ESE-7 Supplement 1 Rev. 7, page D1-5 Rev. 21, specified, in part that the performance requirements for the RTDs must meet +0.2"F repeatability; first order time response 5 seconds with well for step change of at least 20F with a water flow of 7 ft/sec. ...Time response testing has been successfully performed via type testing on a sample model of this RTD. The performance requirement appears to require a 5-second RTD/thermowell response time for qualification directly measured across the thermowell medium. The inspectors are concerned that the installed RTD/thermowell configuration was not verified to meet the performance requirements for qualification. It appeared that, due to the installation issues, the RTD response time increased, as measured by LCSR testing methods, the total delay time of 9.8 seconds. However, Westinghouse used a total response time of only 9.0 seconds for their analyses at the direction of TVA specification per WBT-TVA-3027, Revision 0, PIN ELICB-055 Evaluation to Support a 9.0-second Total RTD Response Time, August 2015. The analyses determined that some accident margins were impacted at 9.0 seconds. The inspectors questioned what the impact of the additional delay would have on the accident analyses and qualification. The inspectors questioned how the LCSR test method could accurately account for increased thermal resistance between the RTDs and the thermowells and whether the original 10-percent uncertainty for LCSR testing was adequate in the currently installed configuration. The validity of the LCSR method depends on how well the temperature sensor design satisfies LCSR test assumptions. The original installations relied on specific RTD thermowell bonding to establish a predictable thermal resistance and initial response time. It is unclear how the actual response time was determined this installation. This URI is being opened to determine if a PD exists. A review of documents and specifications provided by licensee indicated that new information requests would be likely. This issue has existed since September 2015. This issue was captured in CR 1398936, RCS Narrow Range RTDs Design and Qualification Requirements. |
| Site: | Watts Bar  |
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| Report | IR 05000390/2018010 Section 1R17 |
| Date counted | Mar 31, 2018 (2018Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.17 |
| Inspectors (proximate) | T Fanelli R Patterson C Franklin M Sykes |
| Violation of: | Pending |
| INPO aspect | |
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Finding - Watts Bar - IR 05000390/2018010 | |||||||||||||||||||||||||||||||||||||||
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Finding List (Watts Bar) @ 2018Q1
Self-Identified List (Watts Bar)
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