05000269/FIN-2014007-04
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Finding | |
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Title | Degraded Voltage Relay Scheme |
Description | The team identified that the licensees degraded voltage relays did not monitor the safety-related 4.16kV buses, but rather they monitored the switchyard 230kV Yellow bus. This resulted in a lack of degraded voltage protection whenever the 4.16kV safety-related buses were not being fed through the start-up transformers. During normal power operation, the 4.16kV safety-related buses were supplied from the unit auxiliary transformers. Additionally, for degraded voltage detected on the 230kV switchyard Yellow bus with no accident signal present, the degraded voltage relay alarm in the main control room would have only resulted in manual actions to resolve the degraded voltage condition or to disconnect from the degraded source. It was estimated that the manual actions could take as long as 12 minutes to resolve the degraded voltage condition. The use of degraded voltage relays only on the 230kV switchyard Yellow bus and the use of manual actions for a degraded voltage condition appeared to be contrary to the design criteria for degraded voltage protection stated in an NRC letter to the licensee dated June 3, 1977 and NRC Regulatory Issue Summary 2011-12. Lastly, the team identified that Oconee currently credits operation of the loss-of-voltage relays monitoring the 4.16kV main feeder buses to disconnect from offsite power on a loss of voltage condition and subsequent re-connection to Keowee Hydro to meet the UFSAR Chapter 15 plant accident analyses. However, the loss of voltage relay setpoints and associated time delays were not included in the plant TS. This appeared to be contrary to 10 CFR 50.36(c)(2)(ii)(C) Criterion 3. The team determined that consultation with the Office of Nuclear Reactor Regulation was warranted for the NRC to determine: (1) whether Oconees existing licensing and design bases are adequate and meet all NRC regulations and requirements with their current degraded voltage relays design and off-site/station electric power system design, (2) whether the automatic actions for the loss-of-voltage relays meet the intent of the degraded voltage relays, and (3) whether the current plant TS meet the requirements of 10 CFR 50.36(c)(2)(ii)(C) which state, in part, that a TS limiting condition for operation of a nuclear reactor must be established for a structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier. The licensee entered this issue into their corrective action program as PIP O-14-2034. This issue is being tracked as URI 05000269/2014007-04, 05000270/2014007-04, 05000287/2014007-04, Degraded Voltage Relay Scheme. |
Site: | Oconee ![]() |
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Report | IR 05000269/2014007 Section 1R21 |
Date counted | Jun 30, 2014 (2014Q2) |
Type: | URI: |
cornerstone | Mitigating Systems |
Identified by: | NRC identified |
Inspection Procedure: | IP 71111.21 |
Inspectors (proximate) | G Nicely J Eargle R Nease R Williams S Pindale S Sanchez T Fanelli T Tinkel W Monk |
INPO aspect | |
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Finding - Oconee - IR 05000269/2014007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Oconee) @ 2014Q2
Self-Identified List (Oconee)
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