05000369/FIN-2018001-01
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Finding | |
|---|---|
| Title | Non-conservative Change to Core Exit Thermocouple (CET) Acceptance Criteria in Procedure PT/1/A/4600/003 D, Monthly Surveillance Items |
| Description | On December 27, 2017, the licensee made a procedure change to PT/1/A/4600/003 D, Enclosure 13.1, Main Control Board Instrumentation Checklist, to expand the acceptance criteria for operable CET readings. The existing acceptance criteria specified an upper limit of saturation temperature (TSAT) and a lower limit of TCOLD. The procedure change subtracted 20 degrees Fahrenheit from TCOLD by applying CET total loop uncertainty. The licensee surmised that a CET could be reading as low as 20 degrees Fahrenheit below TCOLD and still be operating as designed. The purpose of the change was to allow the acceptance of CETs reading below TCOLD, as a number of CETs were failed and the margin to the required number of operable CETs was challenged. The inspectors noted that this logic would only apply to CETs that may be exposed to significant bypass flow (water at or near TCOLD). However, the vast majority of CETs would be exposed to water at hot leg temperature (THOT) or higher (90 degrees Fahrenheit or more higher than the new lower limit). The new acceptance criteria would increase the probability that a CET reading significantly lower than the actual water temperature would be considered operable. Since a low reading CET is non-conservative with respect to calculating sub-cooling margin, over time enough low reading CETs could be accepted such that the average core exit temperature used to calculate sub-cooling margin would be non-conservatively biased. This could have an adverse impact on appropriate operator actions for loss of sub-cooling conditions during accident mitigation.Corrective Actions: The licensee made a procedure change to PT/1/A/4600/003 D, to require an NCR to be written for CETs reading below TCOLD to prompt an engineering evaluation of the acceptability of any low reading CET. Additionally, the licensee created an action register item to track completion of repairs/replacement of existing inoperable CETs for both units.Corrective Action Reference: The licensee entered this issue into their corrective action program (CAP)as NCR 2176763. |
| Site: | McGuire  |
|---|---|
| Report | IR 05000369/2018001 Section 1R22 |
| Date counted | Mar 31, 2018 (2018Q1) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.22 |
| Inspectors (proximate) | A Hutto R Cureton F Ehrhardt |
| Violation of: | Technical Specification - Procedures |
| INPO aspect | DM.2 |
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Finding - McGuire - IR 05000369/2018001 | |||||||||||||||||||||||||
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Finding List (McGuire) @ 2018Q1
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