ML18066A834
| ML18066A834 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 01/16/1997 |
| From: | Bordine T CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9701270175 | |
| Download: ML18066A834 (4) | |
Text
consumers Power POWERING llllClllliAN"S l'IUllillUS Palisades Nuclear Plant: 27780 Blue Star Memorial Highway, Covert, Ml 49043 January 16, 1997 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT Thomas C. Bordlne Manager, Licensing INOPERABLE CORE EXIT THERMOCOUPLE REPORT REQUIRED BY TECHNICAL SPECIFICATION 3.17.4.7 Consumers Power Company's Palisades Nuclear Plant Technical Specifications require a report to the NRC within 30 days when one channel of the Core Exit Thermocouple System is inoperable and not restored within 7 days when the reactor is above 300°F. The required report is attached.
SUMMARY
OF COMMITMENTS This letter c.antains no new commitments and no revisions to existing commitments.
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\\). Thomas C. Sardine
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Manager, Licensing CC Administrator, Region Ill, USNRC Project Manager, NRR, USNRC 2? O O l GRC Resident Inspector - Palisades Attachment 9701270175 970116 ~
PDR ADOCK 0500025.5 p
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A CMS' ENERGY COMPANY
9, ATTACHMENT CONSUMERS POWER COMPANY PALISADES PLANT DOCKET 50-255 INOPERABLE CORE EXIT THERMOCOUPLE REPORT REQUIRED BY TECHNICAL SPECIFICATION 3.17.4.7
Event Description and Analysis On December 11, 1996, with the plant nearing the end of a refueling outage, the Primary Coolant temperature at 95°F, and the Reactor Vessel head installed and tensioned, Core Exit Thermocouple (CET) #19 was declared inoperable due to a crack in its electrical connector on the In-Core Instrumentation (ICI) detector string. CETs are integral parts of the ICI detector string which includes five in-core neutron detectors located at various elevations in the core to monitor core power distribution and a CET located just above the top of the corresponding fuel assembly. The crack occurred in the heat affected zone of a weld that connects two pieces of the electrical connectors environmental cover.
CET #19 was one of the sixteen (of a total of 43 CETs) qualified in-core CET's (four per core quadrant) that are used to comply with Palisades Technical Specification 3.17.4 which identifies the Accident Monitoring Instruments that need to be operable when the Primary Coolant System (PCS) temperature is greater than 300°F. For a CET to comply with this Technical Specification, it must be environmentally qualified to operate in post-accident conditions. This requires both the ICI cable and the ICI detector string to be environmentally qualified. The CET was determined to be inoperable for post-accident monitoring since the crack in the electrical connector invalidated the, environmental qualification (EQ) of the ICI detector string. The in-core detectors on this same ICI string remained operable for monitoring core power distribution.
The crack was identified by a Westinghouse QC inspector who was present to verify proper torquing of the ICI cables to the ICI detector strings. The identification occurred prior to the attachment of the cable to the detector. This is significant since it eliminates the torquing of the ICI cable to the detector as a potential cause of failure. Following discovery of the cracked electrical connector, the QC inspector performed a visual verification on all the remaining 42 ICI detector strings. No abnormal indications were noted on any of the other electrical connectors. The cable and detector attachment was then completed.
Following the identification of the failed electrical connector, the supplier of. the ICI detector strings was contacted to discuss three issues. The first issue was the possibility of obtaining a replacement ICI string. Each ICI detector string is unique, since each one is of different length. This does not allow for standardized replacements to be maintained in inventory. Therefore, each ICI detector string is procured on an as needed basis. According to the manufacturer, the lead time for a ICI detector string is approximately 24 weeks.
The second issue included options to perform a field repair to the ICI detector to allow the detector to meet the necessary EQ requirements. The vendor indicated that a field repair was not a viable option.
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The third issue was the consideration of possible failure mechanisms to determine if the operability or reliability of the remaining ICI detectors could be subject to a similar failure. The vendor was requested to perform a technical review of their records and inspection process for the ICI detector strings and, more specifically, the electrical connectors provided to Palisades. This review concluded that this is an isolated incident and there is no documented history of failures for electrical connectors of the type observed at Palisades. This information supports the initial conclusion that this was indeed an isolated failure.
It was determined that the crack must have occurred during handling of the ICI detectors following receipt inspection. The specific timing and cause of the damage remain unknown. The crack did occur in the heat affected zone of a weld that connects two pieces of the electrical connector environmental cover. The weld area heat affected zone could have contained excessive residual stresses and additional stress could have been applied to the affected area as the ICI was moved into containment or during the installation of the ICI detector.
On December 12, 1996, a Software Change Request was written to remove CET #19 from the calculation of the average qualified CET temperature. The remaining 15 qualified CETs used in the calculation and were adequate to provide a valid indication under post accident conditions.
On December 19, 1996, at 1445, the PCS temperature was increased to greater than 300°F in preparation for startup. This placed the plant into the condition where Technical Specification 3.17.4 applies. This section of the Technical Specifications allows plant operation to continue to the next refueling outage, provided at least 3.
qualified CETs in any one quadrant remain operable.
Historically, only the 16 ICI detectors that were to be used to satisfy the technical specification requirement CETs were required to be environmentally qualified. The remaining 27 ICI detectors were not required to meet the same quality standards. At the time of the event, it was assumed that only 16 of the CETs were qualified. On December 29, 1996, it was determined that all 43 ICI detector strings had been manufactured to the same standard. Any ICI detector string could be used as a qualified instrument, provided it is connected to one of the 16 qualified cables.
Corrective Actions On January 19, 1997, with the plant in cold shutdown, CET #18 was interchanged with CET #19, in order to return the number of operable qualified CET's to 16. This fully complies with Palisades Technical Specification 3.17.4 requirements for operable CETs.
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