05000298/LER-2015-004, Regarding Isolation of Shutdown Cooling Results in a Loss of Safety Function
| ML15216A362 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 07/29/2015 |
| From: | Limpias O Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2015095 LER 15-004-00 | |
| Download: ML15216A362 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 2982015004R00 - NRC Website | |
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Nebraska Public Power District Always there when you need us NLS2015095 July 29, 2015 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2015-004-00 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2015-004-00.
There are no new commitments contained in this letter.
Vice President Nuclear-Chief Nuclear Officer
/jo Attachment: Licensee Event Report 2015-004-00 cc:
Regional Administrator w/attachment USNRC - Region IV Cooper Project Manager w/attachment USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/attachment USNRC - CNS SRAB Administrator w/attachment NPG Distribution w/attachment INPO Records Center w/attachment via ICES entry SORC Chairman w/attachment CNS Records w/attachment COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 www.nppd.com
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 01/3112017
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, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REV NUMBER NO Cooper Nuclear Station 05000298 2015
- - 004
- - 00 3 of 3 During the loss of SDC, forced circulation of the reactor core was not lost. The Reactor Recirculation '(RR) loop "A" system remained in service. Based on indications from the RR system "A" loop, temperature indications showed in an increase of 18 degrees F, from 186 to 204 degrees F. The vessel drain temperature increased from 190 to 210 degrees F for a heat up of 20 degrees F during the same time period.
BASIS FOR REPORT This event is reportable under 10 CFR 50.73(a)(2)(v)(B). This was a condition which could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat.
SAFETY SIGNIFICANCE
This is a Safety System Functional Failure. The actual and potential safety consequences of this event were minimal because the isolation of the RHR Shutdown Cooling suction valves occurred due to a momentary isolation signal and did not impact the ability to restore the valves to the open position for restoring SDC to service. The interlock feature performed as designed and caused RHR-MO-17 and RHR-MO-18 to close when high pressure was present.
This event did not challenge the ability to maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
CAUSE
The root cause of the event was determined to be a design vulnerability and subsequent operation of the SDC system that resulted in a trip of the SDC suction valves due to sub-cooling and flashing in the RHR or RR system.
CORRECTIVE ACTIONS
To prevent recurrence of this event, CNS will initiate an Engineering Change request to move the location of the input pressure signals required to meet requirements of Technical Specification 3.3.6.1, Table 3.3.6.1-1, 6(a) from the RR line to the Vessel Steam Dome.
PREVIOUS EVENTS On October 14, 2012, flashing of the hot reactor coolant to steam occurred, causing a pressure spike that exceeded 72 psig. Consequently, RHR-MO-17 and RHR-MO-18 closed, isolating the RHR SDC loop. This event was reported under LER 2012-004-00, Isolation of Shutdown Cooling Results in Loss of Safety Function, dated December 6, 2012.