05000298/LER-2003-007, Regarding Automatic Reactor Scram Following Reactor Feed System Control Malfunction
| ML040300514 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 01/25/2004 |
| From: | Jason Christensen Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2003131 LER 03-007-00 | |
| Download: ML040300514 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| 2982003007R00 - NRC Website | |
text
Nebraska Public Power District Always there when you need us NLS2003 131 January 25, 2004 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2003-007 Cooper Nuclear Station, NRC Docket 50-298, DPR-46 The subject Licensee Event Report is forwarded as an enclosure to this letter.
Sincerely, John Christensen Plant Manager
/dwv Enclosure cc: Regional Administrator USNRC - Region IV Senior Project Manager USNRC - NRR Project Directorate IV-I Senior Resident Inspector USNRC NPG Distribution INPO Records Center SORC Administrator Records COOPER NUCLEAR STATION P.O. Box 98/ Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 www.nppd.com i (:: :::PI
I ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS(D Correspondence Number:
NLS2003131 The following table identifies those actions committed to by Nebraska Public Power District (NPPD) in this document. Any other actions discussed in the submittal represent intended or planned actions by NPPD. They are described for information only and are not regulatory commitments. Please notify the Licensing & Regulatory Affairs Manager at Cooper Nuclear Station of any questions regarding this document or any associated regulatory commitments.
COMMITTED DATE
COMMITMENT
OR OUTAGE CNS will modify the feedwater control system to attenuate May 21, 2004 frequencies greater than one kilohertz.
I PROCEDURE 0.42 l
REVISION 13 l
PAGE 14 OF 16 l
Abstract
On November 28, 2003, 'B" Reactor Feed Pump (RFP) transferred to manual and lowered to approximately 3100 revolutions per minute causing the reactor to automatically scram on low reactor vessel water level at 2202 hours0.0255 days <br />0.612 hours <br />0.00364 weeks <br />8.37861e-4 months <br />.
Subsequent to the scram, reactor vessel water level dropped to approximately 47 inches below instrument zero resulting in Primary Containment Isolation System Group 2, 3, and 6 isolations, start of High Pressure Coolant Injection and Reactor Core Isolation Cooling systems, and automatic trip of the Reactor Recirculation pumps.
An evaluation of plant response determined all control rods fully inserted and systems controlling reactor pressure and level responded as designed.
The approximate root cause of this event is a spurious signal entered the reactor feed pump turbine controller.
Immediate action was taken to place the plant in a safe shutdown condition in Mode 3 (Hot Shutdown). Prior to plant startup, 1) operators were trained on the event, 2) radio frequency interference suppression, to attenuate frequencies greater than one megahertz, was installed on the reactor feed control input signals, 3) a modification was completed that added annunciation for a RFP in manual and provided additional signal monitoring, and 4) installed ground wires from feedwater control station cases to cabinet ground bus. Subsequent to startup and still to be completed is a modification that will attenuate frequencies greater than one kilohertz. This will prevent spurious signals in the reactor feed pump turbine controller, dampen noise on the master controller, and filter noise.
NRC FORM 366 (7-2001)
(if more space is required, use additional copies of ( more space is required, use additional copies of NRC Form 366A)
CAUSE
The approximate root cause of this event is a spurious signal entered the reactor feed pump turbine controller.
SAFETY SIGNIFICANCE
This transient was caused by the '13" RFP controller switching to manual and running back to approximately 3100 revolutions per minute. All other systems responded as expected and the '13" RFP was used to control reactor water level. This event is considered a T3A transient in the PRA model. The T3A transient scenario contains the following sequence of events:
Transients that do not result in an immediate loss of the condenser as a heat sink but which can cause a trip of the feedwater system. The feedwater system can be restarted once the trip signal is removed.
The Conditional Core Damage Probability (CCDP) for this event was 7.19E-07. This was calculated setting all initiators to 0.0 except T3A. The CCDP is bounded by the average test and maintenance CDF for T3A sequences. The CCDP is less than 1 E-06, therefore this event was not risk significant.
CORRECTIVE ACTIONS
Immediate Actions:
- 1)
Conducted operator training on the event and on response to a transfer of the RFP to manual.
- 2)
Installed radio frequency interference suppression on the reactor feed control input signals to attenuate frequencies greater than one megahertz.
- 3)
Performed a modification that added annunciation for a RFP in manual and provided additional signal monitoring.
- 4)
Installed ground wires from feedwater control station cases to cabinet ground bus.
Long Term Action:
CNS will perform a modification that will attenuate frequencies greater than one kilohertz. This will prevent spurious signals in the reactor feed pump turbine controller, dampen noise on the master controller, and filter noise. This modification will be completed by May 21, 2004.
PREVIOUS EVENTS No previous events related to the feedwater controller as this was a new digital system installed during the last refueling outage.
The manual reactor scram of May 26, 2003, at CNS, due to main turbine high vibration, resulted in reactor vessel stratification with related heatup and cooldown problems similar to this event.