05000338/LER-2006-001

LER-2006-001, Virginia Electric and Power Company
North Anna Power Station
P. 0. Box 402
Mineral, Virginia 23117
May 24, 2006
U. S. Nuclear Regulatory Commission- Serial No.: 06-334
Attention: Document Control Desk NAPS: MPW
Washington, D. C. 20555-0001 Docket No.: 50-338
License No.: NPF-4
Dear Sirs:
Pursuant to 10CFR50.73, Virginia Electric and Power Company hereby submits the •
following Licensee Event Report applicable to North Anna Power Station Unit 1. ;
Report No. 50-338/2006-001-00
This report has been reviewed by the Station Nuclear Safety and Operating:Committee
and will be forwarded to the Management Safety Review Committee for its reviemi
Sincerely,
. Davis, Site Vice President
orth Anna Power Station
Enclosure
Commitments contained in this letter: None
cc: United States Nuclear Regulatory Commission
Region II
Sam Nunn Atlanta Federal Center
61 Forsyth Street, SW, Suite 23T85
Atlanta, Georgia 30303-8931
Mr. J. T. Reece
NRC Senior Resident Inspector
North Anna Power Station




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1. FACILITY NAME 2. DOCKET NUMBER 3. PAGE
NORTH ANNA POWER STATION , UNIT 1 05000 338 1 OF 3
4. TITLE
Manual Reactor Trip Due To Shutdown Bank "A" Group 2 Step Counter Inoperable

Document Numbersequential Revisionmonth Day Year Year Month Day Year
Event date:	04-07-2006
Report date:	05-24-2006
3382006001R00 - NRC Website

FACILITY NAME (1) DOCKET LER NUMBER 6) PAGE (3) :.‘. NUMBER� NUMBER 1.0 DESCRIPTION OF THE EVENT On April 7, 2006, Unit 1 was in Mode 3, zero percent power, preparing for restart following a refueling outage. Unit 1 reactor coolant temperature and pressure were 547 degrees Fahrenheit and 2235 psig, respectively. As part of the performance for rod drop time measurement testing, the Shutdown Bank "A" Groups 1 and 2 control rods were being withdrawn from the core. At 2217 hours0.0257 days <br />0.616 hours <br />0.00367 weeks <br />8.435685e-4 months <br />, the group step counters were declared inoperable as a result of Shutdown Bank "A" Group 2 step counter (EIIS System AA, Component CTR) stopping at 215 steps while Group 1 and individual rod position indicators showed continued motion to 225 steps. As a result, at 2231 hours0.0258 days <br />0.62 hours <br />0.00369 weeks <br />8.488955e-4 months <br /> the reactor trip breakers (RTB) (EIIS System AA, Component BKR) were manually opened in accordance with Technical Requirement 3.1.3 due to a mismatch of the Shutdown Bank "A" Group step counters.

Each Unit has eight control bank and four shutdown bank group step counters. All twelve Unit 1 group step counters had been replaced with digital step counters during the recent 2006 refueling outage. The existing mechanical group step counters were obsolete and prone to failure. All twelve step counters were replaced prior to rod drop time measurement testing including the Shutdown Bank "A" Group 2 step counter. The failed digital step counter was replaced on April 8, 2006, and rod drop time measurement testing was subsequently completed satisfactorily.

2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS This event posed no significant safety implications because the reactor was subcritical when the RTBs were opened. Compliance with all Technical Requirements was achieved. Therefore, the health and safety of the public were not affected by this event.

On April 8, 2006, at 0111 hours0.00128 days <br />0.0308 hours <br />1.835317e-4 weeks <br />4.22355e-5 months <br />, a non-emergency 8-hour report was made in accordance with 10 CFR 50.72(b)(3)(iv)(A) due to actuation of the Reactor Protection System (EIIS System-AA). This event is reportable pursuant to 10 CFR 50.73 (a)(2)(iv)(A) for a condition that resulted in actuation of the Reactor Protection System.

3.0 CAUSE The manual reactor trip was the result of having a mismatch in group step counters. This was the result of the Shutdown Bank "A" Group 2 step counter stopping at 215 steps while Group 1 and individual rod position indicators showed continued motion to 225 steps. The failed digital step counter for Shutdown Bank "A" Group 2 was examined upon removal. Internal connections were noted to be inadequate resulting in intermittent operation. The connection issue is attributed to the manufacturing process. The other eleven new digital step counters all performed as designed with no problems noted FACILITY NAME (1) DOCKET DLER NUMBER 6) PAGE (3) 1 NUMBER NUMBER through multiple withdraws, insertions and resets. The extent of condition is limited to the Shutdown Bank "A" Group 2 step counter.

4.0 IMMEDIATE CORRECTIVE ACTION(S) The Control Room Operators performed the required actions of the Technical Requirements within the specified times.

5.0 ADDITIONAL CORRECTIVE ACTIONS A manual reactor trip was initiated by opening the reactor trip breakers, inserting the shutdown banks into the core.

6.0 ACTIONS TO PREVENT RECURRENCE The instrumentation corrective maintenance procedure will be revised to ensure replacement instructions include steps directing pre-installation testing and inspection.

7.0 SIMILAR EVENTS The following events were reported via LERs. The cause for items 1 and 2 was equipment failure and Item 3 was caused by an improper position of the demand step counter cover.

1. LER 50-339/1998-001-00 dated 04/30/98, Manual Reactor Trip Due To Control Bank "B" Group 2 Step Counter Inoperable.

2. LER 50-339/2001-002-00 dated 04/24/01, Manual Reactor Trip Due To Control Bank "B" Group 2 Step Counter Inoperable.

3. LER 50-339/2004-002-00 dated 07/19/04, Manual Reactor Trip Due To Control Bank "D" Group 2 Step Counter Inoperable.

8.0 ADDITIONAL INFORMATION Unit 2 was not affected by this event.

Mechanical Step Counters Manufacturer: Whittaker Corporation Model:D127FD100AS/3 Replacement Digial Step Counters Manufacturer: CJ Enterprises Model:DDRSC100/B