05000237/LER-2009-007

LER-2009-007,
Exel n.
www.exeloncorp.comExelon Generation Company, LLC Nuclear
Dresden Nuclear Power Station
6500 North Dresden Road
Morris, IL 60450-9765
10 CFR 50.73
SVPLTR # 10-0004
January 22, 2010
U. S. Nuclear Regulatory Commission
ATTN: Document Control Desk
Washington, DC 20555-0001
Dresden Nuclear Power Station, Units 2 and 3
Renewed Facility Operating License Nos. DPR-19 and DPR-25
NRC Docket Nos. 50-237 and 50-249
Subject:RLicensee Event Report 237/2009-007-00, "Reactor Protection System
Nonconformance to a Design Standard"
Enclosed is Licensee Event Report 237/2009-007-00, "Reactor Protection System
Nonconformance to a Design Standard," for Dresden Nuclear Power Station. This event is
being reported in accordance with 10 CFR 50.73(a)(2)(v)(A), "Any event or condition that could
have prevented the fulfillment of a safety function of structures or systems that are needed to
shut down the reactor and maintain it in a safe shutdown condition."
There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this letter, please contact Ms. Marri Marchionda at
(815) 416-2800.
Respectfully,
Tim Hanley
Site Vice President
Dresden Nuclear Power Station
Enclosure
cc:RRegional Administrator — NRC Region III
NRC Senior Resident Inspector — Dresden Nuclear Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION
(9-2007)
LICENSEE EVENT REPORT (LER)
(See reverse for required number of
digits/characters for each block)
1. FACILITY NAME
Dresden Nuclear Power Station, Unit 2
4. TITLE
APPROVED BY OMB: NO. 3150-0104O EXPIRES: 08/31/2010
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to, the information collection.
2. DOCKET NUMBER 3. PAGE
05000237 1O OF 3
Reactor Protection System Nonconformance to a Design Standard

Dresden Nuclear Power Station, Unit 2
Event date:	11-27-2009
Report date:	01-22-2010
Reporting criterion:	10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
2372009007R00 - NRC Website

PLANT AND SYSTEM IDENTIFICATION

Dresden Nuclear Power Station (DNPS) Unit 2 is a General Electric Company Boiling Water Reactor with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as [XX].

A. Plant Conditions Prior to Event:

Unit: 02� Event Date: 11-27-2009� Event Time: 2205 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.390025e-4 months <br /> CST Reactor Mode: 5� Mode Name: Refueling� Power Level: 000 percent

B. Description of Event:

During a field walkdown while DNPS Unit 2 was in its fall 2009 refueling outage (D2R21), it was identified that the Reactor Protection System (RPS) [JC] Pressure Switches (PS) 2-0504-A, B, C, and D all share a common sensing line with a single isolation valve (2-0504-A/D-HV). A subsequent review found a similar configuration existed on Unit 3. After further review, it was concluded that Technical Specification RPS functions 8 and 9, 'Turbine Stop Valve - Closure' and 'Turbine Control Valve Fast Closure, Trip Oil Pressure - Low' are susceptible to single point vulnerability due to a nonconformance to Institute of Electrical & Electronics Engineers (IEEE) design standard, "Proposed IEEE Criteria for Nuclear Power Plant Protection Systems", IEEE 279 -1968. Specifically, failure of the common sensing line would bypass an RPS scram function when reactor power is greater than 38.5 percent.

Based on this single point vulnerability, these RPS automatic operating bypass scram functions could have been disabled if the sensing line failed and therefore this event is reportable per 10 CFR 50.73(a)(2)(v)(A), "Any event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition.

C. Cause of Event:

Cause of this design error is unknown. Review of design documents and drawing revisions going back to the 1970s indicate that the four RPS pressure switches were connected to the common sensing line during initial plant construction. The actual cause for connecting the four RPS pressure switches to a single sensing line when two independent sensing lines exist on both units cannot be determined due to the time frame when this discrepancy occurred.

D. Safety Analysis:

No actual failure of the common sensing line existed. Any failure of the sensing line would result in control room annunciation of the condition and operators would be required to take appropriate � compensatory actions within one hour or reduce power to below 38.5 percent within four hours.

Therefore, the safety significance is minor.

E. Corrective Actions:

This discrepancy existed for both DNPS Unit 2 and Unit 3 RPS pressure switches for the Turbine Stop Valve - Closure and Turbine Control Valve Fast Closure, Trip Oil Pressure - Low trip bypass functions. For Unit 2, DNPS took actions to restore compliance to the referenced design standard prior to the return to service of the unit when two of the pressure switches were connected to a second independent sensing line. For Unit 3, DNPS has performed an operability determination, and the safety function remains operable. The Unit 3 discrepancy will be resolved during its 2010 refueling outage.

DNPS reviewed the other RPS operating bypasses on both Units and found no discrepancies.

F. Previous Occurrences:

A review of DNPS Licensee Event Reports (LERs) was performed and no recent RPS design nonconformance was identified.

G. Component Failure Data:

N/A �