05000237/LER-2004-003
| Docket Number | |
| Event date: | 04-28-2004 |
|---|---|
| Report date: | 06-28-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2372004003R00 - NRC Website | |
Dresden Nuclear Power Station Units 2 and 3 are Genera! Electric Company Boiling Water Reactors 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: 4-28-2004� Event Time: 1209 CDT Reactor Mode: 1� Mode Name: Power Operation�Power Level: 52 percent Reactor Coolant System Pressure: 1000 psig
B. Description of Event:
The Units 2 and 3 Control Room Heating, Ventilation and Air Conditioning System (HVAC) has two trains, Train A and B. The Control Room Emergency Ventilation System (CREV) provides a radiologically controlled environment to the Control Room from which the unit can be safely operated following a postulated Design Basis Accident (DBA). The CREV utilizes components in Control Room HVAC Train B.
On April 19, 2004, Control Room HVAC Train B was removed from service and CREV declared inoperable to allow temporary modifications to be made to air damper solenoids to allow work to be performed on a Motor Control Center breaker. The temporary air damper solenoid modifications required the installation of tubing, fittings and pipe plugs that effected the operation of a CREV required damper. On April 22, 2004, the temporary modifications were'removed from the air damper solenoids. Control Room HVAC Train B was tested and CREV declared operable.
On April 28, 2004, with Unit 2 at 52 percent power in Mode 1, it was discovered during routine realignment of the Control Room HVAC from Train A to Train B, that dampers 2/3-5741-053B, 2/3-5741-054A, 2/3-5741-054B, and 2/3-5741-054C Eomp] failed to close. CREV requires damper 2/3-5741-053B to be capable of closure during a postulated DBA. CREV was declared inoperable at 1209 hours0.014 days <br />0.336 hours <br />0.002 weeks <br />4.600245e-4 months <br /> (CDT).
An ENS call was made on April 28, 2004, at 1750 hours0.0203 days <br />0.486 hours <br />0.00289 weeks <br />6.65875e-4 months <br /> (CDT) for the above-described event. The assigned ENS event number was 40712.
Damper 2/3-5741-053B was restored and CREV declared operable at 1201 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.569805e-4 months <br /> (CDT) on April 29, 2004.
This event is being reported In accordance with:
- 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications." Technical Specification 3.7.4, "Control Room Emergency Ventilation (CREV) System," requires that an inoperable CREV be restored to operable status within 7 days. The CREV was inoperable from April 19, 2004 to April 29, 2004.
- 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident." CREV is a single train system and damper 2/3-5741-053B is required to be capable of closure during a postulated DBA.
NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION . (7-2001) Dresden Nuclear Power Station Unit 2 05000237 NUMBER NUMBER
C. Cause of Event:
The root cause of the damper 2/3-5741-053B failure to close was determined to be Inadequate Instructions in procedure DOA 5750-01, "Ventilation System Failure.
On April 19,2004, the work order associated with the temporary modifications to the air damper solenoids used a Figure contained in procedure DOA 5750-01, "Ventilation System Failure," to describe a temporary modification and the materials needed for the work. The installation of the temporary modifications was successful. However, during the installation an Instrument Maintenance (IM) Technician became concerned that the information contained on the Figure and in the work order might not adequately address the removal of temporary piping plugs installed in the air damper solenoids. The IM Technician flagged the temporary piping plugs with a red flag and the words "Take Out.
On April 22, 2004, different IM Technicians removed the temporary air damper modifications. The IM Technicians used the Figure to remove the temporary modifications, however the Figure did not have a specific step to remove the piping plugs. The IM Technicians noticed the red flagged piping plugs but interpreted it to be an aid in finding the location of the temporary modifications and not a requirement to remove the piping plugs. As a result, the piping plugs were left in the air damper solenoids after the removal of all other components of the temporary modification. The post maintenance testing verified that the Control Room HVAC Train B could operate and the Control Room HVAC was realigned to Train A operation. CREV was declared operable The effect of the installed piping plugs in the Control Room HVAC air damper solenoids was: (1) If the Control Room HVAC was started in Train B the dampers would be correctly aligned, (2) the Control Room HVAC could be realigned from Train B to Train A, and (3) the Control Room HVAC could not be successfully realigned from Train A to Train B. The installed piping plugs were discovered as a result of attempting to transfer the Control Room HVAC from Train A to B on April 28, 2004.
The corrective actions to prevent reoccurrence are to revise procedures (1) DOA 5750-01 to include pipe plug installation as a note on Figure 3 and in the body of the procedure, and (2) MA-AA-718-010, "Maintenance Planning," to require signoffs within work orders when attached non-maintenance procedures do not have adequate details for the work to be performed.
D. Safety Analysis:
The CREV Is required to be manually Initiated within 40 minutes of a DBA. Procedure DOA 5750-01 Is used by operations personnel to respond to failures in needed plant ventilation systems including CREV. The temporary air damper modifications performed on April 19, 2004, used a temporary damper modification described in procedure DOA 5750-01 to respond to a failure of CREV to operate. The failure on April 22, 2004, to remove the piping plugs would not have prevented operations personnel from implementing the procedural requirements of DOA 5750-01 in reinstalling the air damper modifications. Thus, there is reasonable assurance that plant operations personnel could have successfully implemented the procedural response to a failure of CREV to operate during a postulated DBA. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
NRC FORM 366A� U.S. NUCLEAR REGULATORY COMMISSION (7-2001) Dresden Nuclear Power Station Unit 2 05000237 NUMBER NUMBER
E. Corrective Actions:
Damper 2/3-5741-0536 was restored to operable.
Procedure DOA 5750-01 was revised to include pipe plug installation as a note on Figure 3 and in the body of the procedure.
Procedure MA-AA-716-010 will be revised to require signoffs within work orders when attached non-maintenance procedures do not have adequate details for the work to be performed.
F. Previous Occurrences:
A review of recent Dresden Nuclear Power Station Licensee Event Reports (LERs) identified the following occurrence.
Unit 2 LER 2002-002, "Smoke Purge Mode Operation Prevents the Fulfillment of the Safety Function of the Control Room Emergency Ventilation System," describes an April 10, 2002 event in which a design error rendered the CREV inoperable when the Control Room HVAC was operated in the smoke purge mode.
G. Component Failure Data:
NA