05000237/LER-2002-002
| Dresden Nuclear Power Station Unit 2 | |
| Event date: | 04-10-2002 |
|---|---|
| Report date: | 06-10-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2372002002R00 - NRC Website | |
LICENSEE EVENT REPORT (LER) 133), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person � is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17)
A. Plant Conditions Prior to Event:
Unit: 02 (03) � Event Date: 04-10-2002 Reactor Mode: 1(1) � Mode Name: Run (Run) Reactor Coolant System Pressure: 1002 (1001) psig
B. Description of Event:
Event Time: 1835 CST Power Level: 95 (100) percent This event is being reported in accordance with 10 CFR 50.73 (a)(2)(v)(D), which requires reporting "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.
On April 10, 2002, at approximately 1835 hours0.0212 days <br />0.51 hours <br />0.00303 weeks <br />6.982175e-4 months <br />, control room personnel received the "CTRL ROOM HVAC FIRE PANEL TROUBLE" annunciator. Additionally, as a result of the alarmed condition, the control room heating ventilation and air conditioning (HVAC) system automatically realigned from its normal mode of operation to the smoke purge mode. Operations personnel were dispatched to the local alarm panel to determine the cause of the alarm condition. The local panel indicated that smoke had been detected in the control room return air ductwork.
A walkdown of potential areas was immediately performed. There was no observed indication of smoke or fire.
The smoke purge mode of operation aligns the control room HVAC system to provide 100 percent outside air to remove smoke from the control room area. The initiation was not capable of being immediately reset. The approximate flow rate of air is 20,000 scfm, which would render the control room emergency air filtration unit incapable of mitigating the control room dose expected during an accident.
Plant personnel investigated the possible causes of the initiation. At approximately 2144 hours0.0248 days <br />0.596 hours <br />0.00354 weeks <br />8.15792e-4 months <br />, the smoke purge system was reset and the control HVAC system was realigned to its normal mode of operation.
C. Cause of Event:
A review of all CREVS modification packages has identified that the original modification that installed the CREVS redundant "B" Train did not have the necessary rigor of evaluation to identify existing radiological issues when the control room "A" train smoke purge was automatically initiated. During this time period, in 1982, the modification 10 CFR 50.59 safety evaluation identified no radiological issues. The lack of personnel knowledge and the rigor of existing procedures resulted in a failure to identify the impact of the automatic initiation of the Smoke Purge Mode on the design functions of the new control room habitability requirements for radioactive contamination protection.
The root cause of this event is the lack of knowledge by personnel developing the CREVS modification packages and safety evaluations during implementation of the NUREG 0737 requirements. Personnel were not knowledgeable of the impact of smoke purge on post Three Mile Island requirements for operating reactors. (NRC Cause Code E)
D. Safety Analysis:
The automatic initiation of the smoke purge mode of operation presented a potential for increased consequences of an accident regarding control room dose. Plant personnel were unable to reset the smoke purged mode for approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. This condition did not increase the frequency of an occurrence, which would have required LICENSEE EVENT REPORT (LER) f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person � is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17) the CREV to be placed in service. Therefore probability of an occurrence concurrent with the smoke purge operation is low. At no time did this condition compromise the health and safety of the public. This condition has minimal safety significance.
E. Corrective Actions:
A temporary configuration control package was implemented to prevent the Train 'A' Heating Ventilation and Air Conditioning system from automatic alignment to smoke purge mode and the smoke purge automatic function will be permanently modified to a manual function.
A sampling of plant modifications that were completed during this period will be performed to ensure that generic implications are addressed.
In the 1990's, the process for 10 CFR 50.59 evaluations was revised to eliminate confusion and strengthened the rigor in the evaluation. Additionally, a stringent training program was established to ensure the appropriate level of personnel knowledge was used in the performance of these evaluations. Therefore, corrective actions to prevent recurrence of this type of event have been previously implemented.
F. Previous Occurrences:
Dresden Station previously issued LER 94-007, Potential Unanalyzed Control Room Habitability Condition Due to Purge Mode, associated with the Control Room HVAC System Smoke Purge Mode. The LER identified the system had been potentially operated in an unanalyzed condition. The LER did not address the automatic initiation feature of the Train 'A' Smoke Purge Mode and its impact on Train 'B' CREVS General Design Criteria (GDC) 19 requirements. At the time of LER 94-007, the Control Room Train 'A' Smoke Purge Mode was only operated manually due to the automatic feature being inoperable. Therefore previous events did not detect this design flaw.
G. Component Failure Data:
N/A