05000237/LER-2002-003
| Dresden Nuclear Power Station Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2372002003R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 (If more space is required, use additional copies of NRC Form 366A)(17)
A. Plant Conditions Prior to Event:
Unit: 02 (03) � Event Date: 05-09-2002 Reactor Mode: 1(1) � Mode Name: Run (Run) Reactor Coolant System Pressure: 1005 (1002) psig
B. Description of Event:
Event Time: 1750 CDT Power Level: 97 (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 May 9, 2002, while performing the Control Room train "B" HVAC and Air Filtration [VI] Surveillance for normal operability run, the refrigeration condensing unit (RCU) compressor tripped due to high discharge pressure. The "B" train of Control Room HVAC system was secured and the "A" train started in accordance with station procedures. A review of the system operating parameters by Operations determined that there was no cooling water flow through the RCU heat exchanger. Troubleshooting of the system determined that the disk from manual valve 2/3-3999-334 (inlet) was separated from the stem and became stuck in the closed position preventing any cooling flow to the Control Room Train B HVAC RCU heat exchanger. Additional investigation determined that manual valve 2/3-3999-332 (outlet) was also found separated from stem but did not block the flowpath. The failed disks of the manual valves were evaluated and found to be corroded over the entire surfaces. A temporary modification was implemented that removed the valve internals, which restored flow to the RCU.
C. Cause of Event:
The root cause of this event was determined to be the combination of using carbon steel material and frequently exercising the valves in a Service Water [BI] environment. (NRC Cause Code E) Frequent exercising of the valves caused the protective corrosion layer on the ears to be removed, which accelerated the rate of corrosion. The immediate corrective actions were to remove the valve internals in accordance with a temporary modification, which allowed flow to the heat exchanger. Extent of condition revealed similar valves in the Diesel Generator Cooling Water System and the Control Room Train B HVAC RCU system.
Corrective actions are in place to disassemble and inspect these valves.
D. Safety Analysis:
The non-safety related Control Room HVAC System "A" train was available and started during the unavailability of the "B" train HVAC system RCU. The "A" train system is the normal supply for the control room. The heat removal capability of the "A" train system is equivalent to the "B" train and the "A" train system can be used if "B" train fails to perform its design function. Station procedures provide instructions to power the "A" Train system via an alternate power source if required, in the event of a loss of offsite power. At no time did this condition compromise the health and safety of the public.
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)
E. Corrective Actions:
A temporary configuration control package was implemented to remove the 2/3-3999-332 and 2/3-3999-334 valve internals, which restored flow to the heat exchangers.
Valves 2/3-3999-332 and 2/3-3999-334 will be replaced with stainless steel valves.
Valves that are susceptible to conditions identified in the root cause in both the Diesel Generator Cooling Water and Control Room Train B' Heating Ventilation and Air Conditioning systems will be inspected to determine if similar conditions exist. The conditions observed during the inspection of these valves will be evaluated to verify that the appropriate corrective measures are in place to prevent recurrence.
F. Previous Occurrences:
None
G. Component Failure Data:
Manufacturer Nomenclature: � Model Number: � Manufacture Part Number:
Nuclear Valve Div. / Borg-Warner � 402HBD4-001 � N/A