05000390/LER-2006-002

LER-2006-002,

Watts Bar Nuclear Plant, Unit 1
Event date:
Report date:
3902006002R00 - NRC Website

I. Plant Concitions:

Watts Bar, Unit 1 was in Mode 1 at 100 percent power.

II. Descriptior of Event:

A. Event:

On January 27, 2006, engineering personnel reviewed operating experience from another station involving a potential loss of cooling water (Energy Industry Identification System (EIIS) Code CC) to the Chemical and Volume Control System (CVCS) Seal Water Heat Exchanger (EIIS Code CB/Hx) during an Appendix R fire event. The scenario involves a loss of Component Cooling System (CCS) flow to the CVCS Seal Water Heat Exchanger due to fire damage results in a potential high suction temperature on the running CVCS Centrifugal Charging Pump (CCP) (EIIS Code CB/P) causing a loss of adequate suction head (NPSH). During an Appendix R fire event, CCP suction is aligned in the Refueling Water Storage Tank (RWST) (EIIS Code BP/TK), normal charging and letdown (EIIS Code CB) are isolated and the only makeup flaw to Reactor Coolant System (RCS) is via the Reactor Coolant Pump (RCP)(EIIS Code AB/P) seal injection flow path. If the Seal Water Heat Exchanger cooling is lost, the CCP recirculation flow (-60 gpm) and RCP seal return flow (-12 gpm) are not cooled. The outlet of the heat exchanger combines with cool water from the RWST. The net result is that the CCP suction temperature could reach saturation temperature leading to pump cavitation. The temperature increase coulJ be high enough to potentially damage both the CCP and the RCP seals, which would result in increased seal leakage and a potential loss of RCS (EIIS Code AB) inventory. This item is being provided in accordance with 10 CFR 50.73 (a)(2)(ii)(B).

B. Inoperable Structures, Components, or Systems that Contributed to the Event There were no additional structures, components or systems inoperable at the start of the event that contributed to the event.

C. Dates and Approximate Times of Major Occurrences Date & Time Occurrences January 27, 2006 - Engineering reviewed operating experience regarding a potential Appendix R fire scenario as described above.

February 3, 2006 - 1530 EST - Precautionary fire watches established in areas potentially affected.

February 3, 2006 - 1900 EST- Abnormal Operating Instruction A01-30.2, "Fire Safe Shutdown" was revised to provide interim operator actions to mitigate the consequences of the event.

February 9, 2006 -1600 EST - Fire Protection Report, Operating Requirement (OR) 14.8.1.b, "Fire-Rated Assemblic:s," entered when engineering determination was finalized providing exactly which areas were affected. The precautionary fire watches previously put in place were adjusted.

D. Other Systems or Secondary Functions Affected

No other systems or secondary functions were affected by this event.

E. Method of Discovery

This con iition was discovered during a review of operating experience of another utility's Licensee Event Report.

F. Operator Actions No operator actions were required.

G. Safety System Responses Not applicable - No safety system responses were required.

III. CAUSE OF EVENT

A. Immediate Cause:

The immediate cause of the condition was failure to protect cooling water flow to the seal water heat exchanger from the effects of an Appendix R fire.

B. Root Cause

The cause of the event is a latent error in WBN Fire Safe Shutdown Analysis. The subject matter experts involved in preparation and review of the analysis did not evaluate the ramifications of not protecting cooling water flow to the CVCS Seal Water Heat Exchanger.

C. Contributing Factor:

There vfere not contributing factors for this condition.

IV. ANALYSIS OF THE EVENT

The folio ming five areas are affected by this condition:

1. Auxiliary Building Room 713.0-A1 between column lines A1-A3 and S-U 2. Auxiliary Building Room 737.0-A1, between column fines Al-A6 and 0-U 3. Auxiliary Building Room 737.0-A3, Heat and Vent Equipment Room 4. Auxiliary Building Room 757.0-A2, 6.9kv and 480V Shutdown Board Room A 5. Auxiliary Building Room 772.0-A1, 480V Board Room 1A The condition identified is applicable to fire areas which affect the availability of cooling for the Seal Water Heat Exchang Br. Since the design of the heat exchanger is such that it can only be cooled by the A-Train header of CCS, the safety significance is applicable for the affected fire areas in which the CCS A-Train header cannot be credited for hot standby functions.

The fire areas identified include full area automatic suppression and detection systems. Therefore, for the fire areas identified, the installed fire protection features would Identify and control the fire, and the onsite fire department would, in all proba Nifty, prevent a fire from developing to the extent that there would be a loss of CCS to the seal water heat exchanger. Additional defense in depth against the affect of a fire is provided by posting fire watches in the affected areas.

Based on it being unlikely that a plant fire would result in a loss of CCS to the seal water heat exchanger, the condition has low safely significance.

V. ASSESSMENT OF SAFETY CONSEQUENCES

Based on the above "Analysis of The Event," this event did not adversely affect the health and safety of plant personnel or the general public.

VI. CORRECTIVE ACTIONS

A. Immediate Corrective Actions

Upon learning of another station's operating experience, WBN placed roving fire watches in the suspected areas until engineering completed their assessment of the issue, and WBN put in place interim operator actions to mitigate the consequences of the event. Upon engineering confirmation that this condition existed at WBN, the roving fire watches were adjusted and limited to the areas described above.

B. Corrective Actions to Prevent Recurrence (TVA does not consider these items to constitute regulatory commitments.

TVA's corrective action program tracks completion of these actions.) The condition identified by this LER is considered to be a non-conforming condition, due to the fact that the current Fire Safe Siutdown analysis did not recognize the need to protect the seal water heat exchanger, or to evaluate the ramifications of not protecting the heat exchanger. TVA has evaluated various options to address this condition. The resolut on involves maintaining cooling water supply to the CVCS Seal Water Heat Exchanger by implementing a design change to reroute and/or provide protection for the identified vulnerable cables.

A. Failed Components

There were no failed components involved in this LER.

B. Previous LERs on Similar Events A review of previous WBN LERs revealed no other similar events within three years of this event that involved a failure to recognize the need to protect a component or to evaluate the ramifications of not protecting this component from a fire.

C. Additional Information:

None.

D. Safety System Functional Failure This event did not involve a safety system functional failure as defined in NEI 99 02, Revision 0.

E. Loss of Normal Heat Removal Consideration This event is not considered a scram with loss of normal heat removal.

VII. COMMITMENTS

None