05000410/LER-2014-006
| Nine Mile Point Unit 2 | |
| Event date: | 3-24-2014 |
|---|---|
| Report date: | 5-23-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 4102014006R00 - NRC Website | |
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I. DESCRIPTION OF EVENT
A. PRE-EVENT PLANT CONDITIONS:
Prior to the event, Nine Mile Point Unit 2 (NMP2) was at 18% reactor power approaching a refueling outage.
B. EVENT:
On March 23 at 2059, Operators lined up auxiliary steam from the operating Auxiliary Boiler 'B' (2ABM-B1B) to the building heating system to support plant shutdown.
At 2303, Operators started Auxiliary Boiler 'A' (2ABM-B1A). An equipment malfunction caused the Auxiliary Boiler 'B' to trip at 2306. Auxiliary Boiler 'A' tripped on high ground current at 2329. This caused a loss of Reactor Building heating which made it necessary for Operators to isolate the Reactor Building as a measure to maintain building temperature and pressure. This action resulted in the non-functionality of the Reactor Building vent radiation monitor which reduced the emergency assessment capability. While responding to lowering temperatures and rising pressure in secondary containment, secondary containment pressure degraded beyond the Technical Specification (TS) limit of 0.25 inch of vacuum water gauge. This required declaring secondary containment inoperable on March 24 at 0031.
The inoperability of secondary containment lasted for a total of 3 minutes. Operators responded by re-aligning the Reactor Building standby gaseous treatment system (GTS) from primary containment purge mode to Reactor Building suction mode and isolating the normal Reactor Building ventilation system to restore operability of secondary containment. Secondary containment was declared operable on March 24 at 0034.
Operators also took action to restore the auxiliary boiler system in order to support restoring Reactor Building heating and ventilation to a normal lineup. On March 24 at 0102, Operators re-started Auxiliary Boiler 'B' to restore Reactor Building heating. The WRGMS was restored on March 24 at 0526.
Nine Mile Point Unit 1 (NMP1) was unaffected by the occurrence of secondary containment inoperability at NMP2.
The loss of secondary containment operability has been entered into the plant's corrective action program as CR-2014-002281.
Nine Mile Point Unit 2 05000410
C. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED
TO THE EVENT:
There were no inoperable structures, components or systems that contributed to the event other than the components identified in Section I.B.
D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:
The dates, times and major occurrences for this event are as follows:
March 23 1943 Operators log the start of Auxiliary Boiler 'B' 2ABM-B1B to support plant shutdown 2059 Operators line up auxiliary steam from the operating Auxiliary boiler 'B' 2ABM-B1B to the auxiliary heat exchangers to support plant shutdown 2303 Auxiliary Boiler 'A' 2ABM-B1A started 2306 Auxiliary Boiler 'B' 2ABM-B1B trips 2329 Auxiliary Boiler 'A' 2ABM-B1A trips on high ground current March 24 0031 Secondary Containment exceeds TS limit 0034 Secondary Containment differential pressure (dP) is restored, Secondary Containment is declared operable 0102 Operators start Auxiliary Boiler 'B' 2ABM-B1B in manual 0526 Vent WRGMS restored
E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:
No other systems or secondary functions were affected beyond the systems discussed in Section I.B.
F. METHOD OF DISCOVERY:
This condition was recognized by Operations as they monitored secondary containment dP becoming positive and exceeding the TS limit.
G. MAJOR OPERATOR ACTION:
Operators managed the event through use of N2-EOP-SC, "Secondary Containment — Flowchart" and EPMP-EPP-13, "Equipment Important to Assuring Implementation Capability of the Emergency Preparedness Program". With the use of these procedures, an alternate means to sample gaseous release from the stack and maintain the secondary containment envelope in a vacuum condition was established. The dP subsequently returned to greater than 0.25 inch vacuum water gauge following a duration of 3 minutes outside of TS limits.
H. SAFETY SYSTEM RESPONSES:
This event was caused when the Reactor Building was isolated and building dP began to exceed the TS limit. The GTS performed as expected to restore the required building dP.
II. CAUSE OF EVENT:
The cause of this event is attributed to the failure of the auxiliary boilers. The loss of this equipment resulted in challenges to Reactor Building heating and operation of the building ventilation. The maintenance of primary containment heating is significant for maintaining the limits of the secondary containment draw down analysis and protecting design attributes such as containment penetration nil ductility temperature. Isolation of the Reactor Building resulted in the loss of Vent WRGMS.
III. ANALYSIS OF THE EVENT:
The event described in this LER is reportable under 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.73(a)(2)(v)(C) as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. In addition, isolation of the Reactor Building vent radiation monitor which occurred during the event is reportable under 10 CFR 50.72 (b)(3)(xiii) and represented a loss of emergency assessment capability.
Decreasing external temperatures combined with the loss of 2ABM-B1B and 2ABM-B1A challenged operators to maintain Reactor Building heating and the operation of building ventilation. Actions taken by Operators resulted in the isolation of the Reactor Building and the non functionality of the Ventilation Wide Range Gaseous Monitoring System. The change in secondary containment dP which eventually exceeded TS limits was detected by operators as they implemented measures to preserve design parameters. The causal analysis noted that inadequate equipment maintenance management and chemistry control adversely impacted the reliability of the auxiliary boilers. The less than adequate maintenance performance preceding the event resulted in the auxiliary boiler equipment failure.
During this event, the required TS action statements and plant procedures were entered and subsequently exited once the secondary containment dP was restored to above the required TS minimum value. In all cases, the TS required completion time was not exceeded. The secondary containment structural integrity, the ability to automatically isolate the non-safety related Reactor Building Ventilation System, and the GTS availability were not impacted.
Based on the above discussion, it is concluded that the safety significance of this event is low and the event did not pose a threat to the health and safety of the public or plant personnel.
This event does not affect the NRC Regulatory Oversight Process Indicators.
IV. CORRECTIVE ACTIONS:
A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL
STATUS:
Operators entered plant procedure N2-EOP-SC as a means to return NMP2 to pre- event normal status.
B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:
Revise a plant procedure for Operations to provide adequate details for system operational requirements and guidelines to ensure operating parameters are maintained within specifications during operation of the boilers.
Revise a plant procedure for Operations to require a chemistry sample be taken each shift, analyzed and reported to Operations when an auxiliary boiler is in operation.
V. ADDITIONAL INFORMATION:
A. FAILED COMPONENTS:
The loss of the auxiliary boilers contributed to this event.
B. PREVIOUS LERs ON SIMILAR EVENTS:
A previous LER on a similar event was not identified.
C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EDS) COMPONENT FUNCTION
IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED
TO IN THIS LER:
COMPONENT
IEEE 803 FUNCTION IEEE 805 SYSTEM
IDENTIFIER IDENTIFICATION
Reactor Building (BWR) N/A NG Reactor Building Ventilation System PDIC VA Reactor Building Vent Radiation Monitoring System
MON IL
Auxiliary Boiler BLR SA
D. SPECIAL COMMENTS:
None