05000328/LER-2014-001
| Sequoyah Nuclear Plant Unit 2 | |
| Event date: | 04-29-2014 |
|---|---|
| Report date: | 06-25-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3282014001R00 - NRC Website | |
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I. PLANT OPERATING CONDITIONS BEFORE THE EVENT
At the time of the event, Sequoyah Nuclear Plant (SQN) Unit 1 reactor was operating at approximately 100 percent rated thermal power and the Unit 2 reactor was operating at approximately 83 percent rated thermal power. The condition described in this LER did not affect SQN Unit 1.
II. DESCRIPTION OF EVENTS
A. Event:
On April 29, 2014, during the performance of 0-SO-30-3, "Containment Purge System Operation," the two containment purge air exhaust radiation monitors (SQN-2-RM-090-130 and SQN-2-RM-090-131) [El IS Code RA] were discovered aligned to train A containment purge [EIIS Code BB]. From April 8 to April 28, 2014, train B containment purge was operated three times with both radiation monitors aligned to train A purge. The containment purge radiation monitors provide containment ventilation isolation (CVI) signals upon a high radiation condition to mitigate the release of radioactivity from inside containment. With the radiation monitors not aligned to the train of containment purge exhaust being operated, the ability to signal a CVI from the containment purge exhaust monitors was lost.
B. Status of structures, components, or systems that were inoperable at the start of the event and contributed to the event:
Upon detecting a condition beyond the high-radiation setpoint, the aligned containment purge exhaust radiation monitor transmits a high-radiation signal to initiate a CVI. This control action is a safety function. On March 31, 2014, procedure 0-SI-CEM-030-410.2, "Containment Upper and Lower Compartment Purge," was performed to align both radiation monitors to train A containment purge. Per the Operator narrative logs, train B containment purge was operated three times between April 8 and April 28, 2014 (see timeline below). With both radiation monitors aligned to train A containment purge and train B purge in service, the containment purge air exhaust radiation monitors were incapable of performing their specified safety function. In this alignment, none of the purge flow was directed through the radiation elements of the two monitors.
Upon discovery of the condition on April 29, 2014, the radiation monitors were immediately aligned to train B of containment purge and train B was placed in service Sequoyah Nuclear Plant Unit 2 05000328 C. Dates and approximate times of occurrences:
Dates Description March 31, 2014 at 2340 Eastern Daylight Time (EDT) Radiation Monitors 2-RM-090-130 and 2- RM-090-131 were aligned to train A.
April 1, 2014 at 0155
EDT
Train A purge was placed in service.
April 8, 2014 at 0917
EDT
Train A purge was removed from service.
April 8, 2014 at 0937
EDT
Train B purge was placed in service.
April 10, 2014 at 1318
EDT
Train B purge was removed from service.
April 10, 2014 at 1333
EDT
Train B purge was placed back in service.
April 14, 2014 at 1428
EDT
Train B purge was removed from service.
April 14, 2014 at 1707
EDT
Train B purge was placed back in service.
April 28, 2014 at 2155
EDT
Train B purge was removed from service April 29, 2014 at 2205
EDT
Operators discovered that 2-RM-090-130 and 2-RM-090-131 were not aligned to train B purge. Realignments were made and train B was placed in service. Service Request (SR) 878333/Problem Evaluation Report (PER) 878321 was issued to document the condition.
D. Manufacturer and model number of each component that failed during the event:
There were no component failures associated with this event. The containment purge radiation monitors were inoperable while aligned to train A with train B purge in service.
E. Other systems or secondary functions affected:
There were no other systems or functions affected by this event.
F. Method of discovery of each component or system failure or procedural error:
The misalignment of the containment purge radiation monitors was discovered during performance of 0-SO-30-3, "Containment Purge System Operation," for placing train B purge in service to lower containment.
G. The failure mode, mechanism, and effect of each failed component, if known:
There were no component failures associated with this event.
H. Operator actions:
Upon discovery of the condition, procedure 2-SO-90-2, "Gaseous Process Radiation Monitoring System," was performed immediately to swap 2-RM-090-130 and 2-RM-090- 131 from train A to train B and to verify that the radiation monitors were properly aligned to train B. Train B purge was then placed in service. SR 878333/PER 878321 was issued.
I. Automatic and manually initiated safety system responses:
There were no automatic or manually initiated safety system responses required.
Ill. CAUSE OF THE EVENT A. The cause of each component or system failure or personnel error, if known:
The train B purge was operated three times between April 8 and April 28, 2014, with both monitors aligned to the train A purge. Operators failed to perform verbatim procedure compliance when ensuring the containment purge radiation monitor alignment prior to placing containment purge in service. This alignment is required per 0-SO-30-3 section 5.4 step 10, which states "ENSURE Containment Purge and Exhaust monitor 2-RM-090- 130 and/or 2-RM-090-131 operable and aligned to the train of purge fans being used in accordance with 1(2)-S0-90-2.
On April 8 and 10, 2014, the same operator ensured both radiation monitors were operable using Main Control Room indication, and then made an assumption the monitors were aligned normally. The operator was satisfied that the step was performed and signed for its completion.
On April 14, 2014, another operator also did not perform the ENSURE step verbatim. The operator stopped the train B purge fan to perform required valve strokes. Upon restarting the fan, the operator made the assumption that the system was aligned correctly when it was stopped; therefore, it would still be aligned correctly.
B. The cause(s) and circumstances of each human performance related root cause:
The two Operators involved in the event demonstrated less than adequate standards and responsibility for procedure use and adherence.
IV. ANALYSIS OF THE EVENT
Containment purge air exhaust radiation monitors SQN-2-RM-090-130 and SQN-2-RM-090-131 can be aligned to pull air samples from either train A or B containment purge. Samples are pulled from the containment purge ducts, and radiation levels are monitored with beta scintillation detectors. Both trains of containment purge discharge through the shield building exhaust.
Available configurations include aligning either radiation monitor to a single train of purge or aligning both monitors to a single train of purge. Alignment is accomplished through a set of valves allowing flow from the purge ducts to the radiation elements. This configuration process is controlled by 0-SO-30-3, "Containment Purge System Operation.
Each monitor is capable of generating a high-radiation alarm at a specified setpoint. Per Table 3.3-6 of Technical Specification (TS) 3.3.3.1, the setpoint for containment purge air is 5 8.5 E-3 pCi/cc. Upon detecting a condition beyond the setpoint, the aligned radiation monitor transmits a high-radiation signal to initiate a CVI. This control action is a safety function. On March 31, 2014, procedure 0-SI-CEM-030-410.2, "Containment Upper and Lower Compartment Purge," was performed to align both radiation monitors to train A containment purge. Per the Operator narrative logs, train B containment purge was operated during the below time ranges:
- April 8, 2014, 0937 through April 10, 2014, 1318
- April 10, 2014, 1333 through April 14, 2014, 1428
- April 14, 2014, 1707 through April 28, 2014, 2155 With both monitors aligned to train A containment purge and train B purge in service, the containment purge air exhaust radiation monitors were incapable of performing their specified safety function. However, during the time frame the purge monitors were misaligned, alternate means of performing a CVI were available. For design basis accidents (excluding the fuel handling event inside containment), an automatic safety injection signal would have been received which would have generated the CVI. In addition, isolation could be generated by manual containment isolation signals (phase A or B) or a manual safety injection signal.
EPIP-1, "Emergency Plan Classification Matrix" references the containment purge radiation monitors only in ALERT Emergency Action Level (EAL) 7.4, Fuel Handling — Major Damage to irradiated fuel or loss of water level that has or will uncover irradiated fuel outside the reactor vessel. The EAL requires a valid alarm on any of multiple listed radiation monitors. All of the radiation monitors listed in EAL 7.4 remained available (with the exception of the containment purge radiation monitors) during the time frame that purge was misaligned. Additionally, the shield building monitor remained functional and would have served as backup to the purge monitors. Since multiple radiation monitors remained available to allow the EAL to be declared, there was no loss of emergency assessment capability resulting from this event.
V. ASSESSMENT OF SAFETY CONSEQUENCES
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event.
This event did not result in a failed system or component. The containment purge radiation monitors were incapable of performing their specified safety function, however, alternate means of performing a CVI were available. For design basis accidents (excluding the fuel handling event inside containment), an automatic safety injection signal would have been received, which would have generated the CVI. In addition, isolation could be generated by manual containment isolation signals (phase A or B) or a manual safety injection signal.
B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
This event did not occur when the reactor was shut down. Safety-related systems that were needed to shut down the reactor, maintain safe shutdown conditions, remove residual heat or mitigate the consequences of an accident remained available throughout the event.
C. For failure that rendered a train of safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service.
On April 8, 2014 at 0937, train B containment purge was placed in service with the containment purge radiation monitors aligned to train A. This was the starting point of inoperability. Train B containment purge was taken out of service on April 28, 2014 at 2155, which marks the ending point of inoperability. On April 29 at 2205, it was discovered that the containment purge radiation monitors were misaligned and they were immediately changed to the proper alignment.
VI. CORRECTIVE ACTIONS
Corrective Actions are being managed by TVA's Corrective Action Program under PER 878321.
A. Immediate Corrective Actions:
- Train B purge realignment was performed per the procedure and placed in service.
- Operations issued a standing order to aid in ensuring procedure compliance and a Performance Observation Program (ePOP) template was created to focus operator observations towards procedure understanding, use, and compliance.
- An Incident Prompt Investigation (IPI) was performed.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future.
Corrective Actions:
- Reinforce management requirements and expectations for procedure use and adherence with shift managers.
- Conduct crew briefs of this event and reinforce requirements and expectations for procedure use and adherence with all crew operators.
VII. ADDITIONAL INFORMATION
A. Previous similar events at the same plant.
A review of previous reportable events for the past 3 years was performed and identified range neutron flux low range trip instrumentation. The direct cause of this event was a failure of Maintenance personnel to perform the maintenance procedure as written.
B. Additional information.
Containment purge radiation monitors 2-RM-090-130 and 2-RM-090-131 are required operable by TS Limiting Condition for Operation (LCO) 3.3.3.1 and TS LCO 3.3.2. TS 3.3.3.1, states, "The radiation monitoring instrumentations channels shown in Table 3.3-6 shall be OPERABLE with their alarm / trip set points within the specified limits." Action b. states, "With one or more radiation monitoring channels inoperable, take ACTION shown in Table 3.3-6." Table 3.3-6, Instrument (item) 2.a. Containment Purge Air references ACTION 28. Action 28 states, "With the number of OPERABLE channels less than required by the Minimum Channels OPERABLE requirement, comply with the ACTION requirements of Specification 3.9.9 (MODE 6) and 3.3.2 (MODES 1, 2, 3, and 4).
TS 3.3.2, states, "The Engineered Safety Feature Actuation System (ESFAS) instrumentation channels and interlocks shown in Table 3.3-3 shall be OPERABLE with their trip setpoints set consistent with the values shown in the Nominal Trip Setpoint column of Table 3.3-4." Action a. states "With an ESFAS instrumentation channel or interlock trip setpoint less conservative than the value shown in the Allowable Values column of Table 3.3-4, declare the channel inoperable and apply the applicable ACTION requirement of Table 3.3-3 until the channel is restored to OPERABLE status with the trip setpoint adjusted consistent with the Nominal Trip Setpoint value." Action b. states "With an ESFAS instrumentation channel or interlock inoperable, take the ACTION shown in Table 3.3-3." Table 3.3-3, FUNCTIONAL UNIT 3.c.3) Containment Purge Air Exhaust Monitor Radioactivity-High references ACTION 19. Action 19 states, "With less than the Minimum Channels OPERABLE, operation may continue provided the containment purge supply and exhaust valves are maintained closed.
Contrary to TS 3.3.2, Table 3.3-3, Action 19, containment purge was stopped and started three times between April 8 and April 28, 2014, with less than the minimum radiation monitoring channels operable. Therefore, the requirement for continued operation was not met.
C. Safety System Functional Failure Consideration.
This event resulted in a safety system functional failure in accordance with 10 CFR 50.73(a)(2)(v)(D).
D. Scrams with Complications Considerations.
This condition did not result in an unplanned scram with complications.
VIII. COMMITMENTS
None