05000368/LER-2015-001
| Arkansas Nuclear One, Unit 2 | |
| Event date: | 10-26-2015 |
|---|---|
| Report date: | 12-21-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3682015001R00 - NRC Website | |
A. Plant Status At the time this condition was discovered, Arkansas Nuclear One, Unit 2 (ANO-2) was operating in Mode 6 during scheduled refueling outage, 2R24, with fuel handling activities in progress in the Containment Building [NH].
B. Event Description
ANO-2 Technical Specification (TS) 3.3.3.1 requires the Containment Purge and Exhaust Isolation Process Monitor to be operable in Modes 5 and 6. On October 25, 2015, ANO-2 was defueled when the power for the Containment Building Purge Radiation Monitor Sample Pump was transferred from the normal power supply to the alternate power supply during preparation for an electrical bus outage to clean and inspect the associated normal 480 VAC load center [ED]. The sample pump secured as designed during the momentary power loss while shifting power from the normal power supply to the alternate power supply, resulting in a loss of sample flow to the Containment Purge and Exhaust Isolation Process Monitor [IL].
On October 26, 2015, at 1803 CDT, ANO-2 entered Mode 6 and commenced refueling operations. On October 26, 2015, at 2300 CDT, the Containment Purge and Exhaust Isolation Process Monitor was identified as inoperable due to not having its required sample pump in operation. ANO-2 entered TS 3.3.3.1, Action B, suspended fuel movement, verified a purge was not in progress, and verified the applicable Super Particulate Iodine and Noble Gas (SPING) monitor was functional and in operation. On October 26, 2015, at 2307 CDT, the Containment Building Purge Radiation Monitor Sample Pump was restarted and at 2308 CDT, ANO-2 exited TS 3.3.3.1, Action B. For approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> ANO-2 was in Mode 6 with refueling operations in progress while the Containment Purge and Exhaust Isolation Process Monitor was inoperable.
C. Apparent Causes A human performance error resulted in this condition due to using the wrong sample flow indication to verify flow to the Containment Purge and Exhaust Isolation Process Monitor.
D. Corrective Actions
Corrective actions completed:
Performed a human performance error review for this event.
Corrective actions planned include:
Revising procedure OP-2107.007, Engineered Safety Features Electrical Bus Outage, Attachment W, to add clarification of starting the Containment Building Purge Radiation Monitor Sample Pump and to clarify the location of its flow indication.
Revising procedure OP-2104.033, Containment Atmosphere Control, to add a step to verify the Containment Building Purge Radiation Monitor Sample Pump is operating when restarting the Containment Purge Exhaust Fan for continuous ventilation.
Revising checklist OPS-B36, Core Alterations Checklist, to require verification that the Containment Building Radiation Monitor Sample Pump is in operation prior to Core Alterations.
E. Safety Significance
Failure of two entire fuel assemblies is the bounding fuel handing accident for ANO-2. The offsite dose consequences from gases released during a fuel handling accident directly to the atmosphere with no filtration, assuming the reactor has been shut down for 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> (TS prohibits fuel handling operations prior to this time), will not exceed the acceptable limits of 10 CFR 50.67. The stated condition in this report affected the monitoring and automatic isolation of the Containment Purge exhaust pathway. The condition would not have prohibited the pathway from being manually secured from the Control Room. The SPING continued to monitor the release pathway and would have provided Control Room alarm upon high radiation signal.
Fuel handling is continuously attended and a fuel handling accident would be required to release the radiation from the fuel assembly. ANO-2 has a specific procedure for a Fuel Handling Accident which utilizes multiple diverse indications to identify fuel damage. The procedure directs that Containment Purge be secured. Based on the alternate indications available to identify a fuel handling accident, the procedural guidance to secure Containment Purge if a fuel handling accident occurs, and the bounding accident requiring two entire assemblies to be damaged and the gases exhausted through an unfiltered exhaust path, this condition had minimal safety significance.
F. Basis For Reportability TS 3.3.3.1 requires that the radiation monitoring instrumentation channels shown in Table 3.3-6 shall be operable with the alarm/trip setpoints within the specified limits.
Table 3.3-6 requires the Containment Purge and Exhaust Isolation Process Monitor to be operable in Modes 5 and 6 or to take action in accordance with Action 16.
Action 16 — With the number of operable channels one less than the minimum channels operable requirement, complete the following:
a. If performing core alterations or moving irradiated fuel within the reactor building, secure the containment purge system or suspend core alterations and movement of irradiated fuel within the reactor building.
b. If a containment purge is in progress, secure the containment purge system.
c. If continuously ventilating, verify the SPING monitor operable or perform the actions of the Offsite Dose Calculation Manual, Appendix 2, Table 2.2-1, or secure the containment purge system.
The operability of the radiation monitoring channel ensures that the radiation levels are continually measured in the areas served by the individual channel and the alarm or automatic action is initiated when the radiation level setpoint is exceeded.
Movement of irradiated fuel assemblies on October 26, 2015, with the Containment Purge and Exhaust Isolation Process Monitor inoperable, resulted in operation prohibited by TS.
This report is submitted in accordance with 10 CFR 50.73(a)(2)(i)(B).
G. Additional Information
10 CFR 50.73(b)(5) states that this report shall contain reference to "any previous similar events at the same plant that are known to the licensee." NUREG-1022, Revision 3, reporting guidance states that the phrase "previous occurrences" should include previous events or conditions that involved the same underlying concern or reason as this event, such as the same root cause, failure, or sequence of events.
A review of the ANO corrective action program and Licensee Event Reports for the previous three years was performed. The following ANO events were related to conditions prohibited by technical specifications.
- October 24, 2014 (2CAN101402), Technical Specification 3.0.4 Violation due to a Mode Change with an Inoperable Emergency Feedwater Pump
- May 15, 2014 (2CAN051405), Operation of Switchgear Rooms' Ventilation Prohibited by Technical Specifications
- October 21, 2013 (2CAN101303), An Inoperable Offsite Power Supply Transformer due to an Inadequate Design Configuration Results in a Condition Prohibited by Technical Specifications
- April 04, 2013 (0CAN041302), An Inoperable Emergency Control Room Chiller due to Maintenance Error Results in a Prevented Safety Function Entergy Industry Identification System (EllS) codes are identified in the text as [XX].