05000302/LER-2009-002
| Crystal River Unit 3 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| Initial Reporting | |
| 3022009002R00 - NRC Website | |
At 10:40, on April 30, 2009, Progress Energy Florida, Inc. (PEF), Crystal River Unit 3 (CR-3) was operating in MODE 1 (POWER OPERATION) at 100 percent RATED THERMAL POWER when the Control Room staff received multiple alarms associated with 480 volt (v) Engineered Safeguards (ES) Motor Control Center (MCC) 3B1 (MTMC-5) [ED, MCC] being de-energized.
During the performance of Work Order 1496283-08, a phase-to-ground arc flash occurred when connecting test equipment to the 'B' phase of 480v molded case circuit breaker MTMC-5-8AR [ED, 52]. As a result of the arc flash, 480v ES Bus 3B (MTSW-3G) [ED, BU] feeder breaker 2B tripped open, de-energizing 480v ES MCC-3B1.
The test equipment was being connected to ITE and Westinghouse molded case circuit breakers to measure kilowatt (KW) loading for various Alternating Current Distribution Panels (ACDPs) [ED, PL] fed from the ES buses to update assumptions in calculations on Emergency Diesel Generator margin.
ITE molded case circuit breakers have insulating material (part of the breaker case) between the conductor lugs and the back of the bucket. This makes it difficult to have an electrical path between phase and ground.
MTMC-5-8AR is a Westinghouse molded case circuit breaker that does not have insulating material between the conductor lugs and the back of the bucket. There is only a 0.5 inch air gap between the lug and the back of the bucket and it is all that separates each energized phase from ground. While attempting to connect the test lead, it was inadvertently placed inside this air gap, which resulted in a phase to ground fault and corresponding arc flash.
When 480v ES MCC-3B1 became de-energized, Improved Technical Specification (ITS) 3.8.9, "Distribution Systems — Operating," Condition A was entered. Condition A states that with one AC electrical power distribution subsystem inoperable, restore the alternating current (AC) electrical power distribution subsystem to an OPERABLE status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
Following the loss of 480v ES MCC 3B1, the following equipment was declared inoperable and the associated actions statements were applicable:
Makeup and Purification System (MU) Main Lube Oil Pump MUP-2C [CB. P] Decay Heat Removal System (DH) Isolation Valve DHV-6 [BP, ISV] "B" Train Low Pressure Injection Flow Control Valve DHV-111 [BP, FCV] DH System Pump Isolation Valve DHV-43 [BP, ISV] Main Feedwater System (FW) FWP-2A Suction Isolation Valve FWV-14 [SJ, ISV] FW System Block Valve FWV-29 [SJ, ISV] FWV-29 Bypass Isolation Valve FWV-32 [SJ, ISV] Emergency Diesel Generator EGDG-1B [EK, DG] Prior to this event, Clearance Order 185177 was in effect to perform Preventive Maintenance Procedure PM-178A, "Preventive Maintenance of Limitorque Actuators 2-Year Inspection," on High Pressure Injection System (HPI) flow control valve MUV-26 [CB, FCV]. With this clearance order in effect, CR-3 was in a planned entry into ITS 3.5.2, "Emergency Core Cooling Systems _NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER (ECCS) — Operating," Condition B. Condition B states that with one or more trains inoperable for reasons other than Condition A and at least 100 percent of the ECCS flow equivalent to a single OPERABLE ECCS train available, restore train(s) to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
Not all portions of the HPI flow path satisfy the independence criteria discussed above.
Specifically, the HPI flow path downstream of the HPI/Makeup pumps is not separable into two distinct trains. At the discharge of the HPI/Makeup pumps, a common header exists with four HPI valves (injection legs). In the event of a postulated break in the HPI injection piping, injection flow is required through a minimum of three (3) injection legs, assuming one pump operation, or through a minimum of two (2) injection legs, assuming two HPI pump operation.
When 480v ES MCC-3B1 became de-energized, loss of safety related AC main lube oil pump MUP-2C resulted in MUP-1C [CB, P] being declared inoperable in accordance with Operating Procedure OP-402, "Makeup and Purification System." Combined with the pre-existing clearance order that was hanging on MUV-26, this condition resulted in one pump operation through two (2) injection legs. The HPI system was declared inoperable and CR-3 entered ITS 3.0.3.
Due to the electrical transient, the following loads tripped off in addition to the loads lost on 480v ES MCC 3B1:
Reactor Building Air Handling Fan AHF-1B [VA, FAN] Control Complex Normal Duty Supply Fan AHF-17B [VI, FAN] Control complex Return Air Fan AHF-19B [VI, FAN] Control Complex Chiller CCHE-1B [VI, CHU] In addition, several Extraction Steam System drain trap bypass valves [SE, V] and Turbine Drain System valves [TF, V] opened. The Unit Load Demand was immediately taken to hand and reactor power was lowered to a band between 2550 megawatts-thermal (MWth) and 2570 MWth due to the additional steam flow. The Extraction Steam System and Turbine Drain System valves were closed. The highest power level observed was approximately 2618 MWth. The Licensed Power Limit for CR-3 is 2609 MWth.
At 12:04 on April 30, 2009, the clearance order on MUV-26 was lifted and verified. MUV-26 remained de-energized due to unavailability of 480v ES MCC-3B1. However, the clearance order lift restored the downstream cross-tie line and the downstream HPI line resulting in three (3) available injection legs. ITS 3.0.3 was exited. CR-3 was in ITS 3.0.3 for one hour and 24 minutes.
Remaining in ITS 3.0.3 status for greater than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> is reportable under 10CFR50.73(a)(2)(i)(B) as a 60-day Licensee Event Report. Although preparations were in progress for an orderly plant shutdown in parallel with activities for lifting the clearance order on MUV-26, no plant shutdown was required or initiated. There is no corresponding notification requirement in 10CFR50.72.
�NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER represent a significantly degraded condition because: (1) no intentional actions were taken to raise core thermal power above the Licensed Power Limit for any period of time, (2) immediate actions were taken to reduce core thermal power upon anticipation of a reactivity event; and, (3) the core thermal power average for a shift did not exceed the Licensed Power Limit.
The event did not result in the release of radioactive material. No design safety limits were exceeded and no fission product barriers or components were damaged.
Based on the above discussion, PEF concludes that being in ITS 3.0.3 for greater than one hour did not represent a reduction in the public health and safety. Since no loss of safety function occurred, this event does not meet the Nuclear Energy Institute (NEI) definition of a Safety System Functional Failure (NEI 99-02, Revision 2).
CAUSE
Two root causes were identified for this event. First, Nuclear Generation Group Safety Procedure SAF-NGGC-2175, "Electrical Safety and Arc Flash Protection," has less than adequate controls in place for working on energized equipment. Work on energized equipment is allowed when it is possible to perform the work with the equipment out of service.
Second, Procedure Adherence / Documentation Culture / Questioning Attitude did not meet expectations. Electricians were concerned with connecting test leads to the back (load side) of the molded case circuit breaker. Engineering provided communication to the Electrical Supervisor that the test leads could be connected anywhere downstream of the breaker on the load side, such as the line side of the transformer or ACDP. This was misinterpreted by the Electrical Supervisor and incorrectly communicated to the Electricians as the line side of the breaker. The work order instructions were not revised to reflect this change. Electricians continued to connect the test leads to the line side of the breaker 18 times over a 6-8 month period.
Per plant procedures NGG Administrative Procedure ADM-NGGC-0104, "Work Management Process," Administrative Instruction Al-600, "Conduct of Maintenance," and Al-607, "Pre-Job and Post-Job Briefings," when it is identified that the work will be performed differently than the work order instructions state, the worker shall stop, notify their Supervisor and take the work order _ package to Planning to have the instructions revised. Workers are trained not to deviate from work order instructions.
CORRECTIVE ACTIONS
1. Performed immediate troubleshooting and returned 480v ES MCC 3B1 to service.
2. Immediately stopped connecting test equipment to the back of Westinghouse molded case circuit breakers.
3. SAF-NGGC-2175 has been revised to specifically address work on energized equipment.
4. Additional corrective actions are identified in Nuclear Condition Report (NCR) 333515.
PREVIOUS SIMILAR EVENTS
No previous similar events have been reported to the NRC.
ATTACHMENTS
Attachment 1 — Abbreviations, Definitions, and Acronyms Attachment 2 — List of Commitments � NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER _NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER The following table identifies those actions committed by PEF in this document. Any other actions discussed in the submittal represent intended or planned actions by PEF. They are described to the NRC for the NRC's information and are not regulatory commitments. Please notify the Supervisor, Licensing and Regulatory Programs of any questions regarding this document or any associated regulatory commitments.
COMMITMENT DUE DATE
No new regulatory commitments are contained in this submittal. N/A �NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER