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| Start date | Title | Description | Topic | |
|---|---|---|---|---|
| ENS 54465 | 7 January 2020 18:41:00 | Chill Water System Inoperable | At 1341(EST), on 01/07/20, it was discovered all trains of the Chilled Water System were simultaneously Inoperable; therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v)(D). During this event, the Bravo train chiller was operating in a maintenance run and the temporary chiller was available and placed in service promptly to restore the safety function. The control room area cooling safety function was restored at time 1435 (EST) when one required train was declared Operable. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.
The purpose of this notification is to retract a previous report made on January 7, 2020, at 1909 EST (EN#54465). A subsequent evaluation determined that the Bravo train chiller, which was running at the time of the event, would be able to perform its safety function and was operable at the time of the event. Therefore, there was no loss of safety function. The NRC Senior Resident Inspector has been notified. Notified R2DO (Coovert). | |
| ENS 42641 | 14 June 2006 18:00:00 | Leaking Decay Heat Removal Isolation Valve Bypass Line | On 2-21-06, during a tour of containment during normal operation at 100% power, a small leak (one (1) to three (3) drops per second) was noted from a 1/2 inch line connected to the decay heat removal (DHR) drop line. It was identified as being a body-bonnet leak on valve 1LP-167 subject to a TS limit of 10 gpm. At approximately 1400 hours on 6-14-06 following a shutdown for an unrelated issue, the source was identified as a leak at a weld in a "tee" joint adjacent to 1LP-167. This is considered RCS pressure boundary leakage, subject to a TS limit of zero leakage. The leak was isolated by closing a normally open valve in the 1/2 inch line and the leakage stopped. Initial Safety Significance: The leak is in a 1/2 inch line which provides over pressure protection from thermal expansion in the volume between 1LP-1 and 1LP-2 (the main pressure boundary isolation valves between the high pressure RCS and the LPI (DHR) system). The leak rate (1 to 3 drops per second) was not significant, except that it was RCS pressure boundary leakage. 1LP-1 is normally closed, but must be opened to establish a DHR path. Valve 1LP-167 is a 1/2 inch check valve which would have limited RCS leakage. Thus, if the leak had grown, it would have been limited to the amount of seat leakage past either 1LP-167 or 1LP-1. It would also have been limited by the 1/2 inch size of the line containing the leak." Technical Specification LCO 3.4.13 applies to RCS leakage in modes 1 to 4. The licensee plans to fix the leak prior to entry into mode 4. The licensee notified the NRC Resident Inspector.
On 6-14-06 at 1908 hours Oconee reported an RCS pressure boundary leak in a 1/2 inch line connected to the decay heat removal (DHR) line near valve 1LP-1 inside containment. Oconee has reviewed the event in greater detail and has concluded that the event is not reportable. The Basis for TS 3.4.13 states that RCS LEAKAGE includes leakage from connected systems up to and including the second normally closed valve (or outermost isolation valve for systems penetrating containment). However TS 1.1 contains a definition of LEAKAGE which includes 'Pressure Boundary LEAKAGE: LEAKAGE (except SG LEAKAGE) through a nonisolable fault in an RCS component body, pipe wall, or vessel wall.' The leakage in this event was isolable, and therefore does not meet the definition of Pressure Boundary LEAKAGE. Therefore the zero leakage criterion of TS 3.4.13 does not apply to this leak. The applicable criterion is 10 gpm identified LEAKAGE. Since the leak does not meet the criterion as Pressure Boundary LEAKAGE, the leak was isolable, and the applicable TS LEAKAGE limit was not exceeded, this event does not meet the reportability criteria for 10 CFR 50.72 or 50.73 and event notification 42641 is hereby RETRACTED. Additional information and clarification: "During normal operation the leak was isolated by one barrier (valves 1LP-167 and 1LP-1, closed in parallel). The leakage observed on 2-21-06 during a containment tour at Mode 1 was recorded as 1 drop per second. As stated in the initial notification, at that time the leak was believed to be a body-bonnet leak. It was observed at Mode 1 again on 5-25-06 and recorded as 3 drops/second. On 6-14-06, the leakage was recorded as one drop/second while at reduced pressure in Mode 4, before the DHR systems was placed in service. At that point, the leak was isolated by closing an additional valve (1LP-166, normally open), and the leak stopped. The Low Pressure Injection system was placed in service for DHR, which opened 1 LP-1. Later, with system pressure at approximately 285 psig in Mode 5 (outside the applicability of TS 3.4.13), 1LP-166 was reopened to allow additional verification of the leak location. At that time the leak was described as a 'spray' but no leak rate was measured before 1LP-166 was reclosed. The leak rate at that time was estimated as well less than 10 GPM. Corrective Action: The affective section of 1/2 inch pipe and associated fittings have been removed for transfer to a Duke laboratory for analysis. Repairs will be completed prior to return to mode 4. The licensee notified the NRC Resident Inspector. Notified the R2DO (Bonser). | Pressure Boundary Leakage Pressure boundary leak |
| ENS 42171 | 27 November 2005 10:30:00 | Loss and Restoration of Back-Up Instrument Air to Feedwater Control Valves | Event: At 0530 hours on 11/27/2005, while in Mode 3 following a Unit 2 refueling outage, it was discovered that the nitrogen backup supply to 2FDW-315 and 2FDW-316 was valved out. 2FDW-315 and 2FDW-316 are the emergency feedwater (EFW) control valves which function to regulate steam generator level on a loss of main feedwater event. Motive force to these valves is normally supplied by instrument air and nitrogen provides backup to instrument air in the event that instrument air becomes unavailable. At 0530 hours on 11/27/2005, both EFW flow paths were declared inoperable and Technical Specification 3.7.5, Conditions B and E were entered. Condition E of TS 3.7.5 specifically deals with the inoperability of two EFW flow paths. The Required Action is to initiate actions to restore one EFW flow path to operable status, immediately. Initial Safety Significance: 2FDW-315 and 2FDW-316 are the control valves for the Unit 2 'A' and 'B' steam generators, respectively. These valves must be able to function in order to control steam generator level during an event where main feedwater is lost. The motive force for these valves is normally instrument air. However, in the unlikely event where main feedwater is lost, and instrument air is unavailable, these valves rely on a nitrogen backup to supply their motive force. The events where this nitrogen backup is credited are a station blackout (SBO) and a loss of instrument air. While nitrogen backup to 2FDW-315 and 2FDW-316 was unavailable between 0530 hours and 0710 hours on 11/27/2005, it is reasonable to assume that the ability to remove decay heat would have been available. In the case of a loss of instrument air, 2FDW-315 and 2FDW-316 fail open, with the motor driven EFW pumps providing EFW supply to both steam generators. In this case, the Emergency Operating Procedure (EOP) provides guidance to realign EFW through the electric powered startup control valves. Should this realignment attempt fail, the EOP provides further guidance to control EFW flow by manually throttling closed on 2FDW-315 and 2FDW-316. In the event of an SBO, power to the instrument air compressors would be lost, resulting in a loss of instrument air header pressure. The motor driven EFW pumps would be unavailable, however, the turbine driven EFW pump would automatically start and provide EFW flow. As with the loss of instrument air event, 2FDW-315 and 2FDW316 would fail open. The EOP provides guidance to dispatch operators to manually throttle closed on these valves to control flow to the steam generators. Additionally, while not credited for this event, Oconee has diesel driven air compressors which auto start on low instrument air pressure and supply the instrument air header. Also, in the event of a SBO, the Standby Shutdown Facility (SSF) is manned within 10 minutes of event initiation. The SSF is a SBO coping facility with a dedicated diesel generator and the pumps and valves necessary to supply and control steam generator feed in the event of an SBO. Corrective Action(s): At 0702 hours on 11/27/2005, nitrogen was realigned to 2FDW-316 and TS 3.7.5, Condition E was exited. At 0710 hours on 11/27/2005, nitrogen was realigned to 2FDW-315 and TS 3.7.5 Condition B was exited. The licensee is investigating the cause of the valve line up problem. The licensee notified the NRC Resident Inspector.
After detailed review of this event, it was concluded that Technical Specification 3.7.5 limiting conditions for operation were met at all times during this event. Control valves 2FDW-315 and 2FDW-316 fail open on loss of air/nitrogen by the spring return design of the actuators. Therefore, the required flow path would not have been lost due to the failure of normal air supply and the isolation of nitrogen supplies to the actuators. It has been further concluded that all throttling functions of these control valves could have been performed manually by use of a local handwheel on each valve actuator. Appropriate procedure guidance exists to operate the system with these valves failed open until the operators can access the local handwheel and take local control. Therefore, the valves and the associated flow paths were operable during this event. As a result of this determination, no reportability criteria under 50.72 and 50.73 apply to this event and the associated event report is hereby retracted. The licensee notified the NRC Resident Inspector. R2DO(Payne) was notified. | |
| ENS 41869 | 25 July 2005 22:15:00 | Special Nuclear Materials Inventory Discovers a Fuel Pin Missing | As a result of NRC Bulletin 2005-01 "Material Control and Accounting at Reactors and Wet Spent Fuel Storage Facilities", Oconee has been conducting an inventory of Special Nuclear Materials (SNM), other than complete fuel assemblies, stored in the spent fuel pools at Oconee. One canister, documented as containing 383 fuel pins, was found to actually contain 382 fuel pins. At this time it is uncertain if this is a record keeping error or an actual "lost" pin. Initial Safety Significance: The inventory process for other canisters is not complete, and it is possible that the pin may be in another container. These containers being inventoried have been stored underwater in the spent fuel pool for years. The affected canister was filled in 1982. Oconee has no reason to believe that this pin or any other SNM has been stolen or unlawfully diverted. For reference, one fuel assembly contains 208 fuel pins. Corrective Action(s): The inventory process is continuing. This notification is being trade per 10 CFR 74.11. The NRC Resident Inspector will be notified.
On July 17, 2005 at 1838 (ET) Oconee reported that during an inventory of Special Nuclear Material (SNM), other than complete fuel assemblies stored in the spend fuel pools at Oconee, one canister, documented as containing 383 fuel pins, was found to actually contain 382 fuel pins. At that time it was uncertain if this is a record keeping error or an actual "lost" pin. Further investigation has located the suspect fuel pin in a different canister; consequently, this issue no longer meets the reporting requirements as previously stated and this report is being retracted. Initial Safety Significance: There is no initial safety significance. Corrective Action(s): No additional corrective actions planned at this time. R2DO (C. Julian), NMSS EO (M. Burgess) and IRD Manger (M. Leach) notified. NRC resident Inspector was notified of this retraction by the licensee. | Stolen |
| ENS 41618 | 20 April 2005 20:10:00 | Both Penetration Room Ventilation System Trains Temporarily Inoperable | At 16:10 on 4-20-05, Oconee Unit 3 entered Technical Specification 3.0.3 due to (valve) 3PR-20 being failed closed for testing on the Penetration Room Ventilation System. 3PR-20 is the suction cross connect valve for the two trains of the Penetration Room Ventilation System. Technical Specification Surveillance requirement 3.7.10.5 requires that 3PR-20 be verified capable of being opened every 18 months. This surveillance cannot be met if 3PR-20 is failed closed. Therefore, both Penetration Room Ventilation System trains had to be declared inoperable since the LCO was declared not met. Entry into Technical Specification 3.0.3 conservatively indicates that a loss of safety function could have occurred. Therefore, this condition warrants reporting via an eight-hour non-emergency report as a condition which could result in a loss of safety function. The Technical Specification 3.0.3 entry condition was recognized 'after the fact' by the Shift Technical Advisor. Following recognition of this condition, operating air was restored to 3PR-20 and it was returned to operable at 18:24 on 4-20-05. The Penetration Room Ventilation System functions to channel Reactor Building penetration leakage to a high-efficiency carbon/HEPA filtration system prior to release via a ventilation stack. The Penetration Room Ventilation System consists of two trains. Each Penetration Room Ventilation System train has a fan, ducting, suction and discharge valves, and in-line carbon and HEPA filters. The Penetration Room Ventilation System discharges to a larger high-efficiency carbon/HEPA filtration system before being released via a ventilation stack. 3PR-20 is the suction cross connect valve for the two trains of the Penetration Room Ventilation System. 3PR-20 was originally installed to provide cooling of an idle filter train if one trains of the Penetration Room Ventilation System failed. However, subsequent analyses have concluded that 3PR-20 is no longer required to provide this cooling since natural circulation around the idle train filter assembly is adequate to remove decay heat to prevent carbon bed ignition. Appropriate changes to the Technical Specification for this issue have not yet been completed. Therefore, the safety significance of this condition is LOW. Corrective Action(s): 1) 3PR 20 was returned to operable. 2) A Technical Specification change will be developed to address the discrepancies between design basis and Technical Specifications requirements (licensing basis). The licensee has notified the NRC Resident Inspector.
Withdrawal of Event Number 41618 On 04/20/2005 at 22:40 (ET) Oconee reported Unit 3 entry into Technical Specification (TS) 3.0.3 due to valve 3PR-20 being failed closed. 3PR-20 is the suction cross connect valve for the two trains of the Penetration Room Ventilation System. TS Surveillance Requirement 3.7.10.5 can not be met if 3PR-20 is failed closed. Further review concluded that it was inappropriate to enter TS 3.0.3. The appropriate TS condition was TS 3.7.10 Conditon A for one train inoperable. Therefore this event does not meet reportability requirements and is hereby retracted. Initial Safety Significance: UFSAR sections 6.5.1.3 and 9.4.7.2 clarify that 3PR-20 was originally installed to open in the event of failure of one fan to allow air flow to be maintained through that fan's filters by connecting to the other train which is assumed to be operating. This would prevent carbon bed ignition by removing decay heat of radioactive materials trapped on the filters. Analysis performed in 1990 concluded that natural circulation around the idle train filter assembly provides adequate heat transfer. Therefore there is no physical or analytical need for 3PR-20 to perform its TS function. A TS amendment was approved 6-1-2004 which will delete TS 3.7.10, and the requirement for 3PR-20, but the implementation of that TS change is awaiting completion of certain modifications. However, since the existing TS credits 3PR-20 with mitigating a single failure, the result of the inoperability of 3PR-20 is that it cannot mitigate that single failure. It is noted that Oconee Unit 3 is currently in TS 3.7.10 Condition A due to indicated low flow in the 3A PRVS train. While in that TS condition, it is not required to assume a single failure which would make the remaining train inoperable. Therefore 3PR-20 is not required while in Condition A. NRC R2DO (C. Julian) notified. The NRC Resident Inspector was notified of this retraction by the licensee. | |
| ENS 41140 | 19 October 2004 21:30:00 | Standby Emergency Electrical Power Paths Inoperable for 41 Minutes | The Keowee Hydro Units provide the emergency power source for the Oconee Units. At 0357 on 10/19/04, Keowee Unit 1 (and the overhead emergency power path) was declared inoperable in order to perform scheduled maintenance. At 1730, Keowee Unit 2 (and the underground emergency power path) was declared inoperable due to the loss of breaker control power associated with Keowee Unit 2 auxiliaries. At 1811, as required by Technical Specification 3.8.1 condition I, both standby buses were energized from a Lee Combustion Turbine via an isolated power path. At 1828, a Operability Verification of Keowee Unit 2 to the overhead emergency power path was performed with all acceptance criteria met. At 1904, Keowee Unit 2 to the overhead emergency power path was declared operable. Technical Specification 3.8.1 condition I was exited. Initial Safety Significance: Between times 1730 to 1811, both on site emergency power paths were inoperable. During this time period a condition existed that could have prevented the fulfillment of the safety function of systems that are needed to mitigate the consequences of an accident. Corrective Action(s): At 1828, an Operability Verification of Keowee Unit 2 to the overhead emergency power path was performed with all acceptance criteria met. At 1904, Keowee Unit 2 to the overhead emergency power path was declared operable. Technical Specification 3.8.1. condition I was exited. A team is established to investigate the loss of breaker control power associated with Keowee Unit 2 auxiliaries. The licensee will notify the NRC Resident Inspector.
The Keowee Hydro Units (KHUs) provide the emergency power source for the three Oconee Units. On 10/20/04 at 0135 Oconee made a notification to the NRC of a loss of safety function. Reference Event Number: 41140. The event was due to an unexpected failure on KHU 2. At the time of the event, KHU 1 was out of service for planned maintenance and was in the early stages of testing for return to service. Each KHU can be aligned to either an overhead or an underground power path to supply emergency power to Oconee. At 1730, KHU 2 and the underground emergency power path were declared inoperable due to the loss of breaker control power associated with KHU 2 auxiliaries while aligned to the underground path. By the Oconee Technical Specification 3.8.1 Bases, this breaker (ACB-8) is required to be operable in order to consider KHU 2 operable while aligned to the underground path. Since KHU 2 did not meet the TS configuration, and since KHU 1 testing was not complete, both trains were inoperable and the event was reported as a loss of safety function. At 1811, as required by Technical Specification 3.8.1 condition I, both standby buses were energized from a Lee Combustion Turbine via a dedicated power path. KHU 2 was re-aligned to the overhead path and its associated auxiliary power breaker (ACB-6). The event was terminated at 1904 when KHU 2 was declared operable to the overhead emergency power path after completion of an Operability Verification test. Justification for conclusion that there was no loss of safely function while KHU 2 was declared inoperable (approximately one hour duration): KHUs are capable of 'black start', i.e. starting and operating on battery power alone. Therefore, if there had been an event resulting in an emergency start signal during the one hour interval of vulnerability, KHU 2 would have been able to start and operate for approximately one hour with the loss of control power to ACB-8. Operations procedures include guidance to close breaker ACB-8 manually using a maintenance closure handle. These steps would have been performed approximately 30 minutes into the postulated event. Based on the results of testing and troubleshooting of ACB-8, Oconee has concluded that ACB-8 could have been closed manually and, once closed, would have successfully provided auxiliary power for the duration of any event. Thus Oconee concludes that KHU 2 should be considered available, with reasonable expectation for performing its safety function during this event. Therefore Oconee has concluded that this event was not a reportable loss of safety function and Event Number 41140 is withdrawn. The resident inspector and R2DO (Bonser) have been notified. |