05000382/LER-2004-004
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | |
|---|---|
| Report date: | |
| 3822004004R00 - NRC Website | |
containment electrical penetrations [NH] did not have adequately sized over-current protection devices that met the Technical Specification ,(TS) 3.8.4.1 requirements of having operable primary and backup containment penetration conductor over-current protective devices. The over-current protection devices for this circuit consist of a two-pole Tri-Pack fused breaker [EJ]. The breaker contains a time delay thermal trip element, an instantaneous magnetic trip element, and one fuse [EJ] per pole (2 poles) since this is a DC ungrounded circuit. The Technical Requirements Manual (TRM) listed the two pole fuses as primary and backup protection devices; however, these fuses will not actuate to protect the associated containment electrical penetrations on a design fault. The thermal trip element of the breaker, which is not listed in the TRM, is similar to a standard molded case circuit breaker [EJ] and provides an additional circuit over-current protection device to isolate the design fault prior to impairing the physical integrity of the associated containment electrical penetrations.
The applicable TS action statement, 3.8.4.1a, requires in part that with one or more of the containment penetration conductor over-current devices inoperable:
(1) Restore the protective device(s) to OPERABLE status or de-energize the circuit(s) by tripping, racking out, or removing the alternate device or racking out or removing the inoperable device within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, and (2) Declare the affected system or component inoperable, and (3) Verify at least once per 7 days thereafter the alternate device is tripped, racked out, or removed, or the device is racked out or removed.
Therefore, this event is being reported per 10CFR50.73 (a)(2)(i)(B), as an operation or condition prohibited by the plant's Technical Specifications, as the circuit did not have backup over-current protection as required by TS since original construction and the action statement was not performed within the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed outage time
INITIAL CONDITIONS
Prior to the discovery of this event, the plant was operating at 100% in Mode 1. There were no procedures being implemented specific to this event. There were no TS Limiting Conditions of Operation (LCO) specific to this event in effect. There was no major equipment out of service specific to this event.
EVENT DESCRIPTION
Background on Previously Related LER-2004-001 In a previously related LER-2004-001, a condition was identified on January 21, 2004, whereby, two electrical AC circuits that go through containment electrical penetrations, did not have backup over current protection as required by the Technical Specification. These circuits powered the plant's hydrogen analyzer panels and position indication for the hydrogen analyzer containment isolation valves. Upon this discovery, the plant followed the required action statement for TS 3.8.4.1, by lifting the circuit leads for the inside containment isolation valve position indication only, declaring the affected valve position indication and circuit inoperable and verifying every 7 days that the circuit leads were disconnected. The hydrogen analyzer remained capable of performing its intended safety function.
The cause of this event was human error in that the personnel did not perform adequate peer and self checking when modifying the affected circuits in 1988 during installation of a station modification package. A contributing cause was inadequate control wiring diagrams (CWDs) for the Hydrogen Analyzers System that did not clearly distinguish the source of the power for the containment isolation valves position indication.
The following interim corrective actions were taken to return the circuits to operable status and ensure all other containment electrical penetrations met TS 3.8.4.1 LCO:
(1) Fuses were added to the circuits as backup over-current protection for containment isolation valve position indication in February 2004; (2) The circuit breakers and fuses were added to the TRM containment electrical penetration table, which contains the list of containment electrical penetrations to be tested in accordance with TS Surveillance 4.8.4.1; and (3) Engineering performed a review of all electrical containment penetration circuits to verify that all other containment electrical penetrations were protected by both primary and backup over-current devices as required by TS 3.8.4.1. During this review, no conditions prohibited by TS 3.8.4.1 were revealed; however, some minor discrepancies were identified with long term corrective actions being identified and tracked in corrective action program Condition Report CR-WF3-2004- 0185.
In addition, long term corrective actions were also identified to minimize recurrence of this condition.
These actions consisted of the following:
(1) Develop and implement lessons learned training for engineering personnel on aspects of extent of condition reviews; (2) Revise applicable CWDs to clarify source of power for the Hydrogen Analyzer containment isolation valve position indication; and (3) Revise the Containment Electrical Penetrations Backup Protection calculation to update the as built data status of the containment electrical penetration protection for assurance that over current protection breaker/fuse curves demonstrate the electrical penetration will not be damaged during a fault in the penetration.
Discovery of a New Reportable Condition As part of the long term corrective action specified in LER-2004-001 to revise the Containment Electrical Penetrations Backup Protection, the 125 VDC circuit breaker CDC-EBKR-AB-24 was identified on November 17, 2004 to have inadequately sized over-current protection devices for two associated containment electrical penetrations that did not meet TS 3.8.4.1 LCO requirements of having operable primary and backup containment penetration conductor over-current protective devices. This condition has existed since Waterford 3 construction.
The over-current protection devices for this circuit consist of a two-pole Tri-Pack fused breaker. The breaker contains a time delay thermal trip element, an instantaneous magnetic trip element, and two fuses; one per pole, since this is a DC ungrounded circuit. The original design by the Architect / Engineering firm credited the two pole fuses as primary and backup protection devices for these penetrations; however, these fuses were designed to isolate the fault current only during an abnormally high fault currents of 1000 amps and above and will not actuate to protect the associated containment electrical penetrations on a design fault. A line-to-line design fault at penetration number 146 for the Control Element Drive Mechanism (CEDM) Cooling Units [AA] vibration alarm circuit will generate approximately 80 amps Similarly, a line-to-line design fault at penetration number144 for the Containment Cooling Units [BK] vibration alarm circuit will generate approximately 60 amps.
Without actuation of the fuses to isolate the fault, the time delay thermal trip element of the breaker is relied upon to provide the circuit over-current protection that will isolate penetration number 146 design fault between 12 to 22 seconds and penetration number 144 design fault between 25 to 55 seconds prior to impairing the physical integrity of the containment electrical penetrations.
The two-pole fuses are credited as the TS 3.8.4.1 required primary and backup protection devices for these circuits and listed as such in the TRM. Periodic testing of fuses is not required to meet the requirements of TS 3.8.4.1. However, circuit breaker CDC-EBKR-AB-24 is not listed in the TRM as a over-current containment penetration protection device and therefore, does not programmatically undergo breaker testing to meet SR 4.8.4.1 18 month and 5 year surveillance test requirements. This safety related breaker has a 10 year test interval and the historical breaker trip test results have shown that the trip time for the thermal time delay element has consistently tripped within the allowable trip times. The documented breaker trip time would isolate the electrical fault and protect the containment electrical penetrations. The breaker was last successfully tested on May 15, 2002.
To address this recent condition, Waterford 3 entered the corrective action process, declared the affected circuit breaker CDC-EBKR-AB-24 inoperable, and entered Technical Specification 3.8.4.1 ACTION statement 'a'. Power to the vibration alarm circuits was removed and the leads to the vibration alarm circuits disconnected for only the equipment inside containment, namely the 4 CEDM Cooling Units and the 4 Containment Cooling Units. The vibration switches provided control room indication of high vibration. The disabling of vibration indication had no impact on the normal operation of the equipment and is not required for equipment operability. Therefore, the equipment remained operable with the associated vibration switches disabled. The lifted leads will continue to be verified as disconnected once every 7 days until the condition is corrected.
CAUSAL FACTORS
The apparent cause for this condition is inadequate original design of containment electrical penetration over-current protection devices due to latent personnel errors. These over-current protection designs were provided during Waterford 3 original construction and are attributed to design errors made in the construction period.
CORRECTIVE ACTIONS
The apparent cause of this condition is directly related to the root cause identified in LER 2004-001 and tracked in corrective action program as Condition Report 2004-0185. This condition, as documented in Condition Report CR-2004-3720, was discovered during an extent of condition review for LER-2004-001 and is tied to inadequate design of penetrations due to latent personnel errors. As a result, there are no new actions required to prevent recurrence. However, the following corrective actions are required to correct the adverse condition:
(1) Complete the plant modification to add two smaller in-line fuses for the CEDM Cooling Units and Containment Cooling Units Vibration Alarms circuits (CDC-EBKR-AB-24) to provide adequate over-current protection for the affected electrical penetrations. TRM and the Containment Electrical Penetrations Backup Protection calculation will be revised to reflect correct protection devices.
(2) Complete the extent of condition review of Containment Electrical Penetrations Backup Protection calculation to ensure the over-current protection devices are sized adequately.
SAFETY SIGNIFICANCE
Backup over-current protection is required for containment electrical penetrations by TS. The backup over-current protection ensures that containment penetration physical integrity is not impaired in the event of an electrical fault inside containment and the failure of one electrical device to interrupt and isolate the fault. During the period when no backup over-current protection existed due to the two inadequately sized credited fuses for containment electrical penetration circuits, the circuit breaker CDC-EBKR-AB-24 was being satisfactorily tested to an equivalent test methodology used for testing TS related circuit breakers. Therefore, if a faulted condition had occurred for the circuit in question, the breaker would have opened to protect the containment electrical penetrations.
As delineated in the safety significance for the condition identified in LER-2004-001, the risk assessment for this condition addressed two aspects: condition isolation function and potential change in Core Damage Frequency (CDF).
The worst case scenario for this condition is also bounded by the previous condition identified in LER 2004-001, but will be restated for completeness of the safety significance. If an electrical fault occurred in either containment penetration which failed to open the circuit breaker CDC-EBKR-AB-24 on over-current as designed, then the potential existed for a one inch diameter hole to develop in the faulted containment electrical penetration as a result of integrity failure of both the inside and outside penetration polysulfone conductor seal and insulation. However, this would be precluded by various factors (e.g. the breaker was capable of tripping on fault condition). In the extremely unlikely event that this failure were to occur in conjunction with a large break loss of coolant accident, the leak rate from containment would be greater than the assumed leak rate in the loss of coolant accident offsite and control room radiological dose consequences analysis.
When combining the probability of core damage frequency in combination with the electrical fault condition on the penetration, the risk impact was determined to be negligible. The electrical fault condition on the penetration had no impact on Core Damage Frequency since the DC bus could support the fault load. The electrical fault condition had no impact on Large Early Release Frequency (LERF) in that the one inch diameter hole is.bounded by the two inch diameter hole in containment assumed in the LERF.
This event is not a Safety System Functional Failure (SSFF).
SIMILAR EVENTS
As stated in LER 2004-001, a similar event was reported to the NRC in LER 95-006-00, that found backup over-current protection devices missing for the Containment Hydrogen Analyzer containment isolation and sample valves. The cause for not having backup over-current protection for the Containment Hydrogen Analyzer containment isolation and sample valves was personnel error.
ADDITIONAL INFORMATION
Energy Industry Identification System (EIIS) codes are identified in the text within brackets [1.