05000388/LER-2006-002

LER-2006-002, Missed Technical Specification LCO 3.8.1 Entry for Unit 2 During Unit 1 ESS Bus Testing

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3882006002R00 - NRC Website

CONDITIONS PRIOR TO EVENT

Unit 1, Mode 5, Refueling Outage Unit 2, Model, 100% Power

BACKGROUND

The primary AC distribution system for Susquehanna Units 1 and 2 each consist of four 4.16 kV Engineered Safeguards System (ESS) buses having a primary and alternate offsite source of power as well as an onsite diesel generator (DG) source that supports one 4.16 kV ESS bus in each unit. In addition, some common support systems required by both units receive power through Unit 1 electrical power distribution subsystems.

EVENT DESCRIPTION

On March 11, 2006, with Unit 1 in a refueling outage, activities for testing the Unit 1 4.16kV ESS Bus 1D (1A204) were in progress. The testing required Unit 2 to enter LCO 3.8.7, Condition C. This was required since Unit 1 busses power common loads, and therefore impact Unit 2 SSCs that are required to be operable when Unit 2 is in Mode 1. PPL personnel later discovered that entry into LCO 3.8.1, Conditions A, B and D for Unit 2 were missed and should have been entered when the Unit 1 bus was de-energized. For a de-energized bus, Condition D requires entry into LCO 3.8.7. Because LCO 3.8.7 was initially entered when the bus was de-energized, the Required Actions for Condition D were met.

The Required Actions for Conditions A and B state that with "One offsite circuit inoperable, verify correct breaker alignment and indicated power availability for each offsite circuit within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter." Although the SR was not completed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, this event was determined not to be reportable since the surveillance test was satisfactorily completed prior to exceeding the time required for Unit 2 to be in Mode 3.

As part of PPL's cause investigation for the late entry into TS LCO 3.8.1 for Unit 2, an extent of condition evaluation was performed. On April 19, 2006, PPL identified that a similar (yet reportable) event had occurred during the 2004 Unit 1 refueling outage. On March 6, 2004, the Unit 1 4.16kV ESS 1A Bus (1A201) was being tested in accordance with plant procedures. The ESS lA Bus was de­ energized and LCO 3.8.7 was entered for Unit 2. A review of operator logs for March 6, 2004, showed that only LCO 3.8.7 was entered when the Unit 1 bus was de-energized. Entry into Unit 2 LCO 3.8.1, Conditions A, B and D was missed, resulting in Required Actions A.1 and B.1 not being performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and the mandated time for Unit 2 to be in Mode 3 being exceeded. Although Condition D was not entered, LCO 3.8.7 was entered when the bus was de-energized and the appropriate Required Actions were taken.

Because Unit 2 TS LCO 3.8.1, Required Actions A.1 and B.1 were not completed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, Action F requires Unit 2 to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Since it was

• not recognized in 2004 that entry into these conditions was required, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), for any operation or condition prohibited by Technical Specifications.

CAUSE OF EVENT

The apparent cause for the 2004 event was attributed to confusing language in TS 3.8.1 which resulted in an inaccurate interpretation by plant personnel regarding which LCOs were required to be entered to support the Unit 1 ESS Bus testing. Based on interviews with PPL personnel, the impact to operability of an offsite source and a DG during ESS Bus testing was recognized. However, the impact was open to interpretation regarding which LCOs were required to be entered.

ANALYSIS / SAFETY SIGNIFICANCE

Actual Consequences:

During the 2004 event, TS LCO 3.8.7 was entered for Unit 2, but entry into TS LCO 3.8.1, Conditions A, B, and D for Unit 2 was missed. Conditions A and B require SR 3.8.1.1 to be performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to verify correct breaker alignment and indicated power availability for each offsite circuit. Although the SR was not performed, a review of operator logs indicated that power was available to both offsite circuits and the 'A', 'B' and 'CY DGs remained operable and therefore, the intent of the SR was met.

Of the three conditions, Condition D imposed the most restrictive completion time (i.e., 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> for Unit 2 to be in Mode 3) for one onsite and one offsite 4.16kV power source inoperable. However, the Required Actions in Condition D are modified by a note that states that when Condition D is entered for a de-energized bus and not an inoperable bus, entry into the applicable Conditions and Actions for LCO 3.8.7 are required. In 2004, the Unit 1 ESS bus was de-energized. Entry into LCO 3.8.7 requires a safety function determination (SFD) to be performed in accordance with LCO 3.0.6 to ensure that a loss of safety function had not occurred. During the 2004 event, a SFD was performed which concluded that no loss of safety function had occurred. As such, there was no impact to the power required to operate safety-related loads necessary to cool the reactor core, maintain containment integrity, and support other vital functions in the event of a postulated accident in one reactor unit, while safely shutting down the unaffected unit.

Potential Consequences:

During the 2004 event, the worst case scenario would have been if Unit 2 had had an event (such as loss of an offsite power source or a DG) which required safety-related loads powered by the Unit 1 bus to be available to mitigate the event. However, based on plant design, sufficient power sources (i.e., 3 DGs or 1 offsite power source) would have been available to provide power to safety-related loads necessary to mitigate an event.

CORRECTIVE ACTIONS

Immediate Corrective Action

• Interim compensatory measures were established to clearly state which TS LCOs were required to be refueling outage.

Action(s) to Prevent Recurrence

• Revise TS 3.8.1 and/or Bases to provide clarity and remove interpretation on LCO applicability during ESS Bus testing.

PREVIOUS SIMILAR EVENTS

None