05000387/LER-2006-001
| Susquehanna Steam Electric Station - Unit 1 | |
| Event date: | 3-4-2006 |
|---|---|
| Report date: | 4-25-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 3872006001R00 - NRC Website | |
EVENT DESCRIPTION
On March 3, 2006, Susquehanna operators (Licensed, Utility) began the process of shutting down Unit 1 fo
- its 14th Refueling and Inspection Outage. As had previously been experienced during Unit l's last shutdown in October 2005, the station anticipated that known control cell (EIIS Code: AC) friction issues would result in the slow settling of some control rods (EIIS Code: JD) as they were inserted to the full in position. The cell friction issues manifested during Unit l's 14th fuel cycle when multiple control rods failed to settle into their targeted latched position within 30 seconds. Although previous experience suggested that operability could be demonstrated for a majority of slow settling control rods, it was conservatively determined that those rods which failed to settle in a reasonable period of time during the shutdown would be declared ir operable. Technical Specification (TS) 3.1.3, Control Rod Operability, would be entered whea l nine rods had been declared inoperable.
As anticipated, TS 3.1.3.f was entered at 0517 hours0.00598 days <br />0.144 hours <br />8.54828e-4 weeks <br />1.967185e-4 months <br /> on March 4, 2006 when the ninth control rod was declared inoperable. Entry into TS 3.1.3.f requires that the Unit be taken to Mode 3, Hot Shutdown, within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. At the time the ninth control rod was declared inoperable, Unit 1 had already been reduced to approximately 0% power. The controlled shutdown continued until 0743 hours0.0086 days <br />0.206 hours <br />0.00123 weeks <br />2.827115e-4 months <br /> when insertion of all rods was completed and Mode 3 had been entered by placing the mode switch to the Shutdown position.
There were no Emergency Core Cooling System (EllS Code: B) initiations and no challenges to containment (EIIS Code: NH) experienced during the shutdown.
Even though the plant shutdown was planned and in-progress, the shutdown became a Technical Specification mandate at 0517 hours0.00598 days <br />0.144 hours <br />8.54828e-4 weeks <br />1.967185e-4 months <br /> on March 4 when the ninth control rod was declared inoperable. Accordingly, this event is being reported as a Tech Spec required shutdown per 10 CFR 50.73(a)(2)(i)(A).
CAUSE OF EVENT
Entry into the shutdown TS was the result of a station strategy that emphasized a controlled Unit shutdown. This strategy recognized the need to enter TS 3.1.3.f. Entry into the Limiting Condition of Operation (LCO) did not impact the course of the shutdown in any way. Entry into TS 3.1.3.f was readily avoidable via manual RPS (EIIS Code: JC) initiation before LCO control rod operability limits were threatened. Such action would have, however, entailed the unnecessary implementation of the scram safety function to complete a normal, planned shutdown and would have precluded the operational advantages inherent with a controlled Unit shutdown.
ANALYSIS / SAFETY SIGNIFICANCE
There was no significance to the administrative entry to TS 3.1.3.f. The control rod drive system (EIIS Code: AA) remained fully capable of performing its function throughout the shutdown. The control rods that were declared inoperable had been fully inserted. Associated control rod drives were hydraulically isolated to prevent rod withdrawal.
Being fully inserted, the control rods were fulfilling their design function. As such, there were no adverse safety consequences resulting from this event.
CORRECTIVE ACTIONS
None required. Entry into the shutdown Technical Specification was the result of a non-impacting shutdown decision strategy.
ADDITIONAL INFORMATION
Channel bow is contributing to the cell friction issues being experienced at Susquehanna. All control cells exhibiting slow to settle control rods were evaluated. Associated fuel assemblies were measured for channel bow if they would remain in a control cell during the upcoming operating cycle. Those fuel assemblies causing interference have either been removed from the core, re channeled (3 Ills outage), or moved to a peripheral location in the core where control blade interference is not possible. The cell friction issue continues to be managed in Susquehanna's corrective action program.
Past Similar Events: Docket No. 50-387 LER 2005-002-00