05000282/LER-2008-001
| Prairie Island Nuclear Generating Plant | |
| 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 |
| 2822008001R00 - NRC Website | |
On March 15, 2008, Prairie Island Nuclear Generating Plant (PINGP) Unit 1 went to Mode 3 at 1059.
On March 23, 2008, with Unit 1 in Mode 1, Technical Specification (TS) 3.7.5 Condition B was entered to conduct surveillance testing on the 11 turbinel-driven auxiliary feedwater2 pump3 (TDAFWP). The test was stopped before it could be completed due to high temperature on the outboard turbine bearing (the procedure requires turbine bearing temperature be maintained less than 220 degrees F). An evaluation concluded the 11 TDAFWP had been inoperable since before the plant entered Mode 3.
EVENT ANALYSIS
The 11 TDAFWP is required per TS 3.7.5 to be operable when the unit reaches Mode 3. TS 3.7.5 Condition B requires the inoperable auxiliary feedwater (AFW) train be restored to operable within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If Condition B is not met, Condition C allows six hours to get to Mode 3 and 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to get to Mode 4. Since Unit 1 was determined to be inoperable as a result of surveillance testing, and was in Mode 3 and was not brought to Mode 4 after 84 hours9.722222e-4 days <br />0.0233 hours <br />1.388889e-4 weeks <br />3.1962e-5 months <br /> in Condition B as required by TS 3.7.5 Condition C, this event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS. In addition, Unit 1 went from Mode 4 to Mode 3 to Mode 2 to Mode 1 with the 11 TDAFWP inoperable, which is also prohibited by TS.
Impact on Safety System Functional Failure Performance Indicator No actual loss of function occurred as a result of this event. The redundant 12 motor4-driven AFW pump was operable while the 11 TDAFWP was inoperable. Thus, this event is not reportable per 10CFR 50.73(a)(2)(v).
SAFETY SIGNIFICANCE
This event only affected the 11 TDAFWP and the redundant AFW pump remained operable, so the safety function was not lost. Thus, this event did not affect the health and safety of the public and the safety significance of this event is considered minimal.
CAUSE
Troubleshooting concluded the high outboard turbine bearing temperature for 11 TDAFWP was caused by insulations issues after the pump was reassembled during the refueling outage. High 1 EIIS Component Identifier: TRB 2 EIIS System Identifier: BA 3 EIIS Component Identifier: P 4 EIIS Component Identifier: MO U.S. NUCLEAR REGULATORY COMMISSIONNRC FORM 366A LICENSEE EVENT REPORT (LER)(9-2007)
CONTINUATION SHEET
radiant heat from surrounding components as well as the insulation configuration not allowing heat to dissipate from the turbine casing led to the high temperatures. In addition, the AFW pumps use bypass flow to cool the bearings. However, this bypass flow is not measurable, so to meet full-flow requirements for inservice testing, the cooling water is isolated for portions of the surveillance testing.
This intermittent isolation of cooling water was determined to be a contributing cause.
CORRECTIVE ACTION
Once the high temperature lines and equipment in close proximity to the bearing housing were reinsulated, the outboard turbine bearing temperature was below the 220 degree action range. The 11 TDAFWP passed the surveillance following the insulation adjustment.
Additional corrective actions include:
1. Revise the surveillance procedures to reduce the time that cooling flow is isolated.
2. Develop and install an insulation package that provides protection to the bearing housing yet allows heat from the turbine to be dissipated to the atmosphere for the TDAFWPs.
PREVIOUS SIMILAR EVENTS
Review of Licensee Event Reports for Unit 1 and Unit 2 since 2005 found a similar event reported in Licensee Event Report 1-06-02 where Unit 1 was operated in a condition prohibited by TS due to an inoperable 11 TDAFWP.
5 EIIS Component Identifier: ISL