05000336/LER-2001-005
| Docket Number | |
| Event date: | 08-23-2000 |
|---|---|
| Report date: | 07-13-2001 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) |
| 3362001005R00 - NRC Website | |
1. Event Description On May 16, 2001, as a result of additional analysis in response to NRC Unresolved Item (URI) 50-336/2001-003-01, it was determined that the turbine driven auxiliary feedwater pump (TDAFP) [BA] had been inoperable from August 23, 2000, until September 20, 2000, without meeting the requirements of Technical Specification (TS) 3.7.1.2, "Auxiliary Feedwater Pumps." At the time of discovery, the plant was in Mode 1 at 100% power. During the time that the TDAFP was inoperable from August 23, 2000, until restored on September 21, 2000, the plant operated in Mode 1.
TS 3.7.1.2, applicable in Modes 1, 2, and 3, stipulates that with one auxiliary feedwater pump inoperable, restore the required auxiliary feedwater pump to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Hot Shutdown within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
During surveillance testing on August 23, 2000, while raising the TDAFP speed, the control room operator noted that the turbine speed would not respond smoothly to motion of the speed control switch [SC]. A Condition Report was initiated at the time, however, upon evaluation it was concluded that the observed governor valve response was not significantly inconsistent with previous experience.
On September 20, 2000, during a surveillance test, control room operators were unable to increase turbine speed above its starting speed through operation of the TDAFP speed control switch. The discharge pressure of the pump at standby speed was insufficient for the pump to provide feedwater to the steam generators. The pump was declared inoperable.
When the TDAFP failed the September 2000 surveillance test, operators entered TS 3.7.1.2, "Auxiliary Feedwater Pumps." The TDAFP was repaired and returned to service before the 72-hour allowed outage time was exceeded.
A reportability assessment performed at the time concluded that the event was not reportable, based on the assumption that the September surveillance test failure was "the time of discovery" for establishing when the pump became inoperable and that there was no firm evidence as to the time of failure (Reference NUREG-1022, Revision 2, Section 3.2.2).
NRC Regional and Resident Inspectors reviewed various aspects associated with the failure of the TDAFP. These are discussed in NRC Inspection Reports 50-336/2000-009, 50-336/2000-011, 50-336/2000-017, and 50-336/2001- 3. URI 50-336/2001-003-01 was opened pending NRC review of additional licensee evaluation regarding past operability, and therefore, reportability.
To address the concerns raised in URI 50-336/2001-003-01, Dominion Nuclear Connecticut, Inc. (DNC) contracted a third-party to perform a failure analysis of the TDAFP governor spring. That report concluded that the spring failed while the governor speed control was moving in the decreasing direction, i.e., return to standby condition. DNC concluded on May 16, 2001, that this constituted "firm evidence" that the TDAFP had been inoperable on August 23, 2000. Since TS 3.7.1.2a was not entered until September 20, 2000, this event is reportable per the criteria of 10CFR50.73(a)(2)(i)(B) as any operation or condition which was prohibited by plant Technical Specifications.
2. Cause The cause of the inoperable TDAFP was a failed spring in the governor speed control. The cause of the spring failure has not been conclusively established but each of the identified possibilities is being addressed. The cause of not recognizing that the pump was inoperable was a failure to effectively implement the corrective action program.
More specifically, plant personnel failed to aggressively investigate the degraded condition of the TDAFP on August 23, 2000. This weakness in implementation of the corrective action program was documented in NRC Inspection Reports 50-336/2001-017 and 50-336/2001-003.
3. Assessment of Safety Consequences The TDAFP is credited for Final Safety Analysis Report (FSAR) Chapter 14 loss of normal feedwater event mitigation as well as station blackout (SBO) and certain 10CFR50 Appendix R programmatic evaluations.
For the FSAR Chapter 14 loss of normal feedwater accident analysis, two of the three auxiliary feedwater (AFW) pumps are credited for event mitigation. Both motor driven AFW pumps were available during the timeframe that the TDAFP was unavailable. While the TDAFP was unavailable, diesel generator testing had occurred. During these short periods of time, should a loss of normal feedwater accident have occurred concurrent with a loss of normal AC power, only one motor driven AFW pump would have been available for event mitigation. A best estimate evaluation of this scenario was performed, and concluded that the acceptance criteria for the accident would have been met.
The TDAFP is relied upon for the SBO scenario and certain Appendix R safe shutdown scenarios. These scenarios assume loss of the motor driven auxiliary feedwater pumps and rely upon the TDAFP for accident mitigation. DNC has concluded that remedial actions could have been performed which reduce the safety impact.
This event has been determined to be of low to moderate safety significance. (Reference Inspection Report 50- 336/2000-011) 4. Corrective Action Corrective actions included: 1) The spring was replaced. 2) Direction and training have been provided to Millstone 2 Senior Reactor Operators which emphasizes the expectation for conservative decision making when dealing with degraded equipment.
An investigation was conducted and appropriate corrective actions are being addressed in accordance with the Millstone Corrective Action Program.
5. Previous Occurrences No previous similar events or conditions were identified in which a failure to aggressively investigate equipment performance concerns resulted in not meeting technical specification action statement requirements.
Energy Industry Identification System (EllS) codes are identified in the text as [XX].