05000483/LER-2008-005
| Callaway Plant Unit 1 | |
| Event date: | 11-11-2008 |
|---|---|
| Report date: | 12-23-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4832008005R00 - NRC Website | |
All times are approximate and Central Standard Time unless
I. DESCRIPTION OF THE REPORTABLE EVENT
otherwise stated.
or condition that resulted in a manual or The systems listed below reactor scram or reactor trip; and
EVENT
reactor power at the time the event
THAT WERE INOPERABLE AT THE
TO THE EVENT
at the start of the event which contributed to
DATES AND APPROXIMATE TIMES
16 were underway at the Callaway Plant. The strainer [EIIS system: SL, component: STR] was arrangement as part of the in-service leak test, power had been increased to approximately 97- MFP turbine [EIIS system: SJ, component: TRB] at 1846.36, the "B" MFP turbine tripped on low for a MFP turbine occurs at 5.5 psig; a MFP feedwater to the steam generators (SG) [EIIS steam during power operations. The loss of the ability to maintain SG water levels at As directed by plant operating procedure reactor was manually tripped at 1846.40.
safety systems responded as designed. An [EIIS system: BA, component: P] actuation ISV] actuation occurred as expected.
this event, no additional operator actions or use of required, and the plant operators were able to
A. REPORTABLE EVENT CLASSIFICATION
10CFR50.73(a)(2)(iv)(A) requires reporting of any event automatic actuation of any of the systems listed in 10CFR50.73(a)(2)(iv)(B).
are relevant to this LER:
(1) Reactor protection system (RPS) including:
(6) PWR auxiliary or emergency feedwater system.
B. PLANT OPERATING CONDITIONS PRIOR TO THE
The plant was in MODE 1, Power Operation, at 97-percent occurred.
C. STATUS OF STRUCTURES, SYSTEMS OR COMPONENTS
START OF THE EVENT AND THAT CONTRIBUTED
No structures, systems, or components were inoperable the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING
On November 11, 2008, startup activities from Refuel main feed pump (MFP) turbine "B" lube oil cooler outlet switched over to the opposite side of the duplex strainer which was completed at 1534. At 1846.33, reactor percent when annunciation was received that the "B" was experiencing low lube oil pressure. Subsequently lube oil pressure. Annunciation for low lube oil pressure turbine trips on lube oil pressure below 4 psig.
The function of the MFPs is to supply Secondary Plant system: AB, component: SG] for conversion to saturated one MFP at power levels greater than 80 percent challenges the required levels to support continued plant operations.
OTO-AE-00001, "Feedwater System Malfunction," the All control rods fully inserted during the event and all Auxiliary Feedwater (both motor-driven and turbine-driven) and a Main Feedwater Isolation [EIIS system: SJ, component:
Because these systems responded properly during other systems/components as a backup function were maintain safe shutdown conditions. Operation of the Auxiliary Feedwater system restored SG levels, and use of the Main Steam Supply System [EIIS system: SB] provided decay heat removal following shutdown. This event was considered an uncomplicated reactor trip.
On November 12, 2008, corrective maintenance was initiated to determine the cause of the low "B" MFP turbine bearing oil pressure. Maintenance technicians found two pieces of an o-ring lodged in the "B" MFP turbine bearing oil supply pressure regulating valve [EIIS system: SL, component: PCV] during disassembly. Engineering determined that the two pieces of o-ring that were recovered formed a complete o-ring that had been dislodged. The regulating valve could not operate properly due to a piece of o-ring that was pinched between the disk and the seat of the valve, resulting in low oil pressure to "B" MFP turbine. Evidence indicates that the o-ring originated from one of the "B" MFP basket strainers. The exact time the o-ring entered the system could not be determined.
The installed o-rings were made of Ethylene Propylene Diene Monomer (EPDM), which is considered to be unsatisfactory for petroleum products; the preferred material is Buna-N (Nitrile). In this situation, the EPDM o-ring had swelled and became dislodged. New o-rings made of Buna-N (Nitrile) were subsequently installed in both "B" MFP Basket Strainers. The plant was restored as indicated above and the forced outage ended on November 12, 2008.
On November 13, 2008, corrective maintenance was initiated to change out the EPDM o-rings in the "A" MFP basket strainers. Maintenance found that the o-ring on the west strainer was intact and not swollen; however, the o-ring on the east strainer was showing characteristics of swelling. These o-rings were ' installed in January 2005. New o-rings made of Buna-N (Nitrile) were installed in the "A" MFP basket strainers.
E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR PROCEDURAL ERROR
Given the annunciation of low lube oil pressure for the "B" MFP turbine at the onset of this event, the condition was self-revealing. Causal factors, as well as a root cause, were discovered through the use of a seven-step root cause analysis. It was determined that the pressure regulating valve was experiencing some blockage. Upon disassembly of the valve, the o-ring was discovered.
II. EVENT DRIVEN INFORMATION
A. SAFETY SYSTEMS THAT RESPONDED
All safety systems functioned as designed. The motor-driven Auxiliary Feedwater actuation, turbine- driven Auxiliary Feedwater actuation, and main feedwater isolation actuation occurred as expected.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
No structures, systems, or components were inoperable during the event which contributed to the event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
As directed by plant operating procedures, a manual reactor trip was initiated in response to the loss of one non-safety grade MFP. A reactor trip is considered an ANS Condition II event which is defined as a condition, that once corrected, will allow the plant to return to operation.
The event actuated safety grade systems that responded as designed and which fulfilled their intended safety functions. Because these systems responded properly during this event, no additional operator actions or use of other systems/components as a backup function were required. The plant operators were able to maintain safe shutdown conditions. Operation of the Auxiliary Feedwater system and main steam supply system adequately removed decay heat following the shutdown. No release of radioactive material was associated with this event.
Ill. CAUSE(S) OF THE EVENT AND CORRECTIVE ACTION(S) This event was evaluated using a seven-step root cause analysis process. The reactor trip was caused from a series of events beginning with one causal factor, a one-time receipt of incorrect o-ring material from the original equipment manufacturer (OEM). Engineering analysis at that time confirmed that the o-rings supplied by the OEM were made of EPDM material. An engineering evaluation that was then performed permitted use of the material based on what had been supplied. Use of this incorrect material was identified as the root cause since it has been confirmed that EPDM is incompatible with petroleum-based lubrication systems. The EPDM o-rings installed in the MFP lube oil basket strainers swelled, dislodged, and degraded the performance of a MFP turbine lube oil pressure regulating valve that ultimately led to the manual trip of the plant.
The cause was that the o-rings in the MFP lube oil system were a material susceptible to swelling in petroleum-based lubrication systems. Specifically, an o-ring swelled, got into the MFP lube oil system, and traveled into a MFP turbine bearing oil supply pressure regulating valve. The Corrective Actions to Prevent Recurrence (CATPRs) included identification of a replacement for the o-rings for the strainer baskets. The correct o-rings were installed in both strainers for "A" and "B" MFP turbine oil system.
Action identified from the extent of cause evaluation is to assure that correct material is being purchased for the Callaway Plant. Procurement controls are being modified to ensure that o-rings having the correct critical characteristics (i.e., size, material, and hardness) are obtained.
IV. PREVIOUS SIMILAR EVENTS
Operating Experience (OE) was reviewed to incompatible materials at Callaway.
and it was determined that there have been no reactor trips due There were no forced outages since the completion of Refuel 14 (November 2005) that impacted either MFP.
V. ADDITIONAL INFORMATION
below are from the IEEE Standard 805-1984 and IEEE System (PWR) Steam Feedwater System (PWR) System Pump Turbine Lube Oil System Pressure The system and component codes listed Standard 803A-1983, respectively.
System: AB, Reactor Coolant Components: SG, Generator, System: BA, Auxiliary/Emergency Components: P, Pump System: SJ, Feedwater Components: ISV, Valve, Isolation TRB, Turbine System: SL, Feedwater Components: PCV, Valve, Control, STR, Strainer