05000334/LER-2009-002
| Docket Number | |
| Event date: | 04-20-2009 |
|---|---|
| Report date: | 06-18-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| Initial Reporting | |
| ENS 45000 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3342009002R00 - NRC Website | |
There were no structures, components, or systems that were inoperable at the start of the event that contributed to the event. Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
DESCRIPTION OF EVENT
During a plant shutdown on April 20, 2009, a feedwater isolation occurred at the Beaver Valley Power Station (BVPS) Unit 1 as a result of two of three narrow range water level transmitters in the 'B' steam generator reaching the Hi-Hi setpoint.
While reducing the plant's temperature in Mode 3 in preparation to commence a refueling outage, each of the three steam generators were being fed using the Main Feedwater System [SJ] through their individual bypass feedwater regulating valves with the Main Feedwater Control System [JB] operating in automatic control. At 01:14, the control room operator noted excessive feedwater flow and a rapidly rising water level on the 'B' steam generator. The operator took manual control of the feedwater bypass regulating valve on the 13' steam generator in an attempt to lower the feedwater flow rate. When the control demand was taken to zero, the feedwater bypass regulating valve did not close, with feedwater flow indication remaining at an excessive flow rate. A Hi-Hi steam generator water level occurred in the 'B' steam generator before other manual actions could be taken to terminate the feedwater level rise.
An automatic Feedwater Isolation Signal was initiated on the Hi-Hi steam generator water condition in the 'B' steam generator, with safety-related plant systems responding as designed, which included tripping of the operating main feedwater pump and closing the main feedwater isolation valves. Both motor-driven auxiliary feedwater pumps started, as designed, in response to all main feedwater pumps being tripped by the Feedwater Isolation Signal. With steam generator feedwater flow now being supplied and controlled by the Auxiliary Feedwater System [BA], a proper feedwater flow rate was re-established, terminating the water level increase in the 'B' steam generator. Steam generator water level was decreased below the Hi-Hi setpoint at 02:04.
The 4-inch bypass feedwater bypass regulating valve is designed to modulate open pneumatically and vents the air to close. This feedwater bypass regulating valve's positioner had been replaced with a new vendor-supplied positioner in November, 2008.
When this feedwater bypass regulating valve was exercised on April 19, 2009, the day before the planned plant shutdown, the field operator noted uncharacteristic varied valve speeds when moving in the closed direction. However, this was determined not to be unacceptable since the valve met its surveillance acceptance criteria. On April 20, 2009, with the plant in Mode 4, approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after the Hi-Hi steam generator water level had occurred, this feedwater bypass regulating valve was successfully stroked full open and full close by manually operation from the control room benchboard.
CAUSE OF EVENT
The direct cause of this event was failure of the positioner associated with the controls of FCV-1FW-489, "B" Bypass Main Feedwater Regulating Valve. The positioner was not providing accurate signals to the boosters on a valve closure input.
The root cause of this event was determined to be foreign material found within the feedwater bypass regulating valve positioner, causing the valve to fail to close during the event. The internal foreign materials found within the positioner were small chipped pieces of the positioner poppet seat and excess thread sealant compound. The foreign material was manufacturing induced and did not represent internal organizational or process weakness related to the procurement and use of this valve.
ANALYSIS OF EVENT
The portion of the main feedwater system which provides feedwater to the steam generators and the main feedwater automatic level control system do not perform safety related functions. The safety function for main feedwater isolation valve closure functioned correctly. This event is bounded by the safety analysis provided in the Updated Final Safety Analysis Report Section 14.1.9 for the bounding excessive feedwater flow condition from a system malfunction.
The plant risk associated with the BVPS Unit 1 Feedwater Isolation event that occurred on April 20, 2009, due a high water level condition in the 'B' Steam Generator is considered to be very low. This is based on the conditional core damage probability for the event when considering the actual plant conditions that were present at the time of the event.
Based on the above, the safety significance of the Feedwater Isolation event on April 20, 2009, was very low.
A Hi-Hi water level condition was experienced in the 'B' Steam Generator, causing an automatic Feedwater Isolation Signal to be generated. This signal automatically stopped the running Main Feed Pump, which then automatically started both motor-driven Auxiliary Feedwater System (AFW) Pumps. Both motor-driven AFW pumps were actuated in response to the valid high steam generator water level condition, as designed. This was a valid actuation of the Auxiliary Feedwater System, which is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) since Auxiliary Feedwater System is an applicable system as listed in 10 CFR 50.73(a)(2)(iv)(B)(6).
This event was reported as specified system actuations pursuant to 10 CFR 50.72(b)(3)iv)(A) at 05:09 on April 20, 2009 (EN Number 45000).
ANALYSIS OF EVENT (Continued) There was no loss of safety function pursuant to 10 CFR 50.73(a)(2)(v) since the applicable safety systems functioned as designed.
CORRECTIVE ACTIONS
1. The applicable bypass feedwater regulating valve has been repaired and tested satisfactory.
2. The applicable Main Feedwater System regulating valve positioners will be re-classified to 'augmented quality' in order to stipulate that newly received positioners receive an internal inspection for foreign material.
3. An operating experience will be issued related to the discovery of foreign matter on the positioner valve.
Completion of the above and other corrective actions are being tracked through the BVPS corrective action program.
PREVIOUS SIMILAR EVENTS
A review found no prior BVPS Unit No. 1 and BVPS Unit No. 2 Licensee Event Reports within the last three years for an event involving manufacturer internal valve foreign material.
CR 09-57474