05000455/LER-2001-002

LER-2001-002,

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
4552001002R00 - NRC Website

NAME

Penny Reister, Regulatory Assurance Manager TELEPHONE NUMBER (Include Area Code) (815) � 234-5441 X2800 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

TO EPIX

D SJ FCV Bailey Yes SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED

SUBMISSION

DATE (15)

YES

(If yes, complete EXPECTED SUBMISSION DATE) X NO ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16) At 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br /> on June 26, 2001, the Unit 2 licensed Nuclear Station Operator (NSO) observed the Unit 2 "D” Steam Generator (SG) level begin to decrease. He attempted to further open the Unit 2 Main Feedwater (FW) Regulating Valve (i.e., 2FW540) for the 2D SG. The valve did not respond and the 2D SG level continued to decrease and approached the low level reactor trip setpoint. In anticipation of the automatic trip signal, the NSO initiated a manual reactor trip signal at 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br />, prior to reaching the low level setpoint on 2D SG. The reactor trip system responded as expected and shutdown the reactor. The Auxiliary Feedwater (AF) System started as expected to supply auxiliary feedwater to the SGs. During the post reactor trip recovery, an unexpected reactor trip and AF actuation signal was generated when the B SG level was allowed to drop below the actuation setpoint. The 2B AF pump had just been secured and consequently, restarted. The cause of the 2FW540 valve closing was due to a retaining clip in the valve's positioner (i.e., Bailey AV1) not being installed correctly.

The cause of the second unexpected actuation signal was due to failure of the licensed Unit Supervisor (US) to verbalize a procedure step concerning SG levels. Corrective actions include revising work instructions to ensure the retaining clip in Bailey AV1 positioners are installed correctly and counseling the US. There were no safety consequences impacting plant or public safety. This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv).

(p: 0 1 lers 455-2001-002-00.doc) APPROVED BY OMB NO. 3150-0104 EXPIRES 06/30/2001 collection request: 50 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry. Forward comments regarding burden estimate to the information and Records Management Branch (t-6 f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, and to the Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 2 STN 05000455 (If more space is required, use additional copies of NRC Form 366A)(17)

A. Plant Conditions Prior to Event:

Unit 2 - Event Date/Time: June 26, 2001 / 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br /> Mode 1 - Power Operations, Reactor Power - 100% Reactor Coolant System [AB]: Normal operating temperature and pressure No structures, systems or components were inoperable at the start of the event that contributed to the event.

B. Description of Event:

At approximately 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br /> on June 26, 2001, the Unit 2 licensed nuclear station operator (NSO) observed the Unit 2 "D" Steam Generator (SG) [SB] level begin to decrease. He attempted to increase Main Feedwater (FW)[SJ] flow by further opening the Unit 2 Main FW Regulating Valve (i.e., 2FW540) for the 2D SG. The valve did not respond and the 2D SG level was still decreasing and approaching the low level reactor trip setpoint. In anticipation of the automatic reactor trip signal, the NSO initiated a manual reactor trip signal at 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br />, prior to the 2D SG level reaching the low level setpoint.

The reactor trip system responded as expected and shutdown the reactor. The Byron Emergency Procedure, 2BEP ES-0.1, "Reactor Trip Response Unit 2." As an expected response to a reactor trip from 100% power, the SG water levels dropped below the low level setpoint for automatic Auxiliary Feedwater [BA](AF) actuation.

This resulted in the expected automatic initiation of both trains of AF.

The licensed Unit Supervisor (US) assumed the position of procedure reader for controlled between 14% and 50%. Since flow from both trains of AF were not needed to control levels, the flow from the diesel driven 2B AF pump to the SGs was isolated and the flow from the motor driven 2A AF pump was throttled appropriately.

The 2B AF pump remained running in recirculation mode.

operator check for stable plant conditions. This included maintaining the SG narrow range levels "at normal level." The US understood this to mean "normal" for current plant conditions, which he believed meant between 14% and 50%.

(p: 011ers455-2001-002-00.doc) APPROVED BY OMB NO. 3150-0104 EXPIRES 06/30/2001 collection request: 50 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry. Forward comments regarding burden estimate to the information and Records Management Branch (t-6 f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, and to the Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 2 STN 05000455 (If more space is required, use additional copies of NRC Form 366A)(17) B. Description of Event, cont.:

Since he knew the levels were in this range, he did not verbalize this step to the NSO, and no additional actions were taken regarding SG levels. However, the intent of the step was to control SG levels to the normal operational level of 60%. At 0654 hours0.00757 days <br />0.182 hours <br />0.00108 weeks <br />2.48847e-4 months <br />, the US began the transition from 2BEP ES-0.1 to Unit 2 Byron General Procedure 2BGP 100-5, "Plant Shutdown and Cooldown.

The US, concerned over a potential inadvertent shutdown of the 2B AF diesel driven pump due to vortexing in the fuel oil day tank, directed a NSO to shutdown the 2B AF pump. Using the appropriate procedure for securing the 2B AF pump, the NSO verified that SG levels were greater than the low level setpoint for AF actuation (i.e., 36.3%) and at 0733 hours0.00848 days <br />0.204 hours <br />0.00121 weeks <br />2.789065e-4 months <br /> the 2B AF Pump was shutdown. The NSO did not recognize that the SG level in the 2B SG was close to the actuation setpoint and decreasing slowly. After approximately 10 seconds, the level in the 2B SG reached the low level setpoint and an unexpected reactor trip and AF actuation signal was generated. No equipment actuated except for the re-start of the 2B AF Pump which had just been shut down.

At 0652 hours0.00755 days <br />0.181 hours <br />0.00108 weeks <br />2.48086e-4 months <br /> on June 26, 2001, an Emergency Notification System (ENS) telephone notification to the NRC was completed in accordance with 10 CFR 50.72(b)(2)(iv) for the reactor trip and the expected automatic actuation of the AF system. At approximately 0733 hours0.00848 days <br />0.204 hours <br />0.00121 weeks <br />2.789065e-4 months <br />, the ENS call was updated to report the second unexpected automatic actuation signal.

C. Cause of Event:

An investigation ensued into the cause of the 2FW540 valve unexpected failure.

2FW540 is an air operated valve with a Bailey AV1 positioner. The positioner cover for the valve was removed and it was observed that the retaining clip that holds the pilot valve stem in the pilot valve body was out of the beam assembly retaining cup and hanging down from the guide on the beam assembly. The purpose of the retaining clip is to hold the pilot valve stem in the pilot valve body. This allowed the pilot valve stem to hang half out of the pilot valve body. With the pilot valve uncoupled from the beam assembly, the positioner could no longer adjust the 2FW540 valve.

(p: 01 lers 455-200 I -002-00.doc) APPROVED BY OMB NO.3150-0104 EXPIRES 06/30/2001 collection request: 50 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry. Forward comments regarding burden estimate to the information and Records Management Branch (t-6 f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, and to the Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 2 STN 05000455 (If more space is required, use additional copies of NRC Form 366A)(17) C. Cause of Event, cont.:

The most probable failure mode for this event was that the retaining clip was not properly inserted into the beam assembly retaining cup and was hung up on the lip of the cup. Normal system vibrations eventually caused the clip to dislodge from the lip of the retaining cup. It is unknown how the retaining clip became hung up on the lip of the cup. This could have happened at the factory, during shipping, during the bench test or during the field test. The positioner was inspected with no damage or distortion found. The retaining clip throat dimensions were verified to be within the equipment manufacturer's tolerance.

On April 12, 2001, maintenance was performed on the 2FW540 valve. The valve had the positioner, booster, regulators, gauges and volume booster replaced; however, the pilot valve was not changed out. The retaining clip was not required to be verified to be seated properly prior to or after installing the positioner.

The root cause of the reactor trip was determined to be a failure to have specific instructions in the work package for the April 12, 2001, maintenance work package to inspect the retaining clip to assure that it is seated properly in the beam assembly cup.

During the investigation it was learned that in November of 1998, Surry Power Station experienced a similar reactor trip due to a mispositioned retaining clip on the pilot valve in their Feedwater Regulating Valves (FRV). The Surry Power Station Licensee Event Report (LER) for their trip was not reviewed at Byron Station for lessons learned. A contributing cause to this event is that our operating experience review program does not require a formal review of other site's LERs, nor did our reactor trip reduction program review reactor trip LERs from reactor designs dissimilar from Byron Station's design.

The root cause for the second unexpected reactor trip and AF actuation signal was determined to be a failure of the US to comply with the Operations Department expectation to verbalize all steps in 2BEP ES-0.1.

D. Safety Analysis:

There were no safety consequences impacting plant or public safety as a result of this event. The NSO appropriately tripped the reactor in anticipation of an automatic reactor trip from a low level condition in the 2D SG. The reactor trip (p: 0 1 lers 455-2001-002-00.doc) APPROVED BY OMB NO. 3150-0104 EXPIRES 06/30/2001 collection request: 50 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry. Forward comments regarding burden estimate to the information and Records Management Branch (t-6 f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, and to the Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 2 STN 05000455 (If more space is required, use additional copies of NRC Form 366A)(17) D. Safety Analysis, cont.:

system functioned as designed and shut down the reactor without incident. The second quarter 2001, Unit 2 NRC performance indicator for unplanned scrams per 7000 critical hours is in the green band at a value of 1.7. There were no safety consequences impacting plant or public safety as a result of the unexpected 2B AF Pump Start. The pump started as designed in response to low level in the SGs. No safety system functional failures occurred.

E. Corrective Actions:

A new positioner for 2FW540 was bench tested and the pilot valve and clip were replaced. The positioner was installed on 2FW540 valve and acceptably tested. The retaining clips in twelve of the same positioners on Unit 2 and 18 new positioners in stores were inspected and all retaining clips were found to be seated correctly.

Based on the above inspection results and Unit 1 continuous operations of 250 days, it was decided that the Unit 1 valves with the same positioner did not need to be inspected at this time. The Unit 1 valves are scheduled to be inspected during the next outage.

The maintenance test reports and procedures for all valves with Bailey AV1 positioners, to include all FRVs, will be revised to include instruction to verify the pilot valve retaining clip is installed correctly prior to final closure of the positioner cover and to depict the positioner retaining clip cups in the drawing.

We will evaluate revising our Operating Experience Program to include other site's LERs in our operating experience program and reactor trip reduction program.

We will evaluate revising the FRV test report and procedure to provide checklists of other critical items that should be inspected prior to final close out of the positioner to prevent new failure modes that have not been identified.

Personal performance issues regarding the US have been addressed.

Operations Manager expectations for procedure readers will be reinforced to Operation personnel in upcoming simulator training.

(p: 01 lers1455-2001-002-00.doc) APPROVED BY OMB NO. 3150-0104 EXPIRES 06/30/2001 collection request: 50 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry. Forward comments regarding burden estimate to the information and Records Management Branch (t-6 f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, and to the Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 2 STN 05 00 0455 (If more space is required, use additional copies of NRC Form 366A)(I7) F. Previous Occurrence:

Generator Level Caused by an Inappropriate Operator Response to a Failed Circuit Card in the Feedwater Flow Control Circuitry," dated August 25, 2000.

Corrective actions in this LER would not have been expected to prevent this event.

G. Component Failure Data:

Manufacturer � Nomenclature � Model Number � Mfr. Part Number Bailey � Positioner � AV1 � N/A (p: Oilers 455-2001-002-00.doc)