05000321/LER-2009-005
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3212009005R00 - NRC Website | |
PRINTED ON RECYCLED PAPER
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On May 15, 2009 at 05:19 EDT, Unit 1 was in the cold shutdown mode to investigate problems in the nuclear instrumentation system (EIIS Code IG) that had been previously identified. At that time, a Group 1 isolation signal on actual low condenser vacuum (EIIS Code SG) was generated when Operations personnel moved the reactor mode switch to the run position per subsection 7.1 of special purpose procedure 42SP-05-12-09-PI-1-1, "Test of Nuclear Instrumentation Response to Diverse Logic System Actuations." Because the Main Steam Isolation Valves (EIIS Code SB), (MSIVs) were open at the time the Group 1 isolation signal was generated; they closed per design resulting in a reactor scram trip signal on MSIVs less than 90 percent open with the mode switch in the run position. Since the unit was in the cold shutdown condition at the time of the event, all controls rods (EIIS Code AA) were already inserted fully and therefore no rod motion occurred. However, the Main Steam Line Drain (EIIS Code SB) and Reactor Water Sample Line (EIIS Code CE) isolation valves also closed per design on the Group 1 isolation signal. Operations personnel returned the reactor mode switch to the shutdown position and reset the isolation and scram signals. Operations personnel left the MSIVs in the closed position.
CAUSE OF EVENT
The direct cause of this event was personnel error resulting in the development of an inadequate test procedure. Specifically, procedure 42SP-05-12-09-PI-1-1 did not contain the necessary steps to defeat the low condenser vacuum isolation logic that is armed when the reactor mode switch is in the run position. Consequently, the MSIVs, and the Main Steam Line Drain and Reactor Water Sample Line isolation valves, closed as designed on an actual low condenser vacuum signal when the reactor mode switch was moved to the run position as directed by the test procedure. The procedure was inadequate because the engineer who drafted the procedure overlooked the low condenser vacuum Group 1 isolation logic on the plant elementary diagrams and misinterpreted the procedure review process thus not requiring a technical review of the procedure prior to issuance.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) because unplanned actuations of safety feature systems listed in 10 CFR 50.73 occurred. In this instance, a Group 1 isolation along with a reactor protection system (EIIS Code IG), (RPS) actuation resulting in a reactor scram.
The Condenser Vacuum - Low Function is provided to prevent over pressurization of the main condenser in the event of a loss of the main condenser vacuum. Since the integrity of the condenser is an assumption in offsite dose calculations, the Condenser Vacuum - Low Function is assumed to be operable and capable of initiatin closure of the MSIVs. The closure of the MSIVs is initiated to � prevent the addition of steam that would lead to additional condenser pressurization and possible rupture of the diaphragm installed to protect the turbine exhaust hood, (EIIS Code TA) thereby preventing a potential radiation leakage path following an accident. Condenser vacuum pressure signals are derived from four pressure switches that sense the pressure in the condenser. Four channels of Condenser Vacuum - Low Function are available and are required to be operable to ensure that no single instrument failure can preclude the isolation function. The Allowable Value is chosen to prevent damage to the condenser due to pressurization, thereby ensuring its integrity for offsite dose analysis. As noted in the technical specifications, the channels are not required to be operable in Modes 2 and 3 when all turbine stop valves (TSVs); (EIIS Code TA) are closed, since the potential for condenser over pressurization is minimized. Switches are provided to manually bypass the channels when all TSVs are closed. This provides an isolation function for the Group 1 valves.
In this event, a Group 1 isolation signal was generated per design when the mode switch was moved to run with the low condenser vacuum isolation logic armed. Although an actual low condenser vacuum condition existed, the Group 1 isolation was not necessary to protect the condenser integrity. With the unit in Cold Shutdown, no steam was present to create the potential for over pressurization and thus condenser integrity could not have been challenged. However, the Group 1 isolation logic functioned as designed and would have prevented over pressurization of the condenser had it been required to do so.
Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety.
CORRECTIVE ACTIONS
Engineering Support personnel reviewed and revised procedure 42SP-05-12-09-PI-1-1 to correct the error. Personnel successfully performed the corrected procedure on May 20, 2009.
The procedure drafter was coached on the importance of a thorough technical review, the proper application of human performance tools, and correct interpretation of the procedure review matrix.
ADDITIONAL INFORMATION
Other Systems Affected: None Failed Components Information: None Commitment Information: This report does not create any new permanent licensing commitments.
Previous Similar Events:
There are no similar events within the past two years in which an inadequate procedure resulted in a Group 1 isolation and reactor scram.
� PRINTED ON RECYCLED PAPERNRC FORM 366A (9-2007)