05000313/LER-2009-003
| Arkansas Nuclear One, Unit 1 | |
| Event date: | 09-22-2009 |
|---|---|
| Report date: | 12-17-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3132009003R01 - NRC Website | |
10. POWER LEVEL
100
12. LICENSEE CONTACT FOR THIS LER
NAME
David B. Bice, Acting Manager, Licensing TELEPHONE NUMBER (Include Area Code) 479-858-4710
13. COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT
CAUSE SYSTEM COMPONENT MANU- FACTURER
REPORTABLE
TO EPIX CAUSE SYSTEM COMPONENT
MANU-
FACTURER
REPORTABLE
TO EPIX
14. SUPPLEMENTAL REPORT EXPECTED
- YES (If yes, complete 15. EXPECTED SUBMISSION DATE) 0 @ 0 NO
15. EXPECTED
SUBMISSION DATE MONTH DAY YEAR
ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) On September 22, 2009, at approximately 1329 CDT, with the plant operating at 100% power, it was discovered during the review of an Arkansas Nuclear One Unit 1 past operability evaluation that an unanalyzed condition may have existed for a short period of time in which a door that serves as a High Energy Line Break (HELB) barrier may have been unlatched. With the door unlatched, an engineering evaluation concluded that a critical crack in the Main Feedwater pipe traversing the south penetration room would force the door (DR-19) open, creating a harsh environment in the adjoining Emergency Feedwater (EFW) pump room. Because the EFW [BA] pump room is not evaluated for harsh conditions, it must be conservatively assumed that both pumps may fail to operate following this HELB event. Investigation revealed that the most probable cause of the latch failure was due to wear of the latch bolt hole.
A. Plant Status At the time this condition was identified, Arkansas Nuclear One, Unit 1 (ANO-1) was operating at 100% power.
B. Event Description
In January, Door 19 (DR-19) was discovered to be in an unlatched condition. The door was immediately latched reestablishing the barrier. An immediate operability was performed which concluded the door was capable of performing its design function based upon its ability to be latched; however, past operability was not thoroughly evaluated for the unlatched condition. On September 22, 2009, at approximately 1329 CDT, it was discovered during the review of this past operability that an unanalyzed condition may have existed for a short period of time when DR-19, which serves as a High Energy Line Break (HELB) barrier, was unlatched.
With the door unlatched, an engineering evaluation concluded that a critical crack in the Main Feedwater [SJ] pipe traversing the south penetration room would force the DR-19 open, creating a harsh environment in the adjoining Emergency Feedwater (EFW) [BA] pump room. Because the EFW pump room is not evaluated for harsh conditions, it must be conservatively assumed that both pumps may fail to operate following this HELB event.
C. Root Cause
Investigation revealed that the most probable cause of the latch failure was due to wear of the latch bolt hole. The repetitive motion of turning the door knob applies stress to the latch, latch holding plate, and bolt hole in the door. Eventually, this repetitive stress results in worn latch mechanism parts, which allow the bolt to back out obstructing the door from closing completely and latching.
D. Corrective Actions
Operability was immediately established by latching the door closed.
A preventative maintenance task which included specific instructions for latch inspections was developed for HELB and airtight doors similar to DR-19.
DR-19 will be replaced in the next refueling outage. Until the door can be replaced, monthly inspections of the DR-19 latch will be performed to verify proper installation. Additionally, daily tours of this area by Operations and other station personnel provide a means of verification that DR-19 remains in the closed, latched position.
E. Safety Significance
With the door unlatched, an engineering evaluation concluded that a critical crack (HELB) in the Main Feedwater pipe traversing the south penetration room would force the door (DR-19) open creating a harsh environment in the adjoining EFW pump room. Because the EFW pump room is not evaluated for harsh conditions, it must be conservatively assumed that both pumps may fail to operate following this HELB event.
F. Basis for Reportability The unlatched door serving as a HELB barrier is reportable under 10 CFR 50.73(a)(2)(ii)(B) and 10 CFR 50.73(a)(2)(v)(B) as an unanalyzed condition that significantly degraded plant safety and a condition the could have prevented the fulfillment of a safety function.
G. Additional Information
There were no previous similar events reported as Licensee Event Reports by ANO.
Energy Industry Identification System (El IS) codes are identified in the text as [XX].