05000498/LER-2004-003
| South Texas | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4982004003R00 - NRC Website | |
I.�DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
This event is reportable pursuant to 10CFR50.73(a)(2)(ii)(B). The South Texas Project determined that the Train B high head safety injection pump flushing line isolation valve was partially open. This resulted in a condition where the radiological control room dose limits of General Design Criterion (GDC) 19, Appendix A of 10CFR50 and the offsite dose limits of 10CFR100 would have been exceeded in the event of a design-basis accident.
This event is also reportable pursuant to 10CFR50.73(a)(2)(v)(C). The partially open isolation valve would have prevented the control room emergency filtration and cleanup system from fulfilling its safety function to control the release of radioactive material within the radiological control room dose limits in accordance with General Design Criterion (GDC) 19.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
South Texas Project Unit 1 was in Mode 1 operating at 100% power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT
THE START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
There were no inoperable structures, systems or components that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES
On March 26, 2004, Train B high head safety injection pump was started for surveillance testing. During the surveillance, the pump room sump alarm actuated. Upon investigation, the sump was discovered to be full. After the sump level was pumped down, the Train B high head safety injection pump flushing line was found at about the same temperature as the rest of the line with flow to the sump. The flushing line isolation valve was found approximately 1/8 turn open and was subsequently closed. A short time later, with the Train B high head safety injection pump still running, the flow into the sump from the flushing line had completely stopped.
A partially opened Train B high head safety injection pump flushing line isolation valve provides a containment bypass leak path during a design-basis loss of coolant accident (LOCA) after the safety injection system switches to re-circulation. Engineering analysis had previously concluded that any essential safety feature system leakage in excess of 436 gallons per day, based on current local leak rate tests (LLRT) and integrated leak rate tests (ILRT) containment boundary leakage, during a design basis LOCA would result in unacceptable onsite and offsite dose consequences. When the flushing line isolation valve was partially open, the valve was leaking in excess of 436 gallons per day. This condition was determined to be reportable at 2230 on March 26, 2004 and an eight-hour notification of this unanalyzed condition that significantly degraded plant safety was made to the Nuclear Regulatory Commission Operations Center at 0108 hours0.00125 days <br />0.03 hours <br />1.785714e-4 weeks <br />4.1094e-5 months <br /> on March 27, 2004.
.NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-2001) 2. DOCKET1. FACILITY NAME 6. LER NUMBER 3. PAGE _ 2004�003�00 3�4
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR
PROCEDURAL OR PERSONNEL ERROR
The Train B high head safety injection pump flushing line isolation valve was discovered partially open while responding to the pump room high level sump alarm.
II.�COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
None. The flushing line isolation valve was shut and leakage stopped.
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
None
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF
COMPONENTS WITH MULTIPLE FUNCTIONS
None
D. FAILED COMPONENT INFORMATION
None III.�ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
None
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
None
C. SAFETY CONSEQUENCES AND IMPLICATIONS
This event is significant because of the potential to have overexposed the plant operating staff to radioactive contamination if a design basis LOCA occurred while this valve was out of position. Local radiation rates in the safety injection pump rooms would have been significantly higher due to the untreated reactor coolant being pumped to the open floor sump. This would have limited access to the area by personnel following such an event. If this valve were to be open during a postulated LOCA, the resulting release from the safety injection system would cause the GDC 19 control room operator dose limits and the 10CFR100 offsite dose limits to be exceeded.
The partially open isolation valve would have prevented the control room emergency filtration and cleanup system from fulfilling its safety function to control the release of radioactive material within the radiological control room dose limits in accordance with General Design Criterion (GDC) 19. This event represents a safety system functional failure.
The estimated leakage from the safety injection system would not have significantly degraded the B train high head safety injection Probabilistic Risk Analysis (PRA) function to provide injection flow to the core given a LOCA event. Also, the water inventory loss for a postulated LOCA event would not have significantly degraded the safety injection re-circulation core cooling PRA function, assuming a 24-hour mission time. The reported safety injection leakage to the fuel handling building sump would provide a containment bypass radioactive release path during the re-circulation phase of a LOCA event, but the amount would not be categorized as a Large Early Release. Based on the aforementioned statements, the impact to core damage frequency (CDF) and large early release frequency (LERF) is considered very small.
There was no radiological release from this event.
IV.CCAUSE OF THE EVENT The cause of the Train B high head safety injection pump flushing line isolation valve being out of position is indeterminate.
The most likely cause of this valve being out of position is someone using the valve handle as an aid in exiting the ladder located next to it. This ladder goes down approximately 7 feet to the sump level below. The ladder is seldom used.
V.CCORRECTIVE ACTIONS A. The valve handles from this flushing line isolation valve and the two valves adjacent to it will be removed in both units. This action is expected to prevent recurrence of accidental misalignment of any of these valves.
B. Site-wide communication and lessons learned will be implemented for personnel to exercise caution around plant equipment to avoid accidental manipulations.
VI.CPREVIOUS SIMILAR EVENTS Within the last three years, there have been no other events at the South Texas Project of valves out of position that would have resulted in exceeding offsite or onsite radiological dose limits during a design-basis accident.