05000424/LER-2002-001
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| 4242002001R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)
A. REQUIREMENT FOR REPORT
This event is reportable per 10 CFR 50.73 (a)(2)(i) because the unit operated in a condition prohibited by the Technical Specifications when a valve in the suction path to the intermediate head safety injection (SI) pumps and the high head centrifugal charging pumps (CCPs) was inoperable.
B. UNIT STATUS AT TIME OF EVENTS
At the time of the discovery of these events on March 7, 2002, and April 1, 2002, Unit 1 was in a refueling outage in Mode 5 (Cold Shutdown) and in Mode 6 (Refueling), respectively. Other than that described herein, there was no inoperable equipment that contributed to the occurrence of this event.
C. DESCRIPTION OF EVENT
During the 1R10 refueling outage, some electricians adopted the practice of utilizing elementary drawing and wiring diagrams to verify wiring terminations prior to lifting leads on motor operated valves scheduled for maintenance. As a result, two wiring errors were discovered that would have prevented the opening of 1HV-8804B during a loss of power to Train A. This valve provides a suction path from the discharge of the Train B Residual Heat Removal (RHR) pump to the suction of the high head CCPs and intermediate head SI pumps, during post-LOCA ECCS recirculation operations.
On March 7, 2002, maintenance was being performed on the Unit 1 common SI miniflow isolation motor operated valve, 1HV-8813. It was discovered that interlock wiring with a second SI motor operated valve, 1HV-8804B, was not terminated in accordance with plant drawings. The wiring error was promptly corrected.
Following the March 7, 2002, discovery of the interlock mis-wiring, additional interlock testing was performed. On April 1, 2002, during testing of the Unit 1 high head CCP miniflow isolation motor operated valve, 1HV-8509B, it was found that interlock wiring with 1HV-8804B was also not terminated in accordance with plant drawings. Again, the wiring error was promptly corrected.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Vogtle Electric Generating Plant — Unit I The Plant Vogtle intermediate head SI pumps and the high head CCPs have mini-flow paths from their pump discharge piping to the Refueling Water Storage Tank. If a single failure of Train A power occurs during a design bases accident, the following would be expected to occur:
1) The two SI pumps have a common miniflow isolation motor operated valve, 1HV-8813, that is Train B powered. This miniflow path is isolated prior to transitioning from the Emergency Core Cooling Injection Mode to the Recirculation Mode of operation. A properly wired interlock allows the opening of 1HV-8804B during switchover from Injection Mode to the Recirculation Mode after the SI pump miniflow path has been isolated by closing 1HV-8813.
2) Similarly, CCP Train A has a miniflow isolation motor operated valve, 1HV-8509B, that is Train B powered. This miniflow path is isolated prior to transitioning from the Emergency Core Cooling Injection Mode to the Recirculation Mode of operation. A properly wired interlock allows the opening of 1HV-8804B during switchover from Injection Mode to the Recirculation Mode after the CCP's miniflow path has been isolated by closing 1HV-8509B.
Valve 1HV-8804B provides a suction path from the discharge of the Train B Residual Heat Removal (RHR) pump to the suction of the CCPs and SI pumps. Valve 1HV-8804B must be open to provide water to the suction of the CCPs and SI pumps if the Train A RHR pump is unavailable.
However, these wiring errors would have prevented 1HV-8804B from being opened.
On March 12, 2002, at 0830 EST, following completion of an engineering evaluation of the March 7, 2002, discovery, it was determined that this condition may represent an unanalyzed condition that significantly degrades plant safety and was reportable per 10 CFR 50.72 (b)(3)(ii)(B). The NRC Operations Center was notified at 1450 EST. Further evaluation by the design engineer determined that the condition did not represent a significant degradation to plant safety and a retraction notice was submitted to the NRC Operations Center on April 24, 2002, at 1047 EDT.
D. CAUSE OF EVENT
A review of work orders has found that these mis-wirings likely occurred during maintenance performed in 1991 and/or 1996. In the case of the SI miniflow isolation motor operated valve, cramped conditions may have contributed to the mis-wiring. However, because of the time lapses involved, the root cause of these human performance errors by licensee employees cannot be conclusively determined.
E. ANALYSIS OF EVENT
The reported condition exists only when a power failure of Train A occurs. In the case of a large break LOCA, all but one of the post-LOCA minimum flow requirements are met with only residual heat removal (MIR) system flow available. This unmet requirement can be considered acceptable by crediting natural circulation flow patterns in the core. In the case of a small break LOCA, no interruption in ECCS flow would have occurred. Therefore, there was no adverse affect on plant safety or on the health and safety of the public as a result of this event.
F. CORRECTIVE ACTIONS
1) Other Unit 1 ECCS motor-operated valve interlocks were verified to operate properly.
Additional wiring discrepancies that did not affect component operability were found and corrected.
2) Prior to the Unit 2 Fall 2002 Refueling Outage, procedure 20429-C, "Short Term Documentation Of Temporary Jumpers And Lifted Wires," will be revised to require electricians to utilize elementary drawing and wiring diagrams to verify wiring terminations prior to lifting leads on safety-related motor operated valves scheduled for maintenance.
3) Prior to the Unit 2 Fall 2002 Refueling Outage, appropriate procedures will be revised to require functional testing of interlocks following maintenance which affects that function.
4) Prior to the Unit 2 Fall 2002 Refueling Outage, this lifted lead event will be added to operating experience training for electricians.
5) During the Unit 2 Fall 2002 Refueling Outage, the corresponding interlock wiring in Unit 2 will be verified to be functionally correct.
G. ADDITIONAL INFORMATION
1) Failed Components:
None 2) Previous Similar Events:
None 3) Energy Industry Identification System Code:
Safety Injection System — BQ Chemical Volume and Control System (including Centrifugal Charging Pumps) — CB Residual Heat Removal System — BP