ML20245B842
| ML20245B842 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 11/30/1987 |
| From: | Stewart J NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20245B685 | List: |
| References | |
| TASK-AE, TASK-T713 AEOD-T713, NUDOCS 8904260315 | |
| Download: ML20245B842 (2) | |
Text
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.n AE0D TECHNICAL REVIEW REP 0PT UNITS:
Susquehanna 2 TR REPORT N0.: AE00/ T713 DOCKET N0.: 50-388 DATE: November 1987 l
LICENSEE:
Pennsylvania Power and Light EVALUATOR CONTACT:
J. Stewart NSSS/AE:
General Electric /Bechtel
SUBJECT:
MISPOSITIONING 0F " REVERSE ACTING" VALVE CONTROLLERS CAUSING SAFETY SYSTEM INOPERABILITY EVENT DATE: October 24, 1986
SUMMARY
Mispositioning of the valve controllers of both emergency service water regulating valves caused both emergency switchaear room coolers to be inoperable.
If a loss-of-coolant-accident occurred, while the valve controllers were mispositioned, and the accident made the controllers inaccessible, then it is postulated that the LPCI and core spray system would become inoperable because of overheated switchgear. The design of the valve controller circuit was such that at the indicated 100% position, the valve would be fully closed and at the
. indicated 0% position the valve would be fully open. This design is referred to as a " reverse acting" controller. - A review of LEP event data showed that no history 2f other events involving the mispositioning of " reverse acting" valves controllers existed in the data base. Additionally, there exists no data base which identifies which plants utilize " reverse acting" controllers on
-safety-related systems and their support systems.
DISCUSSION On~0ctober 24, 1986, during the performance of the Quarterly Emergency Service Water Flow Verification of the "B" emergency switchgear room cooler at Susquehanna 2, the water regulating valve (HV-27203B) failed to open. An operator than repositioned the valve's controller from the 100% position to the 0% position and the valve opened. Similar results-occurred on the "A" emergency switchgear room cooler when it was tested.
It was postulated in the licensee's evaluation that both valve controllers would be inaccessible during an accident. The procedure which was used to align the "A" and "B" emergency switchgear room cooler was determined to incorrectly direct that the valve controllers be placed at the 100% position, which generically represents the full open position. An application of " reverse acting" controller is to regulate the fluid level in tanks by controlling the fluid flow into the tank.
However, in this application,. a reverse acting controller was a poor choice from a human engineering design perspective. A normal assumption, lacking any additional information, was that the valve would be open with a 100% indication.
-since the valve had no regulating function except to either allow no coolant flow or full flow.
The ventilation system to the emergency switchgear and emergency load center rooms, where electrical components essential for the operation of low pres 3ure coolant injection (LPCI) and core spray (CS) are located, consists of two redundant trains, A and B.
Each train is comprised of a filter bank, two sets s904260315 871203 ADOCK0500g8 DR
2 of cooling coils, and a fan. The fan draws air from secondary containment through the filters and past the cooling coils. The second set of coils is used only during normal operating conditions. The first set of coils is supplied with Freon-22 and cools the passing air only during emergency or accident condi-tions. During a LOCA the normal cooling units are tripped and the Freon-22 cooling unit is initiated to cool the rooms. The emergency service water, I
which supplies cooling water to the Freon-22 condenser, could not supply water I
to the condensers with the controllers of the regulating ilves in the 100%
position (closed). Without cooling water the Freon cooling units would trip, which would then cause a loss of cooling to the Emergency Switchgear and Emergency Load Center rooms. Under these conditions the control room operators could restart the fans to circulate the air through the rooms to provide partial removal of the heat generated by electrical components.
It is not known if the room temperature would have exceeded 104*F, the temperature for which the components are environmentally qualified. Therefore, it is postulated that the equipment in the Emergency Switchgear and Emergency Load Center rooms might have failed, resulting in a loss of power to the LPCI and GS systems.
To prevent recurrence, a procedural change was implemented requiring that the controller be placed at the 0% position.
In addition, labels were installed 4
at the controller to show that the valve is open at the 0% position and closed at the 100% position.
FINDINGS AND CONCLUSIONS i
The corrective action implemented at Susquehanna 2 in revising the procedure and labeling the controllers (0% position as open and 100% position as closed) should prevent further mispositioning of the valve. The root causes of the event were:
(1) design error in utilizing a controller as actuating device for a valve which requires only an open and closed position to perform its intended safety function and standby position; (2) lack of Human Factors consideration in failing to label the open and closed controller functions; and (3) inadequate procedure which directed that the valve controllers be placed in the 100%
(closed) position.
An investigation of 400 LER events involving mispositioned valves from 1984 -
1987 did not identify any other safety concerns related to mispositioning of valves due to the use of " reverse acting" controllers.
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