05000423/LER-1988-001, :on 880105,safety Injection Occurred Due to Sensitive Equipment.Operating Procedures Changed to Verify by Indication That Appropriate Blocks & Resets in Place Prior to Taking Action

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:on 880105,safety Injection Occurred Due to Sensitive Equipment.Operating Procedures Changed to Verify by Indication That Appropriate Blocks & Resets in Place Prior to Taking Action
ML20064B188
Person / Time
Site: Millstone Dominion icon.png
Issue date: 10/01/1990
From: Joseph V, Scace S
NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-88-001, LER-88-1, MP-90-1065, NUDOCS 9010150150
Download: ML20064B188 (3)


LER-1988-001, on 880105,safety Injection Occurred Due to Sensitive Equipment.Operating Procedures Changed to Verify by Indication That Appropriate Blocks & Resets in Place Prior to Taking Action
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv), System Actuation
4231988001R00 - NRC Website

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October 1, 1990 MP-90-1065 l:

U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Reference:

Facility Operating License No. NPF-49 c

Docket No. 50-423 Licensee Event Report 88-001-01 Gentlemen:

This letter forwards Licensee Event Report 88-001-01, which is being submitted to revise the anticipated completion date for the action to prevent recurrence, as discussed in the response to Notice of Violation 50-423/90-10. Licensee Event Report 88-001-00 was submitted pursuant to 10CFR50.73(a)(2)(iv), any event or condition that resulted in automatic actuation of the Reactor Protection System.

FOR: Stephen E. Scacc Director, Millstone Station

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Attachment: LER 88-001-01 1

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On January 5,1968 at 1630 with the plant at 0% power,110 degrees and ambient pressure, an inadvertent safety injection signal was received on Train A. The signal was not required for safety and no iniection to the core took place. The immediate cause of the esent was an improper switch position during restoration from instrument and controls tesung. The Slam Board operator was cognizant of the restoration being performed and the potential for an inadsertent Safety injection. His actions, and those of the mstrument technician, were in compliance with the restoration procedure. Immediate action was to verify that a safety injection was not required and reset the signal. No Engmeered Safety Features actuations were required for existing plant conditions, and none occurred.

The root cause of the event is a sensitive switch. As an interim solution, the operating procedure has been I

changed to verffy by indication that appropnate blocks and resets are in place prior to taking an action that l

could result in a safety injection. To prevent recurrence of this problem, this switch will be replaced by a less l

sensitive design prior to the end of the third refuelmg outage (scheduled for February,1091). Similar switches l

un the N1ain Control Boards will be evaluated and also changed if required.

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Descrintion of Event On January 5,1988 at 1630 with the plant at OG power,110 degrees and ambient pressure an inadvertent safety mjection signal was received on Train A The signal was not required for safety and no injection to the core took place. The immediate cause of the event was an improper switch position during restoration from instrument and controls testing. The licensed operator at the hlam Control Board realized that a safety injection signal had been initiated upon receipt of a safety injection actuation annunciator. Train A low steam hne pressure was annunciated as the cause of the safety injection. The hiain Doard operator was cognirant of the restoration being performed and the potential for an inadvertent Safety injection. His actions, and those of the instrument technician, were in compliance with the restoration procedure. Immediate action was to verify that a safety injection was not required and reset the signal. No Engmeered Safety Features actuations were required for existing plant conditions, and none occurred.

II.

cause of Event

The root cause of the event is a sensitive switch. Analysis of the incident shows that all required actions were performed in the correct sequence, but a reset of the automatic safety injection block occurred following the operation of the automatic block switch to the block position. The sw1tch is a three position spring, return to normal type sulich. Tests of the switch revealed that 30 degree, of travel in one direction were required to iniuate the block, but only 5 degrees of travel in the other direction were required to reset the block. The spring force of the switch was sufficient to cause the block to be reset when the switch was released from an off-center position in the block direction of l$ degrees or more, 111.

Anniviis of Event This event is reponable under 10CFR50.73(a)(2)(iv), any event or condition that resulted in the automatic actuation of any Engineered Safety Feature. The health and safety of the public were not affected as there was no requirement for a safety injection to protect the reactor, immediate notification was made under 10CFR50.72(b)(2)(ii), any event or condition that resulted in the automatic actuation of any Engineered Safety Feature.

IV.

Corrective Action

As an interim solution, the operating procedure has been changed to verify by indication that appropriate blocks and resets are in place prior to taking an action that could result m a safety injection. To prevent recurrence of this problem, this switch will be replaced by a less sensitive design prior to the end of the third refueling outage (scheduled to begin in February,1991). Similar switches on the hiain Control Boards will be evaluated and also changed if required.

V.

Additional Information

There has been one similar event LER 87-002, in which a reactor trip occurred due to the inadvertent rotation of a switch requiring SG rotation to actuate when the swnch was casuall) contacted. That switch has been mounted in a protective cup to preclude recurrence. A similar solution would not be appropriate for this occasion as casual contact is not a concern due to switch location on the hiain Board vertical section.

The swnch is a General Electne CR2940 3-position spring return to center switch with a U200BN1 gloved hand operator.

Ells Codes DO High Pressure Safety injecuon G0bO-General Electric HS Switch, hand

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