ML20028H439

LER 90-015-01:on 900919,inadvertent Isolation of Containment Isolation Valves Occurred.On 900920,inadvertent Actuation of Sias,Containment Isolation Actuation Sys & Encl Bldg Filtration Sys occurred.W/901227 Ltr

ML20028H439
Person / Time
Site:	Millstone
Issue date:	12/27/1990
From:	Haynes H, Saccoccio W NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-015, LER-90-15, MP-90-1344, NUDOCS 9101070163
Download: ML20028H439 (5)

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I Re: 10CFR50.73(a)(2)(iv)

December 27, 1990 MP-90-1344 l

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

Reference:

Facility Operating License No. DPR-65 4 Docket No. 50-336 Licensee Event Report 90-015-01 Gentlemen:

This letter forwards update Licensee Event Report 90-015-01.

Very truly yours, NORTHEAST NUCLEAR ENERGY COhiPANY FOR: Stephen E. Scace Director, hiillstone Station

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Mills Uriit 1 Di tor SES/WS:mo

Attachment:

LER 90-015-01 cc: T. T. Martin, Region 1 Adminiurator W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos.1, 2 and 3 G. S. Vissing, NRC Project Manager, Millstone Unit No. 2 gP471450 914 910107o163 901227 ADOCK 05000336 I6 D

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• While in Mode 5 on September 19,1990, at 0244, the Unit experienced an inadvertent isolation of Containment Purge Valves 2- AC-4, 2- AC-5, 2-AC-6, and 2-AC-7, Operators verified that the Engineved Safeguards Actuation System (ESAS) functioned properly, that the actuauon was inadvertent and reopened the vahes. This actuation resuhed from operator error dunng the operation of a wrong circuit breaker. There were no safety impbcatiom.

Esent 2 On September 20. 1990, while in Mode 5, at 1103, the Unit experienced an inadvertent actuation of the Facihty 2 Safety injection Actuation System (SIAS), Containment Isolation Actuation System (CIAS), and Enclosure Buildmg Filtration Actuation System (EBFAS). When the actuation occurred, charging pumps P-16B and C started. Reactor Operators manually opened the charging header isolation valve and one of the two loop charging supply isolation valves to provide a flow path and prevent chall:nging the pumps relief valves. The esumated water addition to the Reactor Coolant System (RCS) was less than 50 gallons. Operators implemented AOP 2571, verified that tre actuation was inadvertent and returned the actuated equipment to the lineup that existed prior to the event. The actuation was caused by voltage transients created when the Channel "A*

Pressurizer Pressure inhibit switch was operated while Channel "D" Pressurizer Pressure was also being-calibrated. As a resuh of electromagnetic interaction between the trip signalisolation module and the block ma rix isolation module, the block matrix module saw a momentary 2 out of 4 logic and removed its blocking voltage from the actuation modules which initiated a SIAS, CIAS, and EBFAS. There were no safety imphcations.

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1. Desmmion of Evenn Event 1 While in Mode 5 on September 19,1990, at 0244, the Unit experienced at inadvertent isolation of Containment Purge Valves 2- AC-4, 2-AC-5, 2- AC-6, and 2- AC-7. Operators verified that the Engineered Safeguards Actuation System (ESAS) functioned properly, that the actuation was inadvertent and reopened the valves. This actuation resulted from a plant equipment operator clearing a tag on circun breaker VA20-16. VA20-16 was opened by mistake and then immediately closed. This circutt breaker provides power to the ESAS Channel *B" sensor cabinet which processes a signal from one of the four containment radiation monitors. These four monitors input to a unique 1 out of 4 logic matrtx for containment purge isolation. The loss of the bistable power for one channel resulted in the logic being satisfied and therefore, an actuation.

Esent 2 On September 20, 1990, while in Mode 5, at 1103, the Unit experienced an madvertent actuation of the Facihty 2 SlAS, CIAS, and EDFAS. When the actuation occurred, charging pumps P-16B and C staned. Reactor Operators manually opened the charging header isolation valve and one of the two loop charging supply isolation valves to provide a flow pith and prevent challenging the pumps rehef vahes.

The estimated water addition to the RCS was less than 50 gallons. Operators implemented AOP 2571, venfied that the actuation was inadvertent and returned the actuated equipment to the hneup that existed pnot to the event.

An ESAS actuation can be initiated when any 2 of 4 Pressuriter Pressure signals reach a specified low pressure setpoint. This actuation can be blocked if any 3 of the 4 pressure signals reach a separate

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• pressure setpoint, and a manual blocking pushbutton is pushed. This is a process routinely followed for placing the unit in a cold shutdown condition. Refer to Attachment 1 for a simple logic diagram that illustrates the relationships between bistables, isolation modules, tnp actuation modules, and block matnx modules.

The block matrix module was in the block condition as a result of the plant being previously shut down.

An 1&C technician began cabbrating Channel *A" Pressurizer Pressure instrument loop with the inhibit key in the "mhibit" position. When starting to perform the pressure transmitter calibration portion of the procedure, he discovered other workers in the area of the transmnter and felt it prudent to work on Channel "D" as authorized by the Work Order. He began exercising the transmitter on Channel *D" above the block reset value and then reahred that the naibn key was still in Channel

• A." He called the control room and requested another I&C technician to remove the key from Channel " A" and put it in Channel "D." When the inhibit key was switched from the " inhibit" to the " operate" position on Channel " A

• a voltaFe transient was created from the deenergitation of a relay in the trip isolation rnodule, Because of the close proximity between the block isolation module and the trip isolation module, the block isolation module circuitry received transmitted Electromagnetic Interference (EMI) and momentanly produced a change in state. This created a 2 out of 4 logic input to the block matrix module resulting in removal of it's block voltage from the actuation modules. This initiated an actuation because the 2 out of 4 logic was satisfied and the blocking signal was removed.

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11. cause o' Es en,s Esent 1 The root cause for the event which occurred on September 19, 1990, was operator error.

Esent 2 The root cause for the event which occurred on September 20, 1990, was EMI resulting from the cellapsing magnetic field of the relay in the tnp isolation module. Tha relay deenergizes when $ne inhibit keyswitch is placed in the " inhibit" position. Failure to follow the proper procedure step tequence also ,

contributed to the conditions that caused the actuation.

Ill. . Anahmis nf Events These events are being reponed pursuant to the requirements of 10CFR50.72(b)(2)(li) and 10CFR50.73(a)(2)(iv), a condition which resulted m manual or automatic actuation of any Engineered Safety Feature.

Esent i For the event which occurred on September 19, 1990, there were no safety consequencet, since the actuation was inadvenent and the ESAS functioned according to design entena.

Esent 2 For the event which occurred on September 20, 1990, there were no safety consequences since the actuation was inadvenent and the Facihty 2 equipment functioned properly, considenng the transient noise actuation. However, the Facility 1 equipment would also have actuated in the event of an actual S!AS signal as is routinely demonstrated by the Automatic Test insener.

IV. Corrective Action $

Es ent .1 For the event that occurred on September 19, 1990, the operator has been counseled to be more attentive to detail when tagging and untagging equipment.

Esent 2 For the event occurring on September 20,- 1990, the technician has aho been counseled to follow procedural sequences and the ESAS calibration procedure has been revised to hmit the calibration of one channel of one parameter at any given time. A vendor suggested solution to the problem is presently being evaluated.

Y,- Additional Information Similar LERs;69-005. 88-004,54-001 Ells Code JE;C560;XC - Engineered Safety Features Actuation System.

Attachment 1 I5$ "" #"

Attachment 1 to LER 90-015-01 Pressurizer i

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[B C l D Pressure Sensor (A ( (Containment) h Control '

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