05000416/LER-1983-115, Updated LER 83-115/03X-1:on 830803 & 04,RHR Pump a Failed to Start.Div I Busses Incorrectly Shown Tripped,Annunciator Panels Came On,Optical Isolator Failed & Breakers Tripped. Caused by Incorrectly Terminated Cable

Updated LER 83-115/03X-1:on 830803 & 04,RHR Pump a Failed to Start.Div I Busses Incorrectly Shown Tripped,Annunciator Panels Came On,Optical Isolator Failed & Breakers Tripped. Caused by Incorrectly Terminated Cable

ML20081M879
Person / Time
Site:	Grand Gulf
Issue date:	11/03/1983
From:	Cathey D, Dale L MISSISSIPPI POWER & LIGHT CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
AECM-83-0718, AECM-83-718, LER-83-115-03X, LER-83-115-3X, NUDOCS 8311170413
Download: ML20081M879 (5)

LER-2083-115, Updated LER 83-115/03X-1:on 830803 & 04,RHR Pump a Failed to Start.Div I Busses Incorrectly Shown Tripped,Annunciator Panels Came On,Optical Isolator Failed & Breakers Tripped. Caused by Incorrectly Terminated Cable

Event date:
Report date:
4162083115R00 - NRC Website

text

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r Attachment to AECM-83/0718 Page 2 of 3 Supplementary Information to LER 83-115/03 X-1 Mississippi Power & Light Company Grand Gulf Nuclear Station - Unit 1 Docket No. 50-416 Technical Specification Involved: 3.4.9.2; 3.5.2; 3.8.3.2; 3.7.1.1; 3.7.1.3 Reported Under Technical Specification: 6.9.1.13.b Ever.t Narrative On May 27, 1983, a computer cable which provides a signal to the computer when an automatic start of the Drywell Recirculation Fan Unit "A" occurs was incorrectly terminated during a drywell ventilation modification which added the recirculation fan to the system. The cable should have been terminated across a set of isolated relay contacts but was instead incorrectly terminated across the overload (0.L.) device (49) in the 120VAC control circuit for Recirculation Fan Unit "A" in MCC15B42. The power for the computer cable is supplied from 1DA1 125VDC bus thru isolation panel 1H22-P501-1.

The breaker to the recirculation fan was not closed until August 3,1983. It was closed to perform preoperational testing. Therefore, no electrical interconnection between AC and DC existed prior to this date. When the breaker was closed, no adverse effects occurred because the 0.L. device 49 was closed, therefore, no AC voltage flowed into the DC circuits. A ground on the DC did exist thru the fan control circuit and had been previously noted and searched for preceding this event.

As part of the preoperational testing, 0.L. device 49 and the penetration cabinet failure relay 8 contact were opened and closed on the evening of August 3,1983, and the morning of August 4,1983. The opening and closing of these contacts inserted and then removed the 120VAC on the 125VDC bus. This resulted in numerous effects which collectively were:

1) A failed optical isolator output card in the RHR "A" pump trip circuit which cauced a continuous pump trip

2) A continuous trip to a Standby Service Water System load center breaker, and

3) Numerous annunciators on the Division I Control Room panel which incorrectly alarmed.

An investigation discovered the computer cable was incorrectly terminated in MCC15B42. The cable was disconnected. The root cause was construction personnel error.

A program has been initiated to eliminate future construction errors through closer supervision of work activities, training, improved inspections, and clearer work instructions.

MP&L's past experience with the effects and consequences of AC voltage imposed onto a DC voltage circuit was unintentionally gained during several instances in the preoperational phase of startup. These occurred as a result of similar

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. Attachm:nt to AECM-83/0718 Page 2 of 3 wiring errors by construction and design. It is known that 120VAC on the 125 VDC logic and control circuits will not generally damage wiring, relay coils, contacts, and most instruments if the voltage is not excessive. It can be expected to damage optical isolator output cards and other solid state devices.

Which components are damaged depends on the logic arrangement of the associated circuits during the time the AC is present. Although it will not damage non-solid state devices, it can affect their operation, such as, a relay may not deenergize with AC.present.

The E12-AT7 optical. isolator output card in the RHR pump trip logic circuit was damaged as a result of the AC voltage during the referenced event. AT7 and E12-AT8 are the only two isolators connected directly to the Division I 125VDC b'us. 'AT8 was not damaged because the output card is in parallel with other relay contacts that were closed. The relay contacts parallel with AT7 were open, therefore, the AC current flowed through the output side of AT7 and destroyed the output transistors. .An optical isolator such as AT7 would be expected to fail if AC voltage is present. The isolator output card was manufactured by General Electric. The model number is 204B6188AAG2 and the serial number is TWRE5-17.

The ESF 480V Standby Service Water load center breaker 52-15501 gave dual indication during the time the AC voltage was present on the DC bus and then tripped. The breaker control circuits receive power from the Division I 125VDC bus. The breaker is equipped with a solid state trip device. The presence of AC voltage apparently caused a trip signal from the solid state trip device but no damage to the device was discovered.

MP&L made the decision not to perform an extensive special inspection and test of other components within or affected by the 125VDC Division I system because:

1) past experience has shown low AC voltage (less than or equal to 120VAC) does not damage non-solid state devices,

2) the 18 month surveillances on the effected circuits and components were expected to be performed within the next 30 days including the 18 month diesel generator LOCA/ LOP tests,

3) the time required to develop, approve, and perform such a test vauld take longer than the time in which the surveillances would be completed,

4) the solid state trip devices in all of the safety related breakers were scheduled to be inspected, tested and possibly replaced due to an unrelated potential failure reported in LER 83-119/03 L-0,

5) daily channel checks and monthly functionals would be adequate to uncover any other damage.

To date no additional damage that can be attributed to the presence of the AC voltage on the Division I 125VDC bus has been discovered either by corrective maintenance or surveillance. All solid state breaker trip devices in Division I have been inspected and tested and no damage was found.

This is reported pursuant to Technical Specification 6.9.1.13.b. This event did not effect the health and safety of the public. It did not threaten plant safety because the effects were limited to Division I with the plant in a Cold Shitdown condition. This is a final report.

l E MISSISSIPPI POWER & LIGHT COMPANY I Helping Build Mississippi P. O. B O X 18 4 0() gK S O N, MIS SIS SIP PI 3 9 20 5 g gPg e er 3, 1983 NUCLEAR PRODUCTION DEPARTMENT U.S. Nuclear Regulatory Commission Region II 101 Marietta St., N.W., Suite 2900 Atlanta, Georgia 30303 Attention: Mr. J. P. O'Reilly, Regional Administrator

SUBJECT:

Grand Gulf Nuclear Station Unit 1 Docket No. 50-416 License No. NPF-13 File: 0260/L-835.0 Update Report - Incorrect Voltage Applied to Division I Control Circuits LER 83-115/03 X-1 AECM-83/0718 This letter submits an update to a previous report submitted on September 2, 1983. The event for which the report was submitted occurred on August 3 and 4, 1983, when an interconnection between the Division I 120VAC and Division I 125VDC circuits caused the insertion of 120VAC onto the Division I 125VDC system. The interconnection was a result of a wiring error made on May 27, 1983, during a drywell ventilation modification which added a drywell recirculation fan to the system. The breaker to the recirculation fan was not closed until August 3, 1983, therefore, no problems evolved from the wiring error or could the wiring error be detected until that date. The breaker was closed to allow performance of preoperational testing and during the course of this testing AC voltage was inserted onto the 125VDC system causing several alarms, trips and component failures.

The purpose of this update is to provide results of an engineering evaluation performed as a result of this event, a detailed account of the event, and the corrective action taken. Also, correction is provided for the previous report where we incorrectly stated that a 120VAC computer cable was incorrectly terminated on a Division I 125VDC circuit in MCC15B42. This is a final report. Attached is LER 83-115/03 X-1 with Supplementary Information.

Yours truly,

/bN L. F. Dale Manager of Nuclear Services EBS/SHH:rg gp,CIAldb Attachment cc: See next page [Mh Member Middle South Utilities System fg L

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. AECM-83/0718 MISSISSIPPI POWER O L12HT COMPANY Jags 2 cc: Mr. J. B.' Richard (w/a)

Mr. R. B. McGehee (w/o)

~Mr. T. B. Conner (w/o)

Mr. G. B. Taylor (w/o)

Mr. Richard'C. DeYoung, Director (w/a) l Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Document Control Desk (w/a)

U. S._ Nuclear Regulatory Commission Washington, D. C. 20555 i

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