ML20005G128

Supplemental Special Rept:On 890716,2 of 12 Loose Parts Monitor Channels Declared Inoperable When Monitors Alarmed Continuously.Caused by Malfunctions in Equipment Inside Containment Bldg.Replacement Scheduled for Next Outage

ML20005G128
Person / Time
Site:	Millstone
Issue date:	01/02/1990
From:	Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
MP-13906, NUDOCS 9001180168
Download: ML20005G128 (2)

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January 2, 1990 MP-13906 Docket No. 50-423 Re: 10CTR50.36 U. S. Nuclear Regulatory Commission Attn: Doewment Control Desk Washington, D.C. 20555 Gentlemen:

Millstone Nuclear Power Station, Unit No. 3 r Malfunctioning Loose Parts Monitor Channels This Special Report'is being submitted as a supplement to the August 25, 1989 Special Report on Malfunctioning Loose Parts Monitor Channels. This supplemental report is being submitted pursuant to Millstone Unit 3 Technical Specification 3.3.3.8 a: Loose Part Detection System.' Technical Specifications requires a Special Report be submitted to the NRC if one or more channels of the Loose Part Detection System are inoperable for more than 30 days.

At 0730 on July 16, 1989 with the plant in Mode 1, at 48% power, 2250 psia, and 586 degrees Fahrenheit, two of twelve Loose Parts Monitor (LPM) channels.were declared to be inoperable because they were alarndng continuously. Analysis of information recorded by the LPM verified that loose parts did not exist. Further investigation revealed that the alarms were caused.by malfunctions in LPM equipment located inside the containment building.

Loose part impacts in the Reactor Coolant System (RCS) arc detected by accelerometers attached to major RCS components. An impact generates an electrical signal from one or more accelerometers, which triggers the Loose Parts Monitor to record information from all channels on a computer disk, L and actuate an alarm on the main control board.

.The two malfunctioning' channels have redundant channels which are operating normally. The malfunctions do not affect other channels. The malfunctioning channels have been turned off, so that valid loose part

' impact. alarms will not be masked.

'The problems with both channels have been localized to within the containment building and require corrective work in high radiation areas.

For this reason,. corrective actions were scheduled for the next reactor Cold Shutdown period.

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W 6 e ' Millstone Unit Number 3 was in Cold Shutdown from 1450 on November 29, 1989 .

to 0546 on Decimber 5, 1989 to replace the.C Pressurizer Code Safety Valve, .[

as reported by Licensee Event Report 89-031-00. During this time, problems  !

with the malfunctioning Loose Parts Monitor channels were investigated  !

p. further. The exact locations of failed components in containment were L .. identified. Replacement of the components would have required extending  !

F the outage by several days in order to remove.and reinstall mirror 1 insulation.on the reactor head and the affected steam' generator.

, Additionally, a replacement part required to fix one of the. channels was-1

. unavailable. Since the. redundant LPM channels monitoring these locations

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were operating satisfactorily, no increase.in plant l safety would be~

i m realized by-extending the outage to replace the components. ;For these

reasons, the component replaceuent has been scheduled for the next-refueling outage. i The LPM was designed ~and built by Northeast Utilities Service Company, and i is installed at Millstone Unit 3 and Connecticut Yankee. This design is not i used at any other~ plants.  !

i. .The licensee contact for this special report is Robert Conway, who may be $

contacted at (203) 447-1791, . extension 5642, a Very Truly Yours, l 5

NORTHEAST NUCLEAR ENERGY COMPANY s

FOR: Stephen E. Scice .i Station Superintendent  !

Millstone Nuclear Power Station 1

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BY: Il II.lTeiiient i Unit 3 Superintendent Millstone Nuclear Power Station j SES/RDC:bjo +

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l cc: W. T. Russell, Region I, Administration  ;

W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos. 1, 2, and 3 l D., H. Jaffe, NRC Project Manager, Millstone Unit No. 3 l

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