ML20196E234

Special Rept:On 881020,discovered That Sensor Channels LM001 & LM009 Were in Low Alarm.Caused by Fraying of Insulated Fibre Jacket of Microdot Connector Cable.Sensor Channels Replaced

ML20196E234
Person / Time
Site:	Braidwood
Issue date:	11/29/1988
From:	Hunsader S COMMONWEALTH EDISON CO.
To:	Murley T Office of Nuclear Reactor Regulation
References
NUDOCS 8812090297
Download: ML20196E234 (2)

Text

7._ ,

g: .

h Commonwealth Edison

- ' One Fird National Plaza. Chcago, Illinois Ac' dress Reply to: Post Offce Box 76,P

.\ Chicago, til>nois 60690 0767 November 29, 1988 Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Comission Washington, DC 20555 Attne Document Control Desk Subject Braidwood Station Unit 1 Loose Parts Monitoring System (LPMS) Special Report NRC Docket No. 50-45ft

Dear Dr. Murley:

In accordance with Braidwood Technical Specification 3/4 3.3.8, Comonwealth Edison is providing the required LPMS Special Report for Braidwood Station Unit 1. Per Specification 3/4 3.3.8, with one or more Loose-Part Detection System channels inoperable for more than 30 days (in Modes 1 and 2), prepare and submit a Special Report to the Comission, pursuant to SpecifJeation 6.9.2, within the next 10 days outlining the cause of the malfunction r.nd the plans for restoring the channel (s) to OPERABLE status.

This re r ort provides the required information addressing the suspected causes of the LPMS problem, the proposed corrective action and the interim measures until such actions are completed. Please direct any questions regarding this matter to this office.

Very truly yours, b

S.C. Hunsader Nuclear Licensing Administrator

/sc1:5298K 2 Att.

ces S. Sands (NRR)

J. Hinds (RIII)

Braidwood Station Inspector 4

\ \

8812090297 881129 PDR ADOCK 05000456 L S PDC __

): a:

.o l

,g.e LOOSE PARTS MONITORING SYSTEM BRAIDWOOD UNIT l' t

SPECIAL REPORT

.SURARY Technical Specification 3/4.3.3.8 requires that a special report be written to the NRC as per Reg. Guide 1.133. The purpose of this report is to delineate the cause of sensor channel malfunction, if known, and outilne the steps required to correct the problem.

i.

- On 10/20/88 it was discovered that sensor channels LM001 and LM009 were in low alarm. Upon investigation by Technical Staff, it is believed that these channels' cables have lost continuity as very little signal is discernible at the auxillary electric room monitoring panel. The locations of these sensors are the reactor vessel upper head and Steam Generator C Inlet plenum respectively. Switching to the spare sensor channels at these locations (LM002 and LM010) proved successful for the Stem Generator C inlet plenum location, as the signal from sensor LM010 was characteristic of signals from other sensors at similar locations on Steam Generators A, B, and D. Sensor Channel LM002, however, indicated

) a very high level of bussing indicative of a grounding problem with that channel. Thic grounding problem may be due to fraying of the Insulated

, fibre jacket of the microdot connector cable. Regardless of cause, this

! sensor channel is also malfunctioning as the high level of bussing  ;

1 prevents discerning any other signals present. Per Reg. Guide 1.133, i l the failure of both sensors at the reactor vessel head, a natural l j collection region, constitutes an inoperable system and therefore the  ;

j LC0AR was entered.

{

i f PROPOSED H ?. ION i 1

4 l Upon enterisg an outage of sufficient duration the Instrument j Maintenance Department, assisted by Tech Staff if necessary, will make a i containment eetry to determine the exact cause of sensor channel failure. It is believed that the microdot cables are the root problem

{

la a; D instances.- It has been verified that adsquate spares are  :

, available for replacing the subject cables. I INTERIM MEASURES FOR LOOSE PARTS DETECTION  !

In the interim, the loose parts detectors are aligned to the following f sensors LM003, 4, 5, 7, 10, 12, 17 and 18. These sensors correspond [

to two at the reactor vessel bottom head and one each at the inlet plenums of Steam Generators A, B, C and D and the lower narrow range taps of Steam Generatora A and B, respectively. The alarm level for I Detector 1 (Sensor LM003) is 2, which corresponds to 110% above j background ratio. For detectors 2 through 8 the alarm level is 6 which +

corresponds to a ratio of 200% above background level. These levelo, I coupled with the required daily operating surveillances for audible

{

detection of a loose part, will adequately detect any loose part occurrence until the sensors at the reactor vessel upper head can be repaired. l l

SH/sc1:5298K 2-3 l I

.