PNO-III-80-229, on 801211,unit Manually Tripped Following hi-hi Alarm from Scram Discharge Vol Continuous Monitoring Sys.Caused by Water Leaking Into SDV During Maint on Control Rod Drive Hydraulic Control Unit 18-11.Drawing Encl
| ML17193A840 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/11/1980 |
| From: | Boyd D, Heishman R, Reimann F NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| References | |
| PNO-III-80-229, NUDOCS 8103030942 | |
| Download: ML17193A840 (3) | |
, ii
~RELIMINARY NOTIFICATION Date: December 11, 1980 PRELIMINARY NOTIFICAtION OF EVENT OR UNUSUAL OCCURRENCE--PN6-III-B0-229 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance.. The information presented is as initi~llY received without verific~tion or evaluation and is basically all that 1s known by IE staff as of this date.
Facility:
Subject:
Commonwealth Edison Company Dresden Unit 2 (Docket No. 50-237)
Morris, IL MANUAL REACTOR SCRAM DUE TO HI~HI ANNUNCIATOR ON SCRAM DISCHARGE YOLUME (SDV)
The unit was manually tripped at 5:53 a.m.,,. (CST) December 11, 1980, following receipt of a HiHi alai;m from the newly installed Scram Discharge Volume. (SDV)
Continuous ~onitoring System (CMS).
All safety features operated as designed and no apparent threat to public health and safety resulted from the event.
The SDV HiHi level alarm resulted from a small amount of water leaking into the SDV while maintenance was being.performed on Control Rod Drive Hydraulic Control Unit No. 18-11 (one of 177 similar units for each Control Rod Drive).
Refer to attached figure in regard to the following description of the cause of the event.
Hydraulic*.,C.ontrol Unit 18-11 was taken out of service for scheduled replacement of valve seals in the Sqram Air Solenoid Valves.
Manual valves 101, 112 and 116 were closed and the scram accumulator precharge pressure was released to allow the maintenance.
When the air pressure to the Scram Inlet and Outlet valves (126 and* 127) was released, improper seating of valve 112 allowed a small undetermined amount 9f water to leak into the SDV.
The water collected in a low point in the SDV p,iping, which is also. the location of the CMS sensors, causing the high ievel alarn;i.. Recently implemented li~ensee procedures require an inunediate manual scram should this alarm be received.
Although the exact amount of water which accumulated in the SDV is unknown,.
the licens~e has stated that ~ecent testing experience has indicated that as little as 10 gallons of water accumulating in the SDV can trigger the alarm.
The licens~e has also stated that the current setpoint of 1~ inches for the alarm is based upon an NSSS vendor analysis, which is conservative for Browns Ferry-3 which has a smaller SDV volume than this unit.
The analysis provides for the HiHi alarm to occur before the SDV becomes 45% filled, which allows conservative margin to meet scram design criteria.
The licensee has also requested ia unit specific study fran the NSSS vendor to justify relaxation of the l~ inc,h se tpoint.
I The licens.ee notified IE:HQ of the event via the ENS at approximately 5:55 a.m.,
(CST) December 11, 1980.
No press release is planned by the licensee nor Region III The. State,of Illinois will be notified.
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e PRELIMINARY NOTIFICATION PNO-III 229 Page 2 of 2 This PN is* for information only.
Followup of the event will occur concurrent with a*ctio:ns required for Supplement 4 to IE Bulletin 80-17.
- i Thia infor~ation is current as of 2:00 p;m. (CST) December 11, 1980.
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D. c. Boyd R. F.1neishman
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Contact:
F. Reimann, RIII f ;815 / 94 2-926 7 384-~546
'384-2540 Distribution:
Transmitted H St. 3.::l l.c Chairman Ahearne Commissioner Gilinsky Commissioner Hendrie Corrmissioner Bradford ACRS I
i Transmi~te~:
MNBB W. J. Dlrcks, EDO
,if;~ P. Bldg. 3*3z_
I C. Michels~n, AEOD J. J. Fou~hard, PA N. M. Ha ll1er, MPA G. W. Kerr,, OSP H. K.
Sha~ar, ELD H. R. Denton, NRR R. H. Vollmer, NRR R. J. Mattson, NRR D. F. Ross, NRR D. Eisenhut, NRR S. H. Hanauer Willste Bldg~ 33~
J. G. Davis, NMSS T. E. !-!urley, RES PRELIMINARY NOTI FI CAT ION
~
S. J. Chilk, SECY C. C. Karrrnerer, CA (For Distribution)
IE:XOOS ~~ (IE:HQ Dist.)
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J. J. Cummings, OIA MAIL
~inogue, SD IE:XOOS Document Mgt. Br. (For PDR/LPDF S. Ebbin, Executive Director Nuclear Safety Oversight Committe 1133 15th Street NW, Suite 307 Washington, DC 20005