ML20084R808

Ro:On 741122,torus Vent Valve 3-1601-20B Failed to Close After Being Opened.Caused by Settings on Pressure Switch. Valve Closed.Valve Required Open Only During Vacuum Buildup in Torus

ML20084R808
Person / Time
Site:	Dresden
Issue date:	12/16/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
894-74, NUDOCS 8306150594
Download: ML20084R808 (2)

Text

-

y r

w..

g3 Comm;~;ealth Edison

~

(Q x

One First;Iiedly to Post Ofh:e Box 7G7

mal Ptva Chea,o, lit nots r

=g

'.4.

Address Chicago Ilhnois 60690 BBS Ltr. //894-74 Dresden Nuclear Power Stat 1on._l.

R. R. #1 g\\bt Forris, Illinoin 6c4501-

/

C)

Dece'nber 16, 1974 O

y s

f(

C Mr. James G. Koppler, Regional Director Directorate of Regulatory Operationc-Region III

.) N g.<# "

l- /

, O,/

UI U. S. Atomic Energy Co=nicsion

\\

f 799 Roosevelt Road (hrl,\\y'sg -1 < ;,. \\'

Glen Ellyn, Illinoin 60137 N

-f Niu

SUBJECT:

REPORT OF E'15SUAL EVENT PER SECTIO!! 6.6.C_ OF THE TECH'!ICAL SPECIPICATIC:'S DRESD:C:i IT.11T 3. AEC DOCKET 50-249.

Reference:

1) Regulatory Guide 1.16 Fev. 1 Appendix A 1

2) Dresden Station Drawing 356 3

Report Date December 16, 1974 j

E Occurrence Date: November 22, 1974-Facility: Dresden Nuclear Power Station, Morris, Illinois e

IDE'7PIFICATION OF OCCURRE!!CE I

Failure of torus vont valve 3-1601-20B to cloco.

1 CONDITIONS PRIOR TO OCCURRIO:CE L

Prior to the failure of A0 valvo 3-1601-20B the unit was in the i'Run" mode with a thennal power of 1603 negwatts. The unit was operating at a cteady j

electrical load of 516 megwatts. During the occurrence the instrument department

(

was performing nurveillance testing of the procsure switches which control A63.-1601-20A and B.

No icproper valve pocition was noted prior to the y2 curveillance test en 3.-1601-203, s

DESCRIPI'IC:: OF OCCURRE";CE Q

h On November 22, 1974 at about 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> torus vent valve AC-3-1601-203 failed to c1csc after being opened. No apparent cauce of the failurc

'(3 could i=ncdiately be determined. The valve was then ru ually blocked in the Y

eloced position and an investigation initiated.

y 50' f

F" t

g%5,8 tow 5fg

" " "" g

^

k E

o 12841

+

9

Mr. J >:es G. Keppler December 16, 1974 f

I DESIc::7.T:0:: q? APPiTC.T CATE OF CCC'E'.T.'CE i'

Prom the invectication it unc determined that the failure was due to cettings on the preccuro ct.Meh which cauroc the valve to fall cafe on low inctrt.=ent air preccure. The cettinco ihr the cwitch ucro feund to trip at 76 poi f

decreasin; and 31 noi increaring. A revicu of the curveillanco records indicates that the precouro mritch was found to be 61 poi decrcacing and 65 poi increacing at the last curveillance, since the valvo ic cpring accicted in the open directicn the ac-found cettings had no effcet en the open occuence. However, then the valvo centrol cuitch was placed in the

" auto" pocition, uhich chould cloco the valve, inctru=cnt air proccuro dropped belou the 73 pai trip cctting of the preocure cwitch. The valvo proforc.cd as decicntd, as a recult of thic apparent loco of control air cignal, by utilizing the spring accict to return to the full open position.

With the valve full open, instrument air preccure returned to about 90 poi which recet the pressure cwitch.

It is concluded that vhc valve r:alfunction can be partially attributed to the nementary decreare in instrunent air precoure. Thic concntary decreace in instru.cnt air proccure coupled uith the ac-found set point of the valve proccuro cwitch cauced the valve to remain open.

I ANALYSIS CP CCCURRE:!CE t

The failure of the 3--1601-20B valve to cloco did not put the cafety of the plant or public in jeopardy. The purpoce of the 203 valvo is to vent the toruc if a vacuum build up occurra. During the failure of the 20B valve a parallel vent line existed throuch the 20A valve.

+

~.

CORRECT _lV._E ACTIC::S q

The ir:=cdiate corrective taken was to block the 203 valvo closed c'iilco it is only requirtd to be open daring a vacuum buildup in the toruc. To correct the condition the trip and react cetting were chanced frcm 78 poi decreasin and 81 poi inercacing to 61 pci decreacing and 65 poi increasing. No 2

additional corecctive actions ucre ta%cn becauce the probica wac--discovered during routine curveillance torting which in decicned to detect thic type l

of preocure cct point drift.

PAIUJRE l'ATA There have been no failuren of tMc type accociated with the 1601,20A, and B valvec on cither unit 2 or 3.

Sinccrp1f,

/

A (. f fs (q,f 6%

-y,,

~

/

l t

n

. B. Styphencon EFG:TEL n=p 4

9

..