Text

Ro:On 980218,potential Reactor Safety Failure Discovered W/ Reactor Shutdown.Caused by Manual Scram Function Bypassed by Sticking Reset Contact in Console Power key-switch. Protective Action Reset Switches Wired
	ML20217A089
Person / Time
Site:	05000128
Issue date:	03/18/1998
From:	Reece W; TEXAS A&M UNIV., COLLEGE STATION, TX
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
	NUDOCS 9803240246
	Download: ML20217A089 (5)
	v • d • e

4 ..

TEXAS ENGINEERING EXPERIMENT STATION TEXAS A&M UNIVERSITY COLLEGE STATION, TEXAS 77843-3575 j#

JNK J L

NUCLEAR SCIENCE CENTER 409/845-7551 March 18,1998 98-0048 U.S. Nuclear Regulatory Commission ATTN: Document Control Washington, D.C. 20555-0001

Subject:

Potential Reactor Safety System Failure Discovered with Reactor Shutdown

Reference:

Facility License R-83, Docket 50-128 Gentlemen:

On or about February 18, it was noted that Oregon State University Research Reactor had experienced a failure ofits protective system. The manual scram function was apparently bypassed by a sticking reset contact in the console power key-switch.

The Nuclear Science Center (NSC) staffimmediately checked the logic diagrams for the console and determined that the same type of failure should not be possible at our facility.

However, there was concern that this failure mode be investigated directly by testing.

Following reactor shutdown, the Senior Reactor Operator tested all scram circuits and found that three reactor protective trips could be prevented by pressing and holding the individual alarm / scram acknowledge button. It was directed that no reactor operations //

were to occur until this condition was corrected. The NSC Director and the Reactor //

Safety Board Chairman were informed. The problem affected the reactor high _

temperature scram, the experiment scram, and the manual scram. gn

. The NSC Console does not have a Master Reset for protective actions. Each individual scram has a single alarm acknowledge button. The push-button is spring returned to normal (See Figure 1). The alarm acknowledge button will clear the lock-in alarm on the console and allow the scram relay coil to be reenergized (if the signal is clear). These particular push-buttons were selected for high reliability. The same style of reset switch has been in use at the facility for nearly 30 years with no record of failure.

Figure 2'is a section of drawing of the NSC logic diagram and protective circuitry. The "as found" wiring condition is shown on the diagram. The actual console wiring was in

- accordance with drawings from 1971. These diagrams are available but are difficult to

. logically decipher. This wiring did not reflect the logic diagram drawn in 1976. It is not njt13 pEsuRcH AND DEVnOMENT FOR WNWND 9903240246 990318,'.

PDR ADOCK 05000128

'i 8 PDR;,

e

1 3

1

. 98-0048 Page 2 clear from facility records as to when the logic was physically wired but the time period

. was within a few years of a major console and reactor upgrade in 1%8. It_is believed that the 1976 diagram (Figure 2) was drawn based on systems knowledge of how it should be -

configured.

The protective action reset switches were wired in parallel with the normally closed scram contacts. These switches should have been in series as shown in the 1976 logic diagram. If the operator pushed and held the reset button, the scram relay coil would stay energized while a reactor protective contact was open. This could have prevented an individual scram signal but would not have disabled all scram sianals.

On February.19, a NSC staff meeting was convened to review the circuit and approve

. changes as per 10 CFR 50.59. The Reactor Safety Board Chairman was info'rmed of the proposed changes and a Reactor Safety Board Subcommittee went to the NSC to review the proposed change. The change would place the reset switch in series with the protective action contacts as drawn in the 1976 logic diagram. The change was approved, implemented and tested. The reset push-buttons do not override any protective action.

The reconfigured protection system was tested in multiple operation and potential failure modes. The tests were extended to other reactor console equipment that did not directly affect reactor safety. Wiring diagrams and maintenance logs were checked and it was determined that the console was wired correctly. The protection system designed and installed around 1%7 was apparently not analyzed for all failure modes and effects. The system has been redesigned as noted above.

l Please contact Sean O' Kelly or myselfifyou require additional information. {

l Sinepr .y

( {f n

-sr-3 W. D. R rector WDR/tli Attachment .

xc: 12110/ Central File 17122, NRC/R-83 File Theodore Michaels l

i s_

. ~

' V at5 vat, h et 5tnan RCstr t

L i :

t :

i : i

1-'

' ! : I g e

i t 8 i I .

^' SC W ewN

"'M F 4 8M RELAY 5 REAAy5 . ,e (jh RELAY 5

gg g % . RELAY 5 ,

, o

/

(' s' l

l I f

,# 1 -

j l \ / ,

'\ -

f

.. f : . .-

g f I i \

/

,.,,,,,, Y, g g , _ 9 99-1*

s

\ ./

1

s. o

\ \-

h"h',Yst s s

' sem

'~s (.; Wh

_1 PERion SctAM s _ evntemt wira RAM RE5f7 s

N, c Mstf

~~- ,a sw- .. . < ---

wt .

AFETY AMP BRi Sh scen -% 8("

E LPL # 7N ,, POOL Ds P4 MALA 4 e ,

ScaAm h c4H$ett.

lNTf tiggg ,

I staan PLu f,.

M SCRAM SE TT,yp

. IRA. St4Ang trat I

IN 8FPA5$ MODE ITCH pjr!

o 6 NSC REACTOR l SCRAM g.oetC, , .

34TE77 AMPunfA Sc4APS 1.06sc h

p Of bk0 0 m _ s g u m., a a a

).

4 l

l l

c J

.J .

>oc !

M B _

a _

R t

.\_ l <

E L u e s A r l y

E

~ s so $ L o

cm o a

A nto As 6tr ro O e c

K~

m m=

= Mmf !) h t 1 3 ' 1

( o e

f w e \

( s g

p h \

\ iI I Ii

.\

3 s

~

._t R

E hE" E

A l -

A <

.n , S esm $

p '

Y "['

4 g_

g,

,a eu

,. e r,

mve r F

Y-

/

s j 3 88 t.w :e I

i a

v h.

vu

~ e

- i e r g ( t e (

\,n Y \ /

\ i g l

\

Ii\

's,

- _ ^ l I' c e s 'f Y S -

sR wo

n s.

ec. a, m

C

. e a A. gs Ae na<

ar .mo )- / W' aW~t p -

aC p-ne nts ,

nr , s c

a (- ,

f

\

m.e.

t t

^ 7

( g l I

,\ y (i .

.w .%

I t

j'g 5

- i g o f 1

. V

- ' A s

'o .

t.

H 3 3 i l f '

g -

I

,\ O T

T E

c,

- .s S0 RM

\

, - s E P L

W5N I _

,i ,

A 5 Ts0 _

e Y e l - Cf H

t M m,,:_d

,,,e n .

'hy

.a -

' A E

' M Y

,m

- a *'

.\

' I 11 I .

w * "s I I q .\-

1 p #g s

- ~

~-

- e T

'. p( Q "

$ ?.,. sh

.v 4G f %

c. P T O l

.o W E _

5R A

vS r V f 'yv9 9 L --

ti

-5~4 - ,

~

)

A }!

n P

i

. \

o__ _ _ _ _ . ,,_ ._,

, _ _l _ _- , , _ __ [. ,

. , ,p_-[_>'__ ,[ , , , _.__,

' -@, @',' () .) O d), , O O' i

@ @ ii@ @ ' i @ @ ' i ,, _j @ i,@

i i s

),' p>' @. O(D,,

i ,

i i, ,_ ,,_ i i ,,_ ,,__ i i, ,_ ,, _ i ,,_ 'i i,,_ 'i

,* L. __ _J L. __ __J L. _. ._) L_ __ -1 L_ __ __J t k sj m

g i 1%

u: \

4 *s r ri r

.2 c- ~~

t f f >p __.._

J

.J N . '

j S 30 N. o I t u e "-

9 L v1 n L

t, a w '

?.,. - n h $m ,3 d.,i -

s 7, a 3 n n th .f)

W e $ 2, f h, 4

'i Y f, l

?.1 ?< g H G q i<

d d a a a :. d l\

o o o io o o. o ,di cx i o-o r

o

,q io-o r

o r

o o o (i

t 1

f

_ _ _ _ . . _ . . . . _ .. . _ _ _ . __ _ _ _. _ ._ I i

(

k I

_ LJ . _ . _ _ ._ _J h.._ _ _ .

{y 0000OOOOOOO00OO00OO O C>jooOO OOO000OOOOOO

I .

N *- t')

if f i 1I i

,I 7 Ji a i

i ),

OOOOOOOOOOO00O00OOO OOy00 00000000OOOO

- ~ ,o , o ,, s ._ .n - ,. m ,, ,, . >m m 55 %lE5h " 5 #d SS 5 D fa g [; g y a oca dda 77 777777 777.'7774 ?????? 777 W EP E P R P e s E R P !l fe P P !f Peppse esp

!l 4 s k 4 l

ML20217A089

Text

Subject:

Reference:

Navigation menu

Search