NRC-90-0061, Forwards Addl Info Re Proposed Drywell Level Instrument Line Configuration,As Followup to 890927 Tech Spec Change Request.Rept Provides Info Re Reasons for Designating Primary Containment Isolation Valve Normally Opened

Forwards Addl Info Re Proposed Drywell Level Instrument Line Configuration,As Followup to 890927 Tech Spec Change Request.Rept Provides Info Re Reasons for Designating Primary Containment Isolation Valve Normally Opened

ML20012F024
Person / Time
Site:	Fermi
Issue date:	03/27/1990
From:	Slyvia B DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-90-0061, CON-NRC-90-61 NUDOCS 9004090320
Download: ML20012F024 (5)

Text

-

a

. O. Reich srMe

. t.nneto vo sweeiocnt MN a:o eu,,,, t >>. . e "v...y Ed son ="a;:"

i March 27,1990

! NRC-90-0061 5' O. S. Nuclear Regulatory Commission Attn Document Control Desk '

Washingt on. D. C. 20555

References:

1) Fermi 2 NRC Docket No. 50-341 WRC License No. NPF-43

2) Detroit Edison Letter to NRC.

KRC-89-0211. " proposed Technical Specification Change (License taendment) - Primary Containment Isolation Valves (3/4.6.3)." dated September 27. 1989

Subject:

Additional Information Concerning Proposed Drywell Level Inst rument Line Configuration i The purpose of this letter is to transmit additional information concerning the proposed Drywell Level instrument line configuration which is the subject of the Reference 2 Technical Specification change. This information was reo,uested la a meeting between Detroit Edison and the NRC staf f on March 20. 1990. The atteched report l

l provides the requested information concerning the reasons for designating the primary containment isolation valve as "normally l open". .

If you have any questions, please contact Mr. Glen Ohlemacher at (313) ,

586-4275.  ;

Sincerely R & ay A. f i Enclosure l cc A. B. Davis >

R. W. DeFayette W. G. Rogers '

J. F. Stang l Supervisor. Electric Operators. Michigan Public Service Consiesion - J. Padget t M #PIMag3i8' 9004090320 900327 pp/ l

{DR ADOCK05'00{[I

V

'A 9

. / Enclosure to WRC-90-0061 Page 1 L

L H Discussion of Reasons Tor Designating

! the Containn+nt Isolation Valve for i

Drywell Level Inst rument as Normally Open t

i 1 In Reference 7. Detroit Edison proposed to add a new remote manual containment isolation valve. T50-T45P, to the Technical Specification

! Table 3.6.3-1 listing of Primary Cor tsinment Isolation Valves. This i-valve was designated in the Reference 2 discussion as a "normally open" valve. In subsequent discussions with the NRC staf f questions

!' were raised as to whether plant safety would be enhanced by designating the valve as "normally closed." Attached is a sketch of the proposed configuration.

o The new isolation valve is in a new instivment line which is being installed for a drywell pressure transmitter associated with an enhanced primary containment water level instrument. This inst rument

! is primarily being installed to provide a range of painary containment o water level measurement suf ficient to assure reactor core coverage during post-accident eaergency operations.

Dettoit Edison modeled the design for this pressure transmit ter af ter similar essential inst ruments. These instruments use normally open remote manual isolation valves to assure the instrument is in service L when needed. In particular, the penetration for the Reactor Protection System and Containment Isolation System Drywell Pressure instrument is configured with the same valve arrangement and also 3

utilizes QA Level 1. Seismic Levs11 ANSI B31.1 piping for the pressure transmitter connections. The same arrangement of class bleak at the normally open remote manual containment isolation valve is used for the Primary Containment Monitoring System.

The apparent alternative would be to maintain the valve as "normally

closed" and provide for the opening procedurally when Primary Containment flooding is anticipated. This would provide some greater assurance of containment integrity which clearly comes with a prester risk of the inst rument being unavailable when needed. Thus, the question of the normal valve position becomes one of a balancing of

[. considerations.

The designation of the containment isolation valve as "normally closed" would lead to the following detrimental ef fects.

L o The normally closed position creates a new possibility that the inst rue.ent will be unavailable when needed. 7te function would L rely upon the ability of thc valve to reposition. Although the valve is reliable, there is some probability that it may not successfully reposition.

o The inst rument provides a continuous indication of drywell pressure and drywell level in the Main Control Room. This indication would be inoperative and f alse until ruch time as the

!. valve were opened. This is potentially misleading and the L _.

! o . ,.

. Enclosure to NRC-90-0061 Page 2 ,

-1 l operator must be conditioned to disregard this irdication during.

normal operation. He will then have to act in opposition to this conditioned response to the it dication during emergency r operations.

o The Emergency Operating Procedures (EOPs) would then require the operator to open the valve when needed. This is an additional

! complication during these complex events. The inst rument also provides enhanced torus level indication in abnormal ranges as  ;

) well as providing a new drysell pressure indication channel. l With the valve normally open, this new dryvell pressure f I

indication would be the sole indication for drywell pressure which will be available for about one hour during a Station I Blackout event. The other drywell pressure channels would be  ;

i lost for some portion of that first hour. The valve would need

• to be opened to obtain this information in this situation as well r as prior to dryvell flood-up operation.  ;

hTREG-0737 Supplement 1 (1982). states "the use of human I

! f actored, function orient ed, emergency operating procedures will l

improve human reliability and the ability to mitigate the ,

consequences of a broad range of initiating events and subsequent ,

multiple failures or operator errors, without the need to Li diagnose specific events." This document implies that l

!' sympt (e-based rather than event-based guidelines were to be l developed. EWR Owners Group Emergency Procedure Guidelines, j Revision 4. based on this methodology was submit ted to the NRC  !

and approved in an SER on Sept en.ber 12, 1988.

With the isolation valve shut for the Prin.ory Containment Water l Level Instrument each event would have to be analysed to f determine when the valve chould be opened. This is contrary to l the hTREG-0737 guidance.

fc ,

j o Having the instrvment in service continuously would allow l l enhanced monitoring of the instrument's operability. Failures l L which cause erratic indication would be promptly discovered. The ,

l instrument readings (including drywell pressure) would be logged l

! periodically and any discrepancies from expected readings .[

pron.ptly resolved.  !

p L There is scoe additional asrurance of containment integrity with the

[ valve clored since the piping between the isolation valve and the l; transmitter would not be subjected to norn.a1 containment pressure and j

any accident loadings until the valve is opened, I However even with the valve open, norn.a1 containment pressure (less j than 1 psig) does not pose a significant challenge to this piping ,

which is less than two feet in length. The piping is analyzed for i pressure, weight, thermal and :sismic loading. The design pressure is l 56 psig and design tempersture 3 3 340 F which corresponds to t containment eccident design conditions. The penetration component ,

ANSI pressure rating classifications are all greater than 600 pounds. i No other accident loadings apply to this piping system. The stress [

s L -

pm

/- Enclosure to WRC-90-0061 Fage 3 i

analysis performed on this design assumed the valve was open and f determined that the stresses are all less then code allowable values.

The only dynamic load applied to the penetration is the reismic F, . loading which is considered in the stress analysis. The penetration ,

is not subject to any other transient dynamic loadings. The  ;

li penetration has been evaluated as not being vulnerable to pipe whip  :

[ and jet impingement.  ;

L The failure of the penetration during the design basis accident with I the maximum postulated source term would likely lead to consequences j greater than the limits of 10CFR100 for of f-site radiation levels. .

However, this event is not considered credible. As discussed above. l the design includes consideration of all threats to the penetration  !

int egrity. Regulatory Guide 1.11, which provides guidance for evaluation of instrument line configuration, only requires that the consequences for a f ailure of the line be evaluated for normal ,

~

operstion. This was done in the Reference 2 submit tal. The i postulation of a passive failure of the containment structure following the passive failure of the reactor coolant system is not required. A probabilistic study conducted has determined the risk of ,

a core dantage event followed within930 days by a random f ailure of {

this type of instrument line is 10 events per year.  ;

f Eased upon the above. Detroit Edison has concluded that the benefits i j of a "normally open" configuration far outweigh any risks to the [

containment integrity. j i

It should be noted that the test, vent and drain valves ahown will be i

" locked closed". Also, during inst runient installation, the in-line ,

c manual valve will be " locked closed". A " locked closed" valve is one F for which valve manipulation is ispeded by a locking device such as a

• c Icek wire, chain or other means which must be positively overcome to L reposition the valve. This indicates to any operator that this valve }

l 1s not normally repositioned and its current position is strictly 1

! controlled for safety purposes. This is also consistent with 1HPO l guidelines on this subject.  !

l Detroit Edison requests prompt consideration of the above factors and j subsequent issusnee of the requested Technical Specification change. .

To allow for installation, a 30 day period for implementation of the f i Technical Specification change is requested. Should the change be j l

acceptable only under the condition that the valve be maintained r normally closed, an additional 30 days to acconeodate additional l L design and procedure changes which would be needed is requested. The  ;

i design would have to input the new valve position into the instrument

- level computation circuitry so that the Emergency Response Information  ;

i System computer can determine the signal's validity, f

)

) ,

1

NOTE 1 I

ALL PIPING, V Al, VE S, AND FITTINGS ARE STAINLESS STEEL ,ASWE SECTION III, PRES $URE RATING OF 690LBS GA ! OA 1

WINIMUV,

$EIS I $EIS I CROUP O GROUP B ci i q --

SEE NOTE 1 503 I g,  %

DRYWELL PENET. X27 i >< -

i

/ 156F458 15968F202 FAI T59N495 T596eF297 b# IO

( LOC AL )

I 1

l l T5000F201 I

I DRYWELL PRESS.

0ER

,r TORUS PRESS.

73,qgip ORYWELL CAL (;. PC LEVEL l .-

l l

1 I

l w

RACK

(  :

i ROM F EXISTING TORUS I TORUS

) PENETRATION X296F PRIMARY CONTAINMENT WATER LEVEL WEASUREWENT INSTRUMENTATION

,