ML20127H284

Submits Justification for Continued Operation of Plant in Light of Revised Predicted Environ Parameters Resulting from Certain High Energy Line Breaks.Mods Currently Being Designed to Prevent Harsh Environ Effects

ML20127H284
Person / Time
Site:	Byron
Issue date:	05/17/1985
From:	Ainger K COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
0141K, 141K, NUDOCS 8505210263
Download: ML20127H284 (3)

Text

l 4

Commonwealth Edison one First National Plaza. Chicago. Illinois Aodress Reply to: Post Office Box 767 Chicago, Illinois 60690 May 17, 1985 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Byron Station Unit 1 Environmental Effects of High Energy Line Breaks NRC Docket No. 50-454

Dear Mr. Denton:

This letter provides justification for continued operation of Byron Station Unit 1 in light of revised predicted environmental parameters resulting from certain high energy line breaks.

In the event of a rupture of a high energy line in the auxiliary building, an increase in temperature and humidity is expected in general areas of the auxiliary building in addition to the local effects associated with the line break.

High energy line breaks in two systems, Steam Generator Blowdown (SD) and Auxiliary Steam

( AS), have recently been found to have a greater potential effect on environmental conditions than originally predicted.

The SD lines were originally evaluated considering the break to occur while the system was operating at a normal blowdown rate of

~15 gpm per steam generator.

Restrictions in the control valves in the system prevented the total flow from having a significant effect on the general area environmental conditions.

Because of increased concerns about secondary water chemistry, the system is now expected to operate at blowdown rates of 50 to 90 gpm per steam generator.

When this change was identified, the original assessment was that the revised flows would still result in little change in environmental conditions.

However, detailed calculations indicate thEt the higher flow will exceed the auxiliary buildirg HVAC capacity and result in a slow increase in temperature and humidity throughout the auxiliary building.

If the break flow is assurced to continue for 30 minutes without action to isolata the break, the auxiliary building temperature would exceed equipment qualification temperatures.

Subsequent to discovering the problem in the SD system, further investigation revealed a similar problem resulting from a high energy line break in the Auxiliary Steam System.

Although the AS lines are routed in a pipe tunnel and are restricted to non-safety 8505210263 850517 4

gpA PDR ADOCK 05000454 fo e

eon

re a

\\

M

. o!

5 -

n.

+

i t

g

" H..R. Denton' May 17, 1985~

u, r

related f areas, L it: has been determined that some ' flow from; postulated line; breaks could. enter 1 safety-related areas in'the auxiliary building _

.rather1than flowing back to,the1 turbine. building or being handled by

the,HVAC system. LIf the~ break flowiis.assumedut

o. continue for 30 minutesswithout action to isolate the break, the temperature.in-

certain11oca1> areas ofzthe auxiliary building would exceed equipment l qualification temperatures.

,w

. Modifications are currently being _ designed to prev'ent the harsh environmental effects from these.high energy line breaks.

1 Temperature sensors will be. installed in. locations that will promptly detect.-a temperature rise due to the' local. effects of these line 7

-breaks. LA~ signal will be sent from these sensors to automatically-n

- closelanTisolation valve in the affected-line, thereby. terminating the br'eak flow'a; Design, procurement,-installation and testing of these

~

modifications?will be completed by August'31, 1985.

_To allow temporary continued operation of the plant, steam

. generator: blowdown. flow has been reduced to 15 gpm per steam generator t'

!and.the AS line has been isolated such that a break in that line will

. not1 affect safety-related areas in the auxiliary building.

~However ' steam generator water chemistry is degrading due-to

.the; reduced blowd,own.flowrate and this'will ultimately require the.

plantyto-be shutdown.

In order to justify resumption of the higher

blowdown-flowrates required to maintain _ secondary water chemistry,.a.

person will be posted at a location in,the auxiliary building where

'y

the7 effects of the postulated SD line break would be promptly detected,

yet'notLprevent their' ability to communicate the problem to,the' control.

.room or1 create a-personnel safety problem.

Control room operators,.

upon notification of the onset 'of-the' postulated line1 break,1 would

?immediately:close the SD: containment isolation valves._ This person

!will benposted at the location described above whenever the blowdown m

. flow:from anyfsteam generator is greater than 15 gpm.

s fse Auxiliary steam is required to support periodic operation of ithe Unit"1 boric acid evaporators,-radwaste evapo'rators, and Unit 2 f'..

~

systems 4 preoperational testing.

In_ order to allow the continuation of-

_49 Lthese activities,- personnel will tue posted at specific locations in dM.

the auxiliary = building where-the effects of the postulated AS line

.E) breaks would'be:promptly. detected, yet not prevent'their ability to B:

. communicate the. problem to the control' room or create a personnel

-safety 7 problem.. As)with_thelSD line break, control room operators

~ ?^

would.immediately. isolate the AS supply line upon-notification'of the onsetLof:a postulated AS line break.

These personnel will be' posted utol equipment in the auxiliary building.at the required-locations whenever auxiliary stea The auxiliary steam'line will

. belisolated at'its turbine building source ~whenever auxiliary steam is E

not;needed in the auxiliary building.

m g

i

^

y

>YI c

L H. Ri'Denton May 17, 1985 The actions proposed'above to promptly detect and isolate these: postulated ~line breaks will' effectively prevent any unacceptable harsh' environmental effects from occurring.

Based:on the foregoing',

we believe continued operation of Byron Unit 1 is justified.

Immediate NRC approval of this justification for: continued

operation is needed to support the present Byron Unit?1 start upi testing schedule..

~

.Please address'any questions regarding this matter.to this office.

One signed original and fifteen copies of this letter are provided'for NRC review.

e.

Very truly yours, "f

K. A. Ainger.

Nuclear Licensing Administrator

.lm cc:.NRC Resident Inspector - Byron

+

=

0141K' t

I'