ML20112G374

Forwards Addl Info to Justify Interim Operation Re Potential Environ Effects of High Energy Steam Line Break Outside Containment.Evaluation Provides Assurance That Facility Can Operate Safely Pending Resolution of Issue

ML20112G374
Person / Time
Site:	Byron
Issue date:	01/08/1985
From:	Tramm T COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
9598N, NUDOCS 8501160320
Download: ML20112G374 (11)

Text

)

Commonwealth Edison

[ ) one First National Pitta. Chicigo. Illinois kO 7 Address Reply to: Post Offica Box 767

\, _,/ Chicago. lilinois MEM January 8, 1985 i

Mr. Harold R. Denton, Director Office cf Nuclear Reactor Regulation l U.S. Nuclear-Regulatory Commission '

Washington, DC 20555

Subject:

Byron Generating Station Units 1 and 2 Environmental Qualification of Equipment NRC Docket Nos. 50-454 and-50-455 Reference (a): October 18, 1984 letter from T. R. Tramm to H. R. Denton:

Dear Mr. Denton:

This letter provides additional information to justify interim operation of the Byron units with regard to the potential environmental effects of a high energy steamline break outside the containment. This information is provided tc satisfy License

' Condition 2.C.(5)(a) of-the Byron 1 Operating License, NPF-23.

As indicated in reference (a), we believe that the Owner's Group cooperative effort is the most appropriate manner in which to obtain final resolution of this generic safety question. After discussion with the NRC Staff, however, more detailed analyses of

!the Byron /Braidwood equipment have been undertaken to provide a better justification for interim operation. This letter provides the results of those analyses.

Subsequent to reference (a) and our last discussion with the NRC Staff, it was determined that the steamline break mass release estimates made by Westinghouse for another plant would be useable for a similar. evaluation of equipment operability at Byron.

Attachment A to this letter summarizes the results of Sargent and Lundy's temperature calculations for the main steam safety valve room and their evaluation of the possible adverse effects upon Category I equipment in those rooms. No Category I equipment is located in the steam tunnel.

Calculated temperaturg profiles are provided for the 0.2-ft 2 break at full power and 0.5 ftZ break at 70% power. According to these calculations the room temperature could exceed the equipment

_ qualification temperatures for a short period of time. Further evaluation indicates that this minor temperature transient would not threaten'the operability of any of the Category I equipment ,

in'the safety valve room.

m ,

I-w

-?,

~H. R.-Denton January 8, 1985

, This evaluation, in combination with the low probability of

' the catastrophic high energy line break event itself, provide assur-ance'that-the Byron units can.be operated safely pending resolution of1this. issue on a-generic basis.

LPlease address further questions regarding this matter to

- this office.

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

Very truly yours, f he JW T. R. Tramm Nuclear Licensing Administrator lm-cc's Byron Resident Inspector

' Attachment w

9598N-

- *.i .

, e s

3 s% c. g.: , .

l

.c- _y _

, e 1

I

..i;

. .1

~.?-

.'r a t

}

ATTACHMENT A A J

^

Evaluation of Environmental Effects of HELB Outside Containment

- T..

~

Byron /Braidwood e

f e-a s.

4 e

a 7

s t -

4

c. ..

7

. .L -1 1 2 4 I $

p _

3:

- ra x

~

19598NI

_ vg.

W

,'s.' -

,i t -- ,

, ai

. f, ? Y

^

~

_z

r r'

r .-

^'

.r s f t . .t of+- . ' '-a -

. .. t

Page 1 of 8

, ,7

~1. INTRODUCTION Commonwealth Edison was recently notified by Westinghouse of a potential main steam line failure scenario which could result in uncovering the steam generator tube bundle and production of superheated steam in the steam generator. Release of this steam could result in higher temperatures in the main steam tunnel and valve houses than have been used in the Byron /

Braidwood Equipment Qualification program. The potential effects of this increased temperature on equipment required to safely shutdown the plant and maintain it in a safe shut-down condition have been evaluated and are described in this document. The evaluation demo.1strates that the postulated superheated steam event is of low probability and, if the superheated steam condition did occur, necessary safe shut-down equipment would not be rendered inoperable.

2. DESCRIPTION OF DOSTULATED EVENT A spectrum of main steam line breaks (MSLB) ranging fram small

~

cracks to large double ended ruptures, have been postulated over.a wide range of plant operating conditions. Very small

-breaks do not cause uncovering of the steam generator tubes because Auxiliary Feedwater Flow is adequate to maintain steam generator level. Very large breaks result in a rapid

~

_ pressure drop and, consequently, reactor trip and steam-line

. isolation prior to uncovering of the steam generator tubes.

At an intermediate range of break sizes steamline isolation may not occur until sometime af ter the tubes haue been exposed.

If the tubes are exposed, the steam produced in the steam generator can be superheated as it rises. This results in increased temperatures in the area near the postulated break.

The range of break sizes which could result in a superheated condition is dependent upon plant parameters such as Auxiliary Feedwater system design, steam generator design, and piping arrangements. Westinghouse has reviewed the Byron /Braidwood design and confirmed that the information on transient super-heat conditions generated for the Duke Power's Catawba and McGuire plants can be used to assess the potential effects at Byron /Braidwood. Differences between the plants were evaluated and found to have only minor influences on the predicted conditions.

Two limiting cases were_ identified to bound the superheat cases.

A break-of approximate area 0.5 ft2 will result in tube un-

~

.covery and a rapid temperature rise'followed quickly by isolation. A break of approximate area 0.2 ft2 will result in a slowly decreasing level and a gradual increase in temperature with a significant delay before iso:.ation.

ne ,- ,-

Page 2 of 8 In ovaluating the potential offects of these two breaks the smaller break was found to be limiting. Although the rate of

. temperature rise is less, the total time at a temperature

-higher than. the original qualification temperature is greater and the potential for heating a component to unacceptable

' levels is higher.

The predicted temperature transient for the 0.2 f t 2 break is shown.in Figure 1. Steam Generator tube uncovery occurs at 530 seconds after the break. Main Steam isolation occurs at 1114 seconds when the temperature in the valve room is approximately 339 F. The temperature transient for the 0.5 ft 2 break is-shown in Figure 2.

3. AFFECTED SAFE SHUTDOWN EQUIPMENT

' The .. Category I electrical equipment located in the safety valve rooms has been identified and is listed in this section.

No' Category _ I equipment is located in the steam tunnel itself.

~

- The only components listed which are required for safe shut-down'following a main steam line failure are the Main Steam Isolation Valves (MSIV's) and the Main Steam Pressure Trans-mitters. These. are required to isolate the steam generators.

Following.the isolation valve closure, the components are not

' required to-function during the remainder of the transient. The function of all Class lE equipment located in the Safety Valve Room is described below.

A ." Main Steam The Main Steam Isolation Valves (MSIV's),MS7V Bypass Valves and the Steam Generator Power Operated Relief

Valves (SG PORV's) are required to isolate the SG pressure boundary and control cooldown. The MSIV bypass valve is used'during start-up at low flow to temper the lines and

-is' closed during _ normal operation and, therefore,~not required to open.during an MSLB event.

.The PORV's are not required to maintain hot _ stand-by conditions. The Main Steam Safety Valves (which contain no non-metallic parts) will prevent overpressurization of the secondary system. Secondary depressurization can be

-accomplished with hydraulic hand pumps if the electrical controls on the.PORV's are inoperable. PORV operation is

~

'not: required during an MSLB. An analysis shows.that the m chand; pump will be accessible within 30 minutes after Main Steam Isolation. ,

~

The MSIV. Safety function -(closure within 5 seconds at

a. maximum specified qualification temperature of 325 F) must be completed in order to isolate the steam generators to prevent blowdown.of all steam generators. - Qualification-of-the MSIV: actuator.during an MSLB is required-and is described in Section.4.-

, -- .r---,

e n ~ w - e e~s-- -~-,-.-c-,--,-w v,+,,-w,.- .m y - - . - -v~, ~ py y-

o Page 3 of 8

. -n _

+..

3. (Cont'd)

A. (Cont'd)

Environmental effects will not cause a spurious actuation of a valve in the Main Steam system. Failures in the electrical orLhydraulic system of the MSIV's will result in the valve remaining."as-is". The PORV's will close upon loss of elec-

- trical or hydraulic power. The MSIV bypass valves are also fail closed valves. Section 4 demonstrates that environmental effects will not result in failure of the MSIV to actuate and, therefore, Main Steam isolation will be achieved.

B.. Feedwater Valves Feedwater Isolation Valves are normally open and fail as is.

The Feedwater Isolation Bypass valves are normally closed

.and used during start-up, low flow conditions. They are not required to function during an MSLB. The Feedwater bypass

valves are set to provide approximately 10% of the main

, feedwater flow to the upper feedwater nozzle. This flow

. path is automatically isolated by check valves upon loss of feedwater flow and, as a result, the feedwater bypass valves'are not required to function following an MSLB.

'C. Blowdown Valves The steam generator blowdown isolation valves are normally

- open,-fail close valves. The flow in this. system is normally between :15 and 90 gpm per steam generator.

Control valve SD007, located in the Auxiliary Building,

, can .be used to isolate blowdown outside containment.

m

'The Steam Generator Sample Line Isolation valves are m ,

'normally; closed,~ fail close and are used only when taking

!w  : samples.of recondary coolant. Their function is not

. required during MSLB event.-

'D. Main: Steam Instrumentation .

- 1Pressureiswitches on the MSIV hydraulic pump and accumulator 3 -. tank provide alarms'in'the? event of component! failure'or mal-s - function. -Failure'of the' switches will not' result'in. loss of MSIV-operability. -Therefore', these switches do not require.

ma igualification for the Main. Steam'.Line Break transient.

- The. steam. generator-pressure transmitters must-operate during! the MSLB to transmit .the low steam pressure signal o

i -

.which < actuates the MSIV to close < approximately seven 4  : seconds:after the pressure set-point'is reached. The s qualification of these transmitters was'sufficiently-.

. conservative to. envelope the predicted superheat. conditions

, as discussed in1Section=5.

E.: . Radiation Detection Instrumentation Radiation 1 detectors mounted near the Main ~ Steam Penetrations

( Jand in,each' safety room-aregnot required to function during-

~

'an MSLB event.- Their function is to monitor radiation levels.

x Tfrom valve and penetration laakage and to detect radiation

.in'the main steam 11ine in the event'of a tube rupture.

Page 4 of 8

4. MSIV QUALIFICATION The Main Steam Isolation Valves (MSIV's) are required to close to prevent blowdown of all steam generators. When a valve is closed the differential pressure across the valve will maintain the closed position. Therefore, the valve actuator is required to remain functional only until the valve is closed.

The MSIV's have been qualified using an accident transient which peaks at 328*F. To evaluate the effects of higher temper-atures, the individual components of the valve actuator have been reviewed for possible non-metallic material degradation or other high temperature effects which could adversely affect the' performance. The non-metallic materials in the MSIV which are required to withstand the transient are listed below. The normal service limits have been compared with the predicted temper-atures of the individual parts obtained by a conservative heat transfer analysis. A significant margin exists between the service limits and the predicted temperatures demonstrating the adequacy of the MSIV design.

MSIV Materials Material- Use Normal Allowable Temperature Viton Seals on 3-Way solenoid 425*F valves Viton Seals on 4-Way hudraulic 425*F valves

'Viton Seals on pilot check 425*F valv'es lViton &- Seals on hydraulic 425*F tolfon accumulators EPR End seal (internal) on 300*F (Ethylene- pneumatic reservoir and propylene rubber)

~

seals on hydraulic actuation cylinder By comparing the allowable temperature with the transient shown in Figure 1, it can be seen that the only material of concern is the EPR used to seal the pneumatic reservoir and the piston of hydraulic cylinder which actuates the valve.

Al conservative heat transfer analysis has been completed to determine the actual temperature which the seals would experience.

In both cases where EPR is used the seal temperature at the time of MSIV -closure -(1114 seconds) is conservatively estimated to-be 240*F.- 'Therefore, a' temperature margin of.approximately

-60*F exists. Also, the time required for the seals to-reach

the rated ' temperature .(300 *F) is more than twice the time

'the seals are required to remain functional.

? -

w: Page 5 of 8

~

5. STEAM LINE PRESSURE TRANSMITTERS QUALIFICATION i 1The pressure transmitters are required to function only long l enough to provide the main steam isolation signal. Sufficient  :

. margin exists in the environmental _ qualification testing

l

to* assure the operability of the transmitters at the maximum calculated. temperature of 339'F at the time of main steam-

line isolation (1114 seconds). The transmitters are qualified

~

^

for a maximum of 420*F (duration three minutes) followed by ic' - 340*F for 15. minutes and 250'F for 16 days (Ref. EQDP Rev.4,

- March, 1983). The qualification transient is significantly .

.more severe than the predicted transient shown in Figure 1.

i 1 Additionally, the transmitters are mounted on the valve room concrete wall where temperatures will be lower due to steam

.  : condensation. .

!These margins are sufficiently conservative to justify the .

transmitter's perfcrmance during the MSLB.

~

J 6. CONSERVATISM AND MARGIN IN ANALYSIS

_The re-evaluationtof the MSIV and Pressure Transmitter environ-

~

mental: qualification is consistently conservative in assump-0

'tions and procedures. The postulated initiating event, a main steam.line. rupture with a: break area of between 0.2 and 0.5 Ft2,_

is.a very: low probability event. Prior to occurrence of 1.

superheat.conditionsLin the pipe the plant operators will

c. receive _ alarms for-low level-in a steam generator and large

" amounts of steam will be released to the. turbine building and

_s the' environment. .It_would be expected that-the operators

~~

1. .would quickly; isolate the main steam lines,

e.  :

Assuming the event continued,. temperatures in the valve room

~

were calculated assuming'no delay in flow from the break to

~

the safe shutdown equipment.. 'No: credit wasLtaken forithe

.

• amount fof: heat transferred from the steam to > the - structure and equipment,-resultinglin a higher predicted-environmental:

/ ' -

temperature..

c When evaluatin'g'the potential' heat transfer to.the temperature:

< sensitive jomponents,-there.is some uncertainty involved with Lthe heat-transfer rate to a surface.below the steam saturation temperature... (approximately - 212 *F ' for this . case). because of '

1 t the variability.of condensing-heat' transfer. To model this is _;

^

sa _veryTconservative assumption was made that the surface of the u

component.in-question was initially at:212*F _

17'.._ CONCLUSION-

~

~

- ' . :Infthetlibiting: steam superh5at.. case, components could be F + '#t '

exposed =to temperatures slightly above_the qualification

< temperature for about 10 minutes. The most= critical; components:

e.

/contain. seals made of EPR which is: rated for'only-about 300*F.

m 1

4

' _ u u ._;. . . ,' _

. ,..,_.. _._ n..; _ .. _ _ _ ,,, _ .. ,_ _ _ w , . , , , . . , . . , , , ,_,,,,,.4. . . -

I

. Page 6 of 8  !

7. (Cont'd)

Conservative calculations show that the temperature at the seal location would rise only about 30'F prior to the completion of the safety function. This results in a temperature margin of about.60*F and a time margin estimated to be at least equivalent to the duration of the event.

.Given-the extremely low probability of the defined initiating event and the adequacy of t!.e materials for the predicted temperatures, the components in the main steam tunnel have been shown to be qualified for the conditions caused by superheated steam due to low level in a steam generator.

\

h

-L

Page 7 of 8 i FIGURE 1 .

% U.,

[ i 1. t i

- h. ..H ..;_ .j_. . . . . ._; _.- . . .*;)

y _. . _ . . k . .._. ...

+ . +

i~ .i

_. a, . __ DO U . ..

• t

• 7 m

i Q t;- I t

(- ,

2.f ] _:._. !_ .._ _ ; _ . , .q .. O _ . . t( .. . ..._.4...._c___.. . . _ _ _ . . . . _ .

l.

. i nas y i

. . . . . me . . h I i i i e t Q-...'..._;._. ;_4 d > ,-

93 E ;_..4.__..._.___._...... -

. -  : $o

- i uh1.....a.

(

q a;- ..  ! - i t c . . - ;4 < i- g - - t ---. :l r -

-t 5,

g . .

t 3 'e,.  ! t ,t.. . - . l

--J , F - T .I ' b .n, .-b yoo . *: b  ;

i 1 '

-j--l- .

="j-b -

- u y p l -6 k 4---

vy .l-=__. .

-I w-,pp a

4- ,-- ---

M , p - . .

I. :i: :: 9 - g .,J  ;.  ; .

~ '

-- i - r . .m== s_ . f, y-j .- _gg-- ;

- }_ g m2.q .: :y  : :p - 7

=r: -

tA

-N .

.  ;. . . . . . .t>. _

c 3..

c '

-- - ~

-1 =. .J. _-'.'

: ' J ... . .. -. . .

. . \, *l,-... . . --.... 2 L'a

.n.e

. -s

'--~~~T,~ .-

1 ,

%(3

$ 20 --

t- ., .. .

~'

.; .1 .. ,e .

]

. ---1 . c: -

. . t  : 'y

. .x  : l Z [.. .' [ : j ; . ~ ~ h. '

.-]'. I. - -- T - . j - . ._ --j *[

l-

-- - -e r .g...

u); G- .~I - ,

--- 4-- . .

H ~~

-.\H . . . ,. (- . i' .;,. - j

-_. -. c i

y . .:- . _.

I 7 . 2.. . ._ .._ Q..~~.--

L.,

.; m - ' -'-

i

~1 i g .)

_ . . . . . ._ L J

L - I .I . . ..  : -! '

. [ b .I

-1 I'

... .j- -- T , _

. :g .- p q j - V (3 P ]

I.'- _

Qg 7._ ~2

i.

.: . i _ :- .i-

_ ]_g _.__. *M

__., .. u .- ---

. .. 4 J _2 ,

g. ,

r -

F, . .,

3 --- 2 6 .

e

..t

.r  :$ .:t' , 1 W" '

.n rf _ ' t _ . . ._.:_: -- -

.1 c.'

(0,

._g g.c. i n . ._

l, t -  !

we 3

_ d- o . ,l.

~gy'j  : t. . ,

• l l T **'

_~-*

"(~--~~~ ~ - '- o

-..-..}_.. .. . . - . .

%y 7

V ~1

! In - -

p- .

(#- .!.... .j...,. I- ,.!.

-]g g l- . .  ;: m - i. .....t .. . . . : _' : . . . ., . . : (

i 3

o g- .;. . .

p . . . . ,

-j

...: c:

V ,, .- *

[

EC g tJ l ,-.l. ...- .

p . .....

. ,,;; :g-y; ..h g S

g-

. . @- .........T----~ - - Aj gqL, 3,e- q ' p~ ~. _ . . . . , m ... _..

g

.o '

__p m- ~i ', ,77 }_;__

" l.

x :a N .i2 I '  :

g rp{03 ifn (y -

. ;; ..g p g-

-g I P -il  : .

. . _. ._3 -

. n. u,.i l$ .. _. . _.. l.-  :

. . .1:  : .

l' T,_<3?g t.; ' - - - -

- = .. =

T _ O' Qo' .'l .Lo-- - _ _ .  !

! .! l 6 U. i _:.. .u.--.

..w .:_.-.:-.a....:._..-_...-..-.. . ._ . u .

g s, , ,

i i 7 4.

i e i i #

L

1. i i . -01

. . ._: . Q . , .. . . .j

..g- . _ . . _..

_.._....O i . . . .tod _ _ .; . i . _. 4 _ .A e .

.:. K ...-

.E . ., g. - 6 A,

t . . .. _ . ,

i . ed. ..

3_,. . . ,.  :- .

.l I

.-_{ g

..p.= . j.n.

-t .

( ... .I

. 2 .gg; gg,; t,4,i,933 i

- ggggy, 1 i 3 gg& .43ygj.___ q -

L

y

. Pcgo 8 of 8

~

n..:. [t

-t t l t  : + FIGURE 2

, d _:  : u_. n _ . !_._ _..L.J h_..

.) L _ L f . . .

g'..t1 . .

.! 4 'I l 'J l [ }

8

+

i . ,.

~( .

4-. . . _. { _;. . __.l . . . . _ . . _ .

..}....f___......_._..._...._._.'___.

~

n -- -

i

= - - - - - - - - -

6---

, 7. r  ! V

._L......___.

, gy g

l.  :

+

. t i 4t .:, _ -- - _ . _ -..: : _.w _ :. ...--..._._ ..._. . . . .

- . . _.b. ._ .. . . . . - _ . _ .

l . ._ .,. _ .. .-. t. .

[ , . q j

D_I w . ,

; i j i

n

.p .._j . : _ . .. ,

I

' 1. i i L  ;

Al ..

~~62 b -

,y .

j- 4 1 - o. .

_dg_4;: . u .. . . L v .___._ g

-_p : .c.

~ ,

..b..J ~:l.. l8

-}. -

.. '-.l!. , 9) :o L

' 6 m --

- 1. ? c- ' ~ -l

'N tt  : ,'

_ l . _'. :_:-: f- .. :f-

. ~.;; .; -

. I _ . 1.

- ' T . ..-~~

,_q ; ;__. n' * . . _OQ

_._j O.)

' f.

--tJ r .f {

. -- t

= .,

h l

--- 0

'O i , ..

d . .-_. - ~> u

... n. -

.:; .t. 1. - 9

. t . ,! f:' .

/ - ml ._ . H - 't.2-;\;: l . : .. j: - :,.. E.* - ..

- z-3 # a-- ' - ~-

.js t21y 1L. - -

l- r  ! 3  ;

.T . .0 A

.s

<, 1 i l +- .;

q kl- ~

c} .' l. :; .! ' '

i.--

+

. ,- I." -

b.' , -l,- t  ;

~

..- F,.

n . - . _. .- _... n_.

l0s , s l .". . .L 1 i l! y 4_. _ _... .. _

~

.l 1 _ .. __ ~

. . _Q

&g .

. l , ..

. ,, .p. -l - i .: .

_ . _g . .g

. (*-

.# I -

-j \ f

. a N

_y 0; _: _ :.l__.. ', -

.  :=. _ _._: tL .- - '

.p 4  ;

1 i  :

3~ .

+ . u 3,

_N {p I

_M . _ .4i

..y  !

h _ _ __ .

, -g -

1l. ., .. i

l-

.- r _. _.1 - . .

o h't b 2

G _.4 @ .. .a.

yp. . l.

.i L

~

Q

. f . ___. .. N _

^1

,g

.. . .y u E$ 1 .

(0 -

-t- ,

+

- Ill re. ,-

.-r --

11 - it .

a-p -f.d  ; __. c=. . .a . [.

z t'3

.g g. _ q _:

1: . . . _

7 ;

._. g

(

.t .

3. . .

.p i F T.s ' . .n. 7; :- $. :3 E._ .c - H-

}. - x:

i a

1 .

. y ..  :- *- ..'-

. . *d . . P

• O '

11."

Q =;s

1. ._.-

- t'. G44 - ." - 4_ .Q  : . g'

T Y _..: .:

. p t- .i

-. h- -N. i l .....[ ... [6 '-- yJ

- *~

k-- ".h. "T e N:

L ct)

-.l.

- -- : .. -i . . . ._. .- d.

. Ei - !: , . --

~..- . _r wo. .t:  :- -

-- . n a:. 4 ' . v- -

-l? --$ I,  :, 0, 4f' ,.

A

- O" ~F<N v ".

g .#

i _ I _ _ .2. ..

1. .__ # +_

g_y .

u,g 3 OG . - -

i' . T :;. .a. g E ._1 d 1-p _ c M m2>5 _,o

_4_;

il- . :.. .-

.... -- . . l' . . . .

.33 i

.h . , .

.1-g t .: ..,  :;1 - .

4 ._ . . 6 ...

_ 2_

... =_ -

__ . l -. . .

.}.. . .._.

._

• _ . } _ . .;.

. .. . .A. . . .- . . . . . .

5 I h k h ,

s. .. ._.. '. . ....O_... .O.- -

D..:.2. ...... O ..-- .._...O. . . - .. O ..... -

lt 9.

i'.

}:

, .,T

. :IO

y. .,

.. g.

a co 84

.4 N

J-

q. ..

. , . . . 1  %; - "~

.- l: t- t .:  ; . .

i ..

-~ " '" j- -i .

$ &\ 3g gp 4[ $ fg '*' " *{l ?