ML20024C732

Responds to Re ECCS Small Break LOCA Analysis. Use of Pressurizer Indication Will Provide Sufficient Guidance for Operator Action

ML20024C732
Person / Time
Site:	Crane, Bellefonte
Issue date:	01/23/1979
From:	Lightle R, Mcfarland J BABCOCK & WILCOX CO.
To:	Patterson D TENNESSEE VALLEY AUTHORITY
References
TASK-*, TASK-07, TASK-7, TASK-GB D-3132, GPU-0475, GPU-475, NUDOCS 8307130171
Download: ML20024C732 (7)

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January 23,1979 Letter No. D-3132

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Small 3reak LOCA Analysis I

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p Very truly yours,"

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Janes McFarland

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JAN3f.' ISIS 8 II3 i Robert E. Lightle Associate Project Manager i !'

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Response to TVA Letter K-5020. Emergency 5es1

) April 27. 1978

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B&W a report entitled, " Decay Rest B&W 205-yuel-Assembly PWR.." by C.

Via TVA Letter K-3020 TVA transmitted to g

This report presents a simplified, hand Removal During a Very Sas11 locA for a k transient and potential coussquencesh Michelson, dated January,1978.

calculation review of the small brea his paper, the following.

for very s=all breaks not explicitly examined w 1.. Within t breaks:

' concerns were expressed for the very small How is decay heat removed?

If so, could a===11er case he a 1.,

W1N.systemrepressurization' occur?

repressurization occur 7' 2.

worst break 7 If the operator isolates tha break, will systembjected to si'ug o Ifso,willthaisissurareliefvalves'besu.

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d in tha subsequent paragraphs'.

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,, Rasponses to these conce'rns are deve ope

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l overvist of the small break tran-Sma Before discussing these concerns, a genera fly discussed.CS can be described as a s siant in a 3&W 203 plant needs to be brie tensive steam bubble viewed as a slow transient during which the RBecause i

h t so' long.

within the reactor vassal while any s gnMany experim manometer.

• will forn Thus, any.

as a fluid, with qualities less than 70% or so, remains in the loop.

decay heat power levels.the RCS loo r

core ta=perature excursion will occur atproble f

I How-problem as stated above.

their inventory.

Ducar hast removal from the core region is nom as a who h

ever, decay heat removal from the syste ways of re=oving. decay heat from t eBoth of'th his dis-yor the very small LOCAs of interest i There ara cwo break and/or via the steam generator.

further.

While the detail in the TVA letter.

r is necessary.

cussion, it was shown that the break s decay beat and heat removal via the steam generatowas Such a break TVA-predicted break s1== that this occurs ats at is inconseguenti tha aictual break size that it occursize does exist whe al source is basically asmaintained are necessary.

The role of the steam generator as a heat removInitially, natura Once a is easily secomplished.

fill the U-bend at the top of in the system and the necessary heat remov described in the letter.

The intermittant l circulation will cease.

letter will not occer due to the s Once natural circulation cea the hot less is formed, naturanatural circulation discussed nature of the small break transient. vill repressurize somew h

system

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heat re-During this period, between the natural circulation and con ensat onid in moval modes, the letter expresses concerns that'the liquf the rates for the bre the system will be depleted at a rate in excess o i

f the system. IVA analyzed by B&W because of the partial repressurizat o than that

(

s This is not the case.

shown in the small break topical report 3rd-10074A.

J ller the break,.

During the natural circulation phase, it is obvious that the smalonger the h

.the slower the loss of system inventory and t e After natural circulation ceases, system pressure w l

circulation.

h break equals the

. trolled by a " volume balance."a point where the volume of fluid i

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volume.gf steam being created in the core. remains unchange lief out

.j d break si=s. De vol-the break increases with increasing system pressure ani h increasing pressure.

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uma of stars being generated in the' core decreases w till repressurize to a higher h the volume

.As the break decreases in size, the RC system wvalue; thu l

of steam being created decreases, Once the SG becomes available

' lost at a slower rate ks break size decreases.for conde=sa ize

'to approxi=ataly the SG secondary side pressure.

2 break h 0.05 ft of the SG will respond in a similar manner to that o following the 2

l

• advent of condensation heat removal, will be s h41=e to t a be Sas, for the smaller breaks, the system inventory will alw break.

2 greater than that for the 0.05 ftcovered and vill not undergo a t

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i f the' break after

..'i n the paper concerns are raised relative to isolat on oThe scenario prese 2

i tion to natural circulation is lost.Should the break be isolated at that time, syste ble.

the pressurizar. safety valve setpoint is proba Once the systaa. depletes able.

through the safety valves will also probably occur. suffic fer 'across the SC, The the system will depressurizeand no further loss o t re excursion core will remain covered for this secenario and no tem f the, m would then be two-phase flow out the valves, the response of the s l

fety valve stuck occurs.

.open accident and no core uncovery occurs.f the operato l hdiention is noe a

,As far as the appropriateness otion to trip the HPI pumps, J&W av a

.f s the state of the RCS.

=M eressure measurements to-reliable indfemeten a level indiertion. alone with svstas temperatura*y e em is se411 d

I 'EGure cha_-

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_ *

• enerator action.

vide M *4a4==* > M A---

detailed

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In sunnary, while the TVA paper raises valid concerns and gives all, L ~.

examination of the small break transient, the s=a h B&W 205 plant'ECCS provides sufficient anslyses. to ensure the ability of t e systen to control s=all break in the RCS.

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Senior Project Manager

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Attention: Mr. D. R. Patterson p.,

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Chief Mechanical Engineer y

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3ellefste Nuclear Plant Units 1 & 2 CJ. 4 l; l l

1 Contes =t No. 71C62-5h114-2 og

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us iner if further discussion is required.

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Very truly yours, 3

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Jones McFarland Senior Project Manager f y JAN 30 N W

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zia sobert E. Lightle Associate Project Manager E-P. R d

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y Response to TVA letter K-5020, Emergencyses11 78 l

&W a report entitled, " Decay Heat 205-yuel-Assembly PWR," by C.

Via TVA Letter K-5020. TVA transmitted to BThis report

• i Removal During a Very Small LOCA for a 3&W s

k transient and potential consequences Michelson dated January, 1978.

calculation review of the small brea for very s=all breaks not explicitly examined w thin this paper, the for the 205 FA plant, BAU-10074A, Rev.1.. Wit ll breaks:

' concerns were expressed for the very sma How is decay heat removed?

If so, could a smaller case be a

~

1.,

Will. system repressuritation occur?

worstTarsakt repressurisation occur?

2.

If the operator isolates ths $reak, will systembjected to si'us or t I

If so, will the pre'asure relief valves' ba su 3.

the subsequent paragraphs'.

Sw?

Rasponses to chase conce'tus are developed in iew of the small break tran-i Small LOCAs can be,

Refore discussing thase concerns, a general overvfly discussed.n siant in a 3&V 205 plant needs to be brie sive steam bubble viewed as a slow transient during which the RC5 caBe i

o'long.

• will form within the reactor vessel while any s gnMany experim mano=sta=.

o Thus, any 7

remains is tha loop.as a fluid, with qualities less than 70% or s,

r decay heat power levels.the RCS loop core temperature excursion will occur atProblem f

their inventory.

blem as stated above.. How-Dwcay haat removal from the core region is no proas a who ever, decay heat re= oval from the system ways of re=oving. decay heat from the sys Both of rhese items are discusse e ll LOCAs of interest in this dis-further. There are two Break and/or via the steam generator.For the very s is not capable of removing all the While the detail in the TVA letter.

cussion, it was shown that the break alone is necessary.

decay heat and heat removal via the steam generatorot ch Such a b ~reak TVA-predicted break size that this occurs at was nt is inconsegu

~~~~~'~"~~

the actual break size that it occurs aoes_exisi where cessary.

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sigz i d The role of tho' steam generator as a' heat removaInitially, natura Once.a sily accomplished.

described in the letter.in the system and the necessary heat The intermittant steam bubble of sufficient size necessary tolation will cease.ll not o i

i the hot less is formed, natural c rcunatural circulation d 1 vai drops

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natute of the small break transient. system will repres

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7g,u.N...;...,cp e;.g.

h is

• • ,, p r e M %.~.* 1 - /E.l.e;; p.9...

p-j f

is established.

belov the SC meenndary side level and condensation heat trnas er Wensation heat re.

During this period. between the natural cirruxauen id inventory within moval modes, the letter expresses concerns that'the liquf the rates for the bre the system win be depleted at a rate in excess o f the system. TVA 1

analyzed by 3&W because of the partial repressurizatio

("

than that This is not the case.

shown in..tas,small break topical report 3rd-10074A.

u er the break,.

l During the natural circulation phase, it is obvious that the smalonger the p

.tha slower the loss of system inventory and the Af ter natural circulattosi ceases, system nressure vil circulation.

trouad by a " volume balance."*1"4 A dischmered thr"ough the break equals the a poin gt vE Since the cold ~1es f'=44 enthalpy

• a= vo A a'

. volume.of steem being created in the ws. remains Warerduring f out s

d break size..The voJ.-

the break increases with increasing system pressure an ing pressure.

ises of stesa beinz senerated in the' core decreases with increasl repressuria

.As~the break decreases in size, the RC system vilvalue; h the volume

~

of steam being created decreases.

Once the sG becomes available

' lost at a slaver rate hs break siae decreases.for conde=satio i

~

Since the secondary side

.to approxi=ately the SG secondary side pressure.

0.05 ft2 break of the SG will respond in a s4=41=e manner to that of the fonowing the 7

analyzed in the topical, the primary side pressure response, h 0.05 fc2, advent of condensation heat removal, will be similar to that of t e

? =, for the -- 11er breaks, the system inventory v411 alvey g

J) break and the core vill.always remain break.

3 greater ** =* toat tor cha 0.05 ftcov C and win not underzo a temn

(..

isolation of the' break after l

.Y n the paper concerns are raised relative toThe scenario presented in the letter is rea l

I i

i to natural, circulation is lost.Should the break be isolated at that eine, system the pressurizer safety valve setpoint is probable. Once the system, depletes able.

~

through the safety valves will also probably occur.

f oss the 5C3 sufficient inventory to establish condensation heat trans er acrd no f The rsion the systas vill depressurizesD core vill remain covered for this secenario and no tem f the, would then be two-phase flow out the valves, the response of the syste occurs.

f lve stuck

.oPen accident and no core uncovery occurs.

l indica-]

As far as the appropriateness of the operator using pressurizar leve l

y

/

tion to trip the HPI pumps, E&W ae***e that However, use of the cressurizar reliable inddeation of the state of the RCS_.elone with se vin pro-I ensure thme ^= *yeom is still in s substantially subcooled stste.

1evel indiencien.

d de ed<4

4. q..* >.~

% eeerator action.

ld In summary, while the TVA paper raises valid concerns and gives a l report exanination of the small break transient, the sman. break topica05 plant'ECOS

~

provides sufficient analyses to ensure the ability of the BW 2 j

systes to control small break in the RCS.

'XC4C183

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