ML20024B330

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Forwards Preliminary Draft Study Reflecting Thoughts & Concerns Re ECCS Small Break LOCA Analysis N4M-2-14(AR) for Review & Comments.Proposes Meeting in Knoxville,Tn to Discuss Entire Question of Very Small Break LOCA
ML20024B330
Person / Time
Site: Crane, Bellefonte  Constellation icon.png
Issue date: 04/27/1978
From: Patterson D
TENNESSEE VALLEY AUTHORITY
To: Mcfarland J
BABCOCK & WILCOX CO.
References
TASK-*, TASK-06, TASK-07, TASK-6, TASK-7, TASK-GB GPU-2451, NUDOCS 8307080449
Download: ML20024B330 (6)
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TENNESSEE. VALLEY AUTHCRITY

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Q April 27,1978 go'3 itl0 1

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k Babcock and Wilcox di Post Office Box 1260 g},z Lynchburg, Virginia 24505.

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I Attention: Mr. James McFarland b:1.

Gentlemen.

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pi BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 i

pf-NUCLEAR STEAM SUPPLY SYSTEMS I

1 h[q CONTRACT 71C62-54114-2 l

LETTER NO. E-5020 u-N GENCY CORE CCOLING SYSTEM - SMALL BREAK LOCA ANALYSIS N4M-2-14(AR) iYi E

An increase of interest and questioning by ACRS in the aren of very sms11 Ci'.c g

The brM has prompted IVA to take a closer look at this problem.

attached preliminary draft study reflects some of our initial thoughts and g?

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Please review this work and give us your views. We believe concerns.

that a small break LOCA question similar to that asked by ACRS for Pebble Mj.

Springs (Question 6) might be asked in greater depth by NRC for Bellefonte.

Q Ve must be assured that B&W is' preparing for a timely reply. Perhaps p

-Q the attached draft will help.

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After you have reviewed this study, we would like to discuss it with you by telephone. However, we also propose that a meeting be held in Knoxville E-in the near future to examine the entire question of very small break LOCA's in sufficient depth to develop an adequate mutual understanding P

and assure TVA that B&W is working toward a timely resolution of all Ve believe that the following outline of observations and i

concerns.

condition: should be used as s preliminary basis for the proposed ereting.

2 The class of very small break LCCA's of interest probably range up to 0.05 ft (equivalent to the single ended circumferential break of a 3-to 4-inch o

pipe). For breaks in this range, the steam generators must remove a significant portion of the decay heat during the initial phase of blowdown; otherwise, reactor coolant system repressurization occurs since the break is too small tu remove all of the decay heat. Repressuri:ation or even

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prolonged high pressure operation could seriously limit high pressure injection makeup during blowdown and thereby adversely influence the peak clad temperature for those cases wherein the core uncovers during the blowdown.

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f In order to take credit for decay heat removal through the steam generators E"-

and thereby deter prolonged pressurization or repressurization, it is necessary to assure either (a) continuation of natural circulation through -

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the reactor core and steam generators or (b) establishment of pool hr..

boiling in the reactor core region and a steam flow path to the condensing:

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(cooled) portion of the steam generator tubing. There appears to be a i..

number of possible situations that might impede decay heat removal through 1

the steam generators during the natural circulation phase or during the S(-

transition from natural circulation to pool boiling / condensing or back g.p again. For example..,,_

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Since there is no significant temperature loss between the reactor 6.-

core exit and the steam generators, a steam bubble is likely to. form

[~9 in the high point (U-bend) at the top of each steam generator after syste:n g'

overpressure is lost. This would interrupt natural circulation by..

and decay heat removal. At best, an intermittent natural circulation 5 9...

might be re-established for decay heat removal.

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The transition from natural circulation to pool boiling / condensing couli k.

be troublesome because of the time delay while waiting for the sta==

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generator tubes to drain down to the secondary side water level and-E thereby establish a condensing surface. Unless the break can already i.f remove all decay heat, system repressurization will occur while the f

condensing surface is being established for decay heat removal.

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S Reactor vessel level turnaround will occur when the rakeup rate exceeds C.

the fluid leaving the break. Decay heat removal by condensation will W'

cease when the water level inside the steam generator tubes exceeds f

the secondary side water ievel. Repressurization will occur unless l'

the break can remove all decay heat. Natural circulation cannot be gM L

re-established until the tubes have been filled and the steam bubble at the high point (U-bend) has collapsed. If sufficient concondensable gases are present, natural circulation may not be achieved.

Associated with operation in each of these conditions is a concern that the 3 operator might be able to identify and isolate the break and thereby interruptf

been lost and the pool boiling / condensing mode has not been established,

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this interruption could cause full repressurization and a substantial passage L L

of liquid and/or two phase fluid through the pressurizer safety valves. The valves have not been qualified for this severe service. Also associated with operation in each of the above conditions is a concern that the pressurizer level is not a correct indicator of water level over the reactor

,lgd core. Because of the loop seal on the pressurizer, it may be possible to have a full pressurizer while the core is partially uncovered. This p

could lead to incorrect operator actions.

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och and Wilcox I$J il 27, 1978 E'.f.f..E.

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.Ve assume that the situations and concerns which have been identified above @.h:-

and in the attached draft study have been considered in your cwn in-house f{Q based on k'hI,5 Your more detailed transient calculation.:

LOCA analysis work.

realistic system and core thermal-hydraulic c:odels would be an appropriate gf Please let us know.

verification that no serious prcblem exists.

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Very truly yours,

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TEhTESSEE VALI.EY AtHHORITY rg;!s kyk..

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tterson, Chief

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i i,:l'.c.5W With reg:rd to the very :-" brech LOs c aly i:, the cc cern of WA a3

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F enter. sed in.*.ettcr No..C-5000 c:::ters o': the use of the p r-=71 brect

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odel (P1/,'-lC07hA, p.ev.1) f:c '~~" ' elow about 0.05 ft. Vces replT T4
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C! - g-systes cc fact 2: it is cererated in the care, h ch innbilityr hi y

ecs lead to a hi;hc.: thin predicted reactor coolust :/stc=

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presr.:re which it. em::: the fluid blevdec rute Wile ree:ci s

$pl p tbc high pre::ure ige:tien rate. This inerences the net loss b

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of water invcatory 17. the pr$2.srv cytte: over 2st 4.ich..

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would otherwise be preiicted d rdsi; blo.-doc. The d. cal res:lt g?;)

g of ccanideris; this effect vr*.15 be a lower reactor ves
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water level id a Icccer period of ti a r.=d a higher pee'r. clad

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tc=perature if tus core uncev=rs,

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b3 E-The SW c=ll brec :odel does ecmcicer he:t trt: fer espabilities p

f frc:s the core to the coolant but does not crpest to include heat tre : port capabilitics cet of the syste=, Tor bred a larger this O.05 ft', the haat re.cval rate throu;;h the brenh vill exceed the y

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tsJ decay heat Gt:eratic: rate in the core eco, therefere, heat

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tncaTort need tot te included in the =otel, hover, if the 13 b

sa=s rodel is u:ed for brcsh:

-"er thsa abcr-t 0 C3 ft2, it will M1 not correctly or cor.:crvatively p-edi::t the LCCA betsvice because N

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it does not ac:or t for the is:eresse is rescier coolcat cystc=

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prescre d:e to the inntility cf the tresh to rc:r.e all de:cy yd (l

heat.

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r.f A conservative sp,trete.h to rodeh, this protic xculd be to take ld

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credit 0:.17 fcr that pcrtion of the decay hest vtich esa be ; cVed Fj thicush the brc h.

If credi'. As tchen for hest rc: val thro'.q;h the h

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stete: Ge":erators, tit.: the questic: of wht r::ture.1 circulation is C

lost n=d how 10:3 before the :tes: 6Eteritors arc RY3ilable E3 cc=dc=: cts =::t be em:idered, t. ::

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{:. s In ever7 care, consideratien Ob:uld be giren 'o the :t::tnined h'

4 pres:.:re effects of ::Ter:e beit rs. :fer is the steA: cenersters Ej cm3 the 1:711:stic:: of bree.t isolation by autc= tic cr cpe rator M

i action d:: ring blevi:4 :.

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'=t, ple :e indicate whi:h p r' ion: of your re717 Gre ba:ed c= a::aly:e: er.d A 4 ~^ e their rat.ilability to WA and I

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