ML19317D459

Suppl 1 to Status Rept Re B&W ECCS Evaluation Model Conformance to 10CFR50,App K

ML19317D459
Person / Time
Site:	Oconee
Issue date:	11/13/1974
From:	US ATOMIC ENERGY COMMISSION (AEC)
To:
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NUDOCS 7912030328
Download: ML19317D459 (21)

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t SUPPLEMENT 1 TO THE STATUS REPORT BY THE DIRECTORATE OF LICENSING IN THE MATTER OF BABC0CK AND WILCOX ECCS EVALUATION MODEL CONFORMANCE TO 10CFR50. APPPENDIX K XQV 13 TI4 9

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.o; TABLE OF CONTENTS Page A.11NTRODUCTION.............................................

11 J-B.

. ADDITIONAL DISCUSSIONS...................................

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1.2' Sc o pe o f Re v ie w...............................

1 2.1 3

' Compliance with Criteria......................

1 4.1 5-Metal-Water Reaction..........................

2 4.2-Swelling and Rupture of the Cladding and Fuel Rod Thermal Parameters......................

4 4 3 1.1 Break Spectrum................................

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'4'.3 1 3 End of Blowdown........................~.......

6 433 Momentum Equation.............................

7 437 Core Flow Distribution During Blowdown........

8 4.4.2 Containment Pressure..........................

8

4.4 3 Calculation of Reflood Rate..................

8 1-i

~4.4.4 Steam Interaction with Emergency Core Cooling Water. in Pressurized Water Reactors........

14

-4.4 5 Refill ~ and Re flood Heat Trans fer.............. 15 5'.0 small Breaks..................................

16 6.0

~ Documentation................................

16 C.-

ERRATA..................................................

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INTRODUCTION LO'nioctober 2d, 1974, the Regulatory staff reviewed with the r~

f ACRS Subcommittee each of the openLitems which are addressed in

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.the " Status Report by the'D1 rectorate of Licensing in the

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Matter -of Babcock and Wilcox ECCS Evaluation 'Model Conformance 2to 10CFR50. Accendir K." ~.Many of the areas were to be addressed 7again-by' Babcock:and Wilcox in subsequent communications with th'e staff. This Supplement.tofthe Status Report discusses

'eachfor these areas,' presenting resolution where appropriate.

[Also ' included l in this Supplement is an Errata of corrections-tofthe; Status Report.

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-ADDITIONAL INFORMATION

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The[followingdiscussions. relate'totheopenitemspresented.'

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throughout the-staff Status Report:

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II.2 Scoce of Review z

As' indicated.on page 1-6 of the Status Report, it was

. belle.ved that the similarity in. design of the Babcock and Wilcox

' plant. types in categories other than Oconee Class.(Category 1) may permit ~ application-of conclusions of-the present' staff' review.

1 Babcock and Wilcox has agreed to address the. applicability of the present generic model conformance to. Appendix K on a-case basis.

Such an-approach _will confirm that the generic model and the technical bases for-the generic model remain entirely appropriate for these other plant types.

. 2.~1 3 Compliance with' Criteria

'(a)[ As, stated on page 10 of the' Status Report, Babcock and Wilcox 'has ' presented the results of analyses.to demonstrate successful: initial operation of the ECCS by showing that the

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4 entire ~ core has been quenched. Their analyses conservatively 1

l assumed:-that-the. peak linear -heat rate was at the 10' foot elevation. ' For: a large break (8 55 squ'are foot double ended k'

4 break.in o'ne cold leg)3 theirjanalysis shows.that the cladding J

. tem'perature at thef 10 foot elevation is reduced to essentially Lthe.; saturated.. temperature of the.ECCS coolant in the ~ core within

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.:400: secon'ds~.of the [ postulated LOCA.

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r 2-Babcock ~ and' Wilcox describes, for a typical l 177 fuel assembly

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plant, the operator actions needed toLinitiate long-term' cooling,

the operator _ actions. required to maintain long-term cooling for the time' periodL necessary, and the provisions for maintenance of the components and systems required for long-term cooling.

'The review;of' each application for a l construction permit

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' includes theisystems needed to transfer the' fission-product decay.

- heat from the reactor core to the ultimate heat sink. The heat transfer capability. and -the adequacy of the structural design

. of; these systems are included -in these individual reviews.

' The Regulatory staff. concludes that the Babcock and Wilcox ECCS.model along with the individual case reviews of those' systems

- needed-for long-term cooling provides an acceptable means of satisfying' the requirements of criterion 5 of paragraph 50.46.

(b) Page 2-12. ~Babcockf and Wilcox has agreed to supplement their1 topical reports with the complete set of responses previously received to. staff questions by December 15,1974..

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!4.1 5 Metal-Water Beaction Babcock and Wilcox has provided additional information with

- regard tolthe concerns on page 4-11 of the Status Report. The Status Report statas.that. the Babcock and Wilcox method for calculating core ~ wide hydrogen generation is adequate provided it

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can be. shown that the'. temperature.respo'nse ' for each axial elevation

.in tthe I oti Ehannel envelopes the ' temperature. response of other :

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' Lelevations.in'the' core.atlthe same-linear heat generation rate, and

.'that[theluse'ofa' core,powerdistributionwhichyielde'd.thehighest s

{ peak cladding temperature envelopes the~ use ofJall other cure power.: distributions.. :. Babcock and Wilcox has recently proposed to n'

. modify their model to(include _a calculation of the' highest Ltemperature ; response'over a range of linear heat. generation

- rates.and. axial elevations. The' highest metal-water reactions

' for,.each' linear heat: generation rate is then integrated cver the entire, core using a core power distribution.- The power distribution used for calculating metal-water reaction -

is that which y. elds the highest core wide metal-water. reaction.

The _ staff finds this method adequate.

The' Babcock and' Wilcox method for ' calculating the1 total-

' energy.: release has been medified-to reduce the cladding oxide

' thickness'upon rupture.' The oxide is thinned on' both' reacting.

surfaces; consistent.ith".the cladding wall thinning which occurs.

~at rupture.. This -modification is. acceptable to - the : staff..

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4 4.2 Swelling and Ruoture of the Cladding'and Fuel Rod Thermal Parameters

The Status Report accepted.the use of 70% circumferential

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swelling for; rupture temperature above-1700 F.

To prevent cal-culational instabilities. resulting from this restriction, Babcock and.Wilcox-has ' proposed to use a circumferential swelling which.

- begins at their 1700 F value (less than 40% circumferential o

swelling) and increases. linearly to the 70% plateau at 2000 F.-

This approach does not underestimate the degree of swelling and is acceptable.

Babcock and 'Wilcox now calculates the internal fuel rod pressurefin CRAFT 2'(BAW-10092).

Their calculatien employs a variable internal volume process instead of the constant internal.

' pressure assumption previously used. The volume of both plenums eand'.the gas flow paths are accommodated. Their calculational scheme?is acceptable.

Th'e Status Report restricted the initial assumed internal pin pressure to'the maxjtum pressure predicted during normal

- operation' for the design being analyzed. Babcock and-Wil;ox had;previously used 'the end-of-life pressure which bounded all values. ' Recently, Babcock and.Wilcox performed a sensitivity

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study using calculated. internal pin pressures 'and interpolated

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- oxide' thici: ness. Babcock and Wilcox used their approved thermal performance l code.(TAFY) to calculate an initial pin fpressure1(for 'the LOCA) Las a function of exposuru.

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<; g J.e pressure used in ' the sensitivity study - exceeded. the maximum o

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The initial oxide thicknesses w' re based upon e

' measured" values plotted as a function of exposure.

This is an

acceptable asseanment of the combined effects of pin pressure and oxide thickness. The resultant calculated peak cladding temperatures yielded the conclusion that 'the value of the pressure

combined with the' value lof the oxide thickness used by Babcock and WilcoxL in their current model conservatively predict the

' highest. peak cladding temperature.

Also, Babcock and Wilcox has recently proposed to incorporate a calculation for plastic' swelling prior to rupture in both their CRAFT 2- (BAW-10092) and THETA 1B.(BAW-10094) codes.

A limited amount of information has been submitted to the staff and a more

-thorough followup with~ this material is expected.

On a preliminary ' review, it appears that the Babcock and Wilcox calculation adopts the same ' formulation used-by the staff in

-RELAP-4EM (WREM, October 1974). On this basis, the modification

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would comply with this aspect of Appendix K.

4 3 1.1~ Break scectrum

< Page 4-20 indicates that ~ the staff requested furthe; information-2 Lon the'O.5 fts break. This material was provided by Babcock and

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Wilcox.= ~ The staff'c'onsiders the range of break sizes analyzed to be acceptable.

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' 4.~3 1 3; Endtor Blowdown.

(a)I Pdce 4-22. - No new information has been. submitted by Babcock and Wilc 1x with regard to the alternate use of zero

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break flow' to determine end-of-bypass. The staff's positior.

is that.the time of end-of-bypass must be calculated solely on

'the basis.of the threshold-model.

(b)

Page 4-22.

Babcock and Wilcox has presented a justifi-cation of droplet size for their end-of-bypass prediction.

This

. justification has been reviewed and the 1/8-inch diameter droplet used in the threshold model is acceptable to the staff.

(c)

Page 4-23 Babcock and Wilcox has verified that the mass and energy removed from the downcomer is ' lost from the systemi fer the purposes of the -blowdown calculation.

(d)

Page 4-24.

Babecck and _Wilcox has recently provided

' additional material to justify the downcocer noding representation.

. These-sensitivity studies compare the differences in analytical

-results between a heterogeneous downcomer and a homogeneous

- downcomer...The staff has examined this material and has studied t

relevant'; experimental' data; however, the staff remains unconvinced "that the: assumption of a heterogeneous downcomer is appropriate, and_a-homcgeneous noding representation is required in the

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- downcomer forc large. breaks. :

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~ Momentum Ecuation-u

AsLindicated-on page-4-29, the momentum equation used by Babcock.and Wilcox was. ound to' be acceptable except for the f

'foll$ wing terms which needed additional' support:

Term 2--Momentum Convection Term 3--Area Change Momentum Flux Term 6--Pressure Loss Resulting from Area Change

. The staff has reviewed.the data submitted by Babcock and Wilcox on pressure loss resulting frcm area change (Term 6 above). The pressure loss resulting from. area change

. is based on both an analytical model as described by Babcock and Wilcox and measured plant data.

The total system resistance is within 5% sof the measured values and vessel pressure drop is within 1/2% of the measured values. We find this analysis acceptable.

For momentum convection and area change momentum flux terms (Terms 2, 3 above),'no additional information has been received in support of their application in the Babcock and Wilcox model.

- However, the staff has performed sensitivity studies on various representa'tions of the momentum equation.

Although the form of the Babcock and _Wilcox equation. is not exactly

. thatiderived by; the staff, we believe that the sensitivity

. studies performed by the -staff encompass the Babcock and Wilcox model. On the. basis of these sensitivity studies, we conclude

' th'at, the! Babcock and.Wilcox treatment-of these terms results

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' in an acceptable momentum equation.

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Core' Flow Distribution During Blowdown Page 4-35 of the Status Report discusses several areas

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4 1which required further documentation by Babcock and Wilcox.

The unpublished ' report referenced by Babcock and Wilcox with regard to their crossflow correlation will be made an Appendix

-to topical' report BAW-10092. This is acceptable to the staff.

Also, additional. information was recently submitted on each

'of the remaining items. This material was reviewed by the staff and found to be acceptable.

4.4.2

-Containment Precsure Page 4-41 states that input assumptions to the containment backpressure calculation must be justified fo'r the categories of plants-other than Oconee Class. The Regulatory staff will-

verify these parameters on a case basis (see Section 1.2 of

this Supplement).

4.4 3 Calculation of ~ Reflood Rate Page 4-51 indicates that additional information has been requested of. Babcock and Wilcox to' allow the staff.to complete: the evaluation. - This information has been provided and reviewed by the staff. The following comments relate.to.

the. subparagraphs of Section 4.4 3 2 in the Status Report:

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Nod'ing In' general, 'the small number of nodes'is appropriate for the

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relatively. slow moving reflood phenomenon. Any points of concern,

.such as'the node representing the upper annulus of the downcomer,.

~are discussed balov and rouaC s*H_a facte"y:

1-T B..:The Conservation Ecuations The-assumption with regard to integration of the momentum equation is acceptable in regions where the density variation is

'small relative to the' area variation or regions of small pressure

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..-During reflood, these conditions can be censidered to

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. apply and the assumption is' acceptable.

Wit h regard to '.the containment backpressure ' assumption, a constant.ressure-is not used to calculate leak-' flow.. A variable containment pressure is. calculated.by the CONTEMPT code-(see Section;4.4.2 in 'he Status Repert)'.-

t Babcock and Wilcox has indicated that vent valve. resistance was' measured over a range of Reynold's numbers which is applicable-

.to anticipated flows,' and that the flows are never at the critical value. -

The remaining. assumptions in this section are also.

' acceptable.

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,;This calculation-is done according-to standard practice and is~ acceptable -to: thej staff.

1 D.

Core Heat Transfer All assumptions _used in this section are appropriate.

7 E.

Steam Generators In larger. breaks, the two-phase mixture passing through the

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-the. steam generators is completely evaporated and superheated.

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Hence,:the ' assumptions used by Babcock and Wilcox are-not si=portant to the'reflood calculation and are satisfactory for this' purpose.-

4 F. -Primary MetalVHeat Release L A sensitivity study conductedfby Babcock and Wilcox

~(BAW-10091)-indicates that the assumptions are conservative and.are,'therefore,1 acceptable.-

G. :The;ECC'Iniection System LThe1 assumption.that the cover" gas vents to the. break with no Jsignifican'tieffect was' supported by a REFLOOD. calculation idemonstrating(th'at; aL 3-second oscillation in the flooding rate

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y; (occurs when the gas ; enters the~downcomer. Otherwise, no difference-

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[is]predicte'd to'occu4.. [.The following effects, which were not

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jand'Wilcoxidtu*ing correspondence with the staff:

(1) :The nitrogen is addedito the vapor which is' venting' y

..t from:.the -upper plenum. ': This increases-the gas velocity around 4

the; upper portion of the downcomer and the potential for. entrainment.'

'. Babcock and Wilcox has ~ considered the: resulting velocity and Lits effect on entrainment and the reflood rate. When the 4downcomer is: filled to the break elevation, the maximum velocity

' reaches 200 ft-per-sec. and the entrainment becomes significant.

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However, the. ECC water. is-dumping - to containment at this point,

30 there is no resulting reduction in the reflood driving head..

L(2): Dissolved 1 nitrogen will separate out = of solution--

iwith[ time,astheECC:waterpassesdownthedowncomer;andup Ithrough the. core.. In.the ' absence of ' definitive experimental results, several! experts onl thisisubject -have' been consulted

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. and the staff requested that Babcock and Wilcox consider the following: assumptions :

S(a) initiially, th'e accumulator water is to. contain' an

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equilibrium concentration of.' nitrogen.-

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i(b) at:. every point in the' course of its travel -to. the injection -

point, into'the reactor pressure vessel, andLdown the

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.in1 equilibrium as determined:by-the local water

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temperature and ~ pressure.

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c(c) on'this' basis, nitrogen. separates from the injected water:in the downconer as it is heated up by wall heat

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and will subsequently rise.to the upper annulus of the

'downcomer.

' Babcock and Wilcox has investigated the 'effect that these assumptions:would have on -the density of the ECC water in' the downcomer (and, therefore,- the effect on the reflood rate).

Since their: calculations showed less than a 2. percent decrease in density, Babcock and Wilcox-does not consider the overall eff'ect -to be significant enough to _ warrant.a model change.

. Based on the results of-these calculations, the. staff accepts the Babcock and Wilcox position that the' nitrogen effect upon reflood is;not'significant.

H.:-Carryout Rate-The'CRF3 correlation is-acceptables. The manner l

- in which'it is applied in REFLOOD is also acceptable to the

- staff. However,.a concern was raised regarding the resulting

- two-phase -velocities ' and the possibility of critical flow

--thr,ough the ; vent.. valves. Jhis point has been covered in part B of,thisfsection.

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I.. Flow Path of the ECC Water '

AlI assumptions used 'in' this section' are -appropriate.

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Sensitivity Analysis

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It hasibeen established that-.the _ purpose of_ the' study in which the. quantity of: primary metal was. reduced to half itt reference.value was to demonstrate the effect.on the-peak clad'

. temperature of the-primary metal heat release rate.

This-accounts for the conclusion referred to in the part J(a)'or Section 4.4 3 2 in'the Status Report.that the use of nucleate. boiling for the. primary. metal heat model.is appropriately conservative.

-K.

Inout into the REFLOOD Code As. discussed in part B of this section, the containment pressure :is not a constant input value; it is calculated by the CONTEMPT code. No other concerns remain in thisc area, but to point cut.that the input must.all be' justifiable (see Section 4.4.2 of this Supplement).

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g 141 4.4.4 Steam Interaction'with Emergency Core Cooline Water in Pressurized Water Reactors

[(a)

Page 4-52 indicates that.further justification for loop: venting-was required for raised = steam generator plants.

Babcock and_ Wilcox' has submitted additional material to justify

' the reflood loop resistance factors assumed in their analysis.

-U (This material was reviewed by the-staff and is acceptable as

. typical values for raised loop plants. Additionally, Babcock and Wilcox has been requested to present reflood loop resistance factors on a ' case-by-case-bAtsis.

-(b)

On page 4-53 of the Status.Repert, the staff stated that until more information becomes available on the hot wall

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effect, Figure -30 of the technical note "Effect of Hot Walls on Flow in a Simulated ' PWR Downcocer During a-LOCA," TN-188,

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.May 1974, by Dr. James A.. Block and Dr. Graham B. Wallis, should be used. - The staff accepts hot wall delay times taken 15 frem the-- t ot (RS) line of Figure 30 of this report. This d

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position has not. changed.

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-The staff position is that there are. two separate effects.

'that couldLdelay ECC delivery to the core:

(1) transport time

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' travelDtime of ithe ECC water from the' injection point or from

'the cold legs to the--lower plenum.

The transport time can be

calcul'ated ; assuming free fall under gravity.

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Hoi walls, 'as it has lbeen demonstrated experimentally,

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Once the conditions for-

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penetration exist, the accumulated water is free to flow down

to the lower plenum.' -This phenomena would result in an increased.

= lower plenu.n refill time only if the storage capacity of the system 'is not-sufficient to hold the accumulated ECG water.

10therwise, there.is no effect on refill or on peak cladding

-temperature.

(c) l The staff stated in the Status' Report (page 4-54) that the Babcock and Wilcox vent valve flow resistance factor

' of K=3 9 was under review. Babcock and Wilcox has been supplied information contained h1 "Overall Calculational Methods For TVo Phase-Flow," by Peter Griffith..Two-phase flow resistance

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factors. as calculated from _ equations I-17, I-18, and I of 4

this publication, with a -value of _C=15 for gate valves, are acceptable to the staff. Due to the pressure-dependence of of "C", Babco'ck and Wilcox is -permitted to make appropriate correction-fo.' pressure _ effects.

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-4.4 5-Refill 'and Reflood Heat Transfer (a)

Page' 4-55: imposes a 0.8h for _17 x 17 geometry cores until additional.information is available. Babcock and Wilcox

- has' indicated that. they will adopt this limitation untilf they are:able to establishLthat a different.value is proper.

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-(b) - - Page.4-56 indicates that additional information is required for flooding rates less than one inch per second.

Babcock.and ~Wilcox has agreed to. submit this.information lLn a timely. manner. - -Since flooding rates calculated by Babcock and Wilcox to date are greater than one inch per second, this

~ limitation has - no' ' ffect on the current. calculations.

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.o 50-SMALL BREAKS

~ Pages 5-2 3,.and 5-4 suggest that the current Babcock and Wilcox small break model does not -incorporate an end-of-bypass model.to calculate ECC entrainment. A more accurate description-would be that the small break model does ' include an end-of-bypass

. model,:however,. since bypass is not calculated to occur, the

.threshol'd model plays no-part in entraining ECC water.

6.0 DOCUMENTATION The code listings referred to on' page 6-1 of the. Status k

-Report are currently:in a locked file :in Lynchburg. Regulatory

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staff; personnel'have sole access to the contents of this file.

^ Babcock and Wilcox has agreed to ' arrangements for these co'de I);

Llistings to 'be transferred.to the-Regulatory staff in

.7 Ei Bethesda,~ Maryland.

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ERRATA

,1. - TABLE OF CONTENTS!

Correct-the fbilowing section. page numbers in the Table of Contents:

4.1 7................................. 4-13

~4.2.....................s............. 4-14 4 3................................... 4-19 431.................................4-19 4 3 1.1............................... 4-19 4 3 1.2............................... 4-20 4 3 1 3............................... 4-21 7

4 3 1.4............................... 4-24

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432.................................4-27 433.................................4-28 4 3 4................................. 4-29 4 3 5................................. 4-30 436.................................4-31 4 3 7................................. 4-33 6.0................................... 6-1 2.~ - Page 1-6, last paragraph,. first sentence.- Change "eif.st" to "seven".

. 3.' Page 2-1, first paragraph.

Revise the sentence, "The CONTEMPT code is used to...for.the small break analysis" to read, "The CONTEMPT code is used.to initialize REFLOOD with a conservative backpressure

' calculation and the ~ code FOAM is utilized to calculate swollen water. level fbr the ~ small break analysis."-

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Page'2-11,last(sentence.. Change " Criterion (3)" to'" Criterion (4)."

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.-5 1Page 3-1, first sentence. Change "Oconee Unit One" to "Oconee Class."

6.. Pagef 3-2, second paragraph. Change "Oconee~ Unit One"'to "Oconee Class."

7.:: Page, 4-1,. firstL sentence. Change "Part III of the.new rule" to

~ " A'ppendix~ K' to 10CFR50."~

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- 8..Pagei4-44,-subparagraph B.

Insert the werd " steam" before the word

" elevation" to read,~"The steam elevation-pressure drop in the loops

' (both broken and unbroken) is neglected."

.9. 'Page'4152,'last paragraph.

Revise the two sentences,"One portion of

'the'...from the lower -plenum"; and, "There are only three..,.the data range."

to' read, "One portion of the Babcock and Wilcox argument centered '

around only three' data ~ points with regard to credit for venting."

110.

Page 4-53, second paragraph. -Proportionality' symbol should be inserted as

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11.. Page.4-54,: first paragraph.

Revise th'e sentence, " CRAFT makes 4

corrections'...of the flow.".to -read,

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- " CRAFT makes corrections to this value for homogeneous fdensity."

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