WSRC-RP-93-599 c - CoUF- P+06 or--a)L,

DEFLAGRATION ANALYSIS OF THE ITP FACILITY UTILIZWG THE MELCOR/SR CODE (U)

by D. K. Allison

Westinghouse Savannah River Company Savannah River Site Aiken, South Carolina 29808

S. Chow

.J

A document prepared for 1994 AMERICAN NUCLEAR SOCIETY ANNUAL MEETING at NEW ORLEANS, LA from 6/19/94 thru 6/23/94.

DOE Contract No. DE-AC09-89SR18035

This paper was prepared in connection with work done under the above contract number with the U. S. Department of Energy. By acceptance of this paper, the publisher and/or recipient acknowledges the U. S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper, along with the right to reproduce and to authorize others to reproduce all or part of the copyrighted paper.

WSRC-RP-93-599 Revision 0

NUCLEARREAcMlRTECHNO~Y AND SClENTIFIC COMPUTATIONS

KEYWORDS: COMPUTER CODE COMBUSTION IN-TANK PREClPITATION

RETENTION: PERMANENT

Deflagration Analysis of the ITP Facility Utilizing the

MELCOWSR Code (U)

D.K. Allison and S. Chow

July, 1993

Westinghouse Savannah River Company Savannah River Technology Center Aiken, SC 29808

DISCLAIMER

This report was prepared as an account of work sponsomi by an agency of.the United States govern men^ Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or impl ie or assu~pcs any legal liability or .-responsibility for the accuracy, completeness, or*ustfulncss of any idomtion, apparatus, product, orproass dkcIosed,.or represents that its use would not infiringc privately owned rights. Reference h d m to any specific commercial product, process, or scryiCe by trade name, . trad&nark, manufacturer, or otherwise does not neccssatily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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Task Number: SRT-SAE-93-8002

Documcnt WSRC-RP-93-599

Title: Deflagration Analysis of the ITP Facility Utilizing the MELCOWSR Code

, Oa/VLc./.k Q Q L m L 7-78-Q 3

D.K. Allison, Author Dale

U Z / p Y Dale

*& S. Chow?Author

%-I-% Dale

- 03 At46 93 eer, Facility Perfonnance Analysis Dale

% L z d 9( 3 /cy? LA. Wodten, Manager, SAES Dale

fG 4 J k / A4:H M.J. Hikhler, Mi& ger, STS

WSRC-RP-93-599

ABSTRACT

Under certain accident conditions, waste tanlrs in the In-Tank piocesSing f w may contain SignificantcoMxatrationsof~andhydrogen. Becausethesegasesa~efiammabk,asafety analysis was required to demonstrate that the risk posed by tkpossiblecombustion of these gases is acceptable. In support of this d y s k the MEXOWSR computer code was moditied to simulate thecombustion of benzene-hydrogen mixtures,

MELCOWSRwasdeveloped~~ytosnalvzescveffaccidentsthatmayoccurintheSRS production nactozs but many of its modules can be used also for non-reactur applications such as combustion and aerosol and radionuclide transpoIt 'Ibe MEXCOWSR combustion model (package) was originally d g u d for the w o n analysis of hydrogenarbon monoxide mixtmx. With minor changes to the coding in the combustion pachgesubutina, and the addition of benzeae thermodynamic and transport properties to the input decks, MELCOWSR was m o d i f i e d t o a n a l y p e d e € h g d o n s i n ~ h y d r o g e n g a s m i x ~

A MEIX30WSR model was created consisting of two cuntrol volumes cmmcted by flow paths. One volume mpnsents atypemwaste tank; the other, theenvimment. The flow pathsmpment vents that open during the -on. Choked flow and radiative heat transfer from the hot gas to the cooling coils and tank walls aze phenomonalogical aspects aamnted for in the mod&

Results fioxn MELCORISRCompared favorably with Fesults from two other codes: COMPACT, a codesimilar to MEKORBRusedin the preliminary ITP analysis and DPAC, a& developed specifically to analpcleflagrationsin SRS waste tanks. Peakpnssuxespdictcd by MEKOWSR (and by DPAC) for reatistiC waste tank conditions do not exceed tbe presswe required to fail the primary liner of the tank (- 23 psig).

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WSRC-RP-93-599

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TABLE OF CONTENTS

1.0 INIRODUCTION

2.0 THEORY

3.0 MODEL DEscRIIrIzON

4.0 RESULTS: UELCOWSR VS COMPACT

5.0 RESULTS: MEulowsR VS DPAC

6.0 CONCLUSIONS

7.0 REFERENCES

3

5

12

14 -

16

17

18

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. WSRC-RP-93-599

1.0 INTRODUCTION

"le purpose of the In-Tank procesSing (rrp) facility (&em= 1) is to decontaminate salt solution ~vedfiomtheseparationsfacifities.~ntaminat;onisaccompIishedusingabatchprocessin existing waste tanks dedicated to that purpose, The most abundant radioactive species (-137) is precipitated with sodium ktraphenyllborate. Other species such as Sr-90, U, and Pu m adsorbed on sodim titanate particles. The pmipitatefiom this process is Sent to the Defense Wasre processing Facility (DWPF). The decontaminated salt solution is sent to the Saltstone facility.

Under OtRBiZl accideat conditions tbe primary lTP piocessing tank (tank 48) and the tank into itate is placed prior to shipment to DWm; (tank 49) may -rain gaseous mktmx

involving whicbthe3 si cant amouuts of and hydrogen. Bezause and hydrogen axe flammable, analysiswasrequiFed to demonstrate that the* posed by the combustion of mixaxes of these gasesin tanks48 and49is acceptable. 'Ihis risk was calculated fromestimates of tbe probability of ocmmncc of a deaagration coupled with estimates of matcriatreleases derivedfrom calculatons of the eJIpected owqmssm and the expected tankstmctml nxponsc.

A pvious analysis (refemme 2) by personnel at tbe Nuclear Advanced Technology Division (NATD)ofWestinghouseusedthecomputercodcCOMPACTtocalculatttht~p~ resulting from the deflagration of hydrogen or b e n m ~ within tank 48 or 49. COMPACT is a g e d purpose themal hydraulic code developed to predict the response of the containment of a nuclear plant during postulated severe accidents. It approximates a physical system by a network of control volumes and flow paths.

A modeling program was initiated at the Savannah River Technology Center (SRTC) to dine the COMPACT analysis and to bring the capability of doing such analyses to SRTC. Two methods were employed The &st involved the development of a relatively simple, stand-alone code for simulating a deflagmtion in tank 48 or 49. The Defhgration Fbsm Anatysis code @PAC) (=fexences 3 and 4) tracks the mation of hot product gas as a volume expanding against a volume of cold reactant gas. The model includes radintive heat transfer from the hot gas to surfaces within the tank and the change in volume and energy xesulting from dehnation of the tank inner liner. The vent model is based on choked flow and becomes active at a specified ovezpmsum (the overpmme requited to open the vents in the top of the W).

The second method of calculation involved MELcOlUSR, a oode that m a y features with COMPAm. MEICWSR (references 5 and 6) isacomputercode developed to analyze sevete accidents in the SRS production re8ctws. Tbe MELCOWSR comb\lstioI1 model (package) was originally configwed for the deflagration analysis of hydmgen+a&on monoxide mixtunzs. With minor changes to the coding in the combustion package subroatiaes, and the addition of benzene thennodynamicandttansportpropettieStotheinputdec~MELcOwSRwasmodihedto~~ deflagrations in m e - h y d r o g e n gas h.

Like COMPAm, MELCONSR uses control volumes and flow paths to =present the physical system. The MELCOR/SR model employed b is identical to the COMPACI' model with respect to the n u m b of control volumes: om control volume is used to represent the waste tank; another, the environmm~ The COMPACT model a p m t l y represents the vents by a single flow path connecting the two control volumes. For ease of treatment, the h4EKOWSR model qresents the vents by a variable number of flow paths. nle MELCOWSR model includes mdiative heat transfer from the gas within the tank to the tank walls and thecooling coils within the tankwhereas the COMPACI' model does not The MELCOWSR model includes a trip to Simulate lift off of the risers (which prov ide venting) at a certain pressure. The COMPACT model assumes the risers lift off at the beginning of the pressure transient. These last two featuFes make the MELCOWSR model more realistic than the COWACTmodeL

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WSRC-RP-93-599

. The primary diffenenct baw#rr the MELCOIWSR deflagration model and DPAC lies in the manner in which the flame h n t is modeled. In the single tank volume MELCOR/SR model, the pasition of the flame f b t is contmlkd by a function that can depend upon a number of physical

t analysis assumed a constant speed of propagation. parameteas. In thein-of -the Two tank volumes are tracked in the D AC model: an expanding hot product gas volume and a compressed reactant gas volume. The flame front, driven by the expanding hot gas, dcaascs in speed as the deflagration &resses. The two-volume model used in DPAC, compared to the srngle volume model 2 MELCOWSR, &xmases the calculated overpressu~e by inmasing the radiative heat d e r to the walls and cooling coils and by increasing the verrting rare. 'Ihe changing flame front velocity inherent in DPAC also affects the calculated overpressum in a way that depends on the total burn time.

r=

other minor d i f f ~ ~ exist betwleea MELcowsR and DPAC, the most notable of which is the tmatment of venting under a condition of non-chaked flow. MELCOWSR tnursitions from choked flow to a nan-choked flow model when the flow velocity xeaches a certain valw. DPAC does not have a model for non-choked flow. This difhznce between the two codes is apparent primarily at low flame speeds when the peaL ovtlp~cssu~t is close to that q u i d to open the vents.

Ihe intent of the analysis described in this repoit was to duplicate and extend the previous analysis done with COMPACT and to confirm d t s obtained with DPAC. The n u m k and name of the runs done withMEL,COR/SRwuedetarmned in large part by the COMPACT and DPAC analyses. MELCOWSR was used here in a codhatory role because, unlike DPAC, it has not been formally d k d . MELCOR, the code upon which MELCOWSR is based, has undergone extensive validation and vexification (see, e.g., refmce 7). In particular, the control volume and flow path packages have been tested on a variety of problems, MELcoR/sR including modificationstothecombustionpac~describadinthisreport, iscurmtlyun&r@nga pmgram to certify it for use on problems involving deflagrations. Until cdfkatim 1s completed, &ts from MELCOWSR for this application must be consi- to be confirmatory or scoping in name.

4

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2.0 THEORY

WSRC-RP-93-599

The computer code, MELCORfSR-MODQ (5/2lf92), was modified to include benzeae as a mmbustible gas. a typical deflagration p b l e m , the following models (packages) a , ~ ! used: BUR (combustion), CVH (control volume hydrodynamics), FL (flow path), HS (heat sink), NCG (non-condensable gas), and MP (materiais package).

Only the BUR package was required to be modified. The last version of BUR, MH, was modified on Zf24#2. 'Iht modified version which includes benzene combustion is designated BUR v d o n NA.

2.1 BUR Package Modifications

Twelveofthe44submu~assoclated withtheBURpackage~modified,Thisincluded adding the mass balance for the benzeaehydmgen chemical xeaction with air* and modifying the ignition, bum completeaess, and propagation criteria. The deflagration model is desded in the

2.1.1 Chemical Reaction Equations

following scctioIIs.

T h e B U R p a c l r a g e i s d e s c r i b e d i n t b e M E L C O R ( S R ~ ~ ~ M a n u a l ( ~ ~ 6 ) . B U R v ~ o n MH only models combustion of hydrogen and carbon monoxide. In addition to the hydrogen combustion maion,

I 2

H2 +-02 + H20 thebenzenecombustionmction,

15 2 GH,+-OZ +6Cq+3&0

was added to model combustion of benzenehydrogen gas-mixture&

2.1.2 Ignition Criteria

The Ldhtelier's formula for hydrogencarbon monoxide was modified for benzene-hydrogen. Themixturewillignitewhen

WlleE, = Benn?ne mole fraction in control volume. = Hydrogen mole fraction in control volume. = XCHIGN, if there is no igniter in the volume, or = XCHIGY, if them is an igniter in the volume. = XH2IGN, if there is no igniter in the volume, or = XH2IGY, if there is an igniter in the volume.

xw. XH*

L,,

Lwm

XCHIGN= L K h a t e h hemme mole fktion limit for ignition without igniters (Code input variabk).

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WSRC-RP-93-599

. XCHIGY = LeChatelier benaene mole W o n limit for ignition with igniters (Code input variable).

XH21GN = LeQateiier hydrogen mole M o n limit for ignition without igniters (Code input variable).

XH2IGY = Lechatelier hydrogen mole fraction Limit for ignition with igniters (Code input variable).

The above tests a ~ e used only to test the presence of s d i c h t combustible gases. Tests are also made to determine if there is sufficient oxygen and to determine if the amount of steam and carbon dioxide is below the inerting limit The Same values are used when igniters are present as when there are no igniters. The tests are

X H P + X , < XMSCIG

where,

= Oxygen mole fraction in control volume.

= Carbon dioxide mole fraction in control volume.

x02

x, 'H20 = Steam mole fraction in control volume.

X02IG = Minimum oxygen mole fiaction for ignition (Code input variable).

XMSCIG = Maximum diluent mole fraction for ignition (Code input variable).

If al l three tests are satisfied, Le., enough hydrogen and benzene, enough oxygen, and not too much steam and carbon dioxide, a burn is initiated.

2.1.3 Combustion Completeness

MELCOWSR defines the burn complete.ness as:

CC= l-Ymidy,m

where,

cc = Combustion completeness.

Y

= Value of =atelier formula evaluated at the start of the bum (initial amount of combustibles).

= Value of LeChatekr formula evaluated at the end of the burn (fmal amount of combustibles).

The LeChatelier formula For benzene-hydrogen, =

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WSRC-RP-93-599

. XCHCC x +-x wo XH2CC

XCHCC - LeChaeW benzene mole fnrction fm caldatm gcombustion - completeness (Code input variable).

xH2cc = LeChateEer hydrogen mole fraction forcalcularing combustioII completeness (Code input variable).

The combustioll completeuess can be input as a constant value, calculated fiom a user specifid control function, or calculated from a cordation for hydmgen-carbon monoxide gas mixtwes . Far bemae-hydmgen gas mixtures, the COfielatioIl option is not valid. Therefore, the user must input a constant value or specify a contml function. For tbe pnsent analysis, complete combustion was assumd

Once the combustion completeness is specific& Y is forthedenaerationinthe control volume, The burning rate (Section 2.15) bgjusr-OWSR as mxessaq to achieve this value at the end of the burn.

2.1.4 Bum Duration . The burn duration is d- by dividing a user specified charactenstrc dimensionbytheflame speed, i.e.,

mIM= charactens tic dimension of control volume, m.

The flame speed can be input as aconstant v a c a k u b e d from auserspecified control function, or calculated from a correlation for hydmgemcarh monoxide gas mixtures. For benzene- hydrogen gas mixtms, the amelation option is not valid. Tbemfore, the user must input a constant d u e or specify acontrol functioa FortheITp tankCDIM waschosen to be the horizOntadistancearound thetauk at the tankcentedhc.

2.1.5 Combustion Rate

The combustion rate is &fined in MELCOWSR as

where,

to = timethatburnwasinitiated,s.

t = c m n t time in calculation, s.

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WSRC-RP-93-599

. 0M.re the rate is calculated, it is used to determine the decnase in the inventory of the combustible gases for the cumnt MEUSOWSR system time step:

DELH2 = XH2 ( t ) * YRATE * DT/ Y(t) DELCH=X,,(t)*YRATE*DT/Y(t)

where,

DELII2 = Decrease in hydrogen moles in volume during time step from

DELCH= Decrease in benzene moles in volume during time step from

burning.

burning.

IYr = MELCOWSR system time step, s.

DELH2 and DELCH are constrained to p v a t buming more moles of either gas than are present in the volume.

The energy of formation is included in the non-con&nsable gas equation of state. With this formulation, simply changing the relative masses of the Teactants and products will automatically result in the appropriate p m and emperam in-. It is not necessary to calculate a combustion energy release to the control volume. Tbe total mass and energy of a control volume axe not changed by BUR, but the masses of individual species are changed to reflect those from the chemical reaction equations of Section 2.1. Because the specific enthalpies of each species properly account for the energy of formation, the convtdon of the reactants to the products increases the tempera- and pressure of the burning control volume, even though the total energy remains unchanged.

2.1.6 Propagation Criteria

Propagation from a buming control volume to a connected control volume is allowed if certain propagation criteria are satisfied and is controlled by a uset specified &lay time. The delay is intended to account for the time it would take for a flame to reach the edge of a control volume if a flame front was actually being modeled. The propagation delay is calculated Erom:

where,

= Propagation delay, s. tProP TFRAC = Propagation time &action (Code input variable).

If TFRAC equals zero, propagation starts as soon as a control volume begins burning whereas if TFR4C equaLs one, propagation starts at the end of the control volume burn. In the present application the propagation of the burn to a second control volume was not allowed.

Propagation is allowed if the following equation is satisfied,

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WSRC-RP-93-599

Where, LG,,,- = XCHPUP for upward propagation, or

= XCHPHO for horizontal propagation, or = XCHPDN for downward propagation,

L w P 3: XH2PuP for upward propagation, or = XH2PHO for horizontal propagation, or = XH2PDN for downward propagation.

XCHPUP= LeChatelier benzeae mole fraction for upward propagation

XCHPHO= Mhatelier benzene mole fraction for horizontal propagation.

(Code input variable).

(Code input variable).

XCHPDN= LeChatelier benzene mole fraction for downward propagation. (Code input variable).

XH2PUP= LeChatelier hydrogen mole fraction for upward propagation. (Code input Variable).

XH2PHO= LeChatelier hydrogen mole fraction for horizontal propagation. (Code input variable).

XH2PDN= LeChatekr hydrogen mole fraction for downward propagation. (Code input variable).

Determination of the propagation dimtion is made directly from the flow package (FL) path input. If a flow path is not open or is covemi by water, propagation is not allowed.

2.1.7 Detonation Criteria

MELCOWSR does not model & t o ~ t i ~ ~ ~ , but does print out a warning message that a detonation can occur in a control volume if detona!ion limits (spedfied by the user) are satisfed. In the interest of time and bezause MELCOWSR does not model detonations, benzene detonation limits were not added at this time. The hydrogen detonation limit V E T ) was set at 1.0 so that this limit would never be met and therefore the detonation message would be suppressed.

2.2 Benzene Properties

Benzene properties were added through input decks for the non-condensable gas package (NCG) and the makrial properties package (MP). The properties entered through NCG are the specific heat at constant volume, molecular weight, energy of formation, and entropy. Thexmal conductivity and viscosity values were e n t e d through the MP package.

Non-condensable gases such as hydrogen, oxygen, nitrogen, already have their properties spedied in the M p package. A new non-condensable gas such as benzene is a user defined gas and is given the MELCOWSR matesial name, GASA, dong with a MELCOWSR material number.

The specific heat at constant volume, Cv, is ented as a function of temperature along with the lowest and highest temperatures between which the -on is valid. For temperatures outside the temperature range, MELCOWSR assumes a constant spec& heat corresponding to one of the end

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WSRC-RP-93-599

points. Cv (in Units of J/(kg K)) is fitted to the following relationship required as input to the. NCG package:

where C d = 459.75, C,1= 3.147132, Cv2= -9.689~10-4, Cv3= 0, Cvqd = 0, Cvm1= 0, and Cm2= -3.3768152~107. The equation is valid between 353 K and 1500 K. Reference 8 was used to derive the coefficients of the equation.

Benzene's (C €&j) m lecular weight is 0.078 kg/moL The energy of formation for benzene is 1. 8 g 31x10 Jkg (derived from reference 9). MELCOWSR does not currently use entropy; consequently, 0 was entered as a dummy value.

For user defined gases such as benzene, the viscosity and thennal conductivity must be specified in the materials properties package, MP. Benzene thermal conductivity and viscosity values from reference 10 wexe entered as functions of temperature through the tabular function (TF) package of MELCOWSR

2.3 Choked Flow Model

A choked flow model is implemented within the flow path (FL,) package of MELCOWSR. After the flow is detemined in the normal fashion within FL the computed flow is compared with a calculated critical flow to determine if choking should be imposed. If the flow exceeds the critical value the entire solution is ~peated with the velocity comtrahed to be the critical value.

The critical mass flux is taken as the sonic flux at the minimum section which, for an ideal gas, can be related to the sonic flux at stagnation conditions through the relation

where G is the mass flux; PA, the gas density evaluated at stagnation conditions; CS, the velocity of sound; and y, the ratio of specific heats, cp/cv. The use of the superscript d indicates that the donor volume in MELCOWSR is assumed to be at stagnation conditions. The speed of sound is evaluated in the CVT package. y is f m d at a nominal value of 1.4.

2.4 Atmospheric Radiation Models

Radiative heat transfer between surfaces of heat structures and contro1 volume atmospheres can be treated in two ways within the heat structure (HS) package of MELCOWSR One option is an equivalent band model:

f 0 for TI = Tu

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with,

WSRC-RP-93-599

where E and a are the emissivity and absorptivity, respectively. The subscripts g. w, gw, 1 and 2 refer to the gas, the wall, the gas at the wall tempemtwe, 1 path length, and 2 path lengths, respectively. The values ofthe gas emissivity and abscnptivity are obtained from the model in CONTAIN ( E f w 11) which is a function of the gas composition including the pressure of w8ttt vapor, CO, CQ as well as ttre user-specified tsAiatinn path h g h .

The other radiative heat transfer option, the one used in the present analysis, is the gray-gas model implematedas

where the gas emissiyity iscalculated for one path length.

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I WSRC-RP-93-599

3.0 ITP MODEL DESCRIPTION

A type mA waste tankis shown in Figurr: 1. The MELCOWSR model has two control volumes with flow paths connecting tbem ( F i g m 2). One volume represents the tank; the other repments the en+nment. Tbe flow paths connecting the two volumes represent the vents that wil l open during the &flagration. Not shown in F i p 1 ~IE approximately 4 miles of 2.375" diameter cooling coil tube&

I

Tbe volume of the tank is the volume within the primary liner (I&" 1) asswning a 4m cfoss section. Tbe volume of the control volume representing the mvironment is given an arbitrarily large valw The pressure of each control volume is put initially at one atmosphere. For the dry air- the tank contains only atmosphexe (no pool). For the best-estirnatecases, the tank contains pool and atmosphexe. The atmosphere within the tank is composed of air and non- condensables (bename andor hydrogen) and a p&bed amount of water vapor. The control volume representing the environment is composed initialy of dry air.

The vents between the tank and the envhnmeat wem modeled with a number of flow paths, each of a m less than or equal to 50 ft2. Thecasesnm tocompare MELCOWSR with COMPACT involved as much as 750 fi2 vent ~ t e 8 For the cases run to compare with DPAC, one agd two flow paths were used for tanks 48 and 49 e v e l y .

A choked flow model is implemented within the flow path package 0fMELCOWSR The critical mass flux is based on sonic flow at the minimum SeCtioIL Choked flow is used only when the pressure withinthetankgreatlyexceedsthepnssure requid to vent thetank.

Heat tmskfiorn the contents of the tank to the wails of the tank and to the cooling cob within the tank was modeled using the HS package of MELCOWSR. MELCOWSR averages physical parameters over the atmosphere and pool of each control volume. Because the model employed here uses a sin@ volume to represent the tank, ptoducts of the combustion of hydrogen or benzene at each time step ue assumed to be homogeneouSy mixed with the mnaining mactants and other gas species within the fnxboard volume of the tank. This tmatment affects the radiative heat transfet between the ptoducts of combustion and the tank walls and cooling coils, the correct ternjmitm for heat transf.. (the temperatwe of the products) is reduced by averaging while thevolume of ti!& radiating gasisimxsed. Radiative heat transfer is under predicted because of the temperamedepenhe of the Stefan-Bolcanann law.

The surface of thecentral~ rumn of the tankwas modeled as theexterior d a c e of acylinder. The interior surface of the outer r;--& wall was modeled as the interior d a c e of a cylindrical annulus. The tank roof (less the vent am) and the water surface wezemodeled as rectangular slabs. The cooling coils weze representjed t 7 t series of vectical cylinders distributed uniformly throughout the tank,

Values of parameters used in the MELCOWSR model ate shown in Table 1.

3.1 Model Assumptions

Several assumptions were made to simplify the problem and to make the problem more aactable with respect to MEL,COWSR A basic assunption is that the tank can be adequately described by a single control volume. This assumption is appropriate because of the relatively large burn times associated with the deflagration and because internal f e a m of the tank, e.g., the cooling coils, are distributed uniformly throughout the tank or munimportant.

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WSRC-RP-93-599

Forthe purpose of c o m m w i t h COMPAm, it was assumed that the ventpathscould be *

modeled as a h of 5Oft2openin~ COMPACX'models the vent paths as asingle opening. The treatments am equivalent for choked flow conditions; a small ~EIW is introduced at Iarge vent aneas which correspond to low peak pressms. For the purpose of comparison with DPAC, the vent path for tank 48 was assumed to be a single opening. For tank 49, the vent paths were modeled as two openings. DPAC uses a single opening for tank 48 and tank 49. The error caused by the dif€emwe in modeis for tank49 isexmmely small.

BecausetheCOMPACTanalvsinassumestheve~tobewmpletelyopenwhenthe~~on c o m m e n c e s , t b e M E L C O W S R m o d e l u s e d t o d y p l i c a t e t h e ~ ~ A C I ' ~ ~ ~ t h e s a m e assumption. This assumption may be appropriate for large overpmsmxw companding to short rise times. In actuality, ventswill begin to liftoff at various overptessuns depending on their weight and area. The DPAC analysis delays the opening of the vents mtilm overpxwure of 13 psig is mhed. The MELCOWSR model used to c o h the DPAC d t s does b w i s e . One aspect of vent liftoff n o t a d d m d by the thrrxmodels is the delay caused by thc inertia of the plugs. The extent to which this omission affm the peak pnssure is not completely clear but is thought to be small.

Although MELCOWSR allows flexibw in modeling the flame speed during a dedagmhn, a constant flamespeed was usedin the present analysis. Aconstantflamespeedisconsisknt with the COMPACI' model but is inconsistent with DPAC. Comparisons between d t s obtained from the MELCOWSR model and those ob- f h n DPAC wexe made on the basis of bum time ratherthanflamespeed.

Finally, complete combustion of all combustible gases within the tank is assumed. As discussed in Thomas and Hensel (reference 4) this assumption may involve SigniEiCant conservatiSm,

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4.0 RESULTS: MELCOWSR VS COMPACT

WSRC-RP-93-599

The first purpose of this w d was to duplicate the COMPACT analysis. The number and nature of the runs discussed in this section were determined to a large extent by the COMPACT analysis. To simulate the COMPACT analysis, radiative heat transfer in the MELCDR/SR model was disabled and the vats were opened at the beginning of the deflagration.

4.1 Hydrogen Deflagration

The first series of runs were done with stoichiometric hydrogen. The peak pressure versus vent area is shown in Figure 3. These calculations were done with an extremely high flame speed and a tank half full of solution. Far high vent areas the peak pressure predicted by MELCOWSR is lower than the peak pressure predicted by COWACT. For low vent areas the peak pressure predicted by MELCORBR is higher than the peak pressum predicted by COMPACT. The two codes give similar results at - 30 ft2. The vent area for tank 48 is 27.15 ft2 (reference 12). These calculations (COMPACT and MELCOWSR) were perfomed without considering radiative heat transfer to the walls and cooling coils within the tank.

4.2 Benzene Deflagration

A pressure profile generated by MELCOWSR with stoichiometric benzene is shown in Figure 4. his profile was generated for the case of 50 ft2 vent a m . A comparison of this profile with a profile generated by COMPACT (reference 2) under the same conditions shows the peak occurring at roughly the same time for both codes. This result is expected because the same flame speed was used for each run and the peak occurs at the point when all combustibles within the tank are burned. The peak pressure calculated by COMPACT, however, is greater than the peak pressure calculated by MELCOWSR for this case. The COMPACT profde is almost linear for times less than - 0.5 s while the MELCOWSR profile dccrcases substantially in slope far times less than - 0.5 s. The initial slope of the MELCOIUSR profile is similar to the initial slope of the COMPACT profile. For times greater than - 0.5 s the MELCOR/SR p f i l e starts steeper and flattens sooner than the COWACI' profile. Both profiles are flat when the pressure within the tank reaches atmospheric.

For vent areas greater than 27.15 ft2, less material is being vented in the high pressure region of the COMPACT profile than in the high pressure region of the MELCOR/SR profile. This is consistent with the peak pressure from MELCOJVSR being less than the peak pressure from COMPACI: This effect might be caused by differences in the flow path models.

Figure 5 shows a profile generated by MELCOWSR for the same situation as shown in Figure 4 but with a vent area of 10 f?. Qualitatively, this profile more closely resembles the COMPACT pmfile (reference 2) than does the profile generated with a vent area of 50 ft2, especially for times less than - 0.5 s. It is difficult to make a valid comparison for times greater than - 0.5 s. The MELCOFVSR profile at 10 ft2, however, has a peak pressure above the peak pressure predicted by COMPACT. The cause of differences in the shapes of the profiles in Figure 4, therefore, is probably not the cause (at least not the whole cause) of the difference in the peak pressure for the profiles shown in Figure 5.

Other possible causes of differences between the COMPACT and MELCOR/SR results are the properties of the reactants and products of the combustion and the treatment of heat transfer between the pool and atmosphere within the tank.

A comparison of MELCOWSR and COMPACT with respect to vent area for stoichiomemc benzene is shown in Figure 6. As with hydrogen, the peak pressure calculated by MELCOWSR is

-14-

greatezthantbe peak pressue calculated by COMPACT for small vent amas but is less than the peak pressune salcuiated by COMPACT for large vent areas. 'RE cross-over point is -25 ft2.

The effect of tank freeboard volume as calculated by MELCOWSR and COMPACI' is shown in Figure 7 forstoichiometrlc benzene. The MELCOWSR results 8ce consistently lower than the COMPACT results. ?he effect of tank fheboard volume for benzene at the lower flammability limit is shown in figure 8. The MELCOWSR resultr am lower than the COMPACT d t s except at the largest k b o d volume A (0.25 fill fraction).

The effect of chauging th: turbulent multiplier is shown in Figure 9 for stoichiometric benrene. The multipliers a r ~ based on a multiplier of 10 giving a flame speed of 140 ft/s as in reference 2. The peak pmmm calculated by MELCOWSR isconsistently less than the peak pressum calculated by COMPACI'. Thedif%mcedecFeases as the flame speed hxeass. Similar behavior is shown in Fi- 1OfOrbenzeae at the lower flammability limit

-1s-

WSRC-RP-93-599

5.0 RESULTS: MELCOWSR VS DPAC

The second purpose of this work was to ~ ~ I l f t R l l results obtained with DPAC. Cases were m for conditions expected in tanks 48 and 49. These cases included various gas compositions, fill lev&, and flame speeds. All comparisons were made on the basis of equal bum times.

5.1 Air Mixtures

Comparisons were made for two sets of calculations. The values of important parametem m obtained from reference 4. The first set of calculations were done for mixtures of b n e , hydrogen and air. Conditions and results are shown in table 2.

MELCOWSR predicts a lower peak pxtssm than does DPAC for cases in which the peak presswe only marginally exceeds the pressme required to open the mts. This behavior can be traced to the absence of a flow model in DPAC for non-choked flow. MEICORBR pdic ts a hi- peak pnxsmthau does DPAC for cases in w k h the peak pressme substantially exceeds the presswe requid to open the vents. These cases !tsultin relatively high product gas temperatms and theaefore b the heat transfer and venting rate in the tw+vdume model @PAC) d v e to the one-volume model (MELCOWSR). As a result the pressme predicted by DPAC for these cases is lower than the pressure predicted by MELCOWSR For the low p m (and low tem@ratwe) cases the absence of a flow model in DPAC for non-choked flow do- the difkeaces in beat transfer and venting whereas, for the high p s s m (aud high temperatme) cases, the differences in the heat transfer and venting d ominate the absence of a flow model.

5.2 Inerted Mixtures

The second set of calculations wexe done for compositions which included water vapor and more nitrogen than would be pxesent if air were the only sowe of nitrogen. All cases except 7.1,7.2, 8.1,8.2, 13.1, 13.2, 14.1, 14.2, 15.1, and 15.2 are oxygen deficienL Calculations were perfonnedforsomemixnrres even though the concentration of combustibles for these mixtures was below the lower flammability limit and/or the oxygen content was below W minimum oxygen content required for combustion. The values of important parameters were again obtained from Thomas and Hensel (reference 4) who obtained them ftom the work of Morin (reference 13). Conditions and results axe shown in table 3.

I

The peak pmssuie predicted by MELCOWSR for all tank 49 cases is 13.0 pig, the pressure nquired to open thevents. This d t s t e m s f r o m the relatively large vent anzipresent in tank49. Because of the reason discussed above, DPAC overpdcts the peak pmsure for these cases. Similar mdts wexe obtained for several other cases, particuIariy at the l o w concentmtions and flame speeds. In cases 13.1, and 13.2 insu&cient combustibles were available to open the vents.

The results for tank 48 show appropriate trends with inmasing combustible concentration and haeasing flame speed. In allcasesin which the pressure rises sigdicantly above the pressure requid to open the vents, MELEOWSR predicts a slightly higher peak pressure than does DPAC. This result isconsistent with the air mixture II=sults,

I 16-

I

WSRC-RP-93-599

6.0 CONCLUSIONS

The results of tbe COMPACI' d y s i s were successfully duplicated by MEIXORBR Minor diffmmcesinthensultswerenoted but -Sin t h e p e a k p m w i t h respect to flame speed vent ana, freeboatd volume, and combustible concentration weze similar for the two codes.

Results from DPAC for realistic waste tank conditions were confirmed by MELCOWSR Minor differences incalcutated peakpmsmscan be traced to differences between the tw+tanlr volume method used in DPAC and the single-tank volume model used in MELCOWSR and to di.f%ermces in the flow models.

At the higher predicted pmssms, those of most interest to the &flagration analysis, DPAC is consided to be m a accurate than theparticulat MELCOWSR model used here. At peak pressu~es near the pressm quired to open the vents, the MELCOWSR model is consideted to be more accmate. Changesto theMELCOWSRmodel can be made toimproveits acaracy. In particular, a realistic representation of flame speed ppagation might be obtajned by using multiple control volumes to repnsent the tank,

The peak p- prediMed by MEIxlOWSR (and by DPAC) for realistic waste tank conditions &e., the cases shown in Table 3) indicate minimal risk calculated p e a k p ~ a F e f e s s t h a n t h e ~ r e q u i r e d t o f a i l t h e p r i m a r y b r o f the tank (- 23 psig).

' with a possible defhqjmion. The

- 17-

WSRC-RP-93-599

7.0 REFERENCES

1. Safety Analysis Report, Liquid Radioactive Waste Handling Facilities: Addendum 1, AdditionaI Analysis for DWPF Feed Preparation by In-Tank Procam g, DPSTSA-U)(FlO SUP 18 (July 1992)

2. SrinivaS, V., Evaluation of Prtxsum Buildup in the ITP procesS Tanks Due to Deflagration, Westinghouse NATD, Pittsburgh, PA (March 1991) DMFI'

3. Hensel, S. J., Description and Benchmarking of the Deflagration Pressure Analysis Code @PAC), WSRC-RD-93408, Savannah River Technology Center, Aiken, SC (April 1993)

4. Thomas, J. IC. and Hemel, S. J., PresSuFe Resulting from an ITP Waste Tank Deflagration 0, WSRC-RP-93-542, Savannah River Technology Center, A h n , SC (April 1993)

5. MELCOWSR Computer Code Manual, Volume 1: Primer and Package Users' Guide, Science ApplicationsIntemationalCorporarion (June 1992)DRAFT

6. MELCOWSR Computer Code Manuat, Volume 2 Refkrence Manual and Programnks Guides, Scienm Applications Inteanational Corporation (June 1992) DRAFT

7. C. D. high, Ed., MELCOR Validation and Verification 1986 Papers. NUREG/cR-4830 (March 1987)

8. Barin, L and Knack, O., Thermochemical Properties of Inorganic Substances* Springer-Verlag (1973).

9. wark, K, Thermodynamics, Third Edition, McGraw-Hill Book Company (1977)

10. Reid, RC., Prausnitz, J.M., and Sherwood, T.K., The Properties of Gases and Liquids, Third Edition, McGraw-Hill Book Company (1977)

11. User's Manual for CONTAIN 1.1, A Computer Code for Sevexe Nuclear Reactor Accident

12. Estochen, E., Vent A m Results, EPD-SE9W.002263, Interoffice Memorandum, Savannah River Site, AiLen, SC (February 12,1993)

13. Morin, J. P., Analysis of ITP Waste Tank Deflagration Conditions 0, WMER-ENG- 930036, Interoffice Memorandum, Savannah River Site, Aiken, SC (May 21,1993)

Con tainment Analysis, NuREG/cR - m6 (July 1990)

-18-

WSRC-RP-93-5 99

Patataeter value

tank volume 5267.28 m3 vent area (tank 48) vent area (tank 49)

cooling coil surface area (total) tank roof area

27.15 ft2 60.48 ft2 1220.0 m2 5 19.29 m2

tank outer wall area (total) tank inner wall area (total)

818.68 m2 64.22 m2

water surface area S23.94 m2

Table 1. Values of Parameters in MELCOWSR Model

-19-

WSRC-RP-93-5 99

- Case No.

1 2 3 4 5

6 7

8 9

10 11 12 13 14

15 16 17 18 19

20 21

-

-

- Tank No.

49 49 49 49 49

49 49

49 49

48 48 48 48 48

48 48 48 48 48

48 48

-

-

- Fill

Lwel

112 1/2 1/2 112 112

1/10 1/10

3/4 3/4

112 112 112 112 112

1/10 1/10 1/10 1/10 1/10

314 314

-

-

- Comb

2.76 3.57 4.37 5.18 5.98

2.76 5.98

2.76 5.98

2.24 2.75 3.26 3.77 4.28

2.24 2.75 3.26 3.77 4.28

2.24 4.28

-

-

Cone H2

1.66 2.14 2.62 3.11 3.59

1.66 3.59

1.66 3.59

0.90 1.10 1.30 1.5 1 1.71

0.90 1.10 1.30 1.51 1.71

0.90 1.71

- -

-

lIratiC CgHg

1.10 1.43 1.75 2.07 2.39

1.10 2.39

1.10 2.39

1.34 1.65 1.96 2.26 2.57

1.34 1.65 1.96 2.26 2.57

1.34 2.57 -

1s (%)

2 L 20.42 20.25 20.08 19.91 19.74

20.42 19.74

20.42 19.74

20.53 20.42 20.32 20.2 1 20.10

20.53 20.42 20.32 20.21 20.10

20.53 20.10 -

- N2 76.82 76.18 75.55 74.91 74.28

76.82 74.28

76.82 74.28

77.23 76.83 76.42 76.02 75.62

77.23 76.83 76.42 76.02 75.62

77.23 75.62 -

- Cone. Note

LFL 114 112 314

Stoich

LFL Stoich

LFL Stoich

LFL 1/4 112 314

Stoich

LFL 114 1/2 314

Stoich

LFL Stoich

-

-

28.9 14.9 9.47 6.82 5.35

28.6 5.25

29.4 5.53

38.6 18.6 12.3 8.82 6.80

38.1 18.3 12.1 8.63 6.36

39.3 6.9 5

Peak Pressure - DPAC

15.6 16.0 16.3 16.6 16.8

15.6 16.8

15.6 16.7

15.9 16.2 16.5 16.7 16.9

15.9 16.2 16.5 17.3 24.2

15.9 16.9

-

-

pig) MELCOWSR

~ ~~-

13.0 13.0 13.0 13.1 14.0

13.0 19.6

13.0 13.1

13.0 13.0 13.0 15.2 19.2

13.0 13.1 16.4 22.4 30.2

13.0 13.3

Table 2. MELCOWSR vs DPAC for Dry Air Mixtures. Initial conditions are 40 "C and 1 atmosphere.

-20-

- Case NO.

1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.2 5.1 5.2 6.1 6.2

7.1 7.2 8.1 8.2 9.1 9.2 10.1 10.2 11.1 11.2 12.1 12.2

13.1 13.2 14.1 14.2 15.1 15.2 16.1 16.2 17.1 17.2 18.1 18.2 19.1 19.2

-

-

- Tank No.

49 49 49 49 49 49 49 49 49 49 49 49

48 48 48 48 48 48 48 48 48 48 48 48

48 48 48 48 48 48 48 48 48 48 48 48 48 48

-

-

Operating Condition

Normal Normal Normal Normal Normal Normal Normal Normal Normal Normal Normal Normal

Normal N o d Normal N o d Normal Normal Normal Normal N o d Normal Normal Normal

Upset Upset Upset Upset Upset Upset Upset Upset Upset Upset upset upset Upset Upset

- - Time (4

3 3 6 6 12 12 18 18 24 24 30 30

3 3 6 6 12 12 18 18 24 24 30 30

1.0 1.0 4.0 4.0 4.25 4.2 5 11.9 11.9 18.1 18.1 24.0 24.0 29.8 29.8

-

-

WSRC-RP-93-5 99

- - 02

7.77 7.77 9.02 9.02 10.98 10.98 12.40 12.40 13.43 13.43 14.17 14.17

6.62 6.62 6.93 6.93 7.53 7.53 8.08 8.08 8.61 8.61 9.10 9.10

6.30 630 6.26 6.2 6 6.28 6.28 7.60 7.60 8.54

9.32 9.32 10.0 10.0

8.54

-

con N2

82.55 82.55 79.28 79.28 74.13 74.13 70.40 70.40 67.71 67.7 1 65.76 65.76

85.64 85.64 84.92 84.92 83.55 83.55 82.26 82.26 81.05 81.05 79.91 79.9 1

74.25 74.25 74.04 74.04 73.67 73.67 71.36 71.36 69.71 69.7 1 68.3 6 68.36 67.16 67.16

- -

-

ositioi CgHg 0.96 0.96 1.77 1.77 3.05 3.05 3.97 3.97 4.64 4.64 5.12 5.12

0.2 8 0.28 0.53 0.53 1.01 1.01 1.45 1.45 1.87 1.87 2.27 2.27

0.07 0.07 0.33 0.33 0.65 0.65 1.22 1.22 1.62 1.62 1.95 1.95 2.24 2.24 -

0 H2

1.44 1.44 2.65 2.65 4.56 4.56 5.94 5.94 6.94 6.94 7.67 7.67

0.18 0.18 0.33 0.33 0.64 0.64 0.92 0.92 1.19 1.19 1.44 1.44

0.01 0.01 0.01 0.01 0.03 0.03 0.46 0.46 0.76 0.76 1-01 1.01 1.23 1.23

-

-

- H20

7.28 7.28 7.28 7.28

7.28 7.28 7.28 7.28 7.28 7.28 7.28

7.28 7.28 7.28 7.28 7.28 7.28 7.28 7.28 7.28 7.28 7.28 7.28

19.37 19.37 19.37 19.37 19.37 19.37 19.37 19.37 19.37 19.37 19.37 19.37 19.37 19.37

7.28

-

- Bum Time (S 1

17.1 8.27 16.8 8.08 16.3 7.85 16.1 7.72 16.2 7.77 16.2 7.74

22.9 11.4 19.5 9.6 17.0 8.28 16.9 8.18 16.7 8.09 16.6 8.02

29.6 14.8 23.0 11.4 19.4 9.55 17.6 8.58 17.3 8.38 17.0 8.24 16.8 8.13

-

-

Peak Pressure - DPAC

15.1 15.0 15.0 15.0 14.9 14.9 14.8 14.7 14.5 14.5 14.5 14.5

13.7 133 14.2 14.2 15.0 15.0 14.9 14.9 14.9 14.9 14.9 14.8

3.73 3.82 13.8 13.8 14.4 14.4 14.9 14.9 15.0 15.0 15.0 15.0 15.0 15.0

-

-

pig) MELCOWSR -

13.0 13.0 13.0 13.0 13.0 13.0 13.0 13 .O 13.0 13.0 13.0 13.1

13.0 13.0 13.0 13.0 13.0 13.8 13.0 14.2 13.0 14.6 13.0 15.0

4.12 4.3 1 13.0 13.0 13.0 13.0 13.0 13.1 13.0 13.5 13.0 14.0 13.0 14.5

Table 3. MELCOWSR vs DPAC for Best Estimate Mixtures. Initial conditions are 40 'C and 1 atmosphere for cases 1-12 and 60 "C and 1 atmosphere for cases 13- 19. Cases 1-6 have fill level of 0.5 times tank height. Cases 7-15 have fill level of 0.1 times tank height.

-2 1-

1

W SRC-RP-93-S 99

8

9 I -

g I 1 i

-22-

Control Volume 2 (Atmosphere)

I

WSRC-RP-93-5 99

Figure 2. MELCWSR Model

-23-

COMPACT VS MELCOWSR

WSRC-RP-93-5 99

140 140 FT/S FLAME SPEED

FREE BOARD VOLUME ONE-HALF 120 STOICHIOMETRIC HYDROGEN

100

80

_IcI COMPACT 60 _101_ MELCOWSR

40

20 0 400 600 800

VENT AREA (FT2)

Figure 3. Peak Pressure vs Vent Area

-2 4-

Q)

.. VI Q) L R

i 3 0 > - - 0 L c

I I I I I I I I I I ' I

0 0

ro

t

M

0

WSRC-RP-93-5 99

h VI

W

W

I- I -

Z 3 m a

K 0 0

$

0 Q, t M

c- .. .. .-

rr) Q, \ m 0 \ t

2 m a c a N t P) n

L

rc 0

vj >

-25-

WSRC-RP-93-599

a 5

a n

- V V

L

i! 1 0 > 0 I

c 0 0

- - c

I I I I I I I I

/

I" h

W VI

W I u

.- cv a0 ln .. .. 2

m Q, \ CD 0 \ d

i m U 3

a E

c a 9

w

L

Y- 0

.- w vi >

-26-

COMPACT VS MELCOR/SR

200 190 140 FTIS FLAME SPEED 180 1 70 160 150 140 130

FREE BOARD VOLUME ONE-HALF STOICHIOMETRIC BENZENE

120 110 100 90 80 70 60 50 40 30 20

.Ilfi COMPACT __oII MELCOWSR

0 100 200 300 400 500 600 700 800

VENT AREA (m)

Figure 6. Peak Pressure vs Vent Area: Stoichiometric Benzene

-27-

WSRC-RP-93-5 99

COMPACT vs MELCOR/SR

. + COMPACT - ---+- MELCOWSR 110- . 100 - 90 -

80 - \ /

50 Fr2 VENT AREA STOICHIOMETRK: BENZENE 140 FT/S FLAME SPEED

0.2 0.3 0.4 0.5 0.6 0.7 0.8

FREEBOARD VOLUME (FRACTION OF TOTAL VOLUME)

60

Figure 7. Peak Pressure vs Freeboard Volume for Stoichiometric Benzene

-2 8-

70

60

WS RC-RP-9 3-5 9 9

COMPACT VS MELCOWSR

. COMPACT __oI. MELCOWSR

II

. COMPACT __oI. MELCOWSR

II

50FlZMNTAREA LFL BENZENE 140 FT/S FLAME SPEED

.- . 0.2 0.3 0.4 0:s 0: 7 C

FREEBOARD VOLUME (FRACTION OF TOTAL VOLUME)

8

Figure 8. Peak Pressure vs Freeboard Volume for Benzene at the Lower Flammability Limit

-29-

W a 3 Y p: 0

WSRC-RP-93-5 99

COMPACT VS MELCOR/SR

120 COMPACT

100-

1

80 -

60 -

__Q_ MELCOWSR

50 Fr2 VENT AREA STOICHIOM€IRIC BENZENE MULTIPLIER OF 10 GlvEs 140 FT/S FLAME SPEED FREE BOARD VOLUME ONE-HALF

2 4 6 8 10

TURBULENT MULTIPLIER

Figure 9. Peak Pressure vs Turbulent Multiplier for Stoichiometric Benzene

-3 0-

w t v) w z

70

60

50

40

WSRC-RP-93-5 99

COMPACT VS MELCOWSR

'

. __O_ MELCOWSR COMPACT

-

I

. (I

30 - 50 FT2 VENT AREA LFL BENZENE

140 FT/S FLAME SPEED FREE BOAR0 VOLUME ONE-HALF

wnwm OF i o GIVES

2 4 6 a 10

TURBULENT MuLflpuER

Figure IO. Peak Pressure vs Turbulent Multiplier for Benzene at the Lower Flammability Limit

-31-