ML17326A972

Hydrogen Combustion Modeling Assumptions for DC Cook Nuclear Plant

ML17326A972
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Site:	Cook
Issue date:	09/09/1985
From:	Cybulskis P, Leonard M Battelle Memorial Institute, COLUMBUS LABORATORIES
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Attachment 1 to AEP:NRC:0500S HYDROGEN COMBUSTION MODELING ASSUMPTIONS FOR THE D.C.

COOK NUCLEAR PLANT Prepared by Reviewed b

Mark T. Leonard Battelle Columbus Division Peter C

ulskis Battelle Col mbus Division 8509i20i53 850909 PDR ADOCK 050003i5, P.

PDR I

'YDROGEN COMBUSTION MODELING ASSUMPTIONS FOR THE D.C.

COOK NUCLEAR PLANT

SUMMARY

The set of hydrogen combustion and control analysis assumptions, presented in Attachment 2 to letter AEP:NRC:05000 (dated March 29, 1985),

has been modified to reflect comments received from the NRC staff and recent developments in analytical models.

In particular, the criteria for the delib-erate ignition of hydrogen/air mixtures have been modified to account for the potential effects of fog generated in an ice condenser containment atmosphere; the correlations for flame speed and burn completeness have also been updated to those recently proposed by Sandia National Laboratories.

The revised set of hydrogen combustion parameters, presented in this document, are those to be used in the CLASIX and MARCH computer codes to perform the analyses required under 10 CFR 50.44 (c).

BACKGROUND Previous base case

analyses, to demonstrate the effectiveness of the Distributed Ignition System (DIS) for the D.C.

Cook Nuclear Plant, were based on CLASIX calculations which assumed eight volume percent hydrogen for.

ignition, eighty-five percent completeness of combustion, and a flame speed of six feet per second.

Since those analyses were performed, the data base for hydrogen combustion events and related phenomena has improved significantly.

The calculations to be performed for final resolution of the hydrogen control issue (10 CFR 50.44 (c)), will be consistent with the improved data base by utilizing modeling assumptions that reflect the current understanding of hydrogen combustion phenomena.

Of particular interest in the current analyses is the ability of the DIS to effectively ignite lean hydrogen/air mixtures in the ice condenser containment.

The presence of high concentrations of small-diameter water

droplets, or fogs, in the containment atmosphere has been shown in previous analyses to potentially affect the performance of glow plug igniters.

The combustion parameters, described

below, account for this effect by incorp-orating the results of the analysis specific to the D.C.

Cook Nuclear Plant.

FLAME IGNITION and PROPAGATION CRITERIA In hydrogen combustion experiments with glow plug igniters

'perating, combustion is typically found to start well below the eight volume percent previously assumed.

In the continuous injection combustion tests, performed at the Nevada Test Site (NTS) by EPRI, ignition occurred when the volume-averaged hydrogen concentration was between three and five volume percent (depending upon hydrogen source injection rate) (1).

These results are supported by data from several small scale experiments including those conducted by Sandia in the Fully Instrumented Test System (FITS), Fenwal,

Inc.,

and the Whiteshell Nuclear Research Establishment (2).

In general, the current data base suggests the use of ignition criteria near the lower flamm-ability limit.

One additional factor has been considered, however, in defining our assumptions regarding flame ignition.

An analysis performed by Westinghouse (3)

(and supported by data from Factory Mutual) concluded that the presence of high concentrations of small diameter (less than 20 micron) water droplets, or

fogs, may suppress the ignition of otherwise flammable mixtures.

Westinghouse proposed criteria for "fog inerting" of hydrogen/air mixtures and calculated the concentration of fog that would be generated in the D.C.

Cook containment during an S201 accident sequence.

This sequence is also one of the three accident sequences to be investigated in the current analysis.

The proposed fog inerting criteria are reproduced in Figures 1 and 2

for 4.76 and 7.2 volume percent hydrogen, respectively.

The concentration of fog required to inert the mixture is shown to depend upon the assumed size of water droplets that compose the fog.

The Westinghouse analysis recommended a

mean fog droplet diameter of 10 microns.

If the fog inerting criteria are extrapolated to 10 microns, the minimum fog concentration required for inerting 4.76 percent hydrogen is approximately 8.4 x 10 6.

For 7.2 percent hydrogen the Westinghouse theoretical fog inerting criterion (1.0 x 10 4) differed from that indicated by Factory Mutual data (2.1 x 10 5).

Both values were considered in our review.

The fog concentration calculated 'by Westinghouse for each compart-ment of the D.C.

Cook containment during an S2D,sequence is reproduced as Figure 3.

A rough schematic of the D.C.

Cook containment is given in Figure 4, which outlines the regions that comprise the various compartments considered in this analysis.

The upper plenum of the ice condenser is pre-dicted to have the highest fog concentration for most of the time.

Following the upper plenum in fog concentration are the dead end regions and the upper compartment.

The times at which the upper plenum hydrogen concentration were cal-culated to reach 4 and 7 volume percent for this sequence are identified along the time scale of Figure 3; the corresponding fog inerting limits (for 10 micron droplets) are also indicated.

Comparison of these limits to the predicted fog concentrations in each compartment leads to the following conclusions:

(i)

Following the time at which the hydrogen concentration reaches the lower flammability limit in the upper plenum, the upper plenum is predicted to have fog concentrations exceeding the fog inerting limit. It is uncertain whether flame ignition in the dead end region is limited by fog concentration at the lower flammability limit.

1 S2D is the Reactor Safety Study nomenclature for a small break loss-of-coolant accident with failure of all emergency coolant makeup.

~

i lt

(ii)

Ignition of the hydrogen/air mixture in the upper plenum at 7

volume percent is uncertain, therefore, modeling the ignition

. of hydrogen in the upper plenum should be delayed until 8 volume percent is achieved.

The dead end region fog concen-tration is predicted to decrease with time and is likely to be lower than the fog inerting limit at 6 volume percent.

(iii) All compartments, other than the upper plenum and the dead end region, are predicted not to develop fog concentrations high enough to warrant significant increases in the hydrogen concentration at which ignition may be assumed to occur.

The criteria described above define the range of concentrations of hydrogen/air/steam mixtures which may be ignited by an active glow-plug igniter.

Propagation of a flame from the region of the containment containing an igniter into a neighboring gas volume is dependent upon an additional char-acteristic:

the direction (orientation with respect to vertical) the flame must travel.

This dependency was observed in the NTS test results where the volume-averaged hydrogen concentration at which a global burn could be init-iated by an igniter located at the bottom of the test vessel was lower than that at which a global burn could be initiated by an igniter at the top of the vessel (1).

In modeling the propagation of a combustion flame from one region of a containment vessel to another, this directional dependence is accounted for by requiring a higher comportment-averaged hydrogen concentration to propagate a flame against bouyancy forces (downward) than to propagate with the aid of bouyancy forces (upward).

Based upon our review of the available data from relevant hydrogen combustion experiments, and the existing analysis regarding fog inerting in the D.C.

Cook containment the following assumptions for modeling hydrogen ignition and propagation are planned:

(1)

Ignition in the upper plenum of the ice condenser will occur at a compartment-averaged hydrogen concentration of eight volume percent.

Ignition in all other compartments will occur at a

compartment-averaged hydrogen concentration of six volume percent.

In either case, ignition will be subject to the availability of sufficient oxygen

(>5 v/o) and considerations of steam inerting (~55 v/o).

(2)

Flame propagation between compartments will be based on the criteria of Coward and Jones (4) (the default values in PARCH) which take into account hydrogen concentrations and orien-tations of connected compartments.

These criteria are:

Upward Propagation

- 4.1 v/o hydrogen Horizontal Propagation

- 6.0 v/o hydrogen Downward Propagation

- 9.0 v/o hydrogen It should be noted that these criteria do not conflict with the combustion limitations associated with high fog concentrations.

As discussed above, it is primarily the upper plenum of the ice condenser that is restricted by fog

inerting criteria.

The upper compartment is the only compartment from which a

flame may propagate into the upper plenum.

Since the upper compartment is modeled as a volume above the upper plenum, for a flame to propagate into the upper plenum, it wou~d have to originate in the upper compartment and prop-agate downward.

This would require an upper plenum hydrogen concentration of 9.0 v/o which is greater than the concentration at which the upper plenum mixture is assumed to be ignited.

COMBUSTION COMPLETENESS and FLAME SPEED Sandia National Laboratories has developed improved correlations for the completeness of hydrogen combustion and flame speed for the HECTR computer code (5).>

The data base for these correlations is extensive and, in the case of combustion completeness, includes the NTS tests.

The most current HECTR models for combustion completeness and flame speed will be used in the D.C.

Cook analyses.

A newly developed correlation for combustion completeness, planned for incorporation into HECTR version 1.5, will be used.

The new correlation is (6):

xf = Max ((1.8777 - 23a4397 xi) xi, 0.005 xi) xf = fraction of hydrogen burned xi

= initial hydrogen mole fraction This correlation is shown in Figure 5 in comparison to available data and to the old default HECTR correlation (also used as the default in MARCH 2.0).

The correlation for flame speed that will be used is the default model in HECTR version 1.0 ((5), page A-19).

This correlation produces flame speeds slightly lower than those calculated with the current default model in MARCH 2.0 (7).

CONCLUSION The modeling assumptions described above; as well as those presented in Attachment 2 to letter AEP:NRC:05000, form the technical bases for the analyses approved by an NRC letter, dated June 28, 1985 (8).

These assump-tions are based on the most recent experimental data available and reflect our understanding of proper modeling of the important phenomena in hydrogen com-bustion and control.

REFERENCES 1.

L.B. Thompson, J.J.

Haugh, B.R. Sehgal, "Large Scale Hydrogen Combustion Experiments",

International Conference on Containment Design, Toronto,

Canada, June 17-20, 1984.

2.

M. Berman and J.C.

Cummings, "Hydrogen Behavior in Light Water Reactors",

~81 9 1 2, 28.1, 2

y-9 9 y 1989.

3.

S.S.

Tsai and N.J. Liparulo, "Fog Inerting Criteria for Hydrogen/Air Mixtures", Second International Workshop of the Impact of Hydrogen on Water Reactor Safety, Albuquerque, New Mexico, October 3-7, 1982.

(A full report was also submitted to the NRC as Attachment 4 to letter AEP:NRC:0500K, dated Oct.

10, 1983) 4.

E.F.

Coward and G.W. Jones, Limits of Flammabilit of Gases and Va ors, Bulletin 503, Bureau 'of Mines, U.S.

Department of the Interior, 1952.

5.

A.L. Camp, M.J. Wester, S.E.

Dingman, "HECTR Version 1.0 User's Manual",

NUREG/CR-3913, Sandia National Laboratories, February 1985.

6.

Personal communication from C.

Channy Mong (Sandia National Laboratories) to Thomas Crawford (American Electric Power Service Company), letter dated August'12, 1985.

7.

R.O. Wooton, P. Cybulskis, S.F. guayle, MARCH 2 Meltdown Accident Res onse Characteristics Code Desri tion and User's Manual, NUREG/CR-3988, Batte e

Co umbus Laboratories, September 1984.

8.

NRC letter, dated June 28,

1985, from Mr. Steven M. Varga to Mr. John Dolan (American Electric Power).

10-1

'X E

I 102 s

RO I

2 C

IR 10'3 O

CP UO Q

5 0

SPRACO 2163 SP RACO 1405-0604 Q

SPRACO 2020-1704 0 SPRACO 1806-1605 NON-FLAMMABLEZONE MESTINGHOUSE THEORY FLAMMABLEZONE 104 10 100 200 VOLuME MEAN DIAMETER (MICRONS)

FI6URE 1.

COMPARISON BETWEEN THE MESTINGHOUSE THEORY AND FACTORY NTUAL FOG INERTING EXPERIMENTS ON 4.76 PERCENT HYDR06EN.

[3]

103 0 SPRACO 2163-7604 D SPRACO 2020-1704 Q SONICORE 035H NON.FLAhlMABLE ZONE z0 CK IR C7RO 2

C5O WESTINGHOUSL THEORY FLAMMABLE ZONE 7~ H2 IN AIR AT 50 C 10 20 30 40 50 60 70 80 90 100 VOLUMEMEAN DIAMETER {MICRONS)

FIGURE 2.

COMPARISON BETiKEN THE WESTINGHOUSE THEORY AND FACTORY MUTUAL FOG INERTING EXPERIMENTS

'N 7.2 PERCENT HYDROGEN.

[3)

10-2 103 LLI LLDt-1O-4 X

l-u~

~

o '105 CVx I-u z 10-6

-0I-KI-Z ol107 Z0O U0 1O-8 p

Lower Comp

~

Upper Comp p

Lower Plenum Dead End Region 5

Upper Plenum Fan/Acc. Rooms FOG INERTING LIMITS 7.2% H2 (theory) 7.2% H2 (data) 4.76% H2 1O-9 0

1000 2000 3000 TIME (SEC) 4000 6000 6000 7 v/o (Upper Plenum H2 Concentration) 4 v/o FIGURE 3.

FOG CONCENTRATION IN D. C. COOK CONTAINMENT

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UPPER VOLUME TOP DECK DOORS UPPER PLENUM a ";,o; 0'

INTER-NEDIATE DECK DOORS LOWER VOLUME 0';

ICE BED PRESSURI ZER LOWER PLENUM INLET DOORS

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O:Ier 0

'. 4:0'0 0

0.O.o g~0IrI g ~/

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.'tO0 o REACTOR VESSEL STEAM GENERATOR FIGURE 4.

SIMPLIFIED DIAGRAM OF ICE CONDENSER CONTAINMENT COMPONENTS

0/

OLD HECTR MODEL

/

a

//

//

HEM HECTR MODEL 0

0 0 0

C3= VGES Fans On Q= VGES Fans Off

, 6= NTS 0= FITS TSg3 8

12 H2 Concentration

(%)

FIGURE 5.

HYDROGEN CONUSTION AS A FUNCTION OF THE INITIALHp CONCENTRATION.

[6]

20

• Variab1e-Geometry ExperimentaI System

{Sandia)

ATTACHMENT 2 TO AEP:NRC:0500S REFERENCES 1)

"An Analysis of Hydrogen Control Measures at McGuire Nuclear Station,"

submitted by Duke Power Company to Mr. Harold Denton of NRC, February 29, 1984.

2)

"Report on the Safety Evaluation of the Interim Distributed Ignition System," prepared by TVA for the Sequoyah Nuclear Plant Core Degradation

Program, December 15, 1980.

3)

"Containment

Response

to Degraded Core Events," for Sequoyah Nuclear

Plant, November 16, 1981.