ML20105C027

Forwards Evaluation of Glow Plug Igniter Concept for Use in Sequoyah Nuclear Plant, Per Request

ML20105C027
Person / Time
Site:	Sequoyah
Issue date:	01/09/1981
From:	Strehlow R STREHLOW, R.A.
To:	Milhoan J NRC OFFICE OF POLICY EVALUATIONS (OPE)
Shared Package
ML20105B998	List: ML20105C027
References
FOIA-84-577 NUDOCS 8502090294
Download: ML20105C027 (1)

Text

. - - - _ .

' ~ -

ROGER A. STREHLOW..

. coNsutimi 3,- ,- ,ilC D scenmSPOMATON SULCWC assourN swe sTRett UNNEREITY OF LLNOIS 4AW4JON. LUN06 61820 U

AEPHONE 217 350-1985 RSANA

's o~5 =-=== LUNOS81001

=7'a S' ft>

19 AB . 31

- . , .: g.

.....s

....u. ,

~

Janua'ry'- 9,,19 81 - -

i Mr. James Milhoan, P. E.

~

I Office of Policy Evaluation '. - ' ' . ' * ,~ . ,. ,'

Nuclear Regulatory Commission

. r' ,.*<

1717 H Street N. W. C'..'  !...

Washington, D. C. 20555 ' '.-

Dear Jim:

f

.' s . . .* J ,

. . . . . s. . . . . . .

Please find enclosed the report that you requested.' '

., . .'v .-

. ~

-e.

If yon have any questions, please ~

feeY.

free. to co.ntact

( .

i me. ..

i Sin.cere y ours ,' -

i

• I .

' er A Strehlow Consultant, N.'R. C.

RAS :ST-200 ..

Enc.

i 850209 i

PDRFOf94840823 HIATTB4-577 PDR i

1 . .

n , e n.

.. =::.

. 19 AIO: 31

. . .s._,

3 -

u.

i s s

.......v.  : .:w -

Evaluation of the Glow Plug Igniter Concept for use in the Sequoyah Nuclear Plant I

Prepared for Mr. James Milhoan, P. E.

l i Office of Policy Evaluation Nuclear Regulatory Commission Washington , D. C. 20555 i

Prepared by Roger A. Strehlow Consultant January 9, 1981 e , .i , Ab

Qj VO "&YOf

• i; l

1

, _ _ . _ . _ _ , _ - _ . _ . , . . , . _ ,_. ,.(_ ., -

, , , , . .y. ___ . . . _, . .__, , _ _ _ . _ . , _ , , _ . - . _ . . , .

, . L

+ .-

r b

f Overall' Evaluation *

In my opinion, a well designed and maintained glow plug igniter system which is energized only for testing or during an ,

event which has the potential of generating hydrogen is an l effective way to protect the Sequoyah nuclear plants from the i

i, possibility of breaching the containment vessel due-to the i Furthermore, it inadvertent combustion of accumulated hydrogen.

l 1s my opinion that the implementation of this glow plug igniter i technique will have no negative effects on overall safety in such I

a nuclear plant. I base this opinion on the following information f

that was supplied to me 'by the Nuclear Regulatory Commission

,

l Tennessee Valley Authority, Sequoyah Nuclear Plant Core l

Degradation Program, Volume I, Hydrogen Study, i September 11, 1980

}

News Release No.80-159, USNRC, September 11, 1980

' News Release No.80-163, USNRC, September 18, 1980 l Safety evaluation report related to the operation j Sequoyah Nuclear Plant, Units 1 and 2, Docket i No. 50-327 and 50-328, Tennessee Valley Authority, j NUREG-00ll, Supplement No. 3, September,1980 1

j Memorandum for: ACRS members , from: J. C. Mark, Subject l

Notes on hydrogen burn with igniters, December 4, 1980 l Memorandum to: ACRS members , from: H . Etherington , '

j Subject Memorandum P. G. Shemwon to ACRS members:

" Quantity of H 2 at TMI-2 and source ."

l

! Tennessee Valley Authority, Sequoyah Nuclear Plant Core l

Degradation Program, Volume 2, Report on the Safety i Evaluation of the Distributed Ignition System, December 15, 1980

Tennessee Valley Authority, Sequoyah Nuclear Plant, Research

! Program on Hydrogen Combustion and Control, Quarterly

( Progress Report, December 15, 1980 l

Draf t copy of Supplement No. 4 to the Safety evaluation report by the Office of Nuclear Reactor Regulation, U. S . Nuclear Regulatory Commission in the matter of Tennessee Valley Authority Sequoyah Nuclear Plant Units 1 and 2, Docket No's. 50-327 and 50-328, undated.

Attendance at the ACRS subcommittee meeting held in Washington, D. C. on January 6, 1981.

A meeting with Mr. Tinkler and Mr. Butler of the NRC staf f on the morning of January 7,1981.

Other open literature references which helped me form my opinion will be referenced in the detailed supporting statement

that follows. I also have opinions concerning the dynamics of a combustion explosion in a Sequoyah type containment and new research and data accumulation efforts which would be necessary to strengthen and quantify the justification for using glow plug igniters as the only hydrogen control technique. These will also

)'

be disucssed below.

4 Effectiveness of the Glow Plugs.

The Singleton Lab.,- Fenwal and LLNL tests have shown the glow

plugs that are being considered for the Sequoyah plant to be very effective igniters down to 5% hydrogen even in the presence of 15% dry steam. Thus, in a real accident we now know that the igniters would initiate a partial burn at 5% H2 in the CV. Further-more, the ' Singleton lab tests show that in a small vessel even with 3.5% H2 present initially a five minute " burn" reduces the H2 concentration to about 0.1%. This is very encouraging because i it shows that a hot glow plug will act as an H2 scavenger even t

outside the flammability limit for upward propagation of about 4% H2 . Furthermore, sparks of the type that undoubtedly initiated the Three Mile Island burn are not effective at such a low hydrogen

l

. I

. concentration. '

It is important to note that glow-plug initiated burns will be much less dangerous t!.an spark initiated burns. This is because between 4-8% hydrogen in air burns with a very lazy upward propagating flame which ' spreads at a maximum half angle 'of about 20 degrees and extinguishes when it reaches the top of the vessel. Tnis means two things: 1) the pressure rise will be minimal for such a burn, and 2) the hot product gases will be confined to this cone-shaped volume and subsequently will spread .

along the ceiling. In other words, the flame will not contact and therefore not heat most equipment that is in the containment vessel. Also, if the rate of hydrogen generation were slow so that the fans produced a rather uniform hydrogen concentration, the burn would be almost continuous once the hydrogen content reached 4-5%.

On the other hand, a fast leak which caused a localized higher concentration of hydrogen would also not be dangerous when ignited by the glow plug. This is because glow plugs strategically placed above potential

• hydrogen sources would ignite a high hydrogen concentration pluna on contact and only a localized high temperature burn would occur. It is well documented .(Cubbage and )

Marshall,1972) that such a partial burn yields a pressure rise in

a vessel which is proportional to the energy released by the localized burn (Joules) divided by the total volume of the vessel 3

(m ). Thus, a small localized burn cannot cause a r,eally large l

j pressure rise.

In my opinion, properly located and functioning glow plug igniters would reduce the probability of a burn lead,ing to a j t

._----..,_,__,-_m._,_.,..-.-,_.-..-..-,-,._ , _ _ - , , - _ . . _ . - - _ . _ _ _ . . ~ . _ , . , , , . _ _ , - , - . - - - -

' transition to detonation to virtually zero. This is because the very weak flames produced by a 4-5% hydrogen burn cannot generate significant pressure waves or significant flow velocities ahead of the flame. This means that the mechanisms that lead to flame acceleration do not exist under these conditions. In other words, the weak 4-5% hydrogen flames will remain weak irrespective of the environment that they encounter.

Combustion dynamics in the Sequoyah containment vessel.

The Sequoyah containment contains three main compartments :

1) the upper compartment, 2) the lower compartment, and.3) the ice condenser. The upper and lower compartments both have a rather low length-to-diameter (L/D) ratio and therefore if they could be treated as independent vessels they would be capable of supporting only a simple over-pressure explosion. The containment at Three Mile Island was essentially of this type and that is what happened there when the hydrogen concentration reached about 8%.

In such a case, the flame propagates slowly enough such that the pressure is relatively uniform spatially in the vessel during the burn and simply rises with time (approximately as a cubic of time; see Bradley and Mitcheson, 1978 a, b). This is true even if there is some acceleration due to turbulence generation. Under these conditions, there are essentially no pressure waves generated.

Note that at TMI the transit time of a sound wave from top to I bottom to top is about 0.2 seconds and the burn took about 10 seconds.

Unfortunately, in the Sequoyah configuration the upper and l lower compartments are not independent but are connected by the l

' ice condenser. In my opinion, this is a very dangerous configu-a ration because it would generate pressure waves which could possibly lead to local over pressures that could breach the 4 containment. This is because the ice condenser contains hundreds i of tubes (the spaces between the baskets) which have a very lar'ge L/D and which could cause significant flame acceleration and possibly even transition to detonation. This mechanism has been

! adequately documented by Urtiew et al (1965, 1967) and could occur after primary ignition at or above 8% in either the lower or upper j

! compartment. The sequence, without detonation, is as follows :

ignition in one compartment causes a slow pressure rise and starts

! a flow through the condenser, pressurizing the second compartment.

I j The flame then gets into the ice condenser at some location and i

j accelerates in this turbulent flow causing large turbulent jets to l enter the second compartment. Once the flame reaches the second l

compartment, it is already pre-pressurized and the burning velocity is now so large that combustion in this compartment produces pressures that are up to a factor of 2-4 above the calculated

! maximum adiabatic constant volume pressure (Heinrich,1974) .

I i There is another more recently discovered combustion dynamics i possibility. Knystantas et al (1979) have shown that large scale eddy folding of hot combustion products into an already turbulent l jet of reactants can produce shockless initiation of detonation.

[ Here the nachanism is that radicals in the product gases trigger i

! combuscle.1 reactions in the mixing volume and as the system explodes the pressure increase augments the combustion process.

This coupled augmentation eventually culminates in a detonation l

l wa,ve. For hydrocarbon-air mixtures, the critical eddy size is i

(

i large,' about three meters in diameter. Note that at the exit j

of the ice condensus, conditions would be right for the formation of such a large mixing region. The required eddy size for hydrogen-air is not known but it would probably be smaller than i

the critical size for a hydrocarbon-air mixture.

l Thus, in my opinion, the combustion dynamics of an explosion

! in which a continuous flame is able to propagate (i.e., in a i mixture containing greater than 8% H 2 ) is a very dangerous situ-i l ation and would have the potential to breach the containment l vessel. We know that glow plugs have been shown to yield partial i

burns when the flame is lazy and not dangerous. This, coupled I

with the vulnerability of the facility to a dynamic combustion explosion, is one more point in favor of using glow plug igniters to protect the containment vessel from the adverse consequences i

l of an accidental spark-ignited burn, i

l 4 Research Needs.

Glow plug testing should be continued. Specifically, I agree i

with the LLNL recommendations for further work that was presented i

! at the ACRS subcommittee meeting of January 6,1981. I would also

! like to see some continuous burn tests at concentration less than

4% to determine how rapidly a glow plug will scavenge hydrogen at

these low concentrations. In these tests, the effect of f an-induced i

flow across the plug should also be investigated.

{

Even though I feel that the glow plugs will virtually elimi-nate the possibility of detonation in the containment vessel, I still feel that some work on detonation limits should be performed.

l l -- -- --- .. - - - - _ - - . . - -. ---- - . -

I.do not believe the 18% figure that is in the reports. I feel that the limit 15 much lower, possibly 12%. At any rate, this uncertainty can be relatively easily answered by a few rather simple tests that should be performed.

i i,

.I i

l 5

iL l

i I i l

I l

1 l

2 l

• i i

! 3 1

\

References Bradley, D. and Mitcheson, A. (1978a) , Comb and Flame 32, --

pp. 221-236 Bradley, D. and Mitcheson, A. (1978b) , Comb and Flame 32, pp. 237-255 Cubbage, P. A. and Marshall, M. R. (1972), " Pressures generated l in combustion chambers by the ignition of air gas mixtures",

! I. Chem E. Symposium Series #33, Inst. of Chemical Engineers,.

! London, pp. 24-31.

Heinrich, H. J. (3974), " Sum Ablanf von Gas explosionen in mit Rohleitungen verbundenen Behadtern", BAM Berichte #28, Berlin (August 1974).

Knystantas, R.; Lee, J. H.; Guirao, C.; Freuklach, M.; and Wagner, H. G., " Direct Initiation of detonation by a hot turbulent gas jet", 17th Symposium (International) on i Combustion, The Combustion Institute , Pittsburgh, Pa. ,

(pages unknown).

Utriew, P.A'. and Oppenheim, A. K. (1967), " Detonation Initiation by Shock Merging",11th Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, Pa. ,

pp. 665-676.

i Utriew, P. A., Laderman, A. J. and Oppenheim, A. K. (1965),

" Dynamics of the Generation of Pressure Waves by Accelerating Flames",10th Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, Pa. , pp. 797-804 4

I . .

l

. _-. - - - - - . - - - - . ,-- . - .