ML20136G107

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Review of Current Understanding of Potential for Containment Failure from In-Vessel Steam Explosions
ML20136G107
Person / Time
Issue date: 05/31/1985
From: Allen C, Carradini T, Ginsberg T
NRC - STEAM EXPLOSION REVIEW GROUP
To:
Shared Package
ML20136F845 List:
References
FOIA-85-448, RTR-NUREG-1116 NUDOCS 8506250499
Download: ML20136G107 (7)
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Enclosure 3 NUREG-1116 A REVIEW 0F THE CURRENT UNDERSTANDING OF THE POTENTIAL FOR CONTAINMENT FAILURE FROM IN-VESSEL STEAM EXPLOSIONS by THE STEAM EXPLOSION REVIEW GROUP T. Ginsberg, Chairman M. Corradini, Vice-Chairman C. Allen, Executive Secretary May 1985 m

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EXECUTIVE

SUMMARY

A group of experts was convened at the request of Dr. Denwood Ross, Deputy Director of the Office of Nuclear Regulatory Research of the U.S. Nuclear Regulatory Commission, to review the current understanding of the potential for containment failure arising from in'-vessel steam explosions.during core meltdown accidents in a typical PWR and BWR. The Steam Explosion Review Group (SERG) was requested to provide assessments of: (i) the conditional probability of containment failure due to a steam explosion, (ii) the Sandia National Laboratory (SNL) report entitled "An Uncertainty Study of FWR Steam Explosions," NUREG/CR-3369, (iii) a SNL proposed steam explosion research program. This report summarizes the results of the deliberations of the review group. It also presents the detailed analyses of each individual member to each of the issues raised by Dr. Ross.

Fundamental mechanisms involved in steam explosion accident sequences were discussed at a meeting of the SERG. Initial conditions, melt-water mixing, thermal-to-mechanical energy conversion, multiple explosion, slug dynamics and mechanical damage stages of steam ~ explosion sequences were discussed.

In each area the SERG came to some agreements and-identified some areas of disagreement. The agreements were conceptual in nature and a consensus on the validity of specific models of the phenomena was not reached by the group. In the important area of fuel-coolant mixing, the SERG agreed in principle on the validity of transient jet breakup, flooding and/or fluidization limits on the extent of fuel-coolant mixing. Consensus o agreement on the validity of specific analytical models, however, was not reached by the group. The SERG discussions are summarized in Appendix 0 to this report.

Each member of the SERG provided subjective quantitative estimates of the

' conditional probability of containment failure based upon combinations of

r mechanistic and probabilistic arguments. 'The SERG members provided "best estimate" values of the subjective conditional probability of containment

.2 failure that range from 0 to 10 . Of 10 numerical best estimates provided, six of them have values which are less than or equal to 10 and seven are

.3 less than or equal to 10 .

Several SERG members also provided " upper limits" to the subjec'tive ' probability of containment failure which ranged from 0 to 0.1. All but one of these (the 0.1 value) are characterized as being upper limits of the individual's best estimates. Of seven such

.2 numerical estimates provided, six of them are less than or equal to 10 and three are less than or equal to 10' . J0f the two members who did not provide numerical estimates, one believes that WASH-1400 is "very conservative" in its treatment of steam explosions, and the other believes that steam explosions pose no threat to the Federal Republic of Germany's PWR containment.

Based upon the probabi-lity estimates summarized above, the consensus of the SERG is that the occurrence of a steam explosion of sufficient energetics which could lead to alpha-mode containment failure has a low probability.  ;

This conclusion is reached despite the expression of. differing opinions on '

modeling of basic steam explosion sequence phenomenology. An opinion supported by most members of the group is that the probability of containment failure is reduced due to the expectation of limited melt mass involvement in the explosion and/or low thermal-to-mechanical energy conversion. Other members placed more emphasis on reduction by other physical mechanisms. Individual group member quantitative estimates of the subjective conditional probability of containment failure and supporting arguments are presented in the report. These estimates are contrasted with results from WASH-1400.

With broad consensus the SER.G members disagreed with the methodology as used i

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c-in NUREG/CR-3369 for the purpose of establishing the uncertainty in the ,

probability of containment failure by a steam explosion. Nearly all of the members also disagreed with the Sandia conclusion that "Indeed the results (for the conditional probability of containment failure) span the range from 0 to 1." The major factor in the review group's disagreement with the Sandia work is that, in the choice of probability density functions, Sandia does not make direct use of physical models which are representative of current thinking of most of the SERG members.

A consensus was reached among SERG members on the need for a continuing steam explosion research program which would improve our understanding of certain aspects of steam explosion phenomenology and which would be directed toward providing confirmation of the SERG conclusion that the probability of containment failure by steam explosion is low. Most members agreed with a i continuation of the Sandia FITSX test program involving melt masses of up to j 50-100 kg. Most agreed with " Alternate Contact Mode" experiments, involving j explosions in stratified geometry. Consensus could not be reached on the advisability of pursuing the large-scale SEALS experiments (up to 2000 kg melt mass) proposed by Sandia at this time.

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Enclosure 4

1. S. G. Bankoff, " Vapor Explosions: A Critical Review," Proc. 6th Int'l.

Heat Transfer Conference, 6,p 355 (1978).

2. S. G. Bankoff et al., " Steam Explosions - Their Relationships to LWR Safety Assessments," Int'1.- Mtg. on Thermal Reactor Safety, Chic.ago, IL (August 1982).
3. S. -G. Bankoff et al. , "A Model for Fragmentation of. Molten Metal 0xides in Contact with Water," Int'1. Mtg. on LWR Severe Accident Evaluation, Cambridge, MA (August 1983).
4. M. J. Bird, " Thermal Interactions Between UO7 and Water: Experimental Study Using Thermite-Generated UO " Fuel-Coolant Interactions, HTD-V19, ASME Winter Annual Mtgr.2,Wash. DC (November 1981).
5. M. J. Bird, "An Experimental Study o'f Scalir.g in Core Melt / Water Interactions," ASME 22nd NHTC, No. 84-HT-7, Niagara Falls, NY (August 1984).

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6. C. Carachalios et al., "A Transient Two-Phase Model to Describe Thermal Detonation Based on Hydrodynamic Fragmentation," Int'1. Mtg. on LWR Severe Accident Evaluation, Cambridge, MA (August 1983).
7. D. H. Cho et al., "Some Aspects of Mixing in a Large-Mass Energetic FCI," Int'1. Mtg. on FRS, CONF-761001, V4, Chicago, IL (October 1976).
8. M. L. Corradini, D. E. Mitchell, L. S. Nelson, "Recent Experiments and Analysis Regarding Steam Explosions," Fuel-Coolant Interactions, HTO-19, 49 (1081).
9. M. L. Corradini, "Phenomenological Modelling of the Triggering Phase of Small Scale Steam Explosion Experiments," Nuclear Science and Engineering, 78, 154 (1981).
10. M. L. Corradini, D. V. Swenson, R. L. Woodfin, L. E. Voelker,

" Probability of Containment Failure Due to Steam Explosions Following a Postulated Core Meltdown Accident in a Light Water Reactor," Nuclear Engineering and Design, 66, 287 (1981).

11. M. L. Corradini, "A Proposed Model for Fuel-Coolant Mixing During a i

Core-Melt Accident," Int'l. ANS/ ENS Mtg. on Thermal Reactor Safety (August 1982).

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12. M. L. Corradini, " Hydrogen Generstion During Molten Fuel-Coolant
Interactions," Int'1. Mtg. on Hydrogen Behavior (October 1982).
13. M. L. Corradini, D. V. Swenson,.R. L. Woodfin, "An Analysis of Containment Failure by a Steam Explosion Following a Postulated Core Meltdown Accident in an LWR," Nuclear Safety, 23(1), 21 (1982).
14. M. L. Corradini, " Analysis and Modelling of Large Scale Steam Explosion Experiments," Nuclear Science and Engineering, 82 (December 1982).
15. M. L. Corradini, "Modelling Film Boiling Destabilization Que.to.a Pressure Shock Arrival," Nuclear Science and Engineering, !4 (1983).
16. M. L. Corradini, G. A. Moses, "A Dynamic Model for Fuel-Coolant-Mixing," Int'1. Mtg. on Severe Accident Evaluation, Cambridge, MA (August 1983).
17. M. L. Corradini, N. A.. Evans, D. E. Mitchell, " Hydrogen Generation During Fuel-Coolant Interactions," Int'1. Mtg. on Severe Accident Evaluation, Cambridge, MA (August 1983).
18. M. L. Corradini, " Fuel-Coolant Interactions with Molten Core Materials and Water," Nuclear Science and Engineering 36(1984).
19. M. L. Corradini, " Limits to Fuel-Coolant Mixing," Nuclear Science and Engineering (submitted May 1984).
20. H. K: Fauske, R. E. Henry, " Interpretation of Large Scale Vapor

' Explosion Experiments with Application to LWR Accidents," Int'1. Mtg.

on LWR Severe Accident Evaluation, Cambridge, MA (August 1983).

21. R. E. Henry, H. K. Fauske, " Core Melt Progression and the Attainment of a Permanently Coolable State," Proc. Thermal Reactor Fuels Mtg. , Sun Valley, ID (August 1981).
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22. R. E. Henry, H. K. Fauske, " Required Initial Conditions for Energetic Vapor Explosions," Fuel-Coolant Interactions HTD-V19, ASME Winter i

Annual Meeting, Wash. DC (November 1981).

l 23. R. E. Henry et al. , " Vapor Explosion Potentials Under LWR Hypothetical '

Accident Conditions," ANS Thermal Reactor Safety Mtg. , Sun Valley, ID (March 1981).

24. W. Schwalke et al. , " Investigations on Shock Waves in Large Scale Vapor Explosions," Fuel-Coolant Interactions, HTO-V19, ASME Winter Annual
Meeting, Wash. DC (November 1981).

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25. D. Squarer and M. Leverett, " Steam Explosion in Perspective," Int'1.

Mtg. on LWR Severe Accident Evaluations, Cambridge, MA (August 1983).  ;

26. T. G. Theofanous, M. Saito, "An Assessment of Class-9 (Core-Melt)

Accidents for PWR Dry-Containment Systems," Nuclear Eng. & Design, 66, 1 No. 3 (1982).  !

27. P. Turinsky et al., " Boiling Film Growth in a Core-Melt-Water System,"

2nd Proceedinc s of Nuclear Thermal-Hydraulics, ANS Annual Mtg. , New <

Orleans, LA (sune 1984).  !

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28. H. Unger et al., "The Role of Steam Vapor Explosions during Core Meltdown of LWR's," Int'1. Mtg. on Thermal Reactor Safety, Chicago, IL (August 1982).

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