Fuel-coolant interactions

Events of this nature have been described by various terms, e.g., rapid phase transitions (RPTs), vapor explosions, explosive boiling, thermal explosions, and fuel-coolant interactions (FCIs). They have been reported in a number of industrial operations, e.g., when water contacts molten metal, molten salts, or cryogenic liquids such as liquefied natural gas (LNG). In the first two examples noted above, water is the more volatile liquid and explosively boils whereas, in the last example, the cryogenic liquid plays the role of the volatile boiling liquid and water is then the hot fluid. 

Hemy, R. E., Hohmmin, H., and Kottowski, H. (1979). The effect of pressure on NaCl-HjO explosions. Proc. CSNI Spec. Meet. Fuel-Coolant Interact. Nucl. Saf., 4th, 1979, Bournemouth, England. 

A violent vapor explosion can result when a cold volatile liquid is suddenly brought into contact with a hot liquid. The explosion is due to the rapid vaporization of the cold liquid from heat transfer from the hot liquid. Such explosions are referred to as vapor, steam, physical, or thermal explosions rapid-phase-transitions (RPTs) (typically when referring to explosions involving cryogenic liquids) and molten fuel-coolant interactions (FCIs) when applied to nuclear reactor accidents. Accidental vapor explosions are frequent occurrences in the metallurgical, pulp and paper, and cryogenic industries. General reviews of the various aspects of vapor explosions can be found in Reid [1] and Corradini et al. [2]. 

After fourteen tests, mainly with fresh fuel, this accident scenario may fairly well be described.lt has been shown that no violent, energetic fuel-coolant interactions take place, that almost no fuel is ejected out of the fissile zone and that the melt penetration into the neighbouring sub-assemblies proceeds fast. 

Fuel-coolant interactions (including steam explosions) ... 

If the accident cannot be arrested, core debris will accumulate in the lower plenum of the reactor vessel. It is usually estimated that something less than 50% of the core debris will collapse into this plenum which in many accidents will still contain water. Violent fuel coolant interactions could occur when hot or even molten core debris falls into the lower plenum. The stmctural consequences of such interactions are the topic of ongoing debate [S-11]. Assuredly, fuel-coolant interactions could produce dramatic increases in the flow through the reactor coolant system. These abrupt increases in flow will purge the reactor coolant system of suspended radionuclide vapours and particles. Flows might be... 

This technical note provides a good introduction to the literature of the thermal and mechanical processes associated with high temperature melt interactions with water. For further information on such interactions see also Proceedings of the OECD/CSNI Specialists Meeting on Fuel-Coolant Interactions, M. Akiyama, N. Yamano, and J. Sugimoto, editors, NEA/CSNI/R(97)26, May 19-21, 1997, Tokai-Mura, Japan. There has been little study of the implications of these interactions on the accident source term. 

This re-examination of the analyses discussed in S-16 concludes that the source term from fuel-coolant interactions is likely to be small. 

Extensive release of ruthenium in case of violent fuel coolant interactions remains controversial [Ex. 2a - 2b] and though possible explanations have been provided to justify why such releases would be minimal, no experimental validation substaining the magnitude of this phenomenon currently exists. Anyway releases caused by melt interaction with water would only produce temporary increases in the containment atmosphere concentration of radioactive aerosol. So long as containment integrity is preserved, such releases are not risk significant. Again, the mass releases can cause difficulties for some filter systems because of water droplets created by the core debris interactions with coolant. 

Ex-3a. Proceedings of the OECD/CSNI Specialist Meeting on Fuel-Coolant Interactions, May 19-... 

Ex-3b. S. Basu and T. Ginsberg, A Reassessment of the Potential for an Alpha-Mode Containment Failure and a Review of the Current Understanding of Broader Fuel-Coolant Interaction Issues, NUREG-1524, U.S. Nuclear Regulatory Commission, Washington, DC, August 1996. 

IFCI (Integral Fuel-Coolant Interactions Code). 

Marshall, B. W., Jr., Berman, M., and Kreln, K. S., "Recent Intermediate Scale Experiments on Fuel-Coolant Interactions In an Open Geometry (EXO-FITS)," Proceedings of the International American Nuclear Society/European Nuclear Society Topical Meeting on Thermal Reactor Safety. San Diego, CA, Feb. 2-6, 1986. 

Anderson, R. P. and Armstrong, D. R., "Experimental Study of Small Scale Explosions In an Alxjunlnvim-Water System," Fuel-Coolant Interactions. Vol. 19, Heat Transfer Division, American Society of Mechanical Engineers, New York, NY, 1981. 

Sharon, A. and Bankoff, S. G., "Fuel-Coolant Interaction in a Shock Tube with Initially-Established Film Boiling," Northwestern University, Evanston, IL, Rept. No. COO-2512-16, Feb. 1979. 

Kottowskl, H. M. and Mol, M. M., "Importance of the Coolant Impact on the Violence of Vapour Explosion," Presented at the Fourth Committee on the Safety of Nuclear Installations (CSNI) Specialist Meeting on Fuel Coolant Interaction in Nuclear Reactor Safety, Bournemouth, United Kingdom, April 2-5, 1979. 

Application of the Integrated Fuel-Coolant Interaction Code to a FITS-Type Pouring Mode Experiment... 

Kim, B., "Heat Transfer and Fluid Flow Aspects of Small-Scale Single Droplet Fuel-Coolant Interactions," Ph.D. Dissertation,... 

Marshall, B.W., Jr., "Recent Fuel-Coolant Interaction Experiments Conducted in the FITS Vessel," 25th American Society of Mechanical Engineers/American Institute of Chemical Engineers National Heat Transfer Conf., Houston, TX, July 1988. 

Cronenberg, A.W., Recent Developments in the Understanding of Energetic Molten Fuel Coolant Interaction , Nuclear Safety, Vol. 21, May-June 1980, pp. 319-337. 

Young, M.F., Berman, M., and Pong, L.T., Hydrogen Generation During Fuel/Coolant Interactions , Nuclear Science Engineering, Vol. 98, Jan. 1988, pp. 1-15. 

Fletcher, D.F., The Particle Size Distribution of Solidified Melt Debris from Molten Fuel-Coolant Interaction Experiments , Nuclear Engineering fc Design, Vol. 105, Jan. 1988, pp. 313-319. 

Fletcher, D.F., Modelling Transient Energy Release from Molten Fuel Coolant Interaction Debris , AEE Winfrith Rept. AEEW-M2125, Dorchester, Dorset, U.K., 1984. 

Dullforce, T.A., Buchanan, D. J., and Peckover, R.S., Self-Triggering of Small-Scale Fuel-Coolant Interactions 1. Experiments , Journal Physics D Applied Physics, Vol. 9, 1976, pp. 1295-1303. 

The reactor vessel lower head has no vessel penetrations, thus eliminating penetration failure as a potential vessel failure mode. Preventing the relocation of molten core debris to the containment eliminates the occurrence of several severe accident phenomena, such as exvessel fuel-coolant interactions and core-concrete interaction, which may threaten the containment integrity. Therefore, AP 1000, through the prevention of core debris relocation to the containment, significantly reduces the likelihood of contaimnent feilure. 

The hydrogen gas produced in-vessel can escape to containment, where its combustion can pressurize and heat the containment. Violent in-vessel fuel coolant interactions have the potential to fail the reactor vessel, or even containment, with the accompanying forceful ejection of radionuclides. The melting and downward relocation of core materials in the reactor vessel, if unarrested by the restoration of coolant, can breach the reactor vessel resulting in the discharge of hot core debris, radionuclides, and aerosols into Containment, where they may interact with the containment... 

Core SlumDin2.0uenchtn2. Reheating 3.5.1 Fuel-Coolant Interactions (FCIs)... 

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