Runaway Conditions in Metal-Steam Reaction

Ezra Elias, Technion, Haifa, Israel
Dov Hasan, Technion, Haifa, Israel
Yuri Nekhamkin, Technion, Haifa, Israel

The concept of runaway metal-steam reactions was introduced in [1,2] by deriving a conjugate set of heat and mass balance equations for the time evolution of the temperature and oxide layer thickness on metal in an oxidizing steam environment. This classical metal combustion theory was extended to account for characteristic conditions taking place in a partially exposed boiler pipe (e.g., nuclear fuel channel rod during Loss of Flow Accident, LOFA).

We consider the upper section of an exposed heated channel in which the metal undergoes a thermochemical oxidation reaction with steam. The tube is assumed heated by both external power (e.g., electrical or nuclear decay heat) and by thermochemical oxidation reaction, while simultaneously cooled by steam entering the exposed section at a given temperature, and mass flow rate, min. The heat and mass balance equations for the steam, metal and oxide layer at the exposed section were non-dimensionalized and solved simultaneously to define a runaway criterion, ω, that basically defines the range of min and heat transfer coefficients, H, for which runaway oxidation prevails. The critical conditions were conveniently expressed as a 2-D parametric plot describing critical min vs. H for a range of characteristic temperatures that account for external heating, exposed channel dimensions and material properties.

Representative results obtained for (but not limited to) Light Water Reactor-like fuel-channel during LOFA, have demonstrated the utility of the derived criterion to predict runaway situations over a wide range of operational parameters.

Acknowledgments: Work supported by the Israel Ministry of Energy.


  1. Semenov, N. N., ZhRFKhO, Ch. Fiz., 1928, 60, 241.
  2. Elias, E., Hasan, D., Nekhamkin, Y., Zirconium Ignition in Exposed Fuel-Channel, Nuclear Engineering and Design 286, 2015, 205–210.
  3. Semenov, N. N., ZhRFKhO, Ch. Fiz., 1928, 60, 241.

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