Investigation of Nonstationary Combustion of Hydrogen-Steam-Air Mixtures and Decrease of NPP Containment Loads under Severe Accident
Tech Area / Field
- FIR-ENG/Reactor Engineering and NPP/Fission Reactors
3 Approved without Funding
Joint Institute for High Temperatures RAS, Russia, Moscow
- Nuclear Safety Institute, Russia, Moscow\nAtomenergoproekt, Russia, Moscow
- Saitama University / Depatment of Mechanical Engineering, Japan, Saitama\nUniversity of Michigan, USA, MI, Ann Arbor
Project summaryThe purpose of the project is the study unsteady combustion regimes of hydrogen-air mixtures, at which pressures that are much higher than those ones in the front of a stationary detonation appear. Such pressures can form in the reactor containment of a nuclear power plant (NPP) in case of severe accident conditions. The aim of the project is also to investigate the means of reducing the loads on the protecting envelope of a NPP in case of a hydrogen explosion in a NPP by means of a damper made of some porous material.
This project is directed to the development and realization of the results received from the Projects ISTC P-066-94 - «Investigation of accelerated flame propagation and deflagration-detonation transition in large volumes of hydrogen - steam - air mixtures with the aim to determine and to reduce loads on nuclear reactor containment at severe accident conditions» and ISTC P-065-94 - «Forecasting loads on nuclear reactor containment during severe accident conditions».
Any detonation as well as hydrogen - air mixtures unsteady combustion regimes at which fast velocities approach detonation ones are known to present a serious danger both for the containment and the elements of construction. It is a common opinion that the significant flame acceleration in large volumes of hydrogen - air mixtures is impossible and that is why an emergence of such regimes or a transition to detonation in the containment under severe accident is considered to be unlikely. However, the acceleration of flame up to the very fast velocities close to detonation ones is not compulsory for the formation of destructive loads. The investigations of the regimes of hydrogen - air mixtures unsteady combustion in pipes and also in the elements of some other geometry were carried out in the Project P-066-94. These investigations have shown that pressures up to dozen bars have been developed at the presence of places of subsonic burning in case of using some of the investigated shapes.
The essential achievement of project P-066-94 is putting into operation of the spherical explosion chamber with a diameter of 12 m, capable of withstanding the explosion of TNT cartridge up to 1000 kg. It is supposed to use this chamber for investigation of the regimes of unsteady combustion, the initiation and the development of the explosions of hydrogen - air mixtures in large volumes at models of large dimensions at heightened initial pressures. Likewise, it is supposed to carry out experiments in a cylindrical steel explosion chamber with volume of 110 m3, in detonation installations with a receiver, and in shock tubes.
It is supposed to develop the engineering approaches to the estimation of the combustion and explosion waves loads on the elements of construction and in the containment according to experimental and numerical studies.
In case of severe accident at NPP the pressure inside of the containment can be increased up to some bars. Analytical studies have shown, that at a heightened pressure and temperature the time of the ignition delay is decreased, and the speed of combustion of inflammable mixture is increased, leading to a quicker achievement of conditions for three-dimensional explosion, and to more destructive consequences. Experimental and computational studies of the conditions of the origin and development of hydrogen explosion at heightened pressures also will be under consideration in this project.
The problem of the critical energy of an explosion is basically important for the estimation of the possibility of its appearing and destructive consequences. A new, more realistic model of diffraction of the detonation wave was offered in the Project P-066-94. According to this model and diffraction experiments, physical and the numerical models of the definition of the critical energy for the formation of spherical detonation will be developed.
When studying severe accident, the possibility of the abrupt increase of hydrogen generation in case of melted zirconium dispersion has not been investigated. Though this can play a definite role and lead to the formation of extreme cases in a shorter period of time. The regimes of hydrogen generation of such kinds are supposed to be studied in this project.
It was shown in the Project ISTC P-065-94, that it is possible to conserve the protection functions of the NNP containment of VVER 1000 type in case of severe accident and the subsequent explosion of hydrogen-steam-air mixture by means of creating a damper protecting the containment from destructive loads. Using of the damper consisting of a layer of porous material covered by a protecting steel envelope, permits to decrease the blast wave impulse pressure on a wall of the containment up to the permissible value with the simultaneous increase of the time of its action. The description of the blast wave propagation, the method of damper protection calculation, and the method of the calculation of a ferro-concrete envelope under dynamic loads (including the model of the concrete behavior) received in the project P-065-94, and also new data about the pressure impulse magnitude permit to begin the developing of recommendations concerning materials used in a damper, and optimal damper parameters.
Potential Role of Foreign Collaborators
Foreign partners can take part in the elaboration of the investigations of the project, in the discussion of the experiments, in analyzing of the obtained results, and in working out recommendations concerning the application of the results for the designing of new NPPs. The Russian participants of the project are greatly interested in collaboration and cooperation with scientific laboratories of the USA, Germany, Italy, Canada, France, Finland and Japan.
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