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Conditions of Ignition and Combustion of Graphite in NPP-Reactor

#0970


Theoretical and Experimental Investigation of Ignition and Combustion of Reactor Graphite under Conditions of Accident at the Fourth Reactor of the Chernobyl Nuclear Power Plant

Tech Area / Field

  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors

Status
3 Approved without Funding

Registration date
23.04.1997

Leading Institute
Institute of Problems of Chemical Physics, Russia, Moscow reg., Chernogolovka

Supporting institutes

  • Federal State Unitary Enterprise Research and Development Institute of Power Engineering named after N.A.Dollezhal, Russia, Moscow\nKeldysh Research Center, Russia, Moscow

Collaborators

  • AEA Technology, UK, Chesire, Risley Warrington\nUniversité de Poitiers / Laboratoire de Combustion et de Détonique, France, Futuroscope\nOmega Thermal Technologies Inc., USA, NJ, Blackwood\nEuropean Commission / Joint Research Center / Institute for Systems, Informatics and Safety, Italy, Ispra\nUniversity of California / Department of Mechanical Engineering, USA, CA, Berkeley

Project summary

The assessment of the elements state in active zone of the fourth block of Chernobyl Nuclear Power Plant (NPP) performed by Ukrytie, RIMQPP, et.al. showed that currently up to 800 of initial 1760 ton of reactor graphite is in the reactor chamber. Graphite ignition and combustion could be one of possible reasons of such considerable decrease of its amount. At the same time, it is well known that graphite combustion in air is possible only under special conditions. That is why the assessment of possibility and investigation of conditions of graphite ignition and combustion in air is undoubtedly of practical and scientific interest.

The objective of the Project is complex experimental and theoretical research of possibility of reactor graphite ignition and combustion under conditions similar to those in the active zone after the explosion in the fourth block of Chernobyl NPP.

In our opinion, such researches are necessary to improve efficiency of safety systems of nuclear power plants that must take into account the possibility of conflagration caused by ignition and combustion of non-nuclear reactor materials, graphite in particular. Information about ignition conditions and development of graphite combustion will constitute a scientific base for design of efficient tools to prevent and eliminate such conflagrations. On the other hand, such information will supplement the existing pattern of events after the explosion in the fourth block of Chernobyl NPP.

Investigations performed in ICPC RAS show that ignition and combustion of solid fuel under conditions of filtrational combustion can be significantly promoted in superadiabatic combustion regime. Preliminary laboratory experiments performed in ICPC showed that graphite ignites and burns steadily under superadiabatic conditions even at the temperature in the combustion zone of ~1500°C. Then, the principal combustion products are carbon monoxide, as well as hydrogen if steam is present in air. This leads to formation of combustible gases that when mixed with air at outlet from the reactor can give rise to secondary flame outside the filtration zone.

Mineral incombustible components (e.g., concrete pieces) do not prevent but can even activate superadiabatic combustion and can lead to significant raise of local temperature. The mechanism of graphite combustion is similar to that of coal. The main difference is the lower reactivity of graphite and hence the ignition temperature higher than that of coal. The graphite ignition is promoted significantly by zirconium.

The proposed Project is a complex theoretical and experimental investigation and comprises:


1. Analysis of primary information about the state of active zone and materials in it after the explosion in the fourth block of the Chernobyl NPP.
2. Research on kinetics of chemical reactions between graphite and oxygen in the air.
3. Gas dynamics and heat models of the possible developments after the explosion.
4. Theoretical analysis of mechanism of graphite ignition and combustion.
5. Experimental study of mechanisms of graphite ignition and combustion.

The scientific interest in the Project is to determine the special conditions of graphite ignition and combustion in air.

The practical merit of the Project is determined by the possibility to use the results for design of efficient tools to prevent and eliminate conflagrations caused by ignition and combustion of non-nuclear reactor materials.

The potential role of the foreign collaborators will be the discussion of physical models of reactor graphite ignition and combustion, the discussion and statement of the mathematical models taking into account different physic-chemical processes during filtrational ignition and combustion of graphite, the discussion of concrete problems and results obtained, possible extension of methods for analysis of gaseous products of graphite gasification, the development of experimental procedures and carrying out joint researches.


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