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30/01/15 The fourth ARCHER Newsletter was released on 30 January 2015. Read online here

21/01/15 The second ARCHER EUROCOURSE, hosted by NRG, was held in Petten from 19-20 January 2015. Click here for more info

26/11/14 The third ARCHER Newsletter was released on 26 November 2014. Read online here

28/10/14 The ARCHER final meeting was held on 21-22 Jan 2015 at NRG in Petten (NL).

27/10/14 The High Temperature Reactor (HTR) Conference was held from 27-31 October 2014 in Weihai, Shandong Province, China. Click here for more info

29/03/14 The second Newsletter was released on 28 March 2014. Read online here

Supported by

European Commission

Explosive Gas Mixtures: Flammability limits Study at ICARE-CNRS-Orléans

High temperature gas-cooled reactors are graphite-moderated and helium-cooled. The primary system consists of a reactor pressure vessel, a steam generator and a hot gas duct vessel. Water ingress into the reactor pressure vessel can occur if there is a rupture of a heat transfer tube in the steam generator. The mixture of helium and steam will subsequently enter the reactor and lead to the graphite corrosion of both fuel elements and graphite structures.

This oxidation process can be responsible for the formation of He-H2-CO-CO2-H2O-CH4 mixtures. It is then important to assess the ignition risk of these mixtures. The flammability limits of such complex mixtures are being investigated within the ARCHER project.

What are flammability limits?

Flammability limits are defined as the lowest and highest fuel molar fractions for which a self-sustained flame is obtained at fixed initial temperature and pressure. A slight composition change in one direction produces a flammable mixture, in the other direction a non-flammable mixture.

Experimental Setup and Methodology

In the present work, ignitions of different mixtures were performed in a stainless steel spherical combustion chamber or Spherical Bomb (Figure 1). The spherical bomb, made of stainless steel, has an internal diameter of 250 mm and has 4 optical accesses (2 of 70 mm optical diameter and 2 of 20 mm optical diameter) made of quartz glass.

It can sustain a pressure of up to 50 bar. The ignition was initiated at the center of the vessel by laser induced spark (LIS). The ignition and the subsequent flame propagation were visualised through a classical Z-type Schlieren setup with a high speed camera (Figure 2). The temporal behaviour of the induced overpressure following the ignition was measured with a fast piezoelectric pressure transducer (Kistler 601A model). An example of the recorded signal is given in Figure 3.

Example of Flammability Diagrams

The flammability limits of combustible mixtures identified by partners in the projects have been determined using two different diluents: Helium and Carbon Dioxide.