Hydrogen deflagration tests in hydro-sc facility

In severe accidents, large amounts of hydrogen may be released in the safety containment of a nuclear plant and the gas mixture may become explosive. The University of Pisa and ENEA have undertaken an experimental program to study the physics of the flame propagation in a containment model in accidental conditions. Up to now 41 deflagration tests have been performed with HYDRO-SC facility at ambient pressure and temperature. Concentrations, water spray conditions, ignition source and gas turbulence level were varied. The vessel volume was 0.5 m3, the ignition sources were an electrical spark discharge and an electrically heated surface (glow-plug), the hydrogen molar fractions were in the range 4-16%, the turbulence was generated by fan or spray and two different spray nozzles were utilized. The experimental data indicate that the peak pressures nearly fit the adiabatic isochoric values at the highest hydrogen concentrations and gas turbulences. Weak pressure waves were observed for H2 molar fractions greater than 10%. a Careful examination of the pressure and temperature transients gave information on the flame path and on the heat transfer process during and after the combustion. The glow plus igniter has proved to be a reliable tool for use in deliberate ignition schemes for hydrogen control in nuclear plants