Confined vented explosion is a very complex topic as many parameters affect the phenomena, mainly because the flame front develops from an ignition source and travels through a medium which may involve complex boundary conditions and obstructions of various geometries.

Therefore, in the plant safety assessing step, it is important to provide correct estimates of the flame spreading rates as well as overpressures which may result from various explosion initiation scenarios. This will help designers for plant layout optimisation with the aim to minimize the risk associated with those events.

Although hydrogen explosion in unvented compartments was often simulated in the past, there were not many opportunities, so far, to simulate explosion in a vented room. With this purpose, a benchmark exercise was organized, based on simple hydrogen combustion experiments, performed in a vented compartment (Chamber for View of Explosion – CVE) at the Scalbatraio laboratory of University of Pisa (Italy). In that activity, many tests were performed by varying the initial hydrogen concentration and the obstacles inside the compartment.

The numerical codes used in the benchmark were lumped-parameter (LP) ones (ECART, ASTEC), which remain, for the time being, the customary tools for simulating hydrogen combustion accidents in current NPPs, because of their fast-running calculation capabilities also for large-scale scenarios.

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