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NKS Programme Area:
Severe accidents and Reactor Physics
Structural integrity of a reinforced concrete structure and a pipe outlet under hydrogen detonation conditions
Arja Saarenheimo, Ari Silde, Kim Calonius
Structural integrity of a reinforced concrete wall and a pipe penetration under
detonation conditions in a selected reactor building room of Olkiluoto BWR were
studied. Hydrogen leakage from the pressurised containment to the surrounding
reactor building is possible during a severe accident. Leaked hydrogen tends to
accumulate in the reactor building rooms where the leak is located leading to a
stable stratification and locally very high hydrogen concentration. If ignited, a
possibility to flame acceleration and detonation cannot be ruled out.
The structure may survive the peak detonation transient because the eigenperiod
of the structure is considerably longer than the duration of the peak detonation.
However, the relatively slowly decreasing static type pressure after a peak detonation
damages the wall more severely. Elastic deformations in reinforcement
are recoverable and cracks in these areas will close after the pressure decrease.
But there will be remarkable compression crushing and the static type slowly
decreasing over pressure clearly exceeds the loading capacity of the wall.
Structural integrity of a pipe outlet was considered also under detonation conditions.
The effect of drag forces was taken into account. Damping and strain rate
dependence of yield strength were not taken into consideration. The boundary
condition at the end of the pipe line model was varied in order to find out the effect
of the stiffness of the pipeline outside the calculation model. The calculation
model where the lower pipe end is free to move axially, is conservative from the
pipe penetration integrity point of view. Even in this conservative study, the highest
peak value for the maximum plastic deformation is 3.5%. This is well below
the success criteria found in literature.