Assessment of Risk Studies and Severe Nuclear Accidents - The Risks of Nuclear Energy Technology - page 205

Fig. 10.6 BERDA experiments for melt slug impact on head of the reactor pressure vessel
(without and with internal structures) [ 37 , 40 ]

structures results in a decrease of the impact forces and an extension of the time
period for action of these impact forces (Fig. 10.6 ). The reactor head would
remain intact in this process.
- On the whole, at least 2.8 GJ of mechanical energy would have to be released in
the steam explosion to accelerate the core melt plus the gridplate upward,
compress the internal head structures of the reactor pressure vessel, and expand
the head bolts by a few mm.

This 2.8 GJ must be compared to the 0.45 GJ occurring in the steam explosion at
conservatively assumed efficiency of 15 % for the conversion of thermal into
mechanical energy. Even an efficiency of 40 %, i.e. 1.2 GJ, for the conversion of
thermal into mechanical energy in a steam explosion could not jeopardize the
mechanical integrity of the reactor pressure vessel [ 40 - 44 ].
Consequently, the steam explosion with failure of the reactor pressure
vessel and outer containment ( -mode failure) as assumed in WASH-1400 [ 9 ]

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