Modern standards apply the principle of defence in depth: accident prevention, control of abnormal events, redundant and independent systems, containment, and emergency management. The IAEA requires that events with large early releases be prevented or practically eliminated at the design stage. A residual risk remains, as with any large industrial infrastructure, but it is not correct to say that safety relies on a single barrier.
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3.
Are modern nuclear power plants really safe?
Yes, in the engineering sense; it does not mean zero risk.
