Fukushima. The Danger of Re-Criticality of Destroyed Fuel

During the accident at three units of the Fukushima-1 Nuclear Power Plant (NPP) the melt of the core materials (corium) destroyed the lower part of the reactor vessels, and some of the corium spilled onto the structures in the containment. As a result, accumulations of FuelContaining Materials (FCM) were formed.
In the event of re-criticality both the corium remaining in the reactor vessels and FCM may pose a hazard. Thus when extracting them from damaged NPP units, such hazards must be dully accounted for.
The paper focuses on nuclear safety measures both taken and planned in the elimination of the Fukushima-1 NPP accident consequences.