Approaches for protection against external hazards

In a world of natural and human initiated vicissitudes, nuclear power plants are to be configured to protect against external events such as high winds/missiles, earthquakes, floods, fires, aircraft crash [7] and also purposeful attacks such as airplane attack or rocket or tank 

As on-site fuel storage and fuel cooling do not take place for small reactors without on-site refuelling, the need for protecting spent fuel pools or fresh fuel storages does not arise. Protection of fuel shipments could generally follow traditional practice additionally, Pb and Pb-Bi cooled reactor concepts suggest to transport cores or cassettes of fuel encased in frozen Pb or Pb-Bi. 

The design approaches adapted for all small reactors without on-site refuelling fit well with the imperative for siting near population centres they intend to achieve an exceptionally robust safety posture with respect to initiating events both internal and external and combinations thereof 

Some of the concepts adopt an autonomous or semi-autonomous passive load follow feature such that no conceivable combination of multiple equipment and human errors occurring outside the reactor vessel could lead to core damage. As an example, this feature is incorporated in both very small reactors for autonomous operation (Table 3), as well as in the higher-powered Na cooled 4S (14 and 15) and the Pb-Bi/Pb cooled ENHS and STAR (24, 25, and 29) reactor concepts. 

The longer-term concepts of water cooled reactors — PFPWR50 (10), VKR-MT (11), AFPR (12), and FBNR (13) — attempt to exploit the high temperature durability of the TRISO fuel form, which offers a potential to preclude fuel disruption in nearly all conceivable off normal events. 

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