Containment and Seismic Isolation

Surrounding the reactor vessel is a containment vessel composed of a Chromium-Molybdenum alloy. The gap between the two vessels is pressurized with Argon gas. The containment vessel does not have to be large because it only has to be able to contain the fission gases and possible aerosols. This results from the fact that the coolant (Sodium) can only exist in the liquid phase in this reactor (the boiling temperature for Sodium is greater then the melting temperature of the reactor vessel).

Above the top of the containment vessel there is a containment dome. The original ALMR design did not have this dome because, as was explained above, the containment vessel is adequate to hold the fission gases. But from uneasiness about the technology and the fear that the public would view a reactor without a containment dome to be a potential Chernobyl, the NRC "suggested" the introduction of a containment dome for the ALMR.

As protection against damage from seismic events, the entire reactor module is horizontally seismically isolated (meaning the reactor will not move with the ground horizontally) with seismic isolation bearings. These bearings are made of alternating layers of natural rubber and steel. The bearings can secure a safe shutdown with ground motion up to .3-g (30% of the acceleration of gravity). However, the bearings can accomodate ground motion up to 1.0-g (100% of the acceleration of gravity) which would be considered a severe earthquake.