Large-scale enclosure system

In general, micro-scale methods - for example, the formation of mineral precipitates in the pore space of a sediment waste body -will be employed rather than using large-scale enclosure systems such as clay covers or wall constructions. A common feature of geochemically designed deposits, therefore, is their tendency to increase overall stability in time, due to the formation of more stable minerals and closure of pores, thereby reducing water permeation. 

Most new concepts in fixed-bed reactor design are for very large scale production, and hence we only mention them briefly here. The radial reactor, a relatively well-known design, allows radial flow of gas between the tube and shell sides of the conventional multitubular reactor (through perforations in the tube walls). On the other hand, in the newer spherical fixed-bed reactor (see Hartig and Keil, 1993), flow across the catalyst is accomplished by placing it between two perforated spherical shells inside a solid spherical enclosure. The reactant is introduced between the outer shell and the enclosure and flows through the catalyst between the shells into the inner shell from where it exits the system. 

Fabrication of the large size vessels required for the pool-type LMFBR s may be a problem. Field fabrication may be required and strict quality control will be extremely important. The top closure region may prove to be especially difficult as size is increased in that it must serve simultaneously as a shield, gas enclosure, and component support. The loop system appears to offer fewer problems in scaling to large sizes. It will also be much more flexible with respect to possibilities for eventual elimination of the intermediate sodium system. Elimination of the secondary sodium system from a plant containing a pool primary does not appear possible since this would require introduction of water into the reactor vessel. 

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