15.63. The four concepts previously described incorporate passive fea­tures in basically proven systems that have been converted to a smaller size amenable to modular construction. For the two LWRs, the passive features permit substantial system simplification with accompanying eco­nomic benefits. An improvement in public acceptance is also expected.

15.64. Other concepts have been proposed which have an improvement in public acceptance as a major objective. Probably the most interesting of these is the process inherent safety (PIUS) reactor developed in Sweden. Also of interest is the safe integral reactor (SIR), which has evolved from a system originally proposed for maritime use. We will briefly describe each of these.