Work on this system has now largely ceased in the United States and in Europe. However, it does have very different characteristics from either of the other systems and is worth including (Fig. 2.3).

The design considered could employ either stainless steel clad pins or stainless steel cermet. The coolant is supercritical steam; therefore the

system pressure is very high in the range of 3700 psia. Temperatures are very close to those of the LMFBR system.

With steam coolant a direct cycle system is the natural design configura­tion, although steam cycle efficiencies may demand one or more stages of reheat. Table 2.1 shows the main characteristics of the supercritical steam — cooled system.