Are you a Nuke? I completed the nuclear program many years ago as a MM (and top 5%... ok, it's a small horn, but I still blow it from time to time). If you're still in the program, then I don't envy you.

The supercritical steam density is very high! With such a high power density, the actual volume of steam contained in the steam generator need not be high. In fact, the interior volume of the steam generator coil itself is very small (a 1/4" outside diameter tube). The steam generator coil is contained in a protective shell along with everything else. Check out the web site. The greatest accomplishment of the inventor, Harry Schoell, is the system design where he managed to put everything into such a compact and light weight configuration.