I have been looking for decent drawings of the Mark I Reactors. These are the best laymen oriented drawings I have found, courtesy of Mother Jones Magazine.
Mark I Reactor Components: (A) Uranium fuel rods; (B) Steam separator and dryer assemblies (C) Graphite control rods; (D) Vent and head spray; (E) Reactor vessel; (F) Feedwater inlet; (G) Low pressure coolant injection inlet; (H) Steam outlet; (I) Core spray inlet; (J) Jet pump; (K) Recirculation pump; (L) Concrete shell "drywell"; (M) Venting system; (N) Suppression pool; (O) Boron tank; (P) Condensate storage tank; (Q) High pressure coolant injection system; (R) HCIS turbine; (S) Automatic depressurization system; (T) Main turbine; (U) Connection to generator; (V) Condenser; (W) Circulating water; (X) Connection to outside service water; (Y) Concrete shield plug; (Z) Control rod drives. Illustrations by Joe Kloc.
A full color coded set of all four of the system drawings with concise explanations can be found here: Mother Jones Article
Looks ominously similar to this: