The prime examples of this type of circuit are those used in the Magnox, pres- surized-water, and CANDU reactors. The circuits for these reactors are illus­trated in Figures 2.4, 2.8, and 2.11). In normal reactor operation there is a multiplicity of loops, as illustrated in Figures 3.5 and 3.6, which show the posi­tions of the individual loops in the P^TC. and C. ANDU systems, respectively. Note that in the P^TC. the loops come together in the reactor core, whereas in the CANDU reactor they are always totally separate. This has important impli­cations for safety considerations with these reactors, as we shall see in Chapter

4. A typical modern large P’^TC has three or four loops, depending on the size, each loop handling typically 300 ^MW of electric power production (corre­sponding to generation in the reactor core of 900 ^MW of thermal energy for each loop). Smaller reactors have two loops, with the size of the steam genera­tors and other components within a loop kept approximately the same. Some

of the earlier P^WRs had a four-loop design, notwithstanding their smaller over­all size and much smaller output per loop (e. g., the Shippingport and Yankee Rowe reactors). The move toward standardization in the mid-1960s led to much larger reactors and much larger powers per loop.