The neutron flux distribution in an ADR is affected by the degree of subcriticality. Figure 1.30 shows the radial distribution of the total flux in ADRs with ke = 0.995 and 0.95 compared with that in a critical reactor. The core is cylindrical, 1 m high and 2 m in diameter, with properties similar to those of the standard sodium-cooled oxide-fuelled core described in Table 1.1, but with a neutron source located on the axis. It will be seen that the source has little effect on the flux in the outer part of the core, but is higher close to the source and more so the greater the subcriticality. As in a critical reactor the effect on the power distribution can be reduced by varying the composition of the fuel in different radial zones (see section 1.3.2), but the peak close

to the source may necessitate specific design measures to avoid local overheating.

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