CLEMENTINE, a very small reactor with a power of up to 25 kW, is noted as the one reactor which was cooled by mercury. It was fueled by plutonium clad in steel with a slug of natural uranium at each end. Control of the system was achieved by moving uranium reflector and boron-10 safety rods. Figure 4.43 shows a cross section of the reactor (48).

Irradiation defects eventually caused the uranium plugs to swell and burst the cladding, allowing the plutonium and mercury to mix. This mixture is

a pyrophoric solution that vastly complicated the eventual disassembly of the reactor system. In addition, the uranium safety block swelled and stuck immovably.

One interesting safety highlight during the operation of the reactor con­cerned the possibility of damaging the system by propelling some object down the neutron window (seen to the right of the core in Fig. 4.43). Just in case, as a safety measure, the guards in the building were disarmed rather than stand the chance of one of them firing his revolver down into the core.

Safety related incidents are likely to continue; it is up to the safety engi­neer to learn from the errors so far committed, to collect the data from each occurrence, and to create more reliable systems.