Safety uranium carbides

The reactor configuration, shown in Fig. t, consists of a large outer cylindrical reflector shell of beryllium, into which the fuel (in the form of a cylindrical shell Of uranium carbide fuel elements) and an inner beryllium reflector are assembled by a ram which lifts them into the reflector. Originallyi the reactor control and safety systems consisted of rotary drums with a 120-deg boron sector running the full length of the core, which resided permanently in the outer beryllium reflector and were spring loaded for fail-safe control. ... 

Pebble-Bed Modular Reactor (PBMR) A nuclear reactor technology that utilizes tiny silicon carbide-coated uranium oxide granules sealed in pebbles about the size of oranges, made of graphite. Helium is used as the coolant and energy transfer medium. This containment of the radioactive material in small quantities has the potential to achieve an unprecedented level of safety. This technology may become popular in the development of new nuclear power plants. 

In terms of safety, two issues are regularly debated. First, the issue of nuclear waste and, second, concerns over potential terrorist attacks on nuclear power plants. The first objection may be overcome through the introduction of new types of power plants, such as the pebble-bed modular reactor.This type of reactor uses graphite balls flecked with tiny amounts of uranium, rather than conventional fuel rods. With the fuel encased in graphite and impermeable silicon carbide, the theory is that the waste should be relatively easy to dispose of.The terrorism fears are less easily addressed and may ultimately stall the construction of new plants in countries such as the U.S., where these worries are greatest. 

The core comprises fuel assemblies, the moderator, and complementary nuclear safety rods (on delivery to the supporting orbit). FA consists of a bundle (O Fig. 59.12) of densely packed carbide-graphite elements and of twisted carbide FEs of different compositions based on uranium enriched up to 90%. This design allows reducing the nonuniformity of power deposition and the coolant temperature at the FA outlet. 

C. M. HOPPER, Safety Analysis Report for Packaging (Oak Ridge ir-12 Plant Model DTi 14 Package for Enriched Uranium), Y/DD-244 Union Carbide Corporation-Nuclear Division, Oak Ridge Y-12 Plant, Oak Ridge. TN (1978). 

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