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is3_72 - trapped within the fuel's structure very near the...

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Radiological Emergency Management Independent Study Course 3-12 Defense-in-Depth The defense-in-depth approach ensures that any release of hazardous amounts of radioactive materials will be extremely unlikely. This approach uses three barriers to prevent the release of fission products from the reactor core to the environment. These consist of: 1. Fuel rods (fuel pellet and fuel cladding). 2. Reactor vessel and primary coolant system. 3. Containment. The chance of any single barrier failing is unlikely. The chance of all three failing simultaneously is, therefore, extremely remote. Fission Product Barriers Fuel Rods The first barrier designed to prevent an inadvertent release of radioactive material from the reactor core is the nuclear fuel rod itself. During normal operations, about 99 percent of all fission products remain
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Unformatted text preview: trapped within the fuel's structure very near the point at which they were generated by fission. The fuel cladding which encases the nuclear fuel is designed to contain the remaining 1 percent. The release of fission products from the fuel rods would require a breakdown of the fuel cladding. If the core is not sufficiently covered with water to provide cooling, it could overheat resulting in a breakdown of the fuel cladding and the release of fission products in a short period of time. Additional overheating could cause the release of some of the 99 percent of the fission products normally trapped in the fuel structure. Still more overheating could cause the fuel to actually melt. This is often referred to as a "meltdown"....
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