Properties of Spent Fuel

Periodically, a portion of the fuel in a nuclear reactor is removed and replaced with fresh fuel. In the past, the average lifetime of fuel in the reactor was 3 years with one-third of the fuel being removed each year. More recently, attempts are being made to extend fuel lifetimes. 

Initially, the radioactivity levels of the irradiated fuel are very high (Fig. 16.8). Chemically, the 235U content has been reduced from its initial 3 to 1% while the 

238U content has been reduced from 97 to 94% (Fig. 16.9). 239Pu and other Pu isotopes are produced along with the fission products. 

The original plan for this spent fuel was to store it for about 150 d and then transfer it to other facilities for disposal as waste or reprocessing. In the United States, this transfer has not occurred, and most of the fuel has remained in cooling ponds at the reactor sites, for times that have exceeded 20 y. In this case, a closer look at the properties of irradiated fuel is justified. 

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He pointed out that safety requirements on storage, transport and disposal should take the actual properties of spent fuel or high-level reprocessing waste into account and the saf objective set for their treatment. This causes no problems. However, differences between spent fuel and high-level reprocessing waste affect the long term safety in final disposal, they are ... 

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