nuclear fuel in the reactor is transferred out of the reactor. Once it leaves the reactor, the fuel is considered “spent nuclear fuel” — hence the acronym SNF. This begins the long process of storage. The indigo blue color that appears inside the reactor in the accompanying photo is not from a lighting system but instead the result of “Cherenkov radiation” — electrons emitted from the fuel are traveling faster than the speed that light travels in the water.
The first ”home” for spent nuclear fuel is a 40-foot deep water-filled pool constructed of reinforced concrete several feet thick that is lined with stainless steel. The water covers the SNF by approximately 20 feet, which provides a sufficient level of protection to shield workers from its intense radiation and heat. The spent fuel pool is located in very close proximity to the nuclear reactor itself. So the transfer of the fuel from the reactor to the spent fuel pool occurs underwater through specially design canels. After removal from the reactor, spent nuclear fuel must be stored in the spent fuel pool for at least 5 years; however, the industry norm is about 10 years. The SNF is “racked” in the spent fuel pools in an optimum manner to ensure adequate cooling while allowing for maximum storage. During this period of time, the fuel “cools” thermally and sheds a great deal of radiation.
In the early days of the U.S. commercial nuclear industry it was assumed that SNF storage at nuclear reactors would only be stored in spent fuel pool. In addition, it was assumed that storge would be relatively short — on the order of several years to a decade or two — before shipment off-site for either reprocessing or disposal. Today, however, SNF is being stored at nuclear reactor sites in much larger quantities and for much longer periods of time that originally envisioned. In fact, all SNF generated by commercial nuclear reactors in the U.S. current remains on-site — in some cases residing there for in excess of 40 years.
As of the end of 2010, the nuclear industry reported that the total amount of SNF stored in spent nuclear fuel pools in the United States was approximately 48,818 metric tons. While the Nuclear Regulatory Commission and the Department of Energy track the amount of nuclear fuel (in nuclear reactors and in spent fuel pools) closely, the information is withheld from the public for security reasons. The amount of SNF being generated in the US increases each by 2,000 to 2,400 metric tons.