Unlike the volume of high-level or transuranic waste, which typically remains stable, the inventory of spent nuclear fuel at INL increases each year due to new shipments to the INL. This increase will continue until a permanent repository opens for disposal of spent fuel.

SNF is very "hot" when it is removed from a nuclear reactor—both "hot" as in hot to the touch (scientists call this thermal heat) and "hot" as in highly radioactive. It is typical practice to store SNF under water for a period of time after it is removed from a reactor so that water can provide cooling and shielding. Because the fuel normally loses about 99% of its radioactivity within a year of being removed from the reactor, wet storage is only required for about a year.

Because the INL is located directly above the eastern Snake River Plain aquifer, the State of Idaho wants spent fuel to be placed in dry storage as soon as possible.

Dry storage containers can be above or below ground. They don't corrode like wet storage basins do, and they are safer in the event of a catastrophe, like an earthquake or flood. A small break in the integrity of a dry storage container is a correctable problem, while a break in the integrity of a wet storage basin could result in the rapid loss of radioactively contaminated basin water to the environment, including the aquifer.

Some spent nuclear fuel that has already been placed into dry storage includes the damaged fuel and core debris from the Three Mile Island Unit 2 nuclear power plant. That reactor sustained a major accident in 1979, after which the fuel and reactor components were extensively studied by scientists at the INL.

Spent nuclear fuel is one of the three waste streams covered by the Settlement Agreement. (The other two waste streams are high level waste and transuranic waste.) Spent fuel is dealt with a little differently than the other two waste streams because of the role spent fuel plays in enforcing DOE and Navy obligations under the agreement. As part of the requirements of the agreement, the state of Idaho, DOE, and the Navy negotiated limits on the number spent fuel shipments that would be allowed to come to Idaho.

DOE and the Navy must also meet certain obligations in order to continue to ship spent nuclear fuel to the INL. These obligations include moving the spent fuel to safer water basins, placing the spent fuel into dry storage by 2023, and shipping all of the spent fuel out of Idaho by 2035. If DOE or the Navy does not meet its respective obligations, state can close its borders to further shipments.

The Settlement Agreement's spent fuel provisions are also unique because certain types of spent fuel (such as commercial power reactor fuel) are specifically excluded from the types of waste allowed to come to the INL.

As a requirement of the 1995 Settlement Agreement, DOE had to remove all spent nuclear fuel from the aged fuel storage basins by December 31, 2000. These basins, located in INTEC's building CPP-603, did not meet current earthquake safety standards, did not have the stainless steel lining newer basins have, and did not have a leak detection system.

The last basin was emptied eight months before the deadline, on April 28, 2000. Now DOE is evaluating options for decommissioning the storage basins and the canals that connect them, as well as dealing with the 1.5 million gallons of water they hold.

Spent fuel from the Navy's nuclear-powered submarines, aircraft carriers, and research reactors comes to the INL for examination at the Naval Reactors Facility (NRF). This work helps the Navy improve ship reactor operations and reactor design. Naval spent fuel is currently stored in a water basin at NRF. Some of the fuel has been transferred to other basin storage at INTEC. To reduce handling spent fuel in the water pools, NRF is building a Dry Cell Facility, which will allow disassembly and examination of the spent fuel in a dry condition, as well as loading of the spent fuel into dry storage containers.

As part of the federal government's commitment to move spent fuel from wet storage to dry storage, the Naval Reactors Facility has also constructed a Dry Fuel Storage Facility. Naval spent fuel will be moved here from pools at NRF and INTEC to await shipment out of Idaho. This facility will safely store naval spent fuel in a dry condition until it can be moved out of Idaho—to either a permanent disposal location in a geologic repository or to some other storage location outside of Idaho.

DOE has about 60 metric tons of sodium-bonded fuel, nearly all of it in Idaho. Argonne operated a sodium-cooled reactor, EBR-II, from 1961 to 1994, and about 25 metric tons of spent fuel remains from EBR-II operations. Another 34 metric tons came to INL, in the early 1970s, from the Fermi reactor in Michigan. Electrometallurgical Treatment (EMT) is a new process being used at Argonne that stabilizes the sodium-bonded spent fuel and makes it safer for disposal. DOE will treat the EBR-II fuel with this method over a 10-year period.

For interim storage, until the spent fuel can be shipped out of Idaho, the Settlement Agreement required DOE to make decisions about how to best store and transport spent nuclear fuel. After a reviewing all available options, DOE decided that a multipurpose canister would be used for storage and transportation of spent nuclear fuel. Depending on disposal criteria set by the yet-to-be-built spent nuclear fuel repository, the fuel may also be disposed of in the same container.

In 2002, the U.S. Congress designated Yucca Mountain in Nevada as the location to be used for permanent disposal of high level waste and spent nuclear fuel. The facility is currently under construction and a license for its use as a permanent repository has been submitted to the Nuclear Regulatory Commission. The facility should be open and operating with enough time to allow DOE to meet its requirement to have all the spent fuel out of Idaho by 2035.

Recent INL SNF management activities have focused on steps outlined in the Settlement Agreement to place the spent fuel into dry storage and prepare the spent fuel for shipment to a permanent repository. Argonne National Laboratory-West, which is located within the INL site but operated separately by the University of Chicago, and the Naval Reactors Facility have also made significant advances in SNF management.

• All spent nuclear fuel was removed from wet storage in CPP-603 by April 2000, eight months ahead of the Settlement Agreement milestone.
• INL dry storage and transfer facility contract was awarded to Foster Wheeler Environmental in May 2000.
• Movement of Three Mile Island Unit 2 fuel and core debris from wet storage to dry storage at INTEC was completed April 2001.
• Loss of Fluid Test (LOFT) reactor and commercial spent nuclear fuel was moved from wet storage at TAN-607 to dry storage in FY 2002.
• Materials Test Reactor (MTR) fuel was moved from wet to dry storage in FY 2002.
• Power Burst Facility (PBF reactor fuel was moved from wet to dry storage in FY 2003.
• As of 2004, the only wet storage facilities in use are the modern wet storage basin at INTEC (CPP-666), and the fuel basin at Naval Reactors Facility.
• INL dry storage and transfer facility operations are to begin in FY 2005.
• Movement of all spent nuclear fuel from wet to dry storage is scheduled to be completed by 2012, eleven years ahead of the Settlement Agreement milestone.