Reactor 3 at the Fukushima Daiichi nuclear power plant used mixed-oxide (MOX) fuel that represented less than 6 percent of the total fuel in the core. This fuel had only been in the reactor for less than five months. Due to these factors, and the relatively small differences between the radionuclide content of MOX and low-enriched uranium (LEU) fuel, the use of MOX fuel did not have a significant impact on the offsite releases of radioactivity. The other reactors at Fukushima Daiichi did not contain MOX fuel.
MOX fuel has been safely used in over 40 reactors around the world. MOX fuel can be fabricated by using recycled plutonium from used LEU fuel and by using plutonium retrieved from disposing of surplus nuclear weapons. In Japan, as with most countries including France, Belgium, Germany and Switzerland, the MOX fuel used in the reactors was fabricated by recycling LEU used fuel. The U.S. and Russia are developing programs to fabricate MOX fuel from surplus nuclear weapons.
Currently, the U.S. reactor core designs only use LEU fuel. However, the majority of the reactors in the U.S. could utilize MOX fuel assemblies for up to 30 percent to 40 percent of the assemblies in the reactor core. As part of the U.S. program, a few MOX assemblies were fabricated to demonstrate the technical ability of U.S. reactors to safely utilize MOX fuel. Based upon the success of this demonstration program, the United States is pursuing fabrication of MOX fuel as a way to dispose of surplus nuclear weapons.
Which U.S. nuclear plants have previously or are currently involved in testing MOX fuel in their reactors?
“In the United States, mixed oxide (MOX) fuel test assemblies were irradiated at a number of commercial nuclear energy facilities in the 1960s, 1970s and early 1980s. However, MOX commercialization in the United States effectively ended in 1977, with the suspension of federal support for commercial nuclear fuel reprocessing due to proliferation concerns. Active U.S. pursuit of MOX fuel use was revived following the 2000 signing of the Plutonium Management and Disposition Agreement by the United States and the Russian Federation, under which each country intends to irradiate at least 34 metric tons of excess weapons-grade plutonium as fuel in reactors. For its part, the United States is constructing the MOX Fuel Fabrication Facility at DOE’s Savannah River Site in South Carolina to produce more than 1,700 MOX fuel assemblies for domestic use in commercial pressurized water reactors. Supporting the DOE plutonium disposition mission, Duke Energy loaded four MOX lead test assemblies—manufactured in France from U.S.-origin weapons-grade plutonium—into Catawba Unit 1 in 2005. The lead test assemblies were discharged in 2008 after two 18-month cycles.”
(Excerpted quote from: Program on Technology Innovation: Readiness of Existing and New U.S. Reactors for Mixed-Oxide (MOX) Fuel, A. Sowder, EPRI Report #1018895, May 2009.)