The National Nuclear Security Administration and the Tennessee Valley Authority announced last week that they intend to enter into an agreement to “down-blend” highly enriched uranium to low-enriched uranium in order to help produce tritium, a key “boosting” component in nuclear weapons.

The highly enriched uranium used for the “down-blending” is processed, packaged, and shipped from the Y-12 National Security Complex in Oak Ridge, according to the NNSA. Y-12 is the main storage facility for certain categories of highly enriched uranium, which can be used in nuclear weapons and in naval reactors.

Low-enriched uranium, or LEU fuel, is used in a commercial power reactor run by TVA at the Watts Bar Nuclear Plant Unit 1 near Spring City in Rhea County, southwest of Oak Ridge. Tritium is produced there by irradiating lithium-aluminate pellets with neutrons in rods known as tritium-producing burnable absorber rods, or TPBARs.

The irradiated rods are then shipped to the Savannah River Site, an NNSA production facility near Aiken, South Carolina. The Savannah River Site extracts the tritium from the irradiated rods, purifies it, and adds it to the existing inventory, according to the NNSA’s Fiscal Year 2018 Stockpile Stewardship and Management Plan.

Tritium is a radioactive isotope of hydrogen that has two neutrons and one proton. It has been described as an essential component in every nuclear weapon in the U.S. stockpile. It occurs naturally in small quantities but must be manufactured to obtain useful quantities. It enables weapons to produce a larger yield while reducing the overall size and weight of the warhead in a process known as “boosting,” the U.S. Department of Energy said in an environmental impact statement about 20 years ago.

But unlike other nuclear materials used in nuclear weapons, tritium decays at a rate of 5.5 percent per year—its half-life is about 12 years—and it must be replenished periodically.

The NNSA, a separately organized agency within DOE, said the agreement with TVA that was announced last week is for management of the down-blending campaign and the resulting material. It’s separate from an existing interagency agreement for irradiation services that started in 2000 and is in effect until November 30, 2035.

“Without this down-blending campaign, we would need to accelerate the development and execution of a strategy to provide LEU fuel for tritium production by nearly a decade,” said Phil Calbos, NNSA’s acting deputy administrator for defense programs.

The new agreement follows a determination by U.S. Energy Secretary Rick Perry on August 21 that allows the NNSA to continue transfers of enriched uranium from DOE’s inventories in support of national security, the NNSA said in a press release.

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