The National Nuclear Security Administration (NNSA) has authorized irradiation of up to 5,000 tritium rods every 18 months using two Tennessee nuclear reactors, one of seven options it was considering to meet national security requirements.
The semiautonomous Department of Energy branch said in a record of decision released Wednesday that it would implement its preferred alternative, which would involve tritium-producing burnable absorber rod (TPBAR) irradiation using the Watts Bar and Sequoyah nuclear reactor sites.
Tritium, a component of all the nuclear weapons in the U.S. stockpile, must be periodically replenished due to its short half-life. The material is extracted at the Savannah River Site in South Carolina from rods irradiated in one of the Tennessee reactors.
Currently, 704 TPBARs are irradiated at Watts Bar Unit 1 per 18-month cycle. The next cycle, to begin March 2017 in Unit 1, will increase that number to 1,104 TPBARs. The cycle after that is expected to involve irradiation of 1,504 TPBARs, according to an NNSA expert.
The agency expects to irradiate 3,000 TPBARs using two reactors around 2025. Unit 2 at Watts Bar will be used to reach that number, though the reactor is not yet fully operational, the expert said.
According to NNSA’s record of decision, although irradiation of 2,500 TPBARs over 18 months would be enough to meet near-term tritium requirements, authorizing the irradiation of up to 5,000 TPBARs better prepares the agency to meet future needs based on unexpected changes to its tritium requirements or events such as a prolonged reactor outage.
The latest environmental impact statement lowers the total amount of rods allowed to be irradiated to 5,000, down from the 6,000 TPBARs considered as the upper limit in a 1999 impact statement. The NNSA expert noted that the primary function of the latest record of decision is to allow the agency to ramp up its irradiation numbers to the 5,000 limit if necessary. However, the agency has not yet approached that number.
“The exact number of TPBARs to be irradiated during each/any 18-month reactor core cycle will be determined by both national security requirements and [Tennessee Valley Authority] reactor availability,” the record of decision said.
The agency could use up to four commercial light-water reactors between the two sites, each of which has two reactors. The agency chose this option to address the full range of tritium rods “that could, under any currently foreseeable circumstances, be irradiated in an 18-month period, at either or both the Watts Bar and Sequoyah sites, to satisfy national security requirements,” the decision said.
The other alternatives explored by the NNSA in a March 2016 supplemental environmental impact statement on tritium production included the no-action option, which would involve irradiation of up to 2,040 TPBARs every 18 months; one option for irradiation of up to 2,500 TPBARs and another for up to 5,000 TPBARs only at the Watts Bar site; and two separate options for irradiation of those same amounts only at Sequoyah.
The environmental impact assessment found that tritium releases and exposure from normal operations would not have any significant impact on worker or public health. The NNSA’s chosen irradiation amounts will increase potential tritium doses to workers and the public, the decision said, but all doses would fall “well within regulatory limits.”
The decision noted the Tennessee Valley Authority would construct a 500,000-gallon tritiated, or radioactive, water tank system at Sequoyah to mitigate the potential impacts of tritium releases, similar to the system employed at the Watts Bar site. These tank systems would store tritiated water coming out of the liquid radioactive waste processing system, which would then be released to the Tennessee River, the decision said. The water would be released during higher river flows for better dilution, the decision said, and the waste released would fall below regulatory concentration limits.
