In another sign of the shrinking U.S. nuclear weapons stockpile, the Energy Department has curtailed operations at its Savannah River Site that produces radioactive tritium gas for warheads to increase their explosive yield.

Officials with the National Nuclear Security Administration (NNSA), the semi-autonomous DoE agency that operates the department’s nuclear weapons complex, confirmed last week that the Tritium Extraction Facility (TEF) at the South Carolina site has been placed in a “responsive operations mode” in which tritium is produced “on a limited basis.” NNSA also said TEF workers are being used in other operations.

NNSA officials said the TEF cutbacks began in November and will save the agency about $10 million per year.

The officials also said there are no “current shutdown plans” for TEF, which extracts tritium from nuclear fuel rods that are irradiated at the Tennessee Valley Authority’s Watts Bar reactor in Tennessee and then shipped in casks to Savannah River for processing.

However, two inspectors at Savannah River for the Defense Nuclear Facilities Safety Board (DNFSB), a federal agency that oversees safety at DoE sites, said in a March 27 memo that NNSA was considering a “temporary shutdown” of the TEF for up to 10 years.

Extended shutdown of the TEF would be notable because the new $506 million facility was just started up in November 2006.

In addition, a prolonged outage would indicate NNSA already has substantial reserves of tritium, which has a radioactive half-life of only 12.7 years and thus must be replenished in warheads periodically to maintain its effectiveness.

The DNFSB memo also said the “responsive operations” mode called for fully operating the TEF at least once a year for the next four years to avoid triggering costly “operational readiness review” requirements. The safety reviews are mandated for any complex DoE nuclear processing facilities that are restarted after prolonged shutdowns.

The curtailed tritium operations were revealed May 1 by Friends of the Earth, which suggested the reduced production signaled that the Obama administration was considering further nuclear weapons cuts.

While NNSA officials rejected that interpretation, the agency has been racheting up the dismantlement of U.S. warheads to meet arms control agreements with Russia, and Obama earlier this year announced a new round of negotiations with the Russians to further chop arsenals.

The DNFSB memo said the curtailed operations at the TEF were due to “a reduction in projected mission requirements.”