OAK RIDGE, Tenn. — The Y-12 nuclear weapons plant in Tennessee has resumed rebuilding parts for W76 warheads for the submarine-launched Trident missile system.

A spokesman for the National Nuclear Security Administration told The Knoxville News Sentinel that classified technical problems that stalled the high-priority work for months have been resolved.

Y-12 rebuilds components as part of a warhead life extension program. The Oak Ridge plant specializes in so-called secondaries — the second stage of nuclear warheads — made of highly enriched uranium.

NNSA spokesman Steve Wyatt says the first production unit for the renewed W76s should be completed “late this year.” The newspaper reports that’s apparently about a year behind schedule.

The W76 entered service in 1978 and has been called “the most critical element of our nation’s strategic deterrent.”