The federal agency overseeing cleanup at the nation's most contaminated nuclear site is delaying a new cost and schedule estimate for a plant under construction there amid technical problems affecting the plant's design and safety.

The $12.3 billion waste treatment plant at south-central Washington's Hanford nuclear reservation is being built to convert highly radioactive waste into a stable glass form.

The plant is currently scheduled to begin operating in 2019, but some workers have raised concerns about erosion and corrosion in tanks and piping. Mixing issues also remain unresolved.

The U.S. Department of Energy said Tuesday that a new estimate will be pushed off for at least a year while it embarks on additional tests to resolve those problems. The tests are expected to cost tens of millions of dollars.