A recent audit found significant problems with the federally-managed nuclear waste treatment plant west of Idaho Falls.
The Post Register reports the audit outlined cost overruns, a lack of rigorous testing and other management issues at the Department of Energy facility known as the Integrated Waste Treatment Unit.
The DOE Office of the Inspector General's report says the project's construction costs have exceeded the $571 million cap set in 2010 and will likely continue to accrue.
The total taxpayer costs could reach $800 million or more before the plant is fully operational.
The plant is supposed to be running by the end of September under a deadline the DOE negotiated last year.
A DOE spokeswoman says the department's priority is to ensure safety before the plant begins operations.