Part of the roof in a waste-storage tunnel collapsed at the Hanford nuclear site in 2017, forcing thousands of workers to take cover. Yet a January report suggests the U.S. Department of Energy has avoided finding out exactly why the collapse happened.

The new Government Accountability Office audit revealed that, while Hanford conducted an engineering evaluation of Plutonium Uranium Extraction (PUREX) Tunnel 1 after the collapse, officials said they did not launch an accident investigation because the incident did not meet the Department of Energy threshold of damages or costs exceeding $2.5 million. “However,” the report states, "GAO’s analysis shows that the costs of responding to the event and stabilizing the tunnel were about $10 million.”

The report also found that various parts of the vast nuclear reservation -- including the Reduction-Oxidation Facility -- have not been entered or remotely inspected in 50 years, leaving “structural conditions” in those sections a mystery.

No Hanford workers were injured in the 2017 partial tunnel collapse, and it appears no radiation escaped into the air. But the GAO report recommended the Energy Department seek out the “root cause” of the collapse and use robotic and other means to conduct routine inspections of the entire nuclear site.

Read the GAO report.

Hanford made plutonium for nuclear weapons during the Cold War. The site in south-central Washington remains widely contaminated with “high-level” radioactive waste, and the U.S. government spends about $2.5 billion per year cleaning it up. The Trump administration is proposing a $700 million budget cut next year for the work.

In January, the state of Washington fined Hanford $1 million for “restricting access to critical data.” The Energy Department plans to appeal the fine.

-- Douglas Perry

@douglasmperry

Subscribe to Oregonian/OregonLive newsletters and podcasts for the latest news and top stories.