Around 8:30 a.m. on May 9, 2017, workers discovered that part of a tunnel had given way at the Hanford nuclear site in Southeast Washington. Hanford’s emergency response was activated and some 9,000 workers were evacuated.

The tunnel holds highly radioactive and chemical waste. It’s part of the PUREX plant, which once extracted plutonium from irradiated rods after they had gone through a nuclear reactor. The plutonium was made for bombs during the Cold War.

Now, that partially collapsed tunnel has been filled with grout, and officials are preparing to fill another larger tunnel nearby with truckloads of grout as well.  Critics worry the radioactive waste and steel in the grouted tunnels will become permanent waste dumps, because safely removing the debris will be difficult and expensive. 

The tunnels at the PUREX plant are just two of the hundreds of waste sites at Hanford that need cleaning up. It’s a job that will take decades and billions of dollars each year to complete. Correspondent Anna King has been covering the nuclear reservation and its cleanup for more than a decade. Here, she digs into the story of Hanford’s tunnels from multiple angles: