This spring, a tunnel at the Hanford nuclear site in southeast Washington caved in, threatening to expose radioactive waste. Declassified blueprints reveal how the failure happened.

The tunnel cave-in happened outside of Hanford’s Plutonium Uranium Extraction Plant - PUREX for short. The plant was built from 1953 to 1955 and opened “hot” in January 1956.

The plant’s main goal:  to concentrate as much plutonium as possible from irradiated rods coming out of Hanford’s reactors.

Near the PUREX plant, Hanford workers filled an underground train tunnel with old railroad freight cars, containing used heavy equipment and contaminated with highly-radioactive waste.

PUREX Tunnel 1 was filled with used heavy equipment.

PUREX Tunnel 1 was filled with used heavy equipment.

MacGregor Campbell/OPB

But the tunnel’s design wasn’t meant to last forever. Blueprints show its design and materials. It was built out of concrete, timbers and heavy-duty roofing covered in desert sand.  

Tunnel 1 was built out of concrete and timbers, topped with desert sand.

Tunnel 1 was built out of concrete and timbers, topped with desert sand.

MacGregor Campbell/OPB

Critics say it should have been stabilized or cleaned up decades ago. And one of the main concerns about the tunnel collapsing even further is that it could send up a radioactive plume of dust that could hurt workers or drift beyond the nuclear site.

Now, the Department of Energy plans to fill the tunnel with grout, so it can’t collapse again.

Right now, federal contractors are preparing to move large trailers near the site for workers. And they’re working on plans to improve the roads to PUREX, so trucks loaded with that grout can get there.

And Washington state’s Department of Ecology says it’s re-evaluating its own schedule to inspect old infrastructure and buildings like the waste tunnel.

But with hundreds of aging buildings and waste sites at Hanford from WWII and the Cold War — this tunnel collapse likely won’t be the last emergency at Hanford.