Stabilisation work on second Hanford tunnel nears completion

05 February 2019

Work to stabilise a 1688-foot (515-metre) long tunnel containing contaminated equipment from historic plutonium production activities at the US Department of Energy's (DOE's) Hanford site in Washington State is over 75% complete.

Grouting work at Hanford (Image: @HanfordSite)

The operation to stabilise PUREX Tunnel 2 with grout began in September 2018. To date, over 28,166 cubic yards (21,534 cubic metres) of grout - 2830 truckloads - have been used in an operation that has seen pouring operations take place eight hours per day and five days per week, according to the latest update from Hanford Site. In total, around 38,900 cubic yards of grout will be needed to complete the interim stabilisation process, which is due for completion in March.

Two tunnels were constructed in the 1950s and 1960s next to the former Plutonium Uranium Extraction Plant (PUREX) near the centre of the Hanford Site called the 200 East Area. The soil-covered tunnels hold railcars that were loaded with contaminated equipment. Tunnel 1, which is about 110 metres long and contains eight rail cars, leads into the longer Tunnel 2, containing 28 railcars. The tunnels were sealed in the mid-1990s and are checked periodically.

In May 2017, a portion of the roof of Tunnel 1 collapsed. No radioactive materials were released and the hole was filled with sand and covered with a temporary cover within 48 hours, but the collapse prompted the Washington Department of Ecology to order the US Department of Energy to ensure both tunnels were stabilised to minimise the danger of further collapses.

Tunnel 1 was subsequently stabilised with grout during October and November 2017. A structural evaluation of Tunnel 2, carried out by the DOE after the collapse of Tunnel 1, found that although the tunnel had been correctly constructed, some components are now stressed above design capacity and are also corroding, with a related risk of future structural failure. The Department of Ecology in September 2018 approved the start of grouting of Tunnel 2 after a 45-day public comment period, finding that grout is the best way to ensure the tunnel and its contents are safe until final decisions can be made on how best to deal with the waste.

Researched and written by World Nuclear News