US to destroy 2,600 t of chemical stockpile

THE US army will start operating a US$4.5bn plant next week to destroy over 2,600 t of its mustard gas stockpile, complying with an international treaty banning chemical weapons.

The pilot plant was built by US construction company Bechtel to destroy around 780,000 munitions shells stored at the Pueblo Chemical Depot (PCD) in Colorado. The plant has proven its largely automated dismantling process using test shells that were rendered inert by the depot due to damage.

Rick Holmes, project manager of the pilot plant said: “This is a significant milestone. By working together – and doing it safely – we have made a once seemingly monumental task a reality.”

Bechtel’s process uses robotic equipment to first remove the explosives from the shells in a sealed chamber. The system then accesses the interior and washes out the mustard agent – which can damage the skin, eyes and airways on contact – with high pressure water and neutralises the agent with a basic solution and hot water. This causes a hydrolysate by-product to form which is treated with microbes to break it down into brine, and is then separated into a salt cake – which will be stored at a permanent facility – and water, which is recycled. The metal components are heat treated at 538°C for 15 minutes before being sent for recycling.

The system can currently destroy 4–6 shells/d, scaling to around 500 shells/d when the plant reaches full capacity next year. The project is expected to be completed in mid-2020, after which, Bechtel said “the plant will be closed in an environmentally responsible manner”. The project is part of wider preparations to eventually close PCD.

Paul Dent, operational readiness manager at the plant added: “Pilot testing…is scheduled to begin in early September with the delivery and receipt of agent-filled munitions, which will be gradually introduced into the plant. During the pilot test phase, data will be gathered to prove the plant operates as designed and permitted.”

Bechtel won the competition to destroy these agents in 2002. Before then, chemical munitions stockpiled during the Second World War and the Cold War were largely destroyed by incineration. The stockpile at PCD is the largest remaining stockpile, however a further 523 t of nerve and blister agents including mustard gas are stored in another facility at the Blue Grass Army Depot in Kentucky.

Bechtel also has a pilot plant at this facility which will use selected neutralisation followed by supercritical water oxidation to destroy these agents. The research team is currently testing samples of the produced hydrolysate to ensure it is properly processed and the destruction of the agent is confirmed using the oxidation method.

Blue Grass is expected to begin destroying its weapons by 2017, finishing in 2023.