Bug custard

日期:2019-03-07 03:13:07 作者:晋鹧聪 阅读:

By Ben Crystall A BACTERIA-infested yellow gel that eats through concrete could soon be helping engineers to clean up radioactive contamination at the Sellafield nuclear reprocessing plant in Cumbria. The bacterium, Thiobacillus thiooxidans, is one of the culprits behind corrosion in concrete buildings and bridges. It feeds on sulphur-containing compounds in the concrete and converts them into dilute sulphuric acid, which eats away at any concrete it meets. Now researchers at British Nuclear Fuels and the Idaho National Engineering and Environmental Laboratory (INEEL) at Idaho Falls have found a way to use T. thiooxidans to dissolve concrete floors and walls contaminated with radionuclides. Cleaning up old nuclear sites often involves removing contaminated concrete—usually a messy, dangerous and expensive business. Workers must chip or blast away the first few millimetres of the surface, and they can be exposed to high levels of radiation and clouds of radioactive dust. So the researchers figured that T. thiooxidans should offer a slower but far safer way to clean up. They mixed the bacteria with sulphur and added dollops of inert cellulose thickener. The result is a bright yellow gel resembling custard that can be spread or sprayed onto concrete surfaces. Humidifiers are used to keep the humidity level around the gel at about 95 per cent, which allows T. thiooxidans to thrive and continue churning out acid. But when engineers decide that they have removed enough concrete, the gel is allowed to dry out. The remains of the gel and the rubble infested with radionuclides can then be collected, sealed in concrete and stored at disposal sites along with other radioactive waste. According to INEEL project manager Melinda Hamilton, none of the bacteria survives the drying process—so the bug’s activity should be arrested before it chews all the way through walls. In lab tests at BNFL’s Capenhurst site in Cheshire, the mixture ate through concrete at a rate of about 1 centimetre a year. The process isn’t fast, admits Tim Milner, project manager at BNFL. But this shouldn’t matter since most contamination occurs in the top few millimetres of a surface. Besides, the bacteria offer key advantages over manual techniques: the mix is cheap and easy to use. “These critters deliver the acid to precisely where you want it,” says Milner. The researchers have spent four years perfecting their custard and as a first test, BNFL plans to put it to work at Sellafield. In the next two months it will be applied to contaminated concrete inside a walkway near the chimney at the Windscale Pile 1 reactor,