Removal of carbon-14 from gaseous streams

The two major sources of carbon-14 in CANDU reactors are the annulus gas system (if nitrogen is used as the annulus gas) and moderator system. A dry process to remove carbon-14 as 14CO2 from gaseous streams at ambient temperatures was developed at Ontario Hydro Research Division. Bench and pilot scale systems were assembled to study the process. Gas streams at flow rates up to 200 1/min. with carbon dioxide concentrations from 5 to 50,000 u1/1 were treated. The effect of gas temperature, flow rate, humidity and reactor vessel geometry on the reaction was studied and a mechanism for the reaction is discussed in the paper. Decontamination factors as high as 104 were achieved for the high carbon dioxide concentration studied and the outlet carbon dioxide concentrations were below 1 u1/1 for the inlet concentrations between 3 and 30 u1/1. The pilot system was tested for over 1000 hours under conditions similar to the moderator cover-gas system operating under normal as well as upset conditions. The performance of the pilot system did not change throughout the long period of testing. Carbon-14 is fixed in a stable solid form in the process suitable for disposal. Although the process is being developed to remove carbon-14 from the moderator cover-gas in CANDU reactors, it can also be applied to nitrogen annulus gas systems with some modifications. The application of the system for off-gas treatment in fuel reprocessing plants is also being considered