Development of a chemical form discrimination system for 14C species in gaseous waste

A new system was developed for discriminating the chemical form of 14C species in gaseous waste from nuclear facilities. The system consists of an air sample reservoir, a concentration apparatus, a radio-gas chromatograph, and microcomputers. An air sample, which is part of the gaseous effluent released from a stack of a facility, is automatically collected in the tank by trigger signals of stack monitors. After passing the air through a silica gel column, carbon species contained in it are recovered in an activated carbon-supported palladium trap held at -120 degrees C. The recovered species are swept with helium gas and analyzed by the radiogas chromatograph using an activated carbon column and gas-flow counters. Output signals of the gas-flow counters are continuously recorded by the microcomputer. By using this system, the chemical forms of 14C, such as CO, CO2, CH4, C2H4, C2H6, and C3H8 are identified and quantified. A detectable concentration of 0.3 mBq cm-3 for 14CO2 can be obtained. The system has been used to monitor the gaseous waste released from the radioisotope production laboratory and the Japan Research Reactor 2 at Japan Atomic Energy Research Institute.