Development and testing of a cryogenic system for radioactive 14CO2 gas separation for nuclear waste monitoring

Abstract

A prototypal system for the separation of CO2 from air and concentration in small volume containers was developed and tested at ENEA in the frame of two European research projects (MetroRWM and MetroDECOM), funded by the European Metrology Research Programme (EMRP). The aim of the proposed system is to separate and concentrate in an effective way the CO2 content from radioactive air stream in nuclear installations or nuclear waste repositories during normal operation or decommissioning phase, by using a cryogenic process. This system is intended to be used as preparatory stage of the CO2 samples to be analysed by a radioactive gas-in-air monitor using a standardised 14CO2. Connecting the ENEA cryogenic system to the monitor will enable a sample of air to be processed and measured, and its 14CO2 activity concentration calculated, from knowledge of the volume of air sampled by the cryogenic system and the response of the monitor.Our work demonstrates the feasibility of a14C monitoring based on cryogenic method, according to which the components of a gaseous mixture can be separated on the basis of the differences between the phase transition properties of each gas components. The initial design was made considering the readily-available commercial instruments and devices and combining them in an optimum way. System testing showed almost 100% CO2 separation and recovery.