Improved Operation of CO ₂ Separator for Preventing Increases in CO ₂ Concentration of Air in the Habitation Room during Closed Habitation Experiments

The main objective of the activities of the Closed Ecology Experiment Facilities (CEEF) is to construct a mathematical model to predict the transfer of radiocarbon (¹⁴C) released from a nuclear fuel reprocessing plant in the village of Rokkasho into the local ecosystem. For this purpose, an artificial ecosystem, including crops, domestic animals, and human inhabitants, needs to be maintained in the CEEF for several months. As a preparatory study, two-week habitation experiments using the CEEF were planned in 2006. In the first habitation experiment, a CO₂ separator was continuously operated with a cycle of 60-minute adsorption and 60-minute desorption periods in order to remove excess CO₂ from the habitation room, and the maximum CO₂ concentration of air in this room slightly exceeded 5000 ppm, which was identical to the maximum 8-hour exposure permitted for industrial settings. In the second habitation experiment, therefore, the duration of both the adsorption and desorption periods for the operation of the CO₂ separator was shortened to 54 minutes in order to increase the cumulative number of adsorption periods per day. The approx. 10% increase in the cumulative number of adsorption periods per day resulted in a decrease of approx. 10% in the maximum CO₂ concentration of air in the habitation room during the second habitation experiment. This result demonstrated how the improved operation of the CO₂ separator contributed to maintaining the CO₂ concentration of air in the habitation room below the maximum 8-hour exposure permitted for industrial settings.