Performance test of the pretreatment unit for Kr-85 recovery system from off-gas in fuel reprocessing plant

In a Kr-85 recovery system using cryogenic distillation method for a spent fuel-reprocessing plant, oxygen may cause hazardous explosion in the presence of hydrocarbon such as acetylene. To prevent such hazards, an automatic control system of hydrogen has been proposed to remove oxygen by the reduction reaction of hydrogen over palladium (Pd) catalyst. The objective of this study is to examine some characteristics of the controller for adjusting the concentration of H2 and O2 in the Pd converter. The automatic control system consists of P-I controller which can set two parameters, proportional band (Kp) and integral time (T sub(I)). In the present test, Kp and T sub(I) were selected from 200% to 500% and from 5 min to 15 min, respectively, and the concentrations of O2 and H2 were measured at the inlet and the outlet of the Pd converter, respectively. The effect of Kp on the maximum concentration of H2 and on the recovery time, and the effects of integral time and dilution on the hydrogen and oxygen concentrations are presented by curves. It is concluded that the automatic hydrogen control system employed in the present study can respond rather quickly to the stepwise change of oxygen concentration with small dilution range. (Aoki, K.)