Making a radiation sensing system with a prolonged use in radioactive waste disposal facilities

Radioactive waste disposals in underground facilities (typically several hundred meters from the surface) are to be monitored for an extended period of time for management. Requested performances for sensing system were investigated and summarized. Three particular radiation sensors were chosen: 1) Calorimetric sensors with optical fibers for which response characteristics toward bentonite or sand rocks were examined. 2) Developing a specific electrode for specific impedance imaging sensors with a measuring cable of 100 m length: An accurate impedance was found to observe up to 100 kHz. 3) Electrochemical monitoring sensors using a complex electrode system involving aqueous heavy metal solutions with corresponding electrodes. Current density change up to 5.4 mA due to the presence of Fe2+ ions (0 ∼ 5.8 x 10-4 mol/kg) in solutions of Ni2+ and Co2+ with a proposed electrode was found. Most promising sensor material was found to be Si3N4 or B4C from the chemical durability point of view. (S. Ohno)