Monitoring Methodologies and Chronology of Radioactive Airborne Releases from Tokai Reprocessing Plant

Tokai reprocessing plant (TRP) has released radionuclides such as 3 H, 14 C, 85 Kr and 129 I into the atmosphere since the start of operation in 1977. We have established the monitoring methodologies for these nuclides, to realize an appropriate and continuous radioactive discharge control. The methodologies having various special technical considerations for matching the monitoring of reprocessing off-gas, were summarized in this paper. Briefly, 3 H was collected by a cold-trap technique and the concentration was evaluated being independent of the water collection efficiency; 14 C was collected by a monoethanolamine bubbler and then measured by liquid scintillation counting without any interferences from 3 H and 85 Kr; 85 Kr was continuously measured by combination of two kinds of detectors to cover very wide range of the concentration; and 129 I was collected by a charcoal filter and a charcoal cartridge in series with a relatively high collecting performance. The monitoring records over the period from the start of operation to fiscal 2006, the end of contract-based reprocessing, certainly ensured that the releases of these nuclides from the TRP have never exceeded the authorized discharge limits.