New criticality accident alarm system detectors at the JAEA Tokai Reprocessing Plant

Tsujimura, Norio   ; Yoshida, Tadayoshi 

In the Tokai Reprocessing Plant (TRP) of the NCL, criticality accident alarm systems (CAAS) were installed in 1984 and have still been in service. Due to the advanced ages of the system, a new CAAS detector was developed for replacement. A new detector was composed of a plastic scintillator coupled with a photomultiplier tube, placed into a cadmium-lined polyethylene moderator, and has a feature to respond to both neutrons and -rays via capture -rays from Cd(n,) reactions. The prototype detectors were built and the operation tests under critical bursts at a pulsed reactor were conducted. The test results demonstrated satisfactory performance. The new systems of commercial version are now under field tests at the TRP and will launch its operation in October 2009.