A. M. El-Messiry1, Kh. M. El-Said2
1 National Center for Nuclear Safety and Radiation Control (NC-NSRC), Atomic Energy Authority (AEA), Cairo, Egypt,
2 Faculty of Science, Helwan University, Cairo, Egypt
Nuclear reactor instrumentation is considered as one of the most important detecting systems in reactor operation and control. In the present work, we consider the nuclear instrumentation of Egypt Test and Research Reactor number 2 of MPR type. Now the reactor is under commissioning. The present work corresponds to demands of the safety review and assessment which require a study of the nuclear instrumentation in respect of the change of its sensitivity and life-time over a long reactor operation. The reactor utilizes two types of out-of-core gas ionization detectors: (a) 235U fission chamber and (b) boronlined, compensated ionization chamber. The detectors are located outside the reactor core in a high neutron flux. The effect of the neutron fluence on the detector reliability, sensitivity, and life-time is investigated and analyzed. The detector life-time is limited by consumption of sensitive material, what is drirectly related to the neutron fluence. The results of the work focus on the time at which the device reaches its failure probability limit assigned by safety issues. The critical time at which the detector looses its function is determined. In particular, it is the time also to replace the detector by a new one.