Self-monitoring fission chamber: theoretical groundwork

摘要

The most common application of fission chambers in a core monitoring system is to measure the neutron flux. As is well known, in such a case, it is advantageous to use the so-called Campbell relationships. However, the application of of the Campbell methods requires some calibration of the chamber. Due to certain events, such as crack of the chamber wall, the calibration might become obsolete, and the system would underestimate the count rate and therefore the flux. This paper investigates the possible application of a simple method to identify whether the measured count rate change is due to the malfunction of the detector or due to the change of neutron flux. The method is based on the change of the frequency dependence of the power spectral density of the fission chamber signal, due to the malfunction. For the current work the filling gas pressure drop due to cracking was considered as the malfunction. In theory the method enables an early failure detection. The experimental verification is under progress.