Abstract: This article analyzes the working principle of the fission ionization chamber and various working modes of wide range measurement. Based on its characteristics of multiple working modes, the measurement technology of wide range neutron fluence rate is studied, and the test method in reactor is discussed. Performance verification was conducted on the fission chamber pulse mode and mean square pressure mode in the reactor. The test results showed that the detector has an ultra wide range, and the maximum linearity between the detector output and neutron fluence rate in pulse counting mode is 1.16%. The maximum linearity in mean square pressure working mode is 2.06%, and the upper limit of neutron flux measurement can reach the level of 10¹⁰ cm^-2·s^-1, which complies with the wide range usage requirements of the intermediate range channel of the AP series external nuclear measurement system, and can be widely used in nuclear power and marine external nuclear measurement and monitoring systems.

Key words: ex-core nuclear instrumentation system, intermediate range, fission lionization chamber, ultra wide rang, test at reactor