Research On Fission Chamber Wide-range Of Digital Neutron Flux Density Measurement

Neutron flux density is an important parameter of a nuclear reactor. Withcontinuous monitoring out pile reactor neutron flux signal, it can provide real-timereactor power and its change period not only for power control system to prevent theshutdown and supercritical states by rising up or dropping down the reactor controlrod, but also for the reactor protection system to ensure that the reactor is running inthe safety range. Fission chamber has the relatively high neutron/gamma rejectionrate, and its three working modes can cover all the reactor power measuring range.Thus we can just use a single type of fission chamber to measure the reactor neutronflux. It provides advantages in simplification for engineering design and operationmaintenance and high reliability for after-accident safety monitoring. Fissionchamber is widely used in the nuclear power plants in United States.In this paper, processing methods and techniques of wide-range digital neutronflux density measurement by using fission chamber was studied in two aspects:(1) Firstly fission chamber signal simulation waveform with electronics noisewas generated by the computer in this paper, according to the fission chamber andpreamplifier circuit parameter model, the mathematic expression of a single pulsesignal from fission chamber was deduced, then according to the characteristics ofthe fission chamber signal, simulation signal was generated under different countrate. And digital signal processing algorithms was studied, in low and high neutronflux density, By using digital trapezoidal shaping filter and adaptive filter algorithmparameters, Not only the accumulation of separation and impulse noise effectivelyidentify processing (pulse counting mode) were implemented, and the accuracy ofcount rate and maximum count rate were improved, but also the accuracy of themean square value calculation was improved (Campbell mode).(2) In order to verify the correctness of above study, a FPGA-based high-speed data acquisition and digital signal processing board based for the wide-range neutronflux density measurement was designed and implemented. The simulated signaloutput of fission chamber was adopted to produce physical output signal by anarbitrary waveform signal generator. It was taken as the output signal generator fromfission chamber. Both the pulse counting mode and Campbell mode were tested onthis FPGA board by the implement of above methods in the function principle.Results showed the efficiency of our signal processing techniques. This will play areference for both the foundation study of the wide range neutron measuring systemusing fission chamber detector, and the engineering design development.