Research Of On-line Neutron Spectrum Measurement Method For Nuclear Reactor

The nuclear safety is regarded as more and more important with the developing of advanced nuclear energy system,and the corresponding nuclear measurement technology of nuclear system Facing more challenges.The neutron spectrum is one of the key parameters for nuclear energy system;it is of great of significance to improve the measurement accuracy of neutron spectrum measurement method.At present,the on-line neutron flux measurement technology in reactor is developed well,and the activation foils neutron spectrum measurement methods is mainly used in reactors.The other neutron spectrum measurement methods have many disadvantages,such as 3He and 6Li neutron spectrum detectors,which have bad radiation resistance,with limited measurement range or without good accuracy.Therefore,to develop high accuracy and wide measurement range on-line neutron spectrum measurement method is a very important research aspect of developing the advanced nuclear control technology.In this thesis,a new spectrum monitoring method is proposed which is based on the Bonner neutron spectrum measurement technology and the ionization chambers which can be operated for long time in reactors;that is an on-line reactor neutron spectrum method with multi-threshold ionization chambers.The main research contents and innovations are summarized as follows:(1)Research on the multi-threshold ionization chambers neutron spectrum measurement method with Monte Carlo simulation.The basic theory of this method is based on unfolding of "Few-channel data",and three miniature ionization chambers were applied,namely one 235U fission chamber,one 238U fission chamber and one NatB ionization chamber covered by a cadmium sleeve.The neutron spectrum can be unfolded with the count rates and response functions of three detectors through unfolding program.The detail description of neutron spectrum measurement methods and neutron spectrum deconvolution principle are presented in this thesis.In order to investigate the feasibility of this method,simulation tests have been made with the referenced neutron spectra and China LEAd-based Reactor(CLEAR).The unfolded neutron spectrum was in good agreement with the calculated neutron spectrum in most of the neutron energy regions.The research results show that this method can provide an alternative means for an on-line neutron spectrum measurement in the reactors.(2)Research on the Dual Functional Lithium-Lead Test Blanket Module(DFLL-TBM)neutronics experiment,which is performed by FDS Team.In this work,the data of tritium produce rates and the activation foils reaction rates were processed.In order to further verify the feasibility of the proposed method of neutron spectrum measurement,the neutron spectra of the DFLL-TBM were unfolded with the information of the activation foils count rate at three different positions.The results show that the unfolded neutron spectra and the calculated neutron spectra were agree well with each other.The primarily experiment results show that the proposed neutron spectrum measurement method can be applied in the fusion the reactors.At last,the sensitivity,uncertainty and the performance parameters of the proposed method were analyzed.In summary,a new on-line neutron spectrum method is developed,which is based on multi-threshold ionization chambers.Both simulation tests and experiment have been made for the feasibility study on the neutron spectrum measurement method.The research results show that the proposed neutron spectrum measurement method can be applied in reactors.The achievements of this research work can extend the on-line neutron spectrum measurement methods,and promote the development of measurement and control technologies for nuclear systems.