Research On Subcriticality Reconstruction Based On Inverse Kinetics Method For Subcritical Systems

Accelerator-Driven Subcritical System(ADS)is an innovative nuclear energy system.Robust and accurate on-line monitoring of the subcriticality is one of the central issues for operation and safety of the future ADS.Since ADS consists of high-intensity extraneous neutron source and deep subcritical reactor core,traditional reactivity measurement and monitoring method could not be applied directly,and a new on-line subcriticality measurement and monitoring method is needed to satisfy the requirement.In this thesis,based on neutron transport theory,the basic principle of subcriticality measurement and monitoring method is investigated.Then,subcriticality reconstruction is achieved based on inverse kinetics method,which solves the problem that traditional reactivity measurement methods can not be used for subcriticality reconstruction.The main research contents and innovations are summarized as follows:(1)A subcritical inverse point kinetics algorithm,based on extraneous neutron source calibration with initial subcriticality and nuclear power,is developed for on-line subcriticality reconstruction.In traditional method for traditional nuclear systems like pressurized water reactors,constant and strong neutron source cannot be explicitly taken into consideration,which leads to the difficulty in subcriticality monitoring.In this thesis,we developed the subcritical inverse point kinetics algorithm,and numerically verified it by Preliminary Design Study-Experimental Accelerator-driven Subcritical System(PDS-XADS)with NTC(Neutronics and Thermal-hydraulics Coupled Simulation Program).Preliminary analysis of inverse kinetics method for reactivity reconstruction at various initial reactivity states was performed.The range of relative error is between 6.81%?13.12%corresponding to initial effective multiplication factor keff between 0.97290 and 0.88991.The results show that subcriticality reconstruction on-line can be realized by the developed subcritical inverse point kinetics method.(2)An inverse spatial-spectral kinetics method for subcriticality monitoring is proposed based on the optimal detector position and neutron response energy group.This makes the subcriticality monitoring achieved based on neutron flux other than nuclear power,which can avoid the spatial-spectral correction.A synthetic test and analysis is carried out with PDS-XADS.At first,optimal detector position and the best energy range are searched.Then,through reactivity perturbation simulation by NTC for PDS-XADS,transient neutron flux are obtained and used for verifying the inverse spatial-spectral kinetics method.Results show that subcriticality reconstruction based on neutron flux other than nuclear power is effectively realized without the influence of spatial-spectral effects.If the initial effective multiplication factor Aeff is 0.97071,the relative error of reconstructed reactivity was below 1%,which shows the better capability compared to that(6.7%)of subcritical inverse point kinetics method.Considering all of the above,a subcritical inverse point kinetics based on nuclear power is developed and verified.Furthermore,an inverse spatial-spectral kinetics method based on neutron flux is proposed and verified for subcriticality reconstruction without the influence of spatial-spectral effects.These methods lay the theoretical foundation for subcriticality reconstruction of source driven subcritical system in the future.