Experimental Neutronics Study On The Zero-power Coupling Device Of The Spallation Target And Reactor

The Accelerator Drived Sub-critical System(ADS)is is one of the most viable means of transmutation long-lived nuclear waste.With the development of ADS system,a higher requirement is made for the neutronics of the device system.In order to ensure the reliability of the design calculation,a coupling device of the spallation target and reactor is established to conduct the comprehensive measurement of neutrons which is with high safety and easy to conduct experiment.The neutron data are closely related to the various nuclear processes occurring in the reactor and the spallation target,such as the absorption of internal material to neutrons,scattering and neutron leakage,etc.So,conducting neutron experiments on the coupling device is an important means of macro-measurement test.In this paper,the off-line and on-line methods are used to study the target-reactor coupling device.The emphasis is on how to improve the accuracy of the neutron flux distribution and the related problems involved in the experiment.Firstly,the activation method was applied and optimized in the spattering experiment.At the same time,the method of on-line measurement of neutron flux was discussed in detail,and a set of optical fiber detector system for the zero-power reactor was developed which was tested on the Venus 1 # sub-critical device.These two experimental methods were applied to the Venus 2 # lead-based zero-power device.The experimental results were compared with the simulation results from MCNPX2.7.0 to verify the cross-section database and calculation model.This doctorial thesis includes those contents and physical results described in the following:(1)By analyzing the water bath experiment of 250 Me V proton beam bombarding the lead target,the spatial distribution of the neutron flux in the whole water bath environment was obtained,and the effective neutron yield of the spattering reaction was 2.23 ± 0.19 n / proton,which was 2.14 ± 0.01 n / proton simulated with MCNPX.The neutron spectrum of the epithermal energy region was obtained by analyzing the activity of Au,In and Mn,which were placed near the target.And it was compared with the MCNPX simulation results from which the influence of self-shielding effect was analyzed.(2)The research on the scintillator fiber detector system of the reactor was completed which used two probes to identify the neutron signal.The system was tested in the 252 Cf fission source.The detector system was used in Venus 1# sub-critical device to measure the neutron relative flux density.The results were in good agreement with the results of solid-state nuclear track detector and MCNPX simulation,which verified the accuracy and reliability of the detector system on the reactor.(3)The neutron flux distribution in the core was measured on the lead-based zero-power device by the metal wire activation method.By analyzing the reaction rate of the Au and In lines,the axial distribution of the nuclear reaction rate in the different radial fuel channels was obtained.The results were compared with the MCNPX simulation results to verify the accuracy of the database.Then the neutron flux density distribution was simulated through the same database.(4)The dynamic experiments were conducted on the lead-based zero-power device using the scintillator fiber detector system,including the dynamic monitoring of reactor start-up,operation and shutdown.The source-jerk method was used to measure the sub-criticality.The relative error of the measurement results compared with results of extrapolation-period method is less than 1%.By comparing the results of different channels,the spatial effection of zero-power device was analyzed.The prompt neutron decay constant were measured by pulsed neutron source method,and compared with the simulated results of MCNPX.The relative error between detector and simulation was analyzed.The spatial distribution of the neutron flux under different sub-critical conditions was measured on the lead-based zero-power device.The relative thermal neutron flux distribution measured by the detector system was compared with the MCNPX simulation results to verify the accuracy of the cross-section database.Then the spatial distribution of the neutron flux density is given by the MCNPX code.The experimental results are helpful to understand the neutron temporal and spatial characteristics of the subcritical system,which is of great significance to the rational design and safe operation of the subcritical system,and also provides the experimental basis for the future development of ADS reactive monitoring system.