High-level waste is an important safety issue in the development of nuclear power.A proposed solution is the transmutation of waste in fast reactors.The exclusion of the risk of supercriticality by using subcritical r...High-level waste is an important safety issue in the development of nuclear power.A proposed solution is the transmutation of waste in fast reactors.The exclusion of the risk of supercriticality by using subcritical reactors is currently under development.Controlling the subcriticality level in such reactors presents difficulties.A problem is posed by the so-called space effect observed when using in reactors many neutron detectors in different locations of the core and reflector.Reactivity obtained from measure-ments,for example,by the Sjo¨strand method,differs by nonnegligible values.Numerical corrections can partially improve this situation.The use of a monoisotopic fission chamber set,designed for a given reactor,when each chamber is intended for a specific position in the system,can improve the situation.A question arises about the sensitivity of the results to reactivity changes.This issue is analyzed by computer simulation for possible fissionable and fissile nuclides for the total range of control rod insertion,changes in reactor fuel enrichment,and fuel temperature.The tested sensitivity was satisfactory at most levels from several dozen to several hundred pcm.A case study was conducted using the VENUS-F core model.展开更多
The detection efficiency of the fission chamber(FC) is very important for studying the neutron flux measurement(NFM) system in ITER. In this article, we mainly focus our attention on the influence of the moderator. Wi...The detection efficiency of the fission chamber(FC) is very important for studying the neutron flux measurement(NFM) system in ITER. In this article, we mainly focus our attention on the influence of the moderator. With the Monte Carlo particle transport simulation tool named Geant4, we make a simulation of FC detection efficiency with different levels of thickness of a beryllium moderator.Two manufactured FCs for ITER-NFM systems are then used to test the parameters and performance. The test results agree well with our simulation.展开更多
Purpose Afission chamber with two layers of 238Ufissile materials has been developed for the measurements of fast neutrons.Methods The developed fission chamber has been tested by 60Co gamma source and 252Cf neutron s...Purpose Afission chamber with two layers of 238Ufissile materials has been developed for the measurements of fast neutrons.Methods The developed fission chamber has been tested by 60Co gamma source and 252Cf neutron source.Results The results have indicated that it is very easy to cut off the gamma rays from the neutrons by using a discriminator,when the fission chamber works in the pulse mode.The detector works well,even if the static air is used as the filling gas.Conclusion To discuss the application of the detector,Monte Carlo simulations have been performed by considering four 238U-coated fission chambers located outside the spallation target for the fast neutron measurement from spallation reaction.The simulation results have indicated that the detector can be used to measure the fast neutron flux and neutron flux ratio of four fission chambers.Furthermore,a 238U-coated fission chamber can be used within a reactor for longer time,in comparison with a 235U-coated fission chamber.展开更多
The ^239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a fiat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influen...The ^239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a fiat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using ^10B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of ^239gpu are measured as 1.791 × 10^-16 2.350 × 10^-16 and 1.385×10^-15 per second for 15 mm thick ^10B cover, 0.5 mm thick Cd cover, and no cover respectively, while the fission reaction rate of 239pu is rapidly increased to 2.569×10^-14 for a 20 mm thick polythene covering fission chamber. The average 239pu fission cross-section of thermal and resonance neutrons is calculated to be 500 b and 24.95 b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30×10^6, 2.24×10^6 and 1.04×10^8 cm^-2·s^-1.展开更多
基金This research was supported by the Polish Ministry of Science and Higher Education,and in part by the PL Grid Infrastructure available at Academic Computer Center CYFRONET AGH.APC was funded by the AGH-University of Science and Technology,Cracow,Poland.
文摘High-level waste is an important safety issue in the development of nuclear power.A proposed solution is the transmutation of waste in fast reactors.The exclusion of the risk of supercriticality by using subcritical reactors is currently under development.Controlling the subcriticality level in such reactors presents difficulties.A problem is posed by the so-called space effect observed when using in reactors many neutron detectors in different locations of the core and reflector.Reactivity obtained from measure-ments,for example,by the Sjo¨strand method,differs by nonnegligible values.Numerical corrections can partially improve this situation.The use of a monoisotopic fission chamber set,designed for a given reactor,when each chamber is intended for a specific position in the system,can improve the situation.A question arises about the sensitivity of the results to reactivity changes.This issue is analyzed by computer simulation for possible fissionable and fissile nuclides for the total range of control rod insertion,changes in reactor fuel enrichment,and fuel temperature.The tested sensitivity was satisfactory at most levels from several dozen to several hundred pcm.A case study was conducted using the VENUS-F core model.
基金supported by the National Natural Science Foundation of China(Nos.10976028 and 11375195)the National Magnetic Confinement Fusion Energy Development Research(No.2013GB104003)
文摘The detection efficiency of the fission chamber(FC) is very important for studying the neutron flux measurement(NFM) system in ITER. In this article, we mainly focus our attention on the influence of the moderator. With the Monte Carlo particle transport simulation tool named Geant4, we make a simulation of FC detection efficiency with different levels of thickness of a beryllium moderator.Two manufactured FCs for ITER-NFM systems are then used to test the parameters and performance. The test results agree well with our simulation.
基金the National Natural Science Foundation ofChina (Nos. U1432123, 11575268, 11875301, 11675238).
文摘Purpose Afission chamber with two layers of 238Ufissile materials has been developed for the measurements of fast neutrons.Methods The developed fission chamber has been tested by 60Co gamma source and 252Cf neutron source.Results The results have indicated that it is very easy to cut off the gamma rays from the neutrons by using a discriminator,when the fission chamber works in the pulse mode.The detector works well,even if the static air is used as the filling gas.Conclusion To discuss the application of the detector,Monte Carlo simulations have been performed by considering four 238U-coated fission chambers located outside the spallation target for the fast neutron measurement from spallation reaction.The simulation results have indicated that the detector can be used to measure the fast neutron flux and neutron flux ratio of four fission chambers.Furthermore,a 238U-coated fission chamber can be used within a reactor for longer time,in comparison with a 235U-coated fission chamber.
基金Supported by National Natural Science Foundation of China(91326109)
文摘The ^239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a fiat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using ^10B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of ^239gpu are measured as 1.791 × 10^-16 2.350 × 10^-16 and 1.385×10^-15 per second for 15 mm thick ^10B cover, 0.5 mm thick Cd cover, and no cover respectively, while the fission reaction rate of 239pu is rapidly increased to 2.569×10^-14 for a 20 mm thick polythene covering fission chamber. The average 239pu fission cross-section of thermal and resonance neutrons is calculated to be 500 b and 24.95 b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30×10^6, 2.24×10^6 and 1.04×10^8 cm^-2·s^-1.
