The solid fuel thorium molten salt reactor(TMSR-SF1) is a 10-MWth fluoride-cooled pebble bed reactor. As a new reactor concept, one of the major limiting factors to reactor lifetime is radiation-induced material damag...The solid fuel thorium molten salt reactor(TMSR-SF1) is a 10-MWth fluoride-cooled pebble bed reactor. As a new reactor concept, one of the major limiting factors to reactor lifetime is radiation-induced material damage. The fast neutron flux(E > 0.1 MeV) can be used to assess possible radiation damage. Hence, a method for calculating high-resolution fast neutron flux distribution of the full-scale TMSR-SF1 reactor is required. In this study,a two-step subsection approach based on MCNP5 involving a global variance reduction method, referred to as forward-weighted consistent adjoint-driven importance sampling, was implemented to provide fast neutron flux distribution throughout the TMSR-SF1 facility. In addition,instead of using the general source specification cards, the user-provided SOURCE subroutine in MCNP5 source code was employed to implement a source biasing technique specialized for TMSR-SF1. In contrast to the one-step analog approach, the two-step subsection approach eliminates zero-scored mesh tally cells and obtains tally results with extremely uniform and low relative uncertainties.Furthermore, the maximum fast neutron fluxes of the main components in TMSR-SF1 are provided, which can be used for radiation damage assessment of the structural materials.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supported by the Chinese TMSR Strategic Pioneer Science and Technology Project(No.XDA02010000)the Frontier Science Key Program of Chinese Academy of Sciences(No.QYZDY-SSW-JSC016)
文摘The solid fuel thorium molten salt reactor(TMSR-SF1) is a 10-MWth fluoride-cooled pebble bed reactor. As a new reactor concept, one of the major limiting factors to reactor lifetime is radiation-induced material damage. The fast neutron flux(E > 0.1 MeV) can be used to assess possible radiation damage. Hence, a method for calculating high-resolution fast neutron flux distribution of the full-scale TMSR-SF1 reactor is required. In this study,a two-step subsection approach based on MCNP5 involving a global variance reduction method, referred to as forward-weighted consistent adjoint-driven importance sampling, was implemented to provide fast neutron flux distribution throughout the TMSR-SF1 facility. In addition,instead of using the general source specification cards, the user-provided SOURCE subroutine in MCNP5 source code was employed to implement a source biasing technique specialized for TMSR-SF1. In contrast to the one-step analog approach, the two-step subsection approach eliminates zero-scored mesh tally cells and obtains tally results with extremely uniform and low relative uncertainties.Furthermore, the maximum fast neutron fluxes of the main components in TMSR-SF1 are provided, which can be used for radiation damage assessment of the structural materials.
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.
