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Research on the Neutron Kinetics for a Molten Salt Reactor

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					B.6.2
         Research on the Neutron Kinetics for a Molten Salt Reactor
                      During the Rod Drop Transient
            ZHANG Da-lin1, QIU Sui-zheng2, SU Guang-hui3 and Liu Chang-liang4
1
  State key laboratory of Multi Phase Flow in Power Engineering, Department of Nuclear
and Thermal Power Engineering, Xi’an Jiaotong University, Xi’an, China
(Tel: +86-029-82665607, E-mail: dlzhang.xjtu@yahoo.com.cn)
2
  State key laboratory of Multi Phase Flow in Power Engineering, Department of Nuclear
and Thermal Power Engineering, Xi’an Jiaotong University, Xi’an, China
(Tel: +86-029-82665607, E-mail: szqiu@mail.xjtu.edu.cn)
3
  State key laboratory of Multi Phase Flow in Power Engineering, Department of Nuclear
and Thermal Power Engineering, Xi’an Jiaotong University, Xi’an, China
(Tel: +86-029-82663401, E-mail: ghsu@ mail.xjtu.edu.cn)
4
  State key laboratory of Multi Phase Flow in Power Engineering, Department of Nuclear
and Thermal Power Engineering, Xi’an Jiaotong University, Xi’an, China
(Tel: +86-029-82665607, E-mail: clliu@stu.xjtu.edu.cn)

Keywords: molten salt reactor; neutron kinetics; rod drop
                                             Abstract
The molten salt reactor, which is one of the ‘Generation IV’ concepts, uses the molten salt
functioning as the fuel solvent, coolant and moderator simultaneously. The neutron kinetics
of the molten salt reactor is significantly influenced by the fuel salt flow, which is very
different from the conventional reactors using solid fuels. Therefore, it’s necessary to
research the characteristics of the neutron kinetics by particular methods. In this study, the
neutron kinetics of the molten salt reactor is conducted during the rod drop transient, and
the velocity field calculated by the standard k- ε model is adopted to consider the flow
effect of the fuel salt. The theoretical model of the neutron kinetics is founded based on the
conservation law, which consists of two-group neutron diffusion equations for the fast and
thermal neutron fluxes, and balance equations for six-group delayed neutron precursors, in
which the convection terms are included to reflect the fuel salt flow. The mathematical
equations are discretized by the finite volume method, in which the implicit scheme is
adopted for the time-dependent terms, and the power law scheme is for the convection
terms. The discretization equations are calculated by numerical method, and the
distributions of the fast neutron, thermal neutron fluxes and the delayed neutron precursors
in the core are obtained. The results show that, the core power reduces to less than 2% of its
original value in 0.02s when the rod drop transient starts, and the ultimate power under the
flow condition is lower than that without flow. Comparing the distributions of the fast,
thermal neutron fluxes and the delayed neutron precursors in the core during the rod drop
transient with those under the steady condition, it can be found that the fast and thermal
fluxes sharply decrease in the rod inserting region significantly, while the neutron fluxes
change a little in the other region. In addition, the results indicate that the delayed neutron
precursors change a little, and the larger the decay constant, the greater the changes of the
delayed neutron precursors. The obtained results serve some valuable information for the
research and design of this new generation reactor.

				
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