Accelerator Driven sub-critical System (ADS), which employs the high-energy proton beam generated by accelerator to bombard the target nucleus and generate spallation neutrons as external neutrons to drive and maintain the operation of its sub-critical reactor, is of great significance in nuclear waste treatment and disposal. As the instability of proton beam would affect the power level of the reactor and threaten the safety of ADS, Beam Trip (BT) and Beam OverPower (BOP) are commonly considered to be its two typical transient accidents. As for the sub-critical reactor, the Transient OverPower (TOP) is also one of typical transient accidents that should be considered, which is mainly caused by reactivity insertion under certain cases, such as SGTR (Steam Generator Tube Rupture) accident. For the subcritical reactors, the transient evolution behaviors are strongly affected by the subcriticality value. On the one hand, the subcriticality values of ADS design should take safety margin and power gain into consideration. On the other hand, the subcriticality value is variable with the burnup of reactors. So it is necessary to study the safety characteristics of the subcritical reactors under different subcriticality values, in this paper, the transient safety characteristics of a single channel for XADS under BT, BOP and TOP accidents of different subcriticality values were investigated by using MPC-LBE code.

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The Computational Fluid Dynamics (CFD)-based thermal-hydraulics and safety analyses of Lead-based Fast Reactor (LFR) have attracted great attentions in recent years. Commercial CFD tools have been widely used in the 3D simulations of pool-type reactors owing to their powerful abilities in geometric modeling and meshing. Compared with the commercial CFD tools, OpenFOAM is a free open-source CFD code, which is more flexible to perform multi-physics coupling activities. In this paper, in order to develop a solver for simulating the coupled flow and heat transfer behaviors of fluid (coolant) and fuel pin in LFR, the fuel pin Heat Conduction (HC) model was coupled to the modified icoFoam solver of OpenFOAM. Verifications were conducted by the steady-state coupled simulation of fluid and fuel pin heat transfer behaviors, comparing with the MPC-LBE code which has been verified by the benchmarks for LFR fuel pin channel. The results simulated by the coupled solver proposed in this paper agreed well with the ones provided by the MPC-LBE code. This study lays a foundation for the further development of transient safety analysis code for LFR in our future work.