Sodium-cooled fast reactor fragment bed migration mechanism model

Abstract

The invention discloses a sodium-cooled fast reactor fragment bed migration mechanism model. The model is provided based on the shear strength concept widely adopted in soil mechanics. The stress analysis is carried out on the state of fragment particles in a fragment bed by combining the factors of particle density, size, shape and position, and a momentum exchange coefficient is introduced to calculate the drag effect of the fluid in the lower chamber of the reactor on fragment particle units. In this way, the shear strength and the shear stress of the fragment particle units after considering the flowing of the external fluid are obtained. And through stress analysis, comparing the calculated shear strength and internal shear stress of the fragment bed particles, and judging whether thefragment bed particles have migration and self-leveling phenomena or not. According to the method, the movement trend in the fragment bed migration process can be correctly predicted, the shape and the thickness in the lower chamber fragment bed migration process in the sodium-cooled fast reactor core disintegrating accident are effectively evaluated, and the problems that the simulation effect of the previous fragment bed migration phenomenon is poor and the reliability is not high are solved.

Description

technical field [0001] The invention belongs to the technical field of nuclear reactor safety facility design, and in particular relates to a sodium-cooled fast reactor debris bed migration mechanism model. Background technique [0002] The fuel enrichment of sodium-cooled fast reactor is high, so in terms of safety, sodium-cooled fast reactor pays special attention to the occurrence of recritical and core disintegration accidents. In the transition stage of the core disintegration accident, on the one hand, the molten core fuel is quenched into debris particles under the action of the coolant, and accumulates into a debris bed in the lower chamber of the core and the lower part of the pressure vessel; on the other hand, the coolant in the bed Boiling occurs under the action of the decay heat of molten particles, so that the molten particles will undergo a process of "migration" and "self-leveling" under the joint "promotion" of gas and liquid. If fuel debris accumulates ex...

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Problems solved by technology

[0003] Although the migration process of the fuel debris bed generally does not consider the melting of core melt particles after heating, it is a complex process involving solid, liquid, and gas three-phase flow heat and mass transfer, and it is difficult to numerically simulate it.

In the simulation process, especially the judgment of the critical point at the initial moment of debris particle migration and the force analysis have been mainly relying on empirical criteria, lacking a specific physical mechanism model, which makes the simulation effect poor and the reliability is not high

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