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摘要
The treatment of low probability events leading to core disruption is one of the key issues of R&D plans for the advanced reactor systems in general, and for sodium fast reactors in particular. Regarding sodium fast reactor systems, a major concern is that the core, at nominal, is not necessarily in its neutronically most reactive state. The simulation of the initiating phase of such accidents is of particular interest both for the prevention and the mitigation of routes leading to a large core disruption and recriticalities. Current analysis of the initiating phase relies on a Point Kinetics model, which neglects spatial variations of the neutron flux (i.e. the flux shape). Because the core geometry may be modified during such accidental conditions, the constant-shape approximation becomes questionable when applied to initiating phase simulations. The present paper investigates space-time effects during the degradation of a sodium fast reactor core. To this aim, a three-dimensional neutron kinetics model has been coupled to a multiple-channel thermal-hydraulics model and applied to evaluate spatial effects during a severe accident transient. As expected, it was found that spatial effects are not likely to be of importance in the pre-boiling portion of the transient reinforcing the use of a Point Kinetics model for the simulation of design-basis transient up to the boiling point. Departure from the Point Kinetics approach is noticeable after the fuel-pin breakup. The fuel being the source of neutrons, its motion within the core boundaries tends to create important spatial changes in the fission source. From this event, the Point Kinetics model fails in reproducing results obtained by the three-dimensional model and the study conducted in the present paper assesses this discrepancy.
- 出版日期2015-11
- 单位中国地震局
