Computational evaluation of severe accident in a nuclear power plant have become increasingly important in recent years. The severe accident in a Sodium-cooled Fast Reactor (SFR) has been evaluated by combining the different lumped-mass computational codes in many cases. In that case, there is a difficulty in connecting the multiple codes through a boundary condition. On the other hand, we have developed the simulation system called SPECTRA (Severe-accident PhEnomenological computational Code for TRansient Assessment) to compute the in- and ex-vessel phenomena simultaneously and to evaluate the various scenarios during severe accident in SFR. The ex-vessel phenomena have some inherent phenomena such as sodium-concrete interaction. This paper provides a newly constructed analysis model for ex-vessel phenomena including gas and aerosol transport, and the sodium-concrete interaction as a part of the SPECTRA.

The SPECTRA consists of the in- and ex-vessel modules. The two modules run simultaneously with exchanging the data such as pressure in the ex-vessel region, and amount of the leaked liquid sodium and debris. The gas and aerosol transport model in the ex-vessel module solves mass, momentum, and energy conservation equations for an atmospheric region in a lumped mass system. This model can achieve fast computation with a full implicit scheme. The sodium-concrete interaction model computes ablation of concrete surface caused by chemical reaction, and one-dimensional mass and energy transport. The reaction products and energy is considered in a source term of the above-mentioned conservation equations.

The newly constructed ex-vessel module was tested through a sodium-concrete interaction analysis and code-to-code comparison. The computational region consists of three layers: an atmospheric layer, a sodium pool layer, and a concrete layer. The computational result showed increase of concentration of the reaction products and temperature in the pool and atmospheric layer. Ablation of concrete surface started after surface temperature reached to a certain value. The computed ablation length agreed with the results by the CONTAIN-LMR code for application to a probabilistic risk assessment of liquid metal fast reactors. This study demonstrated that our computational model could ex-vessel coupled phenomena which includes thermal hydraulics and sodium-concrete interaction.


Development of Ex-Vessel Phenomena Analysis Model for Multi-Scenario Simulation System, SPECTRA

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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