International Conference on Fast Reactors and Related Fuel Cycles FR22: Sustainable Clean Energy for the Future (CN-291)

Model validation of the ASTERIA-SFR code related to freezing phenomena of liquid and liquid/particle mixtures based on THEFIS experimental results

Apr 20, 2022, 1:40 PM

2h

Vienna, Austria

POSTER Track 2. Fast Reactor Safety Poster Session

Speakers

Dr Tomoko Ishizu (Regulatory Standard and Research Department, Secretariat of Nuclear Regulation Authority (S/NRA/R)) Mr Satoshi Fujita (Regulatory Standard and Research Department, Secretariat of Nuclear Regulation Authority (S/NRA/R))

Description

Mechanical consequence which might be caused by core disruptive accidents (CDAs) is one of the major concerns in fast reactor safety. Once core disruption occurs caused by severe re-criticality, core materials are dispersed azimuthally and radially. The dispersed materials, e.g., liquid/particle mixture of fuel and steel, penetrate into the pin bundles and control rod guide tubes (CRGTs), and then, freeze at the edge of penetration due to heat transfer with surrounding structures. Such freezing phenomena might cause to suppress the negative reactivity feedback of fuel dispersion. When tight blockages are created inside CRGTs due to freezing, discharge of core materials could be impeded and a molten core pool formation could be enhanced. A radial motion of the molten core pool, so-called pool sloshing, is one of major causes to induce a prompt critical condition. Thus, penetration and freezing phenomena of core materials play a key role to govern the mechanical consequence of CDA.
S/NRA/R has been developed ASTERIA-SFR, which was renamed from ASTERIA-FBR, to evaluate the mechanical consequences due to severe re-criticality during CDA. For the sake of adequate simulation of penetration and freezing behavior of molten materials into the pin bundles and/or CRGTs, two major models of CONCORD , thermo-fluid dynamics calculation module of ASTERIA-SFR, were improved: heat transfer model and momentum exchange function model. The former model was modified by implementing fuel caps freezing model considering thermal resistance at the interface between molten material or crust and structure. The latter was modified by implementing particle viscosity model.
This paper describes model validation study of ASTERIA-SFR related to freezing phenomena of liquid or liquid/particle mixtures through the THEFIS test simulation. To reproduce the test results, models of heat transfer and momentum exchange function were improved considering interfacial heat resistance and effective viscosity of liquid/particle mixture. As a result, it was found that the calculated penetration depths of liquid or liquid/particle mixtures were in good agreements with the experimental results. Freezing behavior and uncertainty shown in the calculation results were also discussed.