Fast Reactors and Accelerator Driven Systems Knowledge Base

Conference Article: Fast reactor core thermal-hydraulic analyses during transition from forced to natural circulation

Nishimura, M.; Ohshima, H.; Kamide, H. (O-arai Engineering Center, Power Reactor and Nuclear Fuel Development Corporation, O-arai, Ibaraki-ken (Japan))

Abstract

he modeling for inter-subchannel mixing effects was presented to simulate the fast reactor transition from rated to natural circulation decay heat removal conditions which was usually accompanied by all flow regimes: forced, mixed and natural convection. The model was constructed based on correlations for mixing and pressure drop coefficients developed at MIT. This correlation was originally proposed for steady states subchannel analyses. In the present study, application of the mixing correlation was extended to unsteady multi-dimensional analyses by introducing a threshold function. The function enabled to switch the correlations adequately with change of the flow regimes, depending on Richardson number, which is an index of buoyancy effect on the flow field. The modeling was validated through calculation of sodium experiments featuring 37, 61 and 169-pin bundle subassemblies. Comparisons of the experimental and numerical results revealed that the modeling was capable of predicting the core thermal-hydraulic field under wide spectrum of flow rate and heating conditions.

view the full text of this article (18 pages, format: PDF, size= 1085kB)

key words: after-heat removal; comparative evaluations; experimental data; fast reactors; fluid flow; hydrodynamics; many-dimensional calculations; natural convection; numerical data; pressure drop; richardson number; thermal analysis
Reference:
Technical committee meeting on methods and codes for calculations of thermohydraulic parameters for fuel, absorber pins and assemblies of LMFR's with traditional and burner cores. Obninsk (Russian Federation) 27-31 Jul 1998
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--1157, pp:378-395