Studies on flow and temperature distribution in the region of local channel blockages in bundle fuel elements

Technical Report · Tue May 15 04:00:00 EDT 1973

OSTI ID:4311330

Kirsch, D

Work performed under United States --Euratom Fast Reactor Exchange Program. A possible propagation of a fault in liquid-metal cooled fast breeder reactors is considered, which could be initiated by a local coolant blockage arising from an accumulation of small particles at a spacer grid of a rod bundle subassembly. In order to evaluate the coolant temperature rise close to such blockages, flow and temperature distributions downstream of simulated local blockages have been investigated. Experiments determining the flow pattern show that in the investigated rod bundle geometry, a distinct recirculation zone with standing eddies develops downstream of an impermeable blockage. A first indication of whether local boiling is possible in this recirculation zone is given by experiments determining the dimensions of the recirculation zone and the mass exchange between this zone and the main flow. Knowing these values a mean coolant temperature, averaged for the volume of the recirculation zone, can be calculated. With the investigated blockages (obstructing up to 41% of the flow area) these mean coolant temperatures do not exceed the saturation temperature. Moreover an analysis of the measurement method shows that these temperatures have to be considered as conservative. However, local boiling has to be regarded possible as long as one does not know the temperature distribution in the recirculation zone. Since a measurement of the temperature distribution in a sodium-cooled test rig with a heated subassembly mock-up is possible only at considerable expense it was investigated whether the sodium temperatures in the subassembly can be calculated from measurements in a water-cooled test rig. Considerations for a simple geometry without rods lead to the following result: With sufficiently high Reynolds number, similar geometry, and similar heat source distribution, the dimensionless temperature fields in the recirculating flow downstream of a disk set normal to the main flow are equal and independent of the Reynolds and Prandtl number (i.e. equal for sodium and water), provided that one considers only temperatures at some distance from the walls. The assumption that this result also is true for the investigated rod bundle geometry was confirmed by analyzing temperature distributions measured in sodium and water downstream of a blockage in a rod bundle-like geometry. Results of such measurements and the sodium temperatures calculated from the results are given. An attempt to get an estimate of the temperature distribution using SAMBA, a computer code for design calculations with undisturbed geometry, did not succeed. This is due to the solution method used in codes of this kind, which is unsuitable for an estimation of the temperature distribution in the recirculation zone. (auth)

• Research Organization: Kernforschungszentrum Karlsruhe (F.R. Germany). Inst. fuer Reaktorentwicklung
• NSA Number: NSA-29-023579
• OSTI ID: 4311330
• Report Number(s): EURFNR--1106; KFK--1794
• Country of Publication: Germany
• Language: English

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