Transient critical heat flux in loss-of-flow-accidents (L.O.F.A.)

Abstract

Loss of flow transients with reference to L.O.F. accidents in nuclear reactor cores have been systematically studied employing freon 12 as coolant. Two pressures (with reference to BWR and PWR characteristic liquid to vapour densities ratios), three periods of the coast-down flow transients during the simulated pump trips, and different specific mass flow rates have been investigated. The uniformly heated channel ( L = 200 cm, D = 0.75 cm), instrumented with wall thermocouples and inlet to outlet differential pressure enabled recording of the following transients, inlet specific mass flowrate, inlet pressure, inlet to outlet Δp, inlet fluid temperature, outlet wall temperature, outlet bulk temperature. Through the wall temperature being close to the outlet it is possible to detect the onset of DNB and hence the time to DNB from the beginning of the flow transient. All the experimental runs (105) have been systematically compared with the G.E. (PEPE) code with the introduction of a CNEN DNB freon correlation. The results enable a series of conclusions which are extensively shown in the paper.