• Nuclear Engineering and Technology
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• v.18 no.3
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• pp.200-208
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• 1986

The loss of coolant accident based on a double-ended cold leg break is analyzed with the discharge coefficient (Ca) of 0.4. This analysis covers the whole transient period from the start of depressurization to the complete refilling of the core by using RELAP4/MOD6-EM and RELAP4/ MOD6-HOT CHANNEL for the system thermal-hydraulics and the fuel performance during the blowdown phase respectively, and RELAP4/MOD6-FLOOD and TOODEE2 during the reflood phase. A simple analytical method has been developed to account for the lower plenum filling by approximating steam-water countercurrent flows and superheated wall effects at the downcomer during the refill period. Based on the informations. at the time of EOB (end-of-bypass), the refill duration time and the initial reflooding temperature were estimated and compared with the results from the RELAP4/MOD6, resulting in a good agreement. In addition, some parametric studies on the EOB were performed. The form loss coefficient between upper head and upper downcomer was found to be sensitive to the occurrence of the spurious EOB. Appropriate form loss coefficients should be taken into account to avoid the flow oscillations at the downcomer. The analyses with the six and three volume core nodalizations, respectively, show much similar trends in the system thermal-hydraulic performance, but the former case is recommended to obtain good results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.3
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• pp.255-262
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• 2011

In a loss-of-coolantaccident, considerable debris may be generated and transported to the recirculation sump. The accumulation of debris will reduce the netpositivesuctionhead and threaten the safety of thenuclear power plant. Both NEI 04-07 and USNRC SER suggesteda CFD methodology. However, additional investigation is needed to consider the unique characteristics of nuclear power plants. The transport of the generated debris is strongly influenced by the break location and the plant characteristics, including the configuration.In this paper, a CFD methodology for blow-down transport evaluation is proposed and applied to an OPR1000 nuclear power plant. The results show that the percentage of small debris transported to the upper containment is 32%, which is 7% larger than the valuegiven in the NEI 04-07 baseline analysis. This result may be used as a point of reference in future analytical studies.