Because the APR1400 adopts a DVI system, of which the injection nozzle are located 2.1 m above the centerline of the cold leg, ECC bypass is one of the most important technical issues related to the downcomer thermal-hydraulics during the LBLOCA sequences. In this paper, among the ATLAS reflood tests, LB-CL-05, LB-CL-09, and LB-CL-15, which represent the Phase-1, Phase-2, and separate effect test, respectively, were discussed in detail from a ECC bypass characteristics point of view. The LB-CL-05 test is one of parametric effect tests for downcomer boiling in the late reflood phase of a LBLOCA and the LB-CL-09 test is an integral test for the reflood phase of a LBLOCA for investigating the thermal-hydraulic characteristics during an entire reflood period. The LB-CL-15 test was performed as a separate effect test peculiar to the condition of the APR1400. Considering the steam flow rate from the intact cold legs and the system parameters such as the pressure and temperature, the critical void height is calculated in each the tests. The calculated critical void height is significantly lower than the distance from the centerline of the intact cold legs to the top of the water in the downcomer, which confirms that the sweep-out phenomena does not occur in the present tests. ECC bypass has been identified as playing an important role in a depletion of the coolant inventory in the reflood phase of a LBLOCA. Although there were some differences, the fractions of the ECC bypass could be assumed to be about 0.5 during the initial period in the LB-CL-05, 09, and 15 tests.

This content is only available via PDF.
You do not currently have access to this content.