Evaluation of LLTR Series II tests A-1A and A-1B test results

The standard methodology, with minor modifications provides conservative yet realistic predictions of leaksite and other sodium system pressures in the LLTR Series II vessel and piping. The good agreement between predicted and measured pressures indicates that the TRANSWRAP/RELAP modeling developed from the Series I tests is applicable to larger scale units prototypical of the Clinch River steam generator design. Calculated sodium system pressures are sensitive to several modeling parameters including rupture disc modeling, acoustic velocity in the test vessel, and flow rate from the rupture tube. The acoustic velocity which produced best agreement with leaksite pressures was calculated based on the shroud diameter and shroud wall thickness. The corresponding rupture tube discharge coefficient was that of the standard design methodology developed from Series I testing. As found in Series I testing, the Series II data suggests that the leading edge of the flow in the relief line is two phase for a single, doubled-ended guillotine tube rupture. The steam generator shroud acts as if it is relatively transparent to the transmission of radial pressures to the vessel wall. Slightly lower sodium system maximum pressures measured during Test A-1b compared to Test A-1a are attributed to premature failure (failure at a lower pressure) of the rupture disc in contact with the sodium for test A-1b. The delay in failure of the second disc in Test A-1b, which was successfully modeled with TRANSWRAP, is attributed to the limited energy in the nitrogen injection