Susquehanna Steam Electric Station Unit 2 (SSES-2) experienced three main turbine trips on high moisture separator drain tank level during initial startup testing in 1984. The SSES-2, a 3293-MW(thermal) boiling water reactor-4 with Mark II containment, uses two parallel nonreheating moisture separators between the high- and low-pressure turbine stages. Two of the main turbine trips and subsequent scrams occurred due to the high level in the “B” moisture separator drain tank during combined intermediate valve testing. The third trip was also initiated on the same signal, but during a recirculation pump run-back event. A task group was created to determine the cause of the level excursions and to make recommendations to reduce the severity of these transients. The RETRAN-02 computer code was used to evaluate the dynamic response of both the A and B moisture separator drain systems to determine the cause of the events, including why the level excursions only occurred in the B system. RETRAN was also used to evaluate the systems’ dynamic response to several proposed corrective plant modifications. Based on the recommendations of the task group, modifications were made to SSES-2 during the precommercial operation outage. Startup testing following the outage proved the success of the modifications.