Analysis of the ULOF event for the KALIMER 150 by using SAS4A/SASSYS 1

In this study, the analysis of ATWS for the KALIMER 150 was conducted using the SAS4A/SASSYS 1 code to predict and evaluate the system response by nuclear kinetic and thermal hydraulic effects that involve inherently shutting the core down to acceptable power levels, and preclude a coolant boiling and fuel damage. The accident was assumed to occur by an ULOF (unprotected loss of flow), which is one of ATWS (anticipated transients without scram) events. In the KALIMER 150 design, the coolant pumps are specified as an electromagnets (EM) design equipped with synchronous motor generator (MG) sets to provide inertia for flow coast down. Power to the MG sets is provided by a source external to the unit. The initiator for the ULOF accident is assumed to be a failure of the normal power supply for the primary and intermediate loops coolant pumps. The offsite power supply for the EM pump is not a safety grade system, thus a loss of flow event is of high probability to be considered anticipatedin the KALIMER design. The SAS4A/SASSYS 1 code was used as an analysis tool. The SAS4A code system is a tool for analyzing the initial phase of hypothetical core disruptive accidents (HCDAs) up to gross melting or failures of the subassembly wall. SAS4A contains detailed mechanistic models of transient thermal, hydraulic, neutronic, and mechanical phenomena to describe the response of the reactor core, its coolant, fuel elements, and structural members to accident conditions. The core models in SAS4A provide the capability to analyze the initial phase of core disruptive accidents through coolant heatup and boiling, fuel element failure, and fuel melting and relocation. Originally developed to analyze oxide fuel clad with stainless steel, the models in SAS4A were extended to metallic fuel