(A) study on multiphysics startup simulation of the soluble-boron-free ATOM system

Abstract

This thesis is concerned with the feasibility regarding the startup of soluble-boron-free (SBF) reactors based on sole mechanical movement of control rods and its associated CEA (Control Element Assembly) control logic. Specifically, the ATOM (Autonomous Transportable On-demand reactor Module) design was considered to model the SBF system with a decoupled steam-generator, in which its inlet coolant temperature is pre-determined to reflect the variation in the power demand. To acquire the critical CEA height for given power demand, a TH (Thermal-Hydraulics) coupled 3-D quasi-static NEM (Nodal Expansion Method) method was considered, which enables the assessment of the startup in terms of burnup conditions, power ascension scenarios, and the degree of overlap between the control rods. It is shown both slow startup within 72 hours and quick one within 3 hours are achievable with sufficient safety margins, and a new CEA control logic, named Mode-Y, for SBF reactor startups has been devised based on the current results.