Enhancing Safety in Molten Salt Reactors: Understanding How Design Choices Affect Freeze Plug Performance
Muhammad Ilham

Sample

Abstract

Molten salt reactors (MSRs) represent a promising advancement in nuclear technology, offering potential benefits such as improved safety and efficiency. A critical component of MSRs is the freeze plug, which acts as a safety mechanism installed between the reactor vessel and the drain tank. During an emergency, external cooling stops, and the salt inside the freeze plug melts, allowing the fuel salt to be discharged. The melting time (opening time) and the drain time, which are key factors in ensuring MSR passive safety, depend on the drain tube design and the initial shape of the frozen salt formed in the drain tube. Given this, a simulation of the solidification process was first performed, followed by melting and drain time approximation. Systematic numerical simulations were conducted to explore the effects of wall thickness, inner diameter, and tube inclination on the freeze plug used in MSRs. Furthermore, a novel jacket design for melting acceleration and a conical tube for plug structural integrity were proposed. It was found that in the solidification process, the tube design significantly impacted the equilibrium shape of the frozen salt. Melting simulations showed that a small tube shortened the opening time. However, it took a long time to drain the liquid salt from the reactor core into the drain tank after opening. The results indicated that all aspects of the solidification, melting, and drainage processes should be sufficiently understood to utilize the freeze plug as an effective passive safety system in MSRs. Accordingly, a simplified analytical model was developed for a rough estimation of the opening time that reasonably agreed with the full simulation results.

Keywords: Molten salt reactor, Freeze plug, Solidification, Melting, Opening time, Drain time, Inclination, Numerical simulation

Topic: Innovative Nuclear Energy Systems