Transient behavior of the sodium–potassium alloy heat pipe in passive residual heat removal system of molten salt reactor

Highlight
• A new concept PRHRS of MSR using NaK heat pipes is proposed.
• The startup of NaK heat pipe is successfully simulated during the accident of MSR.
• The residual heat of fuel salt is removed significantly and effectively by using NaK heat pipes.
• The compressibility of NaK vapor changed obviously during the startup of NaK heat pipe.

High temperature heat pipes, as highly-effective heat transfer elements, have been extensively employed in thermal management for their remarkable advantages in conductivity, isothermality and self-actuating. It is of significance to apply heat pipes to new concept passive residual heat removal system (PRHRS) of molten salt reactor (MSR). In this paper, the new concept PRHRS of MSR using sodium–potassium alloy (NaK) heat pipes is proposed in detail, and then the transient behavior of high temperature NaK heat pipe is numerically investigated using the Finite Element Method (FEM) in the case of MSR accident. The two-dimensional transient conduction model for the heat pipe wall and wick structure is coupled with the one-dimensional quasi-steady model for the vapor flow when vaporization and condensation occur at the liquid–vapor interface. The governing equations coupled with boundary conditions are solved by FORTRAN code to obtain the distributions of the temperature, velocity and pressure for the heat pipe transient operation. Numerical results indicated that high temperature NaK heat pipe had a good operating performance and removed the residual heat of fuel salt significantly for the accident of MSR.