Uncertainty Analysis of Thermal-hydraulic Characteristics of Silent Heat Pipe Cooled Reactor

Uncertainty analysis has a significant meaning in reactor design, analysis and safety assessment. Based on the uncertainty analysis program DAKOTA and the self-programmed heat pipe cooled reactor single channel thermal analysis program HEART, the steady-state thermal-hydraulic characteristics of silent heat pipe cooled reactor (NUSTER) were analyzed. In order to ensure that the calculation results have reference value, the validity of DAKOTA and HEART was verified. Heat pipe cooled reactor is a new hot type of nuclear reactor rising in recent ten years. Compared to many other reactor concepts, heat pipe cooled reactor has many unique characteristics, such as solid core, passive heat transfer, high power density, low operating noise. Based on the phenomena identification and ranking table (PIRT), design parameters and relevant experimental data of heat pipe cooled reactor, six thermal parameters, including operating power, fuel thermal conductivity, air gap width, cladding thickness, heat pipe evaporator length and matrix thickness were selected, and their reference values and probability density distributions were determined. The statistical distributions of heat pipe evaporator temperature, heat pipe condenser temperature, fuel peak temperature, cladding peak temperature and matrix temperature at 95% confidence level were obtained through a lot of repeated calculations, and the influence of the uncertainty of each parameter on the safety of heat pipe cooled reactor was analyzed. The result shows that fuel peak temperature, cladding peak temperature and matrix temperature are far below their temperature limits, while the temperature of both evaporator and condenser of heat pipe has a probability of about 0.67% exceeding the temperature limit of heat pipe. These indicate that the current heat pipe cooled reactor design may have the potential risk of the heat pipe failure, even though the probability is fairly low for steady-state. Further design optimizations thus become necessary for lowering the heat pipe failure probability. What’s more, according to the results, the uncertainty of fuel thermal conductivity heat has the strong impact to heat pipe evaporator temperature, while the uncertainty of heat pipe evaporator length is less sensitive. Weak effects are found for operating power, air gap width, cladding thickness and matrix thickness. It is also found that the uncertainty of input parameters has the same effect on five different target parameters, which is caused by the solid core of the heat pipe cooled reactor, heat transfer is mainly based on pure heat conduction. The results of this study indicate the general directions for the further thermal-hydraulic design optimizations for heat pipe cooled reactor, which could mitigate the possibility of heat pipe failure occurrence.