Abstract: In response to the operating characteristics of high temperature（240 ℃） and high pressure (12.2 MPa) in the main feedwater of domestic nuclear power plants,a high-precision ultrasonic flowmeter was developed based on the principle of time-difference method,which can achieve small power increase in the main feedwater flow measurement. The working principle,overall structure and design parameters of various components were introduced.The design ideas of the ultrasonic flowmeter scheme are summarized，the sources of uncertainty components in ultrasonic flowmeter measurement were proposed,and evaluation methods for uncertainty components in different situations were provided through experiments. The results indicate that the uncertainty components evaluation method introduced has been validated by utilizing existing flow standard devices in China,ensuring the uncertainty index of high temperature and high pressure ultrasonic flowmeter measurement,and achieving the goal.

Key words: High temperature and high pressure, Ultrasonic flowmeter, Uncertainty, Liquid flow rate