Thermal analysis of HTGR helical tube once through steam generators using 1D and 2D methods

Abstract

The working temperature of High Temperature Gas-cooled Reactor (HTGR) steam generators is much higher than that of Pressurized Water Reactor (PWR) steam generators. Large temperature non-uniformities will make the HTGR steam generator deviate from the designed working temperatures, which should be avoided. The temperature distribution and thermal deviation should be analyzed. One-dimensional (1D) and two-dimensional (2D) methods for analyzing the thermal hydraulic performance of an HTGR steam generator were developed. In the 1D method, the tube and shell side governing equations were solved. They were coupled through the energy source terms. In the 2D method, simulation of the shell side helium cross flow over tube bundles was based on the two-dimensional CFD code Ansys Fluent. The tube side water flow was coupled to the 2D simulation of the cross flow over tube bundles through the heat transfer between the primary and secondary sides. The 1D and 2D methods were validated using the measured data of the Thorium High Temperature Reactor (THTR) steam generators and the High Temperature Gas-cooled Reactor Pebble-bed Module (HTR-PM) test steam generator. The 1D method can give the overall thermal performance of the steam generators. The 2D method can predict temperature non-uniformities in the tube bundles. The overall thermal performance of the steam generator was simulated. The thermal non-uniformities or thermal deviations caused by geometrical and thermal hydraulic deviations were analyzed. Radiation heat transfer contributes to 0.9% of the total thermal power. A one percent change of the secondary side water flow rate of a certain layer of tubes will result in a 5–6 °C variation of the outlet steam temperature of this layer of tubes. A helical diameter deviation of 1 mm will result in a maximum outlet steam temperature variance of 6–7 °C. An inlet helium temperature profile with a 10 °C variance will only result in a variation of 2 °C in the outlet steam temperature.