Transient Analysis of Active Residual Heat Removal Process for HTR-PM

An active residual heat removal process is required by the gas-cooled reactor pebble-bed module plant being constructed in China, in order to improve the economical performance of the plant by shortening the restart duration. This process makes use of steam generator and start-up loop as heat sink, whose structure may suffer cold/heat shock while the sudden load of coolant or hot helium at the beginning. To achieve safety and reliability, transient analysis was carried out based on a one-dimensional mathematical model for steam generator and steam pipe of start-up loop. The calculation results show that steam generator should be discharged and pre-cooled; otherwise, boiling will arise and introduce a cold shock to the boiling tubes and tube sheet when coolant began to circulate prior to the helium. Additionally, in avoiding heat shock caused by the sudden load of helium, the helium circulation should be restricted to start with an extreme low flow rate; meanwhile, the coolant of steam generator (water) should have flow rate as large as possible. Finally, a four-step procedure with pre-cooling process of steam generator was recommended; sensitive study for the main parameters was conducted.