The simulation test to start up the PIUS-type reactor from isothermal fluid condition

A feedback control system of a primary pump is proposed for a PIUS-type reactor based on the temperature distribution in the lower density lock. This control system maintains the fluid temperature at the axial center of the lower density lock at the average of the fluid temperatures below and above the lower density lock in order to prevent the poison water from penetrating into the core during normal operation. This control system was examined in a series of startup tests under different conditions and the test results demonstrated the effectiveness of the control system to startup the reactor from a small initial temperature difference between primary system and poison water system. The startup of a PIUS-type reactor from an isothermal condition, preventing the inflow of the poison water into the core, is the most difficult transient among normal operations. We installed a preheater system at the exit of the primary pump for the startup test from isothermal condition with the purpose of making a initial temperature difference between primary system and poison water pool. It was confirmed from the results of the tests that the preheater and the present pump feedback control system is quite effective to start up the reactor from an isothermal fluid condition. (author)