RECOUPLING AND DECOUPLING OF PARALLEL LOOPS IN SIMULATED PIUS-TYPE REACTOR SHUTDOWN AND RESTART TRANSIENTS

The shutdown and restart transients in the PIUS-type reactor are simul ated experimentally and analytically. A half-height, 1/2,400 volumetri cally-scaled low-pressure facility was used for experiments and a one- dimensional model was employed for analysis. The passive shutdown of t he PIUS-type reactor is achieved by terminating the pumped circulation of reactor coolant through the primary loops and thereby allowing a n atural circulation between the primary-loop riser section and a berate d cold water pool. It is shown that the natural circulation grows quic kly owing to a dynamic force caused by the riser-section fluid deceler ation following the pump trip. The restart of the reactor, on the othe r hand, requires the primary loops to be decoupled from the berated po ol. The reactor restart can be achieved by simply restarting the coola nt pump and then controlling the pump speed. The natural circulation b etween the primary-loop riser section and the reactor pool is terminat ed quickly owing to a dynamic force caused by the riser-section fluid acceleration following the pump restart.