DEVELOPMENT OF AN ADVANCED STARTUP PROCEDURE FOR A PIUS-TYPE REACTOR

An advanced startup procedure for the PIUS-type reactor has been devel oped. the procedure is related to the way to isolate the primary loops from the borated reactor pool by establishing stable hot/cold water i nterfaces in the so-called density lock sections. The procedure starts with accumulating preheated water in the high points of the steam-gen erator-side legs. Then, by restarting the reactor coolant pumps, the p rimary loops can be isolated from the pool as the primary loops reache s a uniformly higher temperature than the pool water. The additional c omponents required for this procedure are only a low-pressure grade he ater and a pump of small capacities. Since the isolation is achieved w ith the density locks left open. the core shutdown and cooling capabil ities by means of the natural circulation of borated water are maintai ned in case of any abnormal events during startup. The feasibility and the predictability of this procedure were investigated by running an experiment in a scaled single-loop facility and conducting an analysis using a one-dimensional model. Both in the experiment and in the anal ysis, the primary loop was successfully isolated from the pool.