Studies on In-situ regeneration of cold trap of a Bench-Top sodium loop

Abstract

A cold trap (CT) is one of the crucial modules of the sodium coolant circuit of a sodium-cooled fast reactor as it controls hydrogen, oxygen and other impurities in liquid sodium within the threshold levels in dynamic mode. The major impurities are crystallized as NaH and Na2O in CT and get loaded during its continuous service. The CT at the secondary sodium circuit needs regeneration at regular intervals of time. In-situ regeneration of the CT during the reactor operation would be cost-effective while generating power. A bench-top sodium loop was employed to carry out the present study. The regeneration of CT was carried out by adopting a thermo-vacuum process in which the NaH decomposed into sodium and hydrogen. During the regeneration process, hydrogen release behavior as a function of time with varying temperature and cover gas pressure was investigated by deploying in-house developed online hydrogen sensors. An electrochemical hydrogen meter (ECHM) to measure hydrogen in liquid sodium in the ppb range, a semiconducting metal oxide-based hydrogen sensor (SMOHS) and a polymer electrolyte membrane-based hydrogen sensor (PEMHS) to measure hydrogen in the argon cover gas were used. Simultaneous measurement of hydrogen in both liquid sodium and cover gas phase played a central role in analyzing the hydrogen distribution phenomenon. The quantity of total hydrogen evolved and decomposed NaH was determined after the successful regeneration of the cold trap.