Release of Sodium and Radioisotopes into Air Associated with Sodium Combustion

摘要

The release of fission products associated with the combustion of sodium was ex-perimentally compared with that of sodium. About 0.5 g of sodium sample was loaded onto a quartz crucible, together with trace amounts of 131I, 137Cs and 89Sr, and set in a combustion tube, where it was burned at a temperature ranging from 400° to 600°C, and in an atmosphere containing 2 to 21v/0 oxygen, flowing at 0.1 to 1.5 Nl/min. The release fractions of radioisotopes-defined as the ratio between the radioactivity carried by the sodium released upon combustion and the total radioactivity including that of combustion products remaining in the crucible-increased almost linearly in relation to the release fraction of sodium similarly defined. The release fractions reached 20% for 131I, 80% for 137Cs and 0.5% for 89Sr, in association with a 30% sodium release fraction. A decrease was observed in the release fraction of sodium as well as of the radioisotopes with increase of the oxygen concentration and of the humidity in the combustion gas. This was ascribed to the formation of sodium oxide and sodium hydroxide scum on the burning surface of the sodium samples, judged from the fact that gas phase reaction was dominant in the sodium combustion.