Development of ATR type steam separator performance analysis code and its validation, (1)

The purpose of the study is to develop a method for predicting steam carryunder which is one of the important characteristics of a steam separator. Bubbles returning to the liquid surface and trapped by the re-circulating flow are calculated by tracking the behavior of bubbles moving in liquid bulk where velocity and temperature distributions have been calculated before-hand in conjunction with the Monte-Carlo method. Regarding the statistics of bubbles, a survey of references and visual tests have been conducted. To validate this method, several tests to measure bubble behavior under air/water conditions at atmospheric pressure and high temperature and pressure ranging 3 ∼ 7 MPa have been conducted with a full-scale steam separator. As a result, the developed method predicted with good precision the carryunder ratio obtained by the full-scale tests under the condition that carried-under void fraction was less than 20 %, but underestimated carryunder ratio in the ATR 'Fugen' reactor in which steam drum water level was shallow and average void fraction in water bulk was high. This method has a characteristic that carryunder ratio is underestimated in the case that void fraction is more than 20 %. (author)