Impurity concentration on boiling heat transfer surface in tube-tube support plate crevice. 2. Estimation of impurity concentration factor on boiling heat transfer surface in tube-tube support plate crevice using conductivity measurement

Local corrosion has been experienced on the secondary side of steam generator tubes in tube-tube support plate crevice of PWR's, because the impurities which were slightly dissolved in feed water have been concentrated in the crevice. Various chemical analysis have been applied to evaluate water quality in the crevice, however, it has been very difficult to analyze exactly by their indirect analysis. In this study, the impurities concentration factors were calculated from the results of high temperature sodium hydroxide aqueous conductivity measurements in the crevice, and the effects of heat flux and solution temperature on the impurities concentration were examined. The conductivity in the crevice were measured in deaerated sodium hydroxide aqueous solutions in the range 260 - 280degC. The main test results were as follows: (1) Conductivity of high temperature water increased with increasing concentration and temperature in deaerated sodium hydroxide solution. (2) The test results showed that the conductivity in the tube-tube support plate crevice solution was higher than that of bulk water, contained with sodium hydroxide, and sodium hydroxide was concentrated in the crevice. So this measuring method was applicable to investigation on the evaluation of the impurities concentration behavior in the crevice. From the calculated results of concentration factor, it was revealed that the factor was about 2000 in the range of the heat flux, range for the region of dry and wet condition, and the impurities concentration in caustic solution was lower than that of field data. (author)