To clarify the concentration behavior of sodium hydroxide, which is a representative impurity in the pressurized water reactor (PWR) secondary water coolant of a heat transfer crevice, an in situ high-temperature aqueous conductivity measurement cell was designed with the simulated tube support plate crevice of a PWR steam generator. The concentration factors of sodium hydroxide were calculated from the results of the conductivity measurement, and the effects of heat flux and solution temperature on the concentration factors were also examined. The conductivities in the crevice were measured in deaerated sodium hydroxide aqueous solutions in a range from 260 to 280°C.

The main test results show that the conductivity of high-temperature water increased with an increase of concentration and temperature in the deaerated sodium hydroxide solution and that the conductivity in the tube-tube-support-plate crevice was higher than that of bulk water because of concentrated sodium hydroxide in a crevice. Therefore, this method is applicable to evaluation of the impurity concentration behavior in a crevice. The calculated results of the concentration factor reveal that the factor was ~2000 in the range of the heat flux, i.e., the range for the region of a dry and wet condition, and the concentration factors in the sodium hydroxide solutions were lower than those of the field data.