Continuous measurement of thinning rate about FAC under water-steam two-phase flow with low thinning rate condition using thin-film UT

Pipe wall thinning phenomena, as often seen in nuclear or thermal power plants, are serious problems especially for the operation and management of nuclear power plants. To operate nuclear power plants with safety for a long time, it is important to predict where the pipe wall thinning phenomena occur. Flow accelerated corrosion (FAC) is one of the pipe wall thinning phenomena. The pipe wall thinning area is large in case of FAC. FAC is a complex phenomena of the corrosion due to water chemistry and the acceleration of corrosion by hydrodynamics. The effect of the water chemistry is mainly represented by the solubility of iron and the effect of hydrodynamics is represented by the mass transfer coefficient. From some researches of FAC under water-steam two-phase flow, the relationship between liquid film and FAC mechanism was almost same as the relationship between that of FAC under water single-phase flow. From these results, FAC predict model under water-steam two-phase flow are constructed based on that of water single-phase flow in CRIEPI. The FAC predict model under water-steam two-phase flow are checked by FAC experimental results under the water-steam two-phase flow. When the thinning rate is low, the measure of change of wall thickness is difficult. The wall thickness is continuous measured by thin-film UT, and then the uncertainty is low, so that the change of the wall thickness is evaluated. (author)