Experimental and theoretical study of iron concentration on clogging phenomenon in secondary circuit of pressurized nuclear power plant

摘要

The clogging phenomenon can be observed in both primary and secondary circuits of a Pressurized Nuclear Power Plant (PWR). This effect is associated to hydrodynamic singularity produced by an important change in flow velocity (e.g. SG tube' support plates) and physico-chemical conditions. In Steam Generator (SG) secondary side the thickness of the clogging can become so important that the performance could be reduced. Two experimental tests were carried out to study the evolution of the clogging on a specimen (important section flow reduction) in single phase conditions of secondary circuit (245 - 275°C, 10 MPa) with low (5 to 9.5 ppb) and high (5 to 27 ppb) iron concentration for 760 and 470 hours respectively. To increase the deposits kinetics, the velocities were set between 5 to 30 m/s. The deposit mean thickness change was calculated by the evolution of the pressure drop coefficient assuming deposit profile and geometry measured at the end of the tests. Moreover, a model based on Graetz mass transfers has been used to estimate the kinetics of deposit formation. The results showed that experimental and model results are in good agreement. It suggests that the clogging effect in our experimental conditions is controlled by mass transfer and not by the electro-kinetic effect. However, the electro-kinetic effect would provide the conditions to initiate the deposit formation. The model was implemented in the CLOSIS program (developed by AREVA) to simulate the clogging effect in a steam generator. Theoretical estimations are in good agreement with SG on-site measurement and this for 20 years experience feedback.