The RCS flow measurement in PWRs is currently performed with a heat balance between primary and secondary systems: thus temperature heterogeneity impacts this measurement.
In case of RCS flow shutdown (incident situation), a relative measurement of the RCS flow is monitored using an existing elbow tap. The goal of the present study is to assess the feasibility of using the existing plant elbow taps to accurately measure an absolute value of the RCS flow continuously and independently of the RCS temperature measurements. RCS flow is basically proportional to the square root of the differential pressure in the pipe elbow taps. Experiments on a scale model and sensitivity analyses with CFD simulations have been carried out and show that only few parameters have an influence on the proportionality coefficient. CFD is seen as able to predict this coefficient with an adequate accuracy.
Potential applications of this method are RCS flow monitoring from start to full load after the change of primary coolant pumps or of steam generators.