La mesure des débits d'eau dans les conduites fermées par la méthode de temps de transit d'un traceur radioactif

Determination of pipe discharge by radioactive tracer transit time measurement

Chef de Département adjoint à la Direction des Etudes et Recherches d'Electricité de France

Abstract

Electricité de France has developed a number of simple, inexpensive radioactive tracer methods for pipe discharge measurement. The equipment is highly adaptable and causes neither flow disturbance nor additional loss of head, nor does it require modification of existing circuits as a general rule. The method described is based on the fluid transit time between two detection stations along the pipe. Discharge is found by dividing the volume between the two measurement stations by the tune the fluid takes to transit from one to the other. To determine transit time, the fluid is "marked" by a tracer with a short half-life, which is produced and fed into the pipe flow by a special "generator/injector" unit. Cesium 137, a radio-element with a long half-life (30 years), produces metastable barium 137, which emits gamma-radiation at 662 keV with a half-life of 2.6 minutes. The cesium is fixed on resin inside a cartridge sealed with filter plugs at both ends. A positive-displacement pump circulates the fluid extracting the barium 137 and stores the resulting aqueous tracer solution in a hydropneumatic accumulator. Direct transit time indication is provided by an electronic detection and processing unit. This equipment is designed to current French regulations, and the "marked" fluid is safe as regards radioactivity.