Patent Number: 048760560
Section: claims

1. A method for measuring the flow of a fluid in a duct having at least a length thereof immersed in a saline sea, the method comprising locating a container adjacent to said duct with said container having an inlet communicating with said sea to allow ingress, as a test fluid, of sea water from said sea, causing said test fluid to enter said container, storing said test fluid in said container, irradiating said test fluid in said container with neutrons so as to generate atoms of a predetermined radioactive nuclide in said test fluid, injecting at spaced time intervals a sample of the irradiated test fluid from said container into said duct, detecting, at a location spaced apart along said duct from the location at which the injection takes place, radiation emitted by said predetermined radioactive atoms, and determining, from the elapsed time between the injection of the test fluid and the detection of the radiation, the flow rate of the fluid. 2. A method as claimed in claim 1 wherein said test fluid is irradiated for a time more than the half-life of said predetermined radioactive nuclide, and the location at which detection is performed is at such a separation from the location at which the injection takes place that the elapsed time is less than the half-life of said predetermined radioactive nuclide.