EVALUATION OF THE PULSED NEUTRON ACTIVATION METHOD USING CFD

摘要

A PNA flowmeter uses a radioactive substance to measure water flow in pipes. The water in the pipe is bombarded with neutron pulses which introduce activity into the pipe. The activity is then transported and mixed with the flow. Gamma radiation emitted from the activity is measured with a detector downstream from the activation point. The average velocity of the water is calculated using the time-resolved signal from the detector. The CFD program FLUENT was used to simulate the transport and mixing after different initial activity distributions. From the calculations it was possible to quantify how much the average initial velocity of the activity differs from the average velocity of the water. The results show that activity initially produced far away from the wall has a substantial effect on the detector signal. It is necessary to include activity produced in a large part of the pipe to accurately simulate the detector signal.