Circus, an experimental facility to study the impact of flashing on the stability of a natural circulation BWR

The stability of a natural circulation Boiling Water Reactor (BWR) under low-power low-pressure conditions is studied. For low pressure, the so-called flashing phenomenon plays an important role. It is shown that an extra dimensionless parameter, the flashing number, is needed to describe the stability of a natural circulation reactor in the dimensionless operational map. As pressure decreases the range in which the reactor is unstable with respect to so-called type-I instabilities broadens. The experimental facility CIRCUS has been built to study the stability of a natural circulation reactor under low-power low-pressure conditions. First test results show flashing induced oscillations, with the oscillation period governed by the loop circulation time.