Experimental study on thermal-hydraulics and neutronics coupling effect on flow instability in a heated channel with THYNC facility

Authors propose an experimental simulation method of neutron dynamics for channel instability in a local hot channel of a BWR under non-nuclear condition using a fast-response conduction-type void fraction meter coupled with a real-time computer calculation in THYNC facility. 'Local neutron feedback effect' model described by Takeuchi et al. was adopted to the experiment with an empirical parameter Ka, which is the ratio of gain of void-to-neutron transfer function in a local channel against that in a full core. The typical value of Ka was estimated to be 0.05-0.1 for the local channel instability using JAERI-developed 3D thermal-neutronic (T/N) coupling code TRAC/SKETCH. T/N coupling effect on channel instability was investigated with THYNC facility under the conditions of pressure=2-7MPa, subcooling=10-40K, and time-averaged mass flux=270-660kg/m2s. THYNC results indicated that T/N coupling has a tendency to destabilize the channel under the experimented conditions. However, the reduction of the channel power at the onset of the channel instability under T/N coupling against no T/N coupling was within 10% at 7MPa in the present THYNC experiment (Ka=0.1)