Experimental study of local sodium boiling detection by use of temperature and flow fluctuations at the outlet of subassembly

*; *; Haga, Kazuo*; Yamaguchi, Katsuhisa; *

PNC TN941 83-97, 71 Pages, 1983/06

PNC-TN941-83-97.pdf:2.53MB

Out-of-pile local boiling experiments were carried out with a wire spacer type 91-pin bundle. A half edge part of its cross-sectional area was blocked by a 5mm thick stainless-steel plate. The purpose of the experiments is to study the feasibility of detecting coolant boiling accident within a LMFBR fuel subassembly using the temperature and flow fluctuations at the outlet of individual subassembly. Initial conditions of the experiment are as follows: (1)Bundle inlet temperature : 400 500 C (2)Heat flux : 72 93 W/cm (3)Coolant flow velocity at the normal bundle section : 0.64 1.13 m/s. Local boiling was generated immediately behind the blockage by increasing heat flux gradually, with inlet sodium temperature and coolant flow rate being held to be constant. Specifications of the instrumentation system for measuring temperature and flow fluctuations are listed below: (1)Thermocouples Chromel-Alumel thermocouples, Grounded-type (O.D. 0.3mm) and ungrounded-type (O.D. 4.8mm) Time constant (63.2%) 10 msec and 2.14 sec respectively (2)Flowmeter Eddy-current type temperature and flowmeter Exciting frequency : 425 Hz (3)Fluctuation measuring circuit : Maximum gain : 60 dB Frequency characteristics : flat in the frequency range from 0.01 to 15 Hz, 20 dB/dec attenuation slope below 0.01 Hz and 200 dB/dec attenuation slope above 15 Hz. The following subjects have been studied. (1)To investigate how boiling informations are transferred. (2)Anomaly detection methods by use of the temperature and flow fluctuations. (3)Feasibility of detecting local boiling accident by fluctuation signals. These studies yielded the following conclusions. (1)Spectral peak arround 4 Hz in the power spectral density functions of the temperature fluctuations was observed at the downstream bundle section of the blockage. This frequency peak is consistent with that of void formation and collapse and may ...