RESULTS OF BURNOUT AND INSTABILITY EXPERIMENTS ON A 7-ROD BUNDLE UP TO 30 ATMOSPHERES PRESSURE-FIRST SERIES WITH ZERO INLET SUBCOOLING AND NATURAL CONVECTION. Special Technical Report No. 4
Technical Report
·
OSTI ID:4620835
Burnout and instability experiments were carried out at saturation temperatures of 140, 180, 200, and 230 deg C on a 7-rod bundle test section simulating a Halden Boiling Water Reactor II fuel element. In these experiments the inlet subcooling was virtually zero and the water velocity determined by natural circulation. Two methods were used to obtain high enough heat fluxes to test burnout without at the same time increasing channel power. In the first method one of the rods was more highly rated than the other six and contained hot patches.'' In the second, the rods were equally heat-rated but hot patches of higher heat flux ratio were used to obtain the necessary heat flux to test burnout. Runs were made in which the predicted reactor axial heat flux profile was approximated by uniform heat flux with superimposed peaks of hot patches. The results of these experiments can be summarized as follows: (1) The pressure drop across the inlet holes of the shroud + bottom spacer was measured as 4.0 and 6.2 velocity heads respectively. (2) The maximum in the flow rate versus power curve occurs at 80, 120, 150, and 170 kw respectively at 140, 180, 200, and 230 deg C. The maximum inlet velocity at 230 deg C was about 0.85 m/sec. The negative slope of the curve beyond the maximum decreases with increasing pressure. (3) Instabilities in flow were detected. At 140 deg C they started at about 290 kw and at 180 deg C at about 300 kw, considerably above the power at which the maximum velocity occurs. The oscillations started quite suddenly with a period of about 0.5 to 0.8 seconds. At 200 and 230 deg C no such indication was obtained up to the powers tested of 420 and 480 kw respectively. (4) The hot patches were made by machining the outside of the rod to give a local reduction in OD. The channel power at which burnout occurred for a patch with sharp edges was significantly lower than a streamlined one for the same operating conditions. (5) Disregarding the runs made with hot patches with sharp edges, burnout at 200 and 230 deg C was only obtained under stable flow conditions, whereas at 140 and 180 deg C burnout was obtained at respectively 350 and 450 kw in unstable flow conditions. The observations made suggest that the position of the burnout point and the conditions under which burnout occurs are governed by a different mechanism in stable and in unstable flow. (6) It was found consistently, that in the cases where stable flow burnout occurred, it did so at the upper of two equally rated hot patches. The highest heat flux obtained in the hot patches was 280 w/cm/sup 2/ at 200 deg C and 260 w/cm/sup 2/ at 230 deg C. (7) An explanation of the results obtained at 200 and 230 deg C could be given by assuming: (a) that in the low quality region the burnout heat flux increases with increasing quality. (b) burnout heat flux decreases with increasing test section length. Both effects have been reported in the literature. (8) From the results obtained in two runs at 230 deg C there is an indication that an outer rod is more dangerous than an inner one. When the loop has been modified by the introduction of a subcooler, a second series of experiments will be made, to assess the effect of inlet subcooling. In these tests, internal hot patches and equally heated rods will be used and burnout and instability data obtained with radial flow symmetry. (auth)
- Research Organization:
- Eindhoven, Netherlands. Technische Hogeschool
- NSA Number:
- NSA-17-040265
- OSTI ID:
- 4620835
- Report Number(s):
- EURAEC-603
- Country of Publication:
- United States
- Language:
- English
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