,25 salt and the actual level change, the difference level indications varies somewhat, with greater lower levels.
between the two bubbler differences observed at
The behavior described above is easily understood, qualitatively at least. The jets from the spray ring, impinging on the salt pool, carry substantial amounts of gas below the surface. The fraction of the gas in the salt decreases with depth until only the very small bubbles that can be dragged down with the salt flow are present. If the low-density region were entirely above the tips of both bubblers, the difference between the level indications would be the same as with the pump off (although both would indicate a level lower than the actual top.of the gas-liquid mixture.) If the low-density region extends into the bubbler zone, the difference between the level indications reflects the density reduction due to the gas. As the amount of salt in the p.unp bowl decreases, the gassy region moves down and more gas appears in the bubbler zone. An implication of this picture is that the density profile should change with pump speed. That is, at reduced speed and head the velocity of the jets and the net downward velocity in the salt pool are less, so there should be less gas at a given depth. This was proved to be the case in experimental operation of the fuel punp at various rotational speeds in Runs 17 - 19 (February - September, 1969). Figure 6 shows the effect of ljlump speed on tion in the zone between the ~two bubbler tips. shifts are cancelled in the calculation of void tive to that of clear salt.) The data for this with approximately the same indicated salt level. show the greater depth of the low-density region
the apparent void frac(The errors due to zero fraction or density relaplot were all obtained The results clearly \ or "gassy zone" at higher
pump speeds and higher salt jet velocities. The points in Fig. 6 also show that in this particular parameter, any difference due to changing from helium to argon cover gas is not discernible and the differences between fuel salt and flush salt have only a minor effect. It will be shown later (Chapter 6), however, that when the gassy region extends sufficiently.deep in the punp bowl, very small changes can produce pronounced effects
in the circulating
loop.
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