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U.S. Department of Energy
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KINETIC STUDIES OF HETEROGENEOUS WATER REACTORS. Annual Summary Report, 1962

Technical Report ·
OSTI ID:4694526
The dominant cause of hydrodynamic instabilities in natural circulation boiling water reactors was found to be unstable linear feedback between flow and steam void volume. The power-void transfer function is also dominated by this flow-void feedback, so both the reactivity feedback type of boiling water reactor instability and the power oscillations arising from hydrodynamic instability have the same cause. The parallel channel interaction in a natural circulation boiling water reactor is such as to allow two modes of hydrodynamic oscillation to exist; one is identical to the single-channel hydrodynamic oscillations observed in the laboratory, while the second is identical to the multi-channel instability which occurs in forcedflow systems. Both modes of multi-channel instability are predictable from laboratory measurements on a single channel. A method of estimating the steady-state steamvoid fraction in a boiling water reactor channel was developed utilizing the principle of minimum entropy production. An analysis of possible causes of severe pressure pulses in heterogeneous reactor transients produced a hypothesis that such pulses could be caused by the very rapid thermal expansion (single phase) of a conductively heated thin film of liquid as the fuel surface temperature passes through the thermodynamic critical temperature. This hypothesis was evaluated analytically, and it was found that a mechanism can cause a very severe pressure transient if a sufficiently large ratio of heated surface to core volume exists, and if the reactor period is short enough. However, the results of applying this analysis to the destructive transient in the BORAX I reactor show that several times the actual surface area ratio would have been required in order for a supercritical pressure pulse to have been caused by this mechanism. This result is dependent on the equation of state used for the superheated liquid film. (auth)
Research Organization:
Space Technology Labs., Inc., Redondo Beach, Calif.
NSA Number:
NSA-17-042195
OSTI ID:
4694526
Report Number(s):
STL-6212
Country of Publication:
United States
Language:
English