ANL-W History - Reactors (BORAX-I)

BORAX-I

BORAX-I during an excursion

In 1952, Samuel Untermyer suggested that direct boiling reactors might be practical. Previous to this time it had been thought that any bubble formation in the core would result in nuclear instabilities. Untermyer suggested that steam formation would actually help stabilize the reaction. Accordingly, a series of experimental boiling water reactors (BWR's) were built on the INEEL site. These reactors were known as the BORAX (Boiling Reactor Experiment) series.

The first reactor in this series, BORAX-I, was built in 1953. Its purpose was to experimentally determine the self-limiting characteristics of water-cooled reactors and the operating characteristics of boiling reactors. BORAX-I could only be used during the summer months because the reactor was not housed.

Inside view of BORAX-I.

BORAX-I was first used for steady state investigations on boiling water reactors. It was used to prove that the formation of steam bubbles in the reactor core did not cause an instability problem. Through the remainder of the summer and early fall, the reactor was put through a series of about 70 intentional "runaway" excursions and periods of steady boiling operation. These tests showed that the formation of steam and consequent water ejection from the core can provide inherent protection against the runaway hazard in suitably designed reactors of the water-cooled water moderated type.

BORAX-I conclusively proved that steam formation is an effective, reliable, and rapid power-limiting process, capable of protecting properly designed reactors against reactivity excursions which produce reactor periods shorter than 5 milliseconds. The reactivity decrease caused by steam formation in reactors like BORAX-I constitutes an inherent, ever-present power-limiting mechanism.

Results of the investigation pointed the way toward more economical power reactors through minimization of hazards, simplification of reactor design, and reduction of the temperature demands on materials.

The Final Experiment:

It was proposed that, before its replacement, BORAX-I be subjected to a single, very quick, destructive excursion. The purpose of such an experiment was to determine its inherent safety under extreme conditions. After discussion with the AEC Reactor Development Divison and the Advisory Committee on Reactor Safeguards, it was decided that such a final experiment was worthwhile.

The facility was deliberately destroyed in July 1954. Fuel plate fragments were scattered for a distance of 200-300 feet, but no widespread dangerous dispersal was observed.

The final test revealed that the predictions of total energy and fuel plate temperatures had been considerably too low. Instead of the melting of a few fuel plates, the test melted a major fraction of the entire core. The discrepancy was attributed to the uncertanties of extrapolation. The results of this energy liberation in the way of peak pressures and explosive violence lie in a region where there had been no previous experimental data. In this respect, the results were more informative than they would have been had the experiment had been performed under conditions which actually gave the predicted energy release.