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days in August the reactor reached {ts dealgn power level of 5,000 thermal kilowatts and then
was operated at 3,500 thermal kilowatts. However, short irregular pulses of power were observed which were not understood.
During September the reactor was shut down. An improved viewing system was used to
observe the outside of the zirconium core vessel in an effort to locate the hole through which
fluid from the core region transfers to the heavy water blanket region. On September 26 an
oval-shaped hole was found, measuring an inch and a half by one inch. Three days later a
cavity was discovered on the outer surface of the core vessel, indicating that corrosion is
occurring on the blanket side of the vessel wall.
Measurements showed that the thickness of the vessel wall had decreased since the reactor was put in operation. There was evidence that the lower section of the core vessel was
corroding more rapidly than the upper section,
Work on the molten salt reactor type continued at Oak Ridge. A test loop was under con-
struction to study the forced circulation of molten salt fuels in a radiation field in the Materials Testing Reactor at NRTS. Calculations were performed comparing use of uranium 235
and uranium 233 as reactor fuel for a 20-year period. For the reactor fueled with uranium 235
it would be necessary to buy 3,000 kilograms of uranium 235 during the period and about 1,000
kilograms would remain unconsumed,. For the reactor fueled with uranium 233 it would be
necessary to buy about 1,350 kilograms of uranium 233 during the period and there would be a
breeding gain of about 100 kilograms.
Fast-breeder type. At NRTS the Experimental Breeder Reactor No. 1 (EBR-1) continued
operation with the third core to provide information on the stability of fast reactors and to
study the causes which led to the melt-down of the second core in 1955. The melt-down is
believed to have resulted from the distortion or “bowing” of the fuel elements. The third core
was designed with supporting devices to control the bowing. Operation of the core with these
devices rigidly supporting the elements indicated that the instabilities associated with the
second core can be removed successfully by proper engineering design and are not inherentin
the reactor type. During the quarter experiments were begun to investigate what effects less
rigid support of the fuel elements would have on reactor stability.
Construction of the Experimental Breeder Reactor No. 2 (EBR-2) continued at NRTS. The
reactor containment vessel was 77 percent complete at the end of September, and construction
was in progress on the laboratory and service building. Fuel development work continued at the
Argonne National Laboratory. The EBR-2, which is to have a thermal capacity of 62,500 kilowatts and an electrical capacity of 16,500 kilowatts, is to be in full power operation in September 1962.
,
Construction of the Transient Reactor Test (TREAT)facility, designed to investigate the
effects of extreme operating conditions in fast reactors, was about 94 percent cumplete at the
end of September at NRTS. Criticality is scheduled for January 1959.
Sodium graphite type.
Operation of the Sodium Reactor Experiment (SRE) at Santa Susana,
California, was continued to test fue] elements and components of the reactor system. A
thorium-uranium fuel loading was being prepared for testing in the SRE. Preliminary results
of the first irradiation of uranium carbide fuel indicates considerable promise for use in
sodium graphite reactors.
Orgenic-moderated type. The Organic-Moderated Reactor Experiment (OMRE) at NRTS
was shut down during most of July to complete modifications. At the end of July the reactor
was started up again with two experimental elements inserted in the core. The OMRE was
operated with increasing concentrations of polymerized (decomposed) organic ‘material in the
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