Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966. Page: 18 of 47
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3. Since a vacuum anneal represented an extra step and thereby an
extra expense and the possible changes in structure did not
appear to be remarkably advantageous, the pursuit of this means
of control of structure was not carried to full-scale reactor
FIRST EXPERIENCE WITH ALLOYED DINGOT METAL
In January of 1959, word was received from Hanford that the dingot metal cores
being irradiated were showing an unfavorable degree of variation in grain size
with a portion of the cores exhibiting a sufficiently coarse structure to cause
serious "bumping" during irradiation. The available information was discussed
at a meeting at Richland on January 28, 1959. Photomacrographs (3X magnifica-
tion) were displayed showing dingot grain sizes ranging from those represent-
ative of ingot fineness to structures that were extremely coarse. Since a
fraction of the dingot metal was entirely satisfactory in structure and since
up to that moment no correlation had been discovered between chemical
composition and grain size, the first area that was deemed worthy of examination
was the question of variations in heat treatment procedures as possible causes
of this lack of structural uniformity.
Arrangements were therefore made to conduct a sequence of beta heat treatments
using cores fabricated from a single dingot in order to provide a common and
invariant composition for the entire group.2 Cores were soaked at four beta
temperatures: namely, 1270, 1310, 1350, and 1390*F. Four soaking times were
used at each temperature: 8, 12, 16, and 20 minutes. Four air delays between
emergence from the beta bath and quenching into 130*F. water were employed:
6, 12, 19, and 43 seconds, respectively. The :examination of the macrostructures
from each of these individual heat treatment patterns revealed an identical,
coarse-grained, beta-quenched structure in all cases save those representing
the combination of a very low beta temperature and a very brief soak in which
the core did not actually fully transform to the beta phase before quench.
The conclusion was therefore drawn that the variation in grain size at Hanford
could not have been an uncontrolled aspect of beta heat treatment but must have
been due to some unappreciated influence of chemical composition.
By sheer coincidence, two dingots were processed at this time using a quantity
of UF4 which had been pre-heated to drive off all possible water and hydrogen
as a portion of the study.of hydrogen.control in dingot metal. It was learned
that this pre-heat of the UF4 had inadvertently caused a pickup of iron, and
these two dingots were rejected for. high iron content: namely, 165 ppm in dingot
number 788, and 190 ppm in dingot number 1325. (The nickel was also high,
being 72 and 46 ppm, respectively.)
Bars from these dingots had been successfully rolled to Hanford-size rods
before rejection for chemistry. Core blanks from these rods were therefore
requested for experimental heat treatment at Weldon Spring out of a curiosity
to see what the effect of this iron contamination might be. In view of the
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Fellows, J. A. Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966., report, January 1, 1966; Weldon Spring, Missouri. (https://digital.library.unt.edu/ark:/67531/metadc1033773/m1/18/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.