Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966. Page: 30 of 47
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URANIUM TEXTURE MEASUREMENT AND RESPONSE TO HEAT TREATMENT
Early in the effort to relate the degree of preferred orientation existing
within uranium fuel cores to the amount of growth that might be expected to take
place during irradiation, it was realized that gradients in texture could exist
within the crossqrsection of a standard fuel element.1 The "growth index"
developed by E. Sturcken at Savannah River Laboratory as a yardstick for the
potential for growth in the reactor was by nature of its calculation, a fruit-
ful parameter to express the variations in preferred orientation existing within
the uranium metal fuel. What was not known was the influence of type of heat
treatment on the magnitude and algebraic sign of the growth index. Nor was there
appreciation of the difference between true randomness and "balanced" textures
yielding the same index value.
Prior to the discovery of alloy additions for control of grain size, much
interest was.devoted to the question of whether both random orientation and fine
grain size could be secured by some novel procedure in beta heat treatment with
or without a supplemental-alpha anneal.33 The idea initially considered was
that the cooling rate from the beta temperature might be important and that some
favorable rate of quench followed by an alpha anneal might be successful in
providing the desired grain refinement. The technique used was that employed
for alloyed steels in studying the response to cooling rate (the Jominy end
quench), permitting the examination of an infinite assortment of cooling
velocities between the quenched face and the remote end of the bar which
represented, in effect, an air cool. Such studies4,-YIB,24 did, in fact,
reveal that a rapidly quenched specimen could be recrystallized during a
following annealing treatment to give what appeared to be an equiaxed structure
with a most favorable grain fineness. What was not realized in the initial
metallographic work was the tendency of drastic quenching to create a columnar
structure. What had therefore appeared to be an equiaxed structure in the
initial sections that were cut parallel to the quenched face was only the
transverse appearance of.columnar grains extending parallel with the axis of
the bar. It is not surprising, therefore, that measurements of growth index
performed at minute increments of distance from the quenched face showed a
pronounced .texture gradient in the region of most rapid cooling.5,e.924,44
While these results were mainly of academic interest, they did trigger the
question as to whether unsuspected. gradients might exist in an beta-quenched
material. Efforts to observe such phenomena led to the development of improved
techniques of scanning the cross-section of uranium fuel cores and thereby
obtaining X-ray diffraction data to characterize the variations in texture
within the various geometries of fuel in use. It was concluded from these
studies, that thermal. gradients in cooling and phase transformation generally
do.create texture gradients and that these may be radial, circumferential, or
longitudinal. It was., in fact, discovered during these studies that beta
quenching is not always completely successful in erasing a previous condition
of pronounced orientation.. Studies of alpha-extruded rod48 gave evidence.that
as cold working and thus the texture of the as-extruded material became more
pronounced, the greater was the likelihood of retaining a significant amount of
texture after beta heat treatment.
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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/m1/30/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.